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This paper analyses day-to-day changes of weather types and links these with synoptic situations, i.e. circulation types, air masses and weather fronts. The weather types were classified according to Woś (1999), while a calendar proposed by Niedźwiedź (2013) was used for synoptic situations. Weather records from Kraków were used covering the period 1961-2010. The frequency of all combinations of day-to-day weather type changes was calculated, identified using specific values of air temperature, cloudiness and precipitation. The analysis of the succession and frequency of the day-to-day changes was linked with the synoptic situations accompanying the change. It was found that the thermal weather types were relatively very stable and remained unchanged on the following day in 61.3% of cases, and that the synoptic situation also remained similar. Weather subtypes, identified with just cloudiness and precipitation, but not temperature, displayed much more day-to-day change in terms of frequency and scale. Synoptically it was the air mass change and/or the occurrence of atmospheric fronts, which tended to cause day-to-day weather type changes, while the impact of circulation was not always clear. Particular attention was devoted to sudden weather type changes caused primarily by dramatic air temperature fluctuations. [ABSTRACT FROM AUTHOR]

Dangendorf, S., Wahl, T., Mudersbach, C. and Jensen, J., 2013. The Seasonal Mean Sea Level Cycle in the Southeastern North Sea The seasonal cycle is a prominent feature in Mean Sea Level (MSL) time series with considerable influences on flood risk in coastal areas. When analyzing MSL it is often assumed that the seasonal cycle is a stationary process, independent from inter-annual variations, but there is no obvious reason for such an assumption. In this paper the seasonal cycle of MSL at 13 tide gauges in the German Bight is investigated for its average character as well as its time dependence over the past 166 years. A seasonal trend decomposition method is used to analyze the inter-annual fluctuations in amplitudes and phases of the seasonal cycle. In the German Bight the seasonal cycle accounts for up to 44 % of the observed monthly MSL variability. The mean seasonal cycle peaks during November at all stations. The mean amplitude varies between 14 and 20 cm and increases from the south-western to the north-eastern stations. Throughout the last 166 years it is found that the amplitudes as well as the phases of the seasonal cycle are marked by a considerable inter-annual variability. While most records, all starting in the 1930's or later, do not exhibit a significant trend the longest record at Cuxhaven displays a significant long-term trend of 0.2 ± 0.1 mm/yr. This trend is mainly caused by large values at the end of the 1970's and the beginning 1980's. Simultaneously, the annual peaks shift from the late autumn to winter months (December to February). These changes are caused by extraordinary large trends during the months from January to March, exceeding those in the remaining months by up to 4 mm/yr. These changes are in phase with an intensification of large-scale atmospheric circulation patterns over the North Atlantic bringing more frequent westerly winds over the North Sea. [ABSTRACT FROM AUTHOR]

This paper performs an attribution analysis of future changes in the frequency of tropical cyclone (TC) passages over the western North Pacific basin projected by seven general circulation models. The models project increases in the passage frequency over the tropical central North Pacific and decreases in regions to the west and northwest, including East Asian countries. The attribution analysis reveals that while changes of the basinwide TC count would decrease the frequency of passages throughout the basin, the gross horizontal contrast in the passage frequency changes is caused by a projected eastward shift of main TC development regions, probably caused by El Niño-like sea surface temperature changes. The change in the frequency of passages is also caused by changes of TC translation vectors and preferable tracks. In particular, the translation vector would rotate clockwise to point in a more easterly direction over oceanic regions south of Japan, decreasing the passage frequency over the Korean peninsula and western Japan while increasing it over eastern Japan. This change in translation direction may be caused by the southward shift of the subtropical jet axis and resultant intensification of westerly steering flows. The El Niño-like change and westerly steering flow change are consistent not only among the seven models but also among a number of other climate models, which suggests the reliability of these results from the viewpoint of intermodel agreement. [ABSTRACT FROM AUTHOR]

Abstract: This paper applies meta-analysis techniques to a database of 401 14C-dated Holocene fluvial units in New Zealand. We use the database to produce a probability-based reconstruction of Holocene river behaviour at a national and regional scale. Records of river activity in northern (North Island) and southern (South Island) New Zealand are compared with independent hydro-climate proxy records that reflect regional, tropical and polar influences on Southern Hemisphere climate. During the Holocene, 12 multi-centennial length episodes of river activity and flooding were identified in the North Island, and in the South Island record 11 periods exceed the mean relative probability of activity. These records show that episodes of river activity have exhibited a predominantly out-of-phase relationship, suggesting the relationship between ENSO and SAM, and the relative dominance of the two modes, may be influencing Holocene river activity in New Zealand. The emerging pattern in the South Island Holocene fluvial record is one of increased river activity in response to enhanced westerly atmospheric circulation associated with a predominance of trough regime synoptic type (negative SAM-like circulation). In the North Island episodes of river activity are driven by increased meridional atmospheric circulation associated with blocking regime synoptic conditions (La Niña-like and positive SAM-like circulation). Analysis of floodplain sedimentation rates shows a rapid increase after ∼500 cal yr BP following the arrival of humans and the beginning of widespread deforestation. Regional climate complexity in New Zealand presents opportunities for palaeoclimate reconstruction, with the New Zealand fluvial 14C-database ideally placed to fill geographical gaps in the long-term hydrological record. [Copyright &y& Elsevier]

This paper reviews the current state and development of different numerical model classes that are used to simulate the global atmospheric system, particularly Earth's climate and climate-chemistry connections. The focus is on Chemistry-Climate Models. In general, these serve to examine dynamical and chemical processes in the Earth atmosphere, their feedback, and interaction with climate. Such models have been established as helpful tools in addition to analyses of observational data. Definitions of the global model classes are given and their capabilities as well as weaknesses are discussed. Examples of scientific studies indicate how numerical exercises contribute to an improved understanding of atmospheric behavior. There, the focus is on synergistic investigations combining observations and model results. The possible future developments and challenges are presented, not only from the scientific point of view but also regarding the computer technology and respective consequences for numerical modeling of atmospheric processes. In the future, a stronger cross-linkage of subject-specific scientists is necessary, to tackle the looming challenges. It should link the specialist discipline and applied computer science. [ABSTRACT FROM AUTHOR]

The chaotic nature of the atmospheric dynamics has stimulated the applications of methods and ideas derived from statistical dynamics. For instance, ensemble systems are used to make weather predictions recently extensive, which are designed to sample the phase space around the initial condition. Such an approach has been shown to improve substantially the usefulness of the forecasts since it allows forecasters to issue probabilistic forecasts. These works have modified the dominant paradigm of the interpretation of the evolution of atmospheric flows (and oceanic motions to some extent) attributing more importance to the probability distribution of the variables of interest rather than to a single representation. The ensemble experiments can be considered as crude attempts to estimate the evolution of the probability distribution of the climate variables, which turn out to be the only physical quantity relevant to practice. However, little work has been done on a direct modeling of the probability evolution itself. In this paper it is shown that it is possible to write the evolution of the probability distribution as a functional integral of the same kind introduced by Feynman in quantum mechanics, using some of the methods and results developed in statistical physics. The approach allows obtaining a formal solution to the Fokker-Planck equation corresponding to the Langevin-like equation of motion with noise. The method is very general and provides a framework generalizable to red noise, as well as to delaying differential equations, and even field equations, i.e., partial differential equations with noise, for example, general circulation models with noise. These concepts will be applied to an example taken from a simple ENSO model. [ABSTRACT FROM AUTHOR]

Summary: Conventional techniques for quantifying and then managing flood risks are invalid under ‘non-stationary’ climate conditions. Trend detection and attribution are problematic given that the outcome depends on the start and end date of the record, choice of index and test statistic, assumed behaviour of the system, and many non-climatic confounding factors. Analyses are further hampered by short and non-homogeneous flow records. In this paper, we use an objective weather classification scheme to reconstruct the atmospheric drivers of fluvial flood occurrence and magnitude in England, Scotland and Wales since the 1870s. We demonstrate the index using long (>50year) annual maximum (AMAX) and peak over threshold (POT) flood records for 114 stations. Synoptic indices show modest skill at hindcasting multi-decadal variations in flood frequency at national, regional and catchment scales, but not for flood magnitudes. Flood rich episodes are identified in the periods 1908–1934, 1977–1988 and from 1998 onwards. We find that five weather types account for 68% of flood occurrence, and just three types were linked to the most widespread winter floods. These flood-generating systems generally show no sustained changes in frequency, persistence, relative contribution, or rain-bearing properties since the 1930s. However, there are emergent patterns in the day-to-day persistence (declining) and mean precipitation yield (rising) of anticyclonic weather types that merit further investigation. Based on our evaluation, we recommend use of objective weather indices derived from observed atmospheric pressure patterns when interpreting fluvial flood risk linked to climate drivers. [Copyright &y& Elsevier]

Coupled ocean-atmosphere general circulation models (GCMs) lack sufficient resolution to model the regional detail of changes to mean circulation and rainfall with projected climate warming. In this paper, changes in mean circulation and rainfall in GCMs are compared to those in a variable resolution regional climate model, the Conformal Cubic Atmospheric Model (CCAM), under a high greenhouse gas emissions scenario. The study site is Tasmania, Australia, which is positioned within the mid-latitude westerlies of the southern hemisphere. CCAM projects a different response in mean sea level pressure and mid-latitude westerly circulation to climate warming to the GCMs used as input, and shows greater regional detail of the boundaries between regions of increasing and decreasing rainfall. Changes in mean circulation dominate the mean rainfall response in western Tasmania, whereas changes to rainfall in the East Coast are less related to mean circulation changes. CCAM projects an amplification of the dominant westerly circulation over Tasmania and this amplifies the seasonal cycle of wet winters and dry summers in the west. There is a larger change in the strength than in the incidence of westerly circulation and rainfall events. We propose the regional climate model displays a more sensitive atmospheric response to the different rates of warming of land and sea than the GCMs as input. The regional variation in these results highlight the need for dynamical downscaling of coupled general circulation models to finely resolve the influence of mean circulation and boundaries between regions of projected increases and decreases in rainfall. [ABSTRACT FROM AUTHOR]

Since several destructive floods have occurred in Germany in the last decades, it is of considerable interest and relevance ( e.g., when undertaking flood defense design) to take a closer look at the climatic factors driving the changes in flood hazard in Germany. Even if there also exist non-climatic factors controlling the flood hazard, the present paper demonstrates that climate change is one main driver responsible for the increasing number of floods. Increasing trends in temperature have been found to be ubiquitous in Germany, with impact on air humidity and changes in (intense) precipitation. Growing trends in flood prone circulation pattern and heavy precipitation are significant in many regions of Germany over a multi-decade interval and this can be translated into the rise of flood hazard and flood risk. [ABSTRACT FROM AUTHOR]

Constraining the low-frequency (LF) behavior of general circulation models (GCMs) requires reliable observational estimates of LF variability. This two-part paper presents multiproxy reconstructions of Niño-3.4 sea surface temperature over the last millennium, applying two techniques [composite plus scale (CPS) and hybrid regularized expectation maximization (RegEM) truncated total least squares (TTLS)] to a network of tropical, high-resolution proxy records. This first part presents the data and methodology before evaluating their predictive skill using frozen network analysis (FNA) and pseudoproxy experiments. The FNA results suggest that about half of the Niño-3.4 variance can be reconstructed back to A.D. 1000, but they show little LF skill during certain intervals. More variance can be reconstructed in the interannual band where climate signals are strongest, but this band is affected by dating uncertainties (which are not formally addressed here). The CPS reliably estimates interannual variability, while LF fluctuations are more faithfully reconstructed with RegEM, albeit with inevitable variance loss. The RegEM approach is also tested on representative pseudoproxy networks derived from two millennium-long integrations of a coupled GCM. The pseudoproxy study confirms that reconstruction skill is significant in both the interannual and LF bands, provided that sufficient variance is exhibited in the target Niño-3.4 index. It also suggests that FNA severely underestimates LF skill, even when LF variability is strong, resulting in overly pessimistic performance assessments. The centennial-scale variance of the historical Niño-3.4 index falls somewhere between the two model simulations, suggesting that the network and methodology presented here would be able to capture the leading LF variations in Niño-3.4 for much of the past millennium, with the caveats noted above. [ABSTRACT FROM AUTHOR]

Abstract: We have used EML Surface Air Sampling Program (SASP) data to analyze the long-term trend in 7Be surface concentration and address possible correlation between this long-term trend and climatic changes, namely changes in precipitation patterns and temperature. In this paper we present 7Be concentration data from 23 sites, spanning over 25 years, all over the world, and extract long-term trend parameter using two independent techniques. The 7Be concentrations in most stations show a pronounced decreasing trend, potentially corresponding to statistically significant changes in transporting 7Be from upper atmosphere source to these sites. Weak negative correlation between 7Be concentration and amount of precipitation was also observed. However, more data from more representative sites around the world are needed the statistical robustness of this trend. [Copyright &y& Elsevier]

The inter-annual variability of the tropical Pacific Subsurface Ocean Temperature Anomaly (SOTA) and the associated anomalous atmospheric circulation over the Asian North Pacific during the El Niño-Southern Oscillation (ENSO) were investigated using National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) atmospheric reanalysis data and simple ocean data simulation (SODA). The relationship between the ENSO and the climate of China was revealed. The main results indicated the following: 1) there are two ENSO modes acting on the subsurface tropical Pacific. The first mode is related to the mature phase of ENSO, which mainly appears during winter. The second mode is associated with a transition stage of the ENSO developing or decaying, which mainly occurs during summer; 2) during the mature phase of El Niño, the meridionality of the atmosphere in the mid-high latitude increases, the Aleutian low and high pressure ridge over Lake Baikal strengthens, northerly winds prevail in northern China, and precipitation in northern China decreases significantly. The ridge of the Ural High strengthens during the decaying phase of El Niño, as atmospheric circulation is sustained during winter, and the northerly wind anomaly appears in northern China during summer. Due to the ascending branch of the Walker circulation over the western Pacific, the western Pacific Subtropical High becomes weaker, and south-southeasterly winds prevail over southern China. As a result, less rainfall occurs over northern China and more rainfall over the Changjiang River basin and the southwestern and eastern region of Inner Mongolia. The flood disaster that occurred south of Changjiang River can be attributed to this. The La Niña event causes an opposite, but weaker effect; 3) the ENSO cycle can influence climate anomalies within China via zonal and meridional heat transport. This is known as the 'atmospheric-bridge', where the energy anomaly within the tropical Pacific transfers to the mid-high latitude in the northern Pacific through Hadley cells and Rossby waves, and to the western Pacific-eastern Indian Ocean through Walker circulation. This research also discusses the special air-sea boundary processes during the ENSO events in the tropical Pacific, and indicates that the influence of the subsurface water of the tropical Pacific on the atmospheric circulation may be realized through the sea surface temperature anomalies of the mixed water, which contact the atmosphere and transfer the anomalous heat and moisture to the atmosphere directly. Moreover, the reason for the heavy flood within the Changjiang River during the summer of 1998 is reviewed in this paper. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric circulation and rainfall are important factors controlling the deposition of atmospheric pollutants. This paper aims to quantify the role of these factors in the deposition of sulphur and nitrogen compounds, using case studies in the United Kingdom and Poland. The FRAME model has been applied to calculate deposition for the base year (2005), dry and wet years (2003 and 2000 for the UK and 2003 and 1974 for Poland, respectively), and for years with contrasting annual wind patterns (1986 and 1996 for the UK, and 1998 and 1996 for Poland). Variation in annual wind and rainfall resulted in statistically significant changes in spatial patterns of deposition and the national deposition budget of sulphur and nitrogen compounds in both countries. The deposition budgets of S and N are 5% lower than for the reference year if the dry year is considered in both countries. For the wet year, there is an increase in country total deposition by up to 17%. Years with an increased frequency of eastern winds are associated with an increase in deposition of up to 14% in Poland and 8% in the UK. The national deposition budget is below the average for the years with high frequencies of W winds, especially for the UK (up to 13%). Wet deposition varies due to meteorological factors to a larger extent than dry deposition. In Poland, the changes in national deposition budget due to meteorological factors exceed the changes resulting from emission abatements in years 2000–2009 for nitrogen compounds. In the UK, emission abatements influence the national deposition budget to a larger extent than meteorological changes (except for NH x ). The findings are important in relation to future climate changes, especially considering the potential increase in annual precipitation. This may lead to an increase in deposition over mountainous areas with sensitive ecosystems, where annual rainfall brings significant load of S and N. Changes in annual wind speed and frequency can modify the spatial pattern of deposition. An increased frequency of W winds will benefit both countries through reduced S and N deposition. NW areas of Poland and the UK will suffer from above-average deposition during years with enhanced easterly flow, and this may result in critical loads for acid and nitrogen deposition being exceeded over the areas that are at present sufficiently protected from acidification and eutrophication, despite the ongoing emission abatements. [Copyright &y& Elsevier]

Marine Isotope Stage (MIS) 13, an interglacial about 500,000 years ago, is unique due to an exceptionally strong East Asia summer monsoon (EASM) occurring in a relatively cool climate with low greenhouse gas concentrations (GHG). This paper attempts to find one of the possible mechanisms for this seeming paradox. Simulations with an Earth System model LOVECLIM show that the presence of ice sheets over North America and Eurasia during MIS-13 induces a positive phase of the winter North Atlantic Oscillation (NAO) like feature. The ocean having a longer memory than the atmosphere, the oceanic anomalies associated with NAO persists until summer. The signals of summer NAO are transmitted to East Asia to reinforce the monsoon there through the stationary waves excited at the Asian Jet entrance. The geopotential height shows clearly a mid-latitude wave train with positive anomalies over the eastern Mediterranean/Caspian Sea and the Okhotsk Sea and a negative anomaly over Lake Baikal. This reinforces the effect of the high-latitude wave train induced independently by the Eurasian ice sheet topography as shown in previous study. These features reinforce the Meiyu front and enhance the precipitation over East Asia. The results obtained from LOVECLIM are further confirmed by an atmospheric general circulation model, ARPEGE. [ABSTRACT FROM AUTHOR]

Abstract: The horizontal transport of water in Earth''s surface layer, including sea level change, deglaciation, and surface runoff, is a manifestation of many geophysical processes. These processes entail ocean and atmosphere circulation and tidal attraction, global climate change, and the hydrological cycle, all having a broad range of spatiotemporal scales. The largest atmospheric mass variations occur mostly at synoptic wavelengths and at seasonal time scales. The longest wavelength component of surface mass transport, the spherical harmonic degree-1, involves the exchange of mass between the northern and southern hemispheres. These degree-1 mass loads deform the solid Earth, including its surface, and induce geocenter motion between the center-of-mass of the total Earth system (CM) and the center-of-figure (CF) of the solid Earth surface. Because geocenter motion also depends on the mechanical properties of the solid Earth, monitoring geocenter motion thus provides an additional opportunity to probe deep into Earth''s interior. Most modern geodetic measurement systems rely on tracking data between ground stations and satellites that orbit around CM. Consequently, geocenter motion is intimately related to the realization of the International Terrestrial Reference Frame (ITRF) origin, and, in various ways, affects many of our measurement objectives for global change monitoring. In the last 15 years, there have been vast improvements in geophysical fluid modeling and in the global coverage, densification, and accuracy of geodetic observations. As a result of these developments, tremendous progress has been made in the study of geocenter motion over the same period. This paper reviews both the theoretical and measurement aspects of geocenter motion and its implications. [Copyright &y& Elsevier]

Zonal and meridional surface temperature gradients are considered to be determinants of large-scale atmospheric circulation patterns. However, there has been limited investigation of these gradients as diagnostic aids. Here, the twentieth-century variability in the Northern Hemisphere equator-to-pole temperature gradient (EPG) and the ocean-land temperature contrast (OLC) is explored. A secular trend in decreasing EPG and OLC is noted. Decadal and interannual (ENSO-related) variations in the joint distribution of EPG and OLC are identified, hinting at multistable climate states that may be indigenous to the climate or due to changing boundary forcings. The NH circulation patterns for cases in the tails of the joint distribution of EPG and OLC are also seen to be different. Given this context, this paper extends past efforts to develop insights into jet stream dynamics using the Lorenz-1984 model, which is forced directly and only by EPG and OLC. The joint probability distribution of jet stream and eddy energy, conditional on EPG and OLC scenarios, is investigated. The scenarios correspond to (i) warmer versus colder climate conditions and (ii) polarized ENSO phases. The latter scenario involves the use of a heuristic ENSO model to drive the Lorenz-1984 model via a modulation of the EPG or the OLC. As with GCMs, the low-order model reveals that the response to El Niño forcing is not similar to an anthropogenic warming signature. The potential uses of EPG and OLC as macro-level indicators of climate change and variability and for comparing results across GCMs and observations are indicated. [ABSTRACT FROM AUTHOR]

This paper assesses the relative uncertainties from GCMs and from hydrological models in modeling climate change impact on runoff across southeast Australia. Five lumped conceptual daily rainfall-runoff models are used to model runoff using historical daily climate series and using future climate series obtained by empirically scaling the historical climate series informed by simulations from 15 GCMs. The majority of the GCMs project a drier future for this region, particularly in the southern parts, and this is amplified as a bigger reduction in the runoff. The results indicate that the uncertainty sourced from the GCMs is much larger than the uncertainty in the rainfall-runoff models. The variability in the climate change impact on runoff results for one rainfall-runoff model informed by 15 GCMs (an about 28%%-35%% difference between the minimum and maximum results for mean annual, mean seasonal, and high runoff) is considerably larger than the variability in the results between the five rainfall-runoff models informed by 1 GCM (a less than 7%% difference between the minimum and maximum results). The difference between the rainfall-runoff modeling results is larger in the drier regions for scenarios of big declines in future rainfall and in the low-flow characteristics. The rainfall-runoff modeling here considers only the runoff sensitivity to changes in the input climate data (primarily daily rainfall), and the difference between the hydrological modeling results is likely to be greater if potential changes in the climate-runoff relationship in a warmer and higher CO2 environment are modeled. [ABSTRACT FROM AUTHOR]

This paper describes recent variations of the North Atlantic eddy-driven jet stream and analyzes the mean response of the jet to anthropogenic forcing in climate models. Jet stream changes are analyzed both using a direct measure of the near-surface westerly wind maximum and using an EOF-based approach. This allows jet stream changes to be related to the widely used leading patterns of variability: the North Atlantic Oscillation (NAO) and East Atlantic (EA) pattern. Viewed in NAO-EA state space, isolines of jet latitude and speed resemble a distorted polar coordinate system, highlighting the dependence of the jet stream quantities on both spatial patterns. Some differences in the results of the two methods are discussed, but both approaches agree on the general characteristics of the climate models. While there is some agreement between models on a poleward shift of the jet stream in response to anthropogenic forcing, there is still considerable spread between different model projections, especially in winter. Furthermore, the model responses to forcing are often weaker than their biases when compared to a reanalysis. Diagnoses of jet stream changes can be sensitive to the methodologies used, and several aspects of this are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews the current understanding of the effect of climate change on extreme sea levels in the South Pacific region. This region contains many locations that are vulnerable to extreme sea levels in the current climate, and projections indicate that this vulnerability will increase in the future. The recent publication of authoritative statements on the relationship between global warming and global sea level rise, tropical cyclones and the El Niño-Southern Oscillation phenomenon has motivated this review. Confident predictions of global mean sea level rise are modified by regional differences in the steric (density-related) component of sea level rise and changing gravitational interactions between the ocean and the ice sheets which affect the regional distribution of the eustatic (mass-related) contribution to sea level rise. The most extreme sea levels in this region are generated by tropical cyclones. The intensity of the strongest tropical cyclones is likely to increase, but many climate models project a substantial decrease in tropical cyclone numbers in this region, which may lead to an overall decrease in the total number of intense tropical cyclones. This projection, however, needs to be better quantified using improved high-resolution climate model simulations of tropical cyclones. Future changes in ENSO may lead to large regional variations in tropical cyclone incidence and sea level rise, but these impacts are also not well constrained. While storm surges from tropical cyclones give the largest sea level extremes in the parts of this region where they occur, other more frequent high sea level events can arise from swell generated by distant storms. Changes in wave climate are projected for the tropical Pacific due to anthropogenically-forced changes in atmospheric circulation. Future changes in sea level extremes will be caused by a combination of changes in mean sea level, regional sea level trends, tropical cyclone incidence and wave climate. Recommendations are given for research to increase understanding of the response of these factors to climate change. Implications of the results for adaptation research are also discussed. [Copyright &y& Elsevier]

Through analyzing the changes of averaged temperature and precipitation along the Brahmaputra Valley from 1980 to 2005, and investigating the correlation between atmospheric circulation indices and these changes, the respondence of the Brahmaputra Valley to the global warming had been analyzed in this paper. It is found that the Brahmaputra Valley climate became warmer and wetter from 1980 to 2005, and the change magnitude is higher than that over the whole Tibetan Plateau. Therefore, the respondence of the Brahmaputra valley to the global warming is more evident than that of the whole plateau during the period. The relationship between atmospheric circulation indices and the regional climate change is significant. When North Atlantic Oscillation index is higher in summer, the climate of the Brahmaputra Valley becomes warmer and dryer; vice versa. When South Oscillation index is higher, it becomes warmer and wetter; vice versa.Worthy of note, the results in this study only emphasize some evidence of change in temperature and precipitation over the Brahmaputra Valley during 1980-2005. [ABSTRACT FROM AUTHOR]

In this paper we reconstructed river runoff to the Baltic Sea since 1500 using temperature and atmospheric circulation indices, showing the important atmospheric processes for river runoff in different regions. Runoff appears to be strongly linked to temperature, wind and rotational circulation components in the northern region and Gulf of Finland, but more associated with rotational and deformation circulation components in the south. No significant long-term change has been detected in total river runoff to the Baltic Sea for 500 years, although decadal and regional variability is large. Analysis of runoff sensitivity to temperature shows that the south region may become drier with rising air temperatures. This is in contrast to the north region and Gulf of Finland where warmer temperatures are associated with more river runoff. Over the past 500 years the total river runoff to the Baltic Sea has decreased by 3% (450 m/s) per degree Celsius increase. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Postglacial expansion of deciduous oak woodlands of the Zagros-Anti-Taurus Mountains, a major biome of the Near East, was delayed until the middle Holocene at ~6300 cal. yr BP. The current hypotheses explain this delay as a consequence of a regional aridity during the early Holocene, slow migration rates of forest trees, and/or a long history of land use and agro-pastoralism in this region. In the present paper, support is given to a hypothesis that suggests different precipitation seasonalities during the early Holocene compared with the late Holocene. The oak species of the Zagros-Anti-Taurus Mts, particularly Quercus brantii Lindl., are strongly dependent on spring precipitation for regeneration and are sensitive to a long dry season. Detailed analysis of modern atmospheric circulation patterns in SW Asia during the late spring suggests that the Indian Summer Monsoon (ISM) intensification can modify the amount of late spring and/or early summer rainfall in western/northwestern Iran and eastern Anatolia, which could in turn have controlled the development of the Zagros-Anti-Taurus deciduous oak woodlands. During the early Holocene, the northwestward shift of the Inter-Tropical Convergence Zone (ITCZ) could have displaced the subtropical anticyclonic belt or associated high pressure ridges to the northwest. The latter could, in turn, have prevented the southeastward penetration of low pressure systems originating from the North Atlantic and Black Sea regions. Such atmospheric configuration could have reduced or eliminated the spring precipitation creating a typical Mediterranean continental climate characterized by winter-dominated precipitation. This scenario highlights the complexity of biome response to climate system interactions in transitional climatic and biogeographical regions. [ABSTRACT FROM AUTHOR]

The Northern Hemisphere extended winter mean stratospheric vortex alternates between a strong and a weak state, which is manifested in a statistically significant bimodal distribution. In the end of the 1970s a regime change took place, increasing the frequency of the strong phase relative to the weak phase. This paper investigates the connection between the regime behavior of the vortex and the equatorial quasi-biennial oscillation (QBO) in three different datasets. Although there are some differences between the datasets, they agree regarding the general picture. It is found that stratospheric equatorial wind between 70 and 8 hPa shows a bimodal structure in the Northern Hemisphere winter. Such bimodality is nontrivial as it requires only weak variability in the amplitude. Unimodality is found above 8 hPa, where the semiannual oscillation dominates. A strong coincidence is found between strong (weak) vortex winters and winter in the westerly (easterly) QBO regime. Furthermore, the change of the vortex in the late 1970s can be related to a change in the QBO from a period with strong bimodality to a period with weak bimodality. Careful consideration of the statistical significance shows that this change in the QBO can be a random process simply related to the annual sampling of the QBO. Finally, previous findings of phase locking between the QBO and the annual cycle are considered; it is shown that the phase locking is related to the seasonal variations in the bimodality of the QBO. [ABSTRACT FROM AUTHOR]

The article presents a study on the climatic fluctuation during the early 20th century. It states that study was guided by review of papers from scientists investigated the climatic fluctuation and its relevance to the continuous climate change. Results show anomaly patterns in the surface air temperature (SAT), sea surface temperature (SST) and related ecosystem that causes anthropogenic climate disturbance attributed to atmospheric circulation.

The idea of using large-scale information to predict local climate variability is widely exploited in climate change impact studies as an alternative to computationally expensive high-resolution models. This approach implies the hypothesis that the statistical relationship between large-scale climate states and local variables defined for the present-day climate remains valid in the altered climate. In this paper, the concept of weather regimes is used to deduce a relationship between large-scale circulation and European winter temperature. The change in temperature with increased greenhouse gases is, however, not homogeneous among the individual regimes. As a result, the impact of the weather regimes on local temperature changes varies in the future, limiting its usefulness for refining temperature changes to the small scale. [ABSTRACT FROM AUTHOR]

To better understand variability in weather and climate, it is vital to address past atmospheric circulation. This need requires meteorological information not just from the surface but also at upper levels. Current global upper-level datasets only reach back to the 1940s or 1950s and do not cover some important periods in the first half of the twentieth century. Extending the observational record is therefore considered important in order to analyze climate variability in the past and verify global climate models used to predict future climate change. Although earlier upper-air data from platforms such as radio-sondes, aircraft, pilot balloons, registering balloons, and kites are available from various sources, no systematic compilation and quality assessment of upper-level data prior to the International Geophysical Year (1957/58) has ever been performed. Here we present the Comprehensive Historical Upper-Air Network (CHUAN). It is a consistent global historical upper-air dataset that has been derived from heterogeneous data available from various sources as well as from newly digitized data. This paper describes the CHUAN dataset, the metadata, the quality control procedures, and the relationship to existing datasets. Some examples are given of its usefulness for analyzing weather and climate during the first half of the twentieth century. The CHUAN dataset comprises 3987 station records worldwide or about 16.4 million profiles (of which 12.6 million are before 1958 and 5.3 million, primarily from pilot balloons, are before 1948). A monthly mean version can be downloaded from the World Wide Web (). A supplement to this article is available online: DOI: [ABSTRACT FROM AUTHOR]

This paper conducts the assimilating experiments and simulating experiments on typhoon "Aere" (No. 0418), by use of bogus data assimilation (BDA) method combined with advanced microwave sounding unit-A (AMSU-A) data assimilation method in the fifth-generation National Center for Atmospheric Research (NCAR)/Penn State Mesoscale Model Version-3 (MM5V3), the Radiative Transfer for TIROS-N Operational Vertical Sounder Version-7 (RTTOV) model, and their adjoint models. The Bogus data constructed with BDA technique are mainly located at sea level, while the peak energy contribution levels of the sounder channels selected in AMSU-A data assimilation technique are mainly located at upper troposphere. The two types of data can reconstruct the meso-scale information and improve the typhoon initial fields under themodel dynamic forcing effect, respectively from the low level and the upper level of atmosphere during the assimilating process. Numerical results show that with four-dimensional variational data assimilation (4DVAR) technique the circulation of initial fields is improved, the "warm core" of typhoon is enhanced, the "cloud water" phenomenon that occurs in the optimal initial fields and the numerical model is changed into "warm start" from "cold start". [ABSTRACT FROM AUTHOR]

Abstract: This paper documents the main features of the climate and climate variability over South America, on the basis of instrumental observations gathered during the 20th Century. It should provide a modern reference framework for paleoclimate research in South America, targeting high-resolution proxies over the past few centuries. Several datasets suitable for present-day climate research are first described, highlighting their advantages as well as their limitations. We then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans. In particular, the diversity of precipitation, temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large-scale circulation caused by the Andes cordillera, the contrasting oceanic boundary conditions and the landmass distribution. Similarly, the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence, as some regions are more influenced by large-scale phenomena rooted in the tropical oceans while others are more influenced by high-latitude phenomena. The impact of these large-scale phenomena over South America is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields. We have included a discussion on the seasonality and long-term stability of such impacts, and complemented our general description by an updated review of the literature on climate variability over specific regions. [Copyright &y& Elsevier]

Abstract: Reconstruction of hydroclimate variability is an important part of understanding natural climate change on decadal to millennial timescales. Peatland records reconstruct ‘bog surface wetness’ (BSW) changes, but it is unclear whether it is a relative dominance of precipitation or temperature that has driven these variations over Holocene timescales. Previously, correlations with instrumental climate data implied that precipitation is the dominant control. However, a recent chironomid inferred July temperature record suggested temperature changes were synchronous with BSW over the mid-late Holocene. This paper provides new analyses of these data to test competing hypotheses of climate controls on bog surface wetness and discusses some of the distal drivers of large-scale spatial patterns of BSW change. Using statistically based estimates of uncertainty in chronologies and proxy records, we show a correlation between Holocene summer temperature and BSW is plausible, but that chronologies are insufficiently precise to demonstrate this conclusively. Simulated summer moisture deficit changes for the last 6000 years forced by temperature alone are relatively small compared with observations over the 20th century. Instrumental records show that summer moisture deficit provides the best explanatory variable for measured water table changes and is more strongly correlated with precipitation than with temperature in both Estonia and the UK. We conclude that BSW is driven primarily by precipitation, reinforced by temperature, which is negatively correlated with precipitation and therefore usually forces summer moisture deficit in the same direction. In western Europe, BSW records are likely to be forced by changes in the strength and location of westerlies, linked to large-scale North Atlantic ocean and atmospheric circulation. [Copyright &y& Elsevier]

Based on the availability of hemispheric gridded data sets from observations, analysis and global climate models, objective cyclone identification methods were developed and applied to these data sets. Due to the large amount of investigation methods combined with the variety of different datasets, a multitude of results exist, not only for the recent climate period but also for the next century, assuming anthropogenic changed conditions. Different thresholds, different physical quantities, and considerations of different atmospheric vertical levels add to a picture that is difficult to combine into a common view of cyclones, their variability and trends, in the real world and in GCM studies. Thus, this paper will give a comprehensive review of the actual knowledge on climatologies of mid-latitude cyclones for the Northern and Southern Hemisphere for the present climate and for its possible changes under anthropogenic climate conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper documents the main features of climate and climate variability across the Monte Desert for the Last Glacial Maximum, the Glacial–Interglacial transition, and the Holocene on the basis of proxy records and for the 20th century using instrumental observations. The climate in the Monte is determined by interactions between regional physiography and atmospheric circulation in the 25–45°S sectors of South America. Although arid and semi-arid conditions prevail across the Monte, its large latitudinal extent and complex topography introduce many particularities at local scales. Paleoclimatic records and model simulations of past climates suggest significant variations in the atmospheric circulation, temperature and rainfall patterns since the Last Glacial Maximum. High-resolution proxy records east of the Andes support the existence of complex climatic patterns with similar temperature changes across the whole region but opposite precipitation variations between subtropical and mid-latitude sectors in the Monte during the past millennium. The present-day climate is depicted in terms of the space and time variability of the near-surface temperature, rainfall and tropospheric wind patterns. Uneven temperature trends over the Monte were recorded for two separate (1920–44 and 1977–2001) global warming periods in the 20th century. Additional warming evidence in the region is provided by extreme temperature records. The non-homogeneous regional pattern of precipitation shows a positive long-term increase between 30 and 40°S during the interval 1985–2001. Ensemble of climate experiments accomplished with general circulation models provide the most likely changes in temperature and rainfall to occur by the end of this century in relation to present climate. Temperature increases, larger in summer than in winter, will be concurrent with more abundant precipitations in summer, but almost no changes or even small reductions in winter across the Monte. [Copyright &y& Elsevier]

This paper traces the history of the use of ships' logbooks in climatological studies from the earliest days of the 17th century to the present day. Although early theories concerning global air circulations by Halley and Hadley were based on information gathered by mariners and recorded in their logbooks, it has only been in the last two decades that interest has returned to this important, but long-overlooked, source of climatic information. Attention is drawn to the many advantages offered by logbooks, in particular the long period of time that they collectively cover, their near-global geographic range, the large number of such documents that have survived, and the degree of detailed and reliable record that they provide. Before the mid-19th century, much of the recorded information is noninstrumental in character but its scientific potential is reflected in the variety of approaches and methods that have been used in its analysis and in the equally wide range of outcomes, from databases to synoptic charts and long-time series indices that have emerged from the most recent research. Attention is also drawn to the benefits to be derived from old and more recent instrumental logbook data. As only a small percentage of the tens of thousands of logbooks that have been preserved have thus far been examined, the potential for yet further development is enormous. [ABSTRACT FROM AUTHOR]

The quasibiennial oscillation (QBO) dominates the variability of the equatorial stratosphere and also affects the circulation and temperature of the extratropical region. In this paper we review previous work showing that the mid- to high-latitude circulation is weaker (stronger) when QBO easterlies (westerlies) dominate in the low equatorial stratosphere. The accepted explanation for the extratropical QBO signature is based on the QBO modulation of upward propagating planetary Rossby waves. This mechanism is consistent with the strong seasonality observed in the extratropical QBO. The largest QBO signature in the northern extratropical stratosphere occurs during winter when the dominating westerly wind allows the penetration of planetary waves in the northern stratosphere. However, during the southern winter, planetary waves do not disrupt the southern stratospheric vortex and the largest QBO signature is found during the late spring (November). To further illustrate these mechanisms, we analyze the QBO signature on the mid- to high-latitude circulation of the stratosphere using data from the ERA-40 reanalysis. The extratropical signature in both hemispheres is evaluated as a function of the latitude–height structure of the zonal wind in the tropical region in order to determine how the extratropical response depends on the vertical phase structure of the tropical QBO. We also analyze the QBO impact on planetary wave activity in order to determine how this modulation can explain the observed extratropical QBO signal. [ABSTRACT FROM AUTHOR]

The Lagoon of Nador (Morocco) has been subject to relevant man-made changes in recent years, which consisted of closing the inlet and opening a new one, wider and deeper, with long lateral jetties. In this paper, we study some of the consequences of this modification, using a 3D hydrodynamic model that allows a comparison of the two configurations (old and new inlet). This would be not possible analysing only the observations and the approach we followed is a general method that can be applied wherever man-made or natural changes affect a coastal system. We have created two numerical grids, one with the old inlet and one with the new inlet, both covering the entire lagoon and a wide part of the coastal area. Using these two configurations, fully baroclinic simulations were run for one year. The results show a significant increase of the tidal amplitude and of the water circulation inside the lagoon, with a tidal prism four times larger. The change of the tidal asymmetry from positive to negative values (−0.7 in the inlet) causes a shift toward the ebb dominance, with implications for the mid-term morphological evolution. With the new inlet the water renewal time of the lagoon decreased from 57 to 15 days and the water temperature got warmer in winter (+1 °C) and colder in summer (−2 °C). As a consequence of this, the evaporation lowered and the salinity reduced by 0.8 PSU. The seasonal variability of the water renewal time shows that the tidal forcing, the baroclinic circulation and the wind contribute to the mixing processes. The mixing capacity of the lagoon (0.7) did not change because it is an intrinsic property of the lagoon morphology and of the atmospheric forcing. Finally, we found that the change of the water renewal time, with the new inlet, is higher than the change predicted, with the old inlet, under the RCP8.5 climate change scenario. • The opening of the new inlet lowers significantly the water renewal time, increases the exchange with sea so that the thermohaline characteristics of the lagoon are more similar to the sea. • The mixing efficiency of the lagoon did not change significantly, because it depends much more on the surface boundary conditions (wind forcing), rather than the lateral boundary conditions. • The new inlet changed the characteristic of the tidal signal from flood dominated (with the old inlet configuration) to ebb dominated. • The residual circulation is significantly influenced by the tidal jet that expands into the lagoon and the dominant N-E wind. • This anthropogenic change lowers the renewal time of the lagoon as like the climate change, but in a much shorter time and with higher magnitude. [ABSTRACT FROM AUTHOR]

A government-funded scheme, the UK Climate Change Communications Initiative (UKCCCI), has provided money for organisations to deliver projects that attempt to impact positively on people's attitudes towards climate change. This devolution of communications is a relatively novel approach after previous centralised campaigns. This paper considers what size of target audience is most appropriate for attitude change initiatives. It compares data from a regional UKCCCI project aimed at residents of two counties with a nationally representative dataset. Regional data are also analysed to see if there are differences in attitudes within the two-counties target audience. The study suggests that attitude change interventions must strike a balance between personalisation of information and the higher cost of targeting smaller groups with more specific material. [ABSTRACT FROM AUTHOR]

Linking sinuosity, a fairly recently developed metric, with high temperature extremes (HTEs) can be both useful and insightful to better understand the physical mechanisms behind HTEs. However, it is not clear whether there exists a relationship between the sinuosity changes and HTE changes in present and future climate conditions over southeastern China. In this paper, the anomalous characteristics of the atmospheric circulation are quantified by sinuosity. Three sinuosity metrics are used in this study: individual sinuosity (SIN), aggregate sinuosity (ASIN), and comprehensive sinuosity (CSIN). Furthermore, we examine the relationship between sinuosity changes and HTE changes in present and future climate conditions. ASIN is strongly correlated with surface air temperature (SAT). We find that the influence of individual sinuosity (SIN) at different latitudes on the SAT of southeastern China is different. The SIN of low (middle) latitude isohypses has significant positive (negative) correlations with the SAT of southeastern China. The SIN of high-latitude isohypses is rather limited and can therefore be ignored. The projected relationship between the sinuosity changes and HTE changes in the late 21st century suggests similar results. The change in SAT is related to the changes in climate variables over southeastern China in the future, and these changes increase with the increase in Z500 or V850 and the decrease in U500. Moreover, the frequencies of large (small) comprehensive sinuosity (CSIN) values at low (mid) latitudes will increase. At the end of the 21st century, Z500 isohypses at different latitudes will have an obvious poleward shift. Our results indicate that measuring the aggregate waviness of the midtropospheric flow (via sinuosity) can provide insight regarding HTEs, and the climate model output can be used to examine the future likelihood of increased HTE. [ABSTRACT FROM AUTHOR]

Extreme weather and climate events have received increased attention in the last years due to their impact on different aspects of human activity. The aim of the present paper is to bring to better understanding of the causes of extreme precipitation occurrence in Bulgaria. An extreme precipitation month is defined as a month registering precipitation totals lower or higher than certain thresholds. Extremely wet months are defined as months with total precipitation amounts higher than 90% percentiles of the gamma distribution in the reference period 1961-1990. As extremely dry month, we consider the month with total precipitation lower than 10% of the gamma distribution. Spatial changes in the occurrence of extreme precipitation are investigated by the application of the cluster analysis. The circulation patterns were analyzed with regard to sea level pressure. The relation between the fluctuations of the extreme months and atmospheric circulation mechanism teleconnection is study by the North Atlantic Oscillation Indices (NAOI), the Eastern Atlantic pattern (EA) and the Mediterranean Oscillation Indices (MOI). [ABSTRACT FROM AUTHOR]

This paper investigates regional sources and transport routes of Asian dust observed in Korea over the past 40 years, that is from 1965 to 2004. These long-term changes were studied in relation to climatic changes and causes. About 87% of dust events in Korea occur in the spring and have been increasing steadily since the 1980s. These trends can be attributed to regional changes in dust sources to windward and the resultant transport pathways of dust storms. This study establishes that dust events have greatly increased during the 3 years from 2000 to 2002. It may be the result of not only an eastward shift in the regional source of dust but also changes in upper-level synoptic transport patterns. Intensified atmospheric circulation and an associated increase in wind speed as well as changes in snow cover, surface wetness and potential evaporation rates throughout Inner Mongolia and Manchuria are likely to be the main causes of the steadily increasing number of dusty days in Korea. [Copyright &y& Elsevier]

Recent dry years (combined dry winter and summer months) within the UK (2005 and 2006) have enhanced concerns relating to long term water resources and future water provision in large conurbations. This paper examines the mechanisms responsible for precipitation variability for five different areas in Edinburgh (precipitation regions) using composite historic precipitation records for the period 1861–2005. Trend analysis and principal component analysis (PCA) were undertaken to examine precipitation variability over time and space. Annual correlation co-efficients were derived for relationships between precipitation areas, atmospheric–oceanographic variations and geographic parameters. Stepwise regression models were constructed to specify annual precipitation, through atmospheric variations, for each of the precipitation areas. Significant downward trends in precipitation ( p < 0.05) were noted in two out of the five precipitation areas, with one principal component representing precipitation variability over Edinburgh and the Pentland Hills. Precipitation variability is best explained by fluctuations in pressure, altitude and proximity to coast. Precipitation trends cannot be explained by changes in atmospheric circulation patterns. [ABSTRACT FROM AUTHOR]

Abstract: The zonal displacement of the western Pacific subtropical high remarkably influences the climate anomalies in China. In this paper, a new zonal index of the subtropical high is defined by modifying previous indices, and is used to investigate the relationship between the zonal displacement of the subtropical high and the dominant modes of 850-hPa circulations. It is found that the zonal displacement of the subtropical high is significantly correlated with the first two leading modes of circulations. In particular, the correlation coefficient between the index and the time series associated with the second mode is as high as 0.78 in 1958–2003 (46years). Since the second mode is not associated with significant anomalies of sea surface temperatures, the above results imply the difficulty in seasonal forecasting of the zonal displacement of the subtropical high. In addition, the interannual variability in the zonal displacement of the subtropical high has been considerably enhanced since 1978, due to the effects of both dominant modes, especially the second mode. This is likely to account for the frequent occurrence of anomalous climate in China during the recent two decades. [Copyright &y& Elsevier]

The fluctuation–dissipation theorem (FDT) states that for systems with certain properties it is possible to generate a linear operator that gives the response of the system to weak external forcing simply by using covariances and lag-covariances of fluctuations of the undisturbed system. This paper points out that the theorem can be shown to hold for systems with properties very close to the properties of the earth’s atmosphere. As a test of the theorem’s applicability to the atmosphere, a three-dimensional operator for steady responses to external forcing is constructed for data from an atmospheric general circulation model (AGCM). The response of this operator is then compared to the response of the AGCM for various heating functions. In most cases, the FDT-based operator gives three-dimensional responses that are very similar in structure and amplitude to the corresponding GCM responses. The operator is also able to give accurate estimates for the inverse problem in which one derives the forcing that will produce a given response in the AGCM. In the few cases where the operator is not accurate, it appears that the fact that the operator was constructed in a reduced space is at least partly responsible. As an example of the potential utility of a response operator with the accuracy found here, the FDT-based operator is applied to a problem that is difficult to solve with an AGCM. It is used to generate an influence function that shows how well heating at each point on the globe excites the AGCM’s Northern Hemisphere annular mode (NAM). Most of the regions highlighted by this influence function, including the Arctic and tropical Indian Ocean, are verified by AGCM solutions as being effective locations for stimulating the NAM. [ABSTRACT FROM AUTHOR]

This paper investigates the mean spatial features of the winds in the Mediterranean and Black Seas using the wind fields observed by the SeaWinds scatterometer. Five years (2000–04) of data have been analyzed on annual and seasonal basis, with particular attention paid to the meso- and local scales. The fields show the existence of structured regional wind systems—in particular, the mistral in the western Mediterranean and the etesians in the Levantine Basin, which are characterized, respectively, by high wind variability and moderate steadiness and by low wind variability and high steadiness. Estimated seasonal mean wind stress τ fields show that the values falling in the top range 0.15 < τ < 0.20 N m-2 affect a large portion of the Mediterranean Basin in winter, in the belt extending from the Gulf of Lion up to the Levantine Basin and the northern Black Sea. In the other seasons, only few regions experience such high values of τ. The analysis of the wind vorticity shows and quantifies the main cyclonic and anticyclonic circulations, and the study of the joint features of wind stress and vorticity has identified the strongest and most persisting local-scale wind circulations produced by the interaction between the wind flow and the orography. They occur at the lee side of Sardinia–Corse and Crete–Rhodos Islands and persist in all seasons, with some seasonal variation in strength and extent. The areas affected by the orographic disturbances are characterized by high values of wind stress and by a structure of vorticity showing alternating areas of cyclonic and anticyclonic circulations, whose strength is comparable to those of the regional-scale cyclones. [ABSTRACT FROM AUTHOR]

The paper uses Greenland GISP2 ice core data together with historical documentary information to investigate the nature of climate changes that took place between AD 1270 and 1450 across the North Atlantic region. Detailed Deuterium and deuterium excess time series resolved to c. 8–10 samples per year are used to reconstruct relative changes in Greenland air temperature and past changes in sea surface temperature across the western North Atlantic. The data show that sea surface temperatures during the late thirteenth century and the majority of the fourteenth century were characterized by relatively high-amplitude warming and cooling ‘events’. These changes preceded a marked reduction in the amplitude of the sea surface temperature changes c. 30–40 years before the well-known change in Northern Hemisphere tropospheric circulation characterized by a marked increase in regional storminess that started between c. AD 1400 and 1420. The time interval between AD 1270 and 1450 also appears over Greenland to have featured several short-lived phases of marked air temperature lowering that were rarely ever equalled during succeeding centuries. We believe that the climate changes described here are of considerable importance in understanding climate dynamics of the North Atlantic region since they took place at a time when the North Atlantic Oscillation (NAO) may have been weak. The results also show that the marked change in atmospheric circulation coincident with a significant increase in North Atlantic storminess at c. AD 1400–1420, possibly the biggest such change in the Holocene, took place after the strong perturbations in North Atlantic sea surface temperature (both warming and cooling) described here as well as after several episodes of air temperature lowering over Greenland. [ABSTRACT FROM AUTHOR]

Aerosol size is still a poorly constrained quantity in general circulation models (GCMs). By using the modal radii of the coarse and fine mode retrieved from 103 stations in the Aerosol Robotic Network (AERONET) and the fine mode aerosol optical depth fraction derived from both the Moderate Resolute Imaging Spectroradiometer (MODIS) Terra and AERONET, a globally and monthly averaged aerosol size distribution dataset was computed assuming internally mixed aerosols. Different methods were employed in creating the size distribution datasets that were input to the ECHAM4 climate model giving a globally averaged aerosol optical depth (AOD) at 500 nm that ranged from 0.11 to 0.20 depending on the method. This translates into a globally averaged direct aerosol top-of-atmosphere forcing range from -1.6 to -3.9 W m-2. Reducing the uncertainty in the aerosol sizes is important when using AOD to validate models since mass burden errors can then be assumed to be the main AOD error source. This paper explores a procedure that can help achieve this goal. [ABSTRACT FROM AUTHOR]

Tropical warm pools appear as the primary mode in the distribution of tropical sea surface temperature (SST). Most previous studies have focused on the role of atmospheric processes in homogenizing temperatures in the warm pool and establishing the observed statistical SST distribution. In this paper, a hierarchy of models is used to illustrate both oceanic and atmospheric mechanisms that contribute to the establishment of tropical warm pools. It is found that individual atmospheric processes have competing effects on the SST distribution: atmospheric heat transport tends to homogenize SST, while the spatial structure of atmospheric humidity and surface wind speeds tends to remove homogeneity. The latter effects dominate, and under atmosphere-only processes there is no warm pool. Ocean dynamics counter this effect by homogenizing SST, and it is argued that ocean dynamics is fundamental to the existence of the warm pool. Under easterly wind stress, the thermocline is deep in the west and shallow in the east. Because of this, poleward Ekman transport of water at the surface, compensated by equatorward geostrophic flow below and linked by equatorial upwelling, creates a cold tongue in the east but homogenizes SST in the west, creating a warm pool. High clouds may also homogenize the SST by reducing the surface solar radiation over the warmest water, but the strength of this feedback is quite uncertain. Implications for the role of these processes in climate change are discussed. [ABSTRACT FROM AUTHOR]

The present study examines variations in summertime (July–September) tropical cyclone (TC) activity over East Asia during the period 1951–2003. To represent TC activity, a total of 853 TC best tracks for the period were converted to TC passage frequencies (TPFs) within 5° × 5° latitude–longitude grids; TPFs are defined as the percentage values obtained by dividing the number of TC appearances in each grid box by the total number of TCs each year. Empirical orthogonal function analysis of the TPF showed three leading modes: two tropical modes that represent the long-term trend and the relationship with ENSO and one midlatitude mode that oscillates between south of Korea and southeast of Japan with an interannual time scale. The latter proved to be the most remarkable climatic fluctuation of summertime TC activity in the midlatitudes and is referred to as the East Asian dipole pattern (EADP) in this paper. Anomalous atmospheric flows directly connected to the EADP are an enhanced anticyclonic (cyclonic) circulation centering around Japan when the TPF is high south of Korea (southeast of Japan), thereby showing an equivalent barotropic structure in the entire troposphere. This regional circulation anomaly varies in conjunction with the zonally oriented quasi-stationary Rossby wave train in the upper troposphere. This wave train is meridionally trapped in the vicinity of the summer-mean jet stream; therefore, the mean jet stream alters its internal meandering structure according to the phase of the wave train. [ABSTRACT FROM AUTHOR]

The relative importance of the processes responsible for the annual cycle in the upper-ocean heat content in the Peru Current, in the southeastern tropical Pacific, was diagnosed from an oceanic analysis dataset. It was found that the annual cycle of heat content is forced mainly by insolation. However, the ocean dynamical processes play an important role in producing different regional budget characteristics. In a band 500 km from the coast of Peru, the annual heat content changes in this region are relatively large and can be approximated as sea surface temperature (SST) changes in a fixed-depth mixed layer. The annual cycle of the albedo associated with low-level clouds enhances the annual cycle in insolation, which explains the relatively strong annual cycle of heat content. These clouds, to a large extent, act as a feedback to SST, but a small additional forcing, which is proposed to be cold air advection in this paper, is needed to explain the fact that the maximum cloudiness leads the lowest SST by around a month. Ocean dynamics is important closer to the coast, where upwelling acts partly as damping of the heat content changes and forces it to peak earlier than farther offshore. In a band farther to the southwest, locally wind-forced thermocline motions, which become shallower (deeper) in the warm (cool) season, partially cancel the effect of net surface heat fluxes, whose annual cycle is comparable to that in the region previously mentioned, producing a relatively small annual cycle of heat content. The local forcing appears to be associated with the annual meridional displacements of the South Pacific anticyclone. The annual cycle in SST is also relatively small, which is probably due to the changes in the temperature of the water entrained into the mixed layer associated with the thermocline motions, but also to a mixed layer deeper than that closer to the coast. [ABSTRACT FROM AUTHOR]

This paper presents the first probability-based record of flooding in Europe that spans the entire Holocene. An analysis of 506 14C dated fluvial units collected across the whole of Great Britain provides a novel and robust methodology for improving flood risk assessment by geographically and temporally extending the record of extreme flood events. Sixteen episodes of increased flooding occurrence are identified, 12 of which (at c. 11 160, 5730, 4840, 4520, 3540, 2730, 2550, 2280, 1950, 1290, 660, 570, cal. BP) are recorded in most regions, whereas four phases (at c. 6820, 5540, 1650, 860 cal. BP) affected some parts of Great Britain more than others. In all regions large variations in flood frequency and magnitude occurred before forest clearance and indicate an underlying climatic control. During the mid-Holocene there is evidence for a hydroclimatic 'system switch', which in terms of catchment hydrology in Great Britain was marked by two sudden increases in both the frequency and severity of floods at c. 5000 cal. BP and, most notably, at c. 3000 cal. BP. The marked non-stationary behaviour of the British flood series at these times reflects a regional hydrologic response to large-scale ocean–atmospheric circulation changes superimposed on a pattern reflecting both long-term land-use change and the preferential preservation of later fluvial units. Centennial-scale variations in the occurrence of extreme flood events in Great Britain appear to be a sensitive indicator of past and present climate change in the North Atlantic region. [ABSTRACT FROM AUTHOR]

Abstract: Although the amplitude of recent climate variations has been much smaller than during the last ice age, they had a large impact on society recorded since medieval times. Those variations are characterized by long term changes in sub-annual variability, involving alterations of the seasonal cycle or the frequency of extreme events. Since instrumental records are inexistent before the mid-17th century, proxy records based on biological, geochemical or historical information have been necessary to reconstruct the climate fluctuations of the last millennium. This paper focuses on proxy records of the climate since the Little Ice Age and their relation with the atmospheric circulation over Western Europe. To cite this article: P. Yiou, V. Masson-Delmotte, C. R. Geoscience 337 (2005). [Copyright &y& Elsevier]

This paper reviews recent research that assesses evidence for the detection of anthropogenic and natural external influences on the climate. Externally driven climate change has been detected by a number of investigators in independent data covering many parts of the climate system, including surface temperature on global and large regional scales, ocean heat content, atmospheric circulation, and variables of the free atmosphere, such as atmospheric temperature and tropopause height. The influence of external forcing is also clearly discernible in reconstructions of hemispheric-scale temperature of the last millennium. These observed climate changes are very unlikely to be due only to natural internal climate variability, and they are consistent with the responses to anthropogenic and natural external forcing of the climate system that are simulated with climate models. The evidence indicates that natural drivers such as solar variability and volcanic activity are at most partially responsible for the large-scale temperature changes observed over the past century, and that a large fraction of the warming over the last 50 yr can be attributed to greenhouse gas increases. Thus, the recent research supports and strengthens the IPCC Third Assessment Report conclusion that “most of the global warming over the past 50 years is likely due to the increase in greenhouse gases.” [ABSTRACT FROM AUTHOR]