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This paper analyzes the relationships between the circulation regimes of the 500-hPa height (z500) and 250-hPa zonal winds (u250) in the Pacific–North America region during boreal winter, and the 45-day Northern Hemisphere oscillation in z500. The regimes were calculated using a k-means clustering applied to the leading 12 principal components of the combined z500–u250 anomaly fields. We divided the oscillation into eight arbitrary phases. The oscillation phase z500 composite maps are spatially well correlated with regime z500 composites: phases 1–2 are best correlated with the Arctic Low, phases 3–5 are best correlated with the Pacific Trough, phase 6 is best correlated with the Arctic High, and phases 7–8 are best correlated with the Alaskan Ridge. We found that these correlations are generally consistent with the regimes that tend to occur during the individual oscillation phases: the Arctic Low occurs above significance in phases 1–2, the Pacific Trough occurs above significance in phase 3, and Alaskan Ridge occurs above significance in phases 7–8. Therefore, the oscillation has a preferred order with respect to the regimes. The regime transitions indicate a pattern that moves through the Pacific Wavetrain, a regime that appears for k = 5 as a mean state. Transitions out of this regime into different regimes are preferred in different phases of the oscillation. These results imply a possible enhancement to regime prediction using the low-frequency oscillations in combination with regimes. Significance Statement: Subseasonal prediction, weather forecasting in the 2–4-week range, is important for many parts of society, e.g., water managers, emergency response units, and farmers. However, current prediction skill in this time range is low. This paper performs an initial analysis of a possible method to increase weather statistic prediction skill beyond 10 days in the winter for the Pacific–North America region. This is done by combining two ways of looking at large, long-lasting patterns of pressure systems in the atmosphere, which are associated with various weather statistics like precipitation extremes and storminess. The results indicate this method holds potential skill for enhancing subseasonal prediction. Further investigation might yield forecasting improvements in this important time range. [ABSTRACT FROM AUTHOR]

How strong is the resemblance between two states of the atmosphere leading to the same outcome? In the following pages this question was addressed by studying the resemblance of the surface pressure fields, obtained by NCEP reanalyses, corresponding to “intense” precipitation events over 5 Italian climatic areas. Such “intense” precipitation events were selected by means of 45 daily precipitation records covering the period from 1951 to 2000. Two pressure patterns that resemble one another are termed soft-analogues in this paper. The mathematical measures used to assess the difference between two pressure patterns were: the root-mean-square difference, the correlation, and the S1 score. The comparison outcomes were categorized into classes according to the previous measures. Once a couple of the pressure patterns were found to be good soft-analogues (that was a rare occurrence), these pressure patterns were compared with all pressure patterns excluded by the initial selection being not associated with intense precipitation events. The few soft-analogues associated with “intense” precipitation events were found to be also soft-analogue to several, and sometimes a great deal of, pressure patterns not associated with the selected “intense” precipitation events. [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]

Direct diagnostic evaluation of the moisture tendency in the moisture equation is very difficult in practice because two poorly measured terms, moisture convergence and precipitation, dominate the equation. Using the near constancy in space and time of the tropical temperature profile, a variety of energy and entropy based equations have been employed to obtain indirect estimates of the moisture budget. In this paper rigorous versions of the energy and entropy equations are developed. The strengths and weakness of these two formulations are complementary, allowing the authors to estimate moistening and drying tendencies with high confidence when the two formulations are used together. This study applies the theory to data from Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The results demonstrate how convection regulates the tropospheric humidity, drying the atmosphere when it becomes too moist, and moistening it when it becomes too dry. [ABSTRACT FROM AUTHOR]

We examine a distributed control problem for internal flow management in a multi-zone climate unit. The problem consists of guaranteeing prescribed indoor climate conditions in a cascade connection of an arbitrarily large number of communicating zones, in which air masses are exchanged to redirect warm air from hot zones (which need to be cooled down) to cold zones (which need to be heated up), and to draw as much fresh air as possible to hot zones, relying on the ventilation capacity of neighbouring "collaborative" zones. The controller of each zone must be designed so as to achieve the prescribed climate condition, while fulfilling the constraints imposed by the neighbouring zones - due to their willingness to cooperate or not in the air exchange - and the conservation of flow, and despite the action of unknown disturbances. We devise control laws which yield hybrid closed-loop systems, depend on local feedback information, take on values in a finite discrete set, and cooperate with neighbour controllers to achieve different compatible control objectives, while avoiding conflicts. [ABSTRACT FROM AUTHOR]

Regression-guided clustering is introduced as a means of constructing circulation-to-environment synoptic climatological classifications. Rather than applying an unsupervised clustering algorithm to synoptic-scale atmospheric circulation data, one instead augments the atmospheric circulation dataset with predictions from a supervised regression model linking circulation to environment. The combined dataset is then entered into the clustering algorithm. The level of influence of the environmental dataset can be controlled by a simple weighting factor. The method is generic in that the choice of regression model and clustering algorithm is left to the user. Examples are given using standard multivariate linear regression models and the k-means clustering algorithm, both established methods in synoptic climatology. Results for southern British Columbia, Canada, indicate that model performance can be made to range between that of a fully unsupervised algorithm and a fully supervised algorithm. [ABSTRACT FROM AUTHOR]

We review recent advances in classifications of circulation patterns as a specific research area within synoptic climatology. The review starts with a general description of goals of classification and the historical development in the field. We put circulation classifications into a broader context within climatology and systematize the varied methodologies and approaches. We characterize three basic groups of classifications: subjective (also called manual), mixed (hybrid), and objective (computer-assisted, automated). The roles of cluster analysis and principal component analysis in the classification process are clarified. Several recent methodological developments in circulation classifications are identified and briefly described: the introduction of nonlinear methods, objectivization of subjective catalogs, efforts to optimize classifications, the need for intercomparisons of classifications, and the progress toward an optimum, if possible unified, classification method. Among the recent tendencies in the applications of circulation classifications, we mention a more extensive use in climate studies, both of past, present, and future climates, innovative applications in the ensemble forecasting, increasing variety of synoptic–climatological investigations, and steps above from the troposphere. After introducing the international activity within the field of circulation classifications, the COST733 Action, we briefly describe outputs of the inventory of classifications in Europe, which was carried out within the Action. Approaches to the evaluation of classifications and their mutual comparisons are also reviewed. A considerable part of the review is devoted to three examples of applications of circulation classifications: in historical climatology, in analyses of recent climate variations, and in analyses of outputs from global climate models. [ABSTRACT FROM AUTHOR]

Without the participation of the United States, for many years the world's largest emitter of greenhouse gases, mitigation of global climate change seems hardly conceivable. Despite the US rejection of the Kyoto Protocol and the reluctance of the Bush administration to engage in post-Kyoto negotiations, recent developments suggest that the US position towards climate policy might change in the medium run. This study provides an overview on current trends in US climate policy. We outline the main elements of national climate policy proposals and state-level initiatives. Based on this overview, recent trends in US climate policy are related to the European approach to combat climate change. Furthermore, we elaborate on the aspects that may be important for Europe to design its own domestic and international climate policy in order to achieve the long-term global goal of stabilizing greenhouse gas concentrations. While it seems likely that the US will take a leading role in international climate policy, it can also be expected to challenge the European position in many respects rather than to simply support any Kyoto-type process. Copyright © 2008 John Wiley & Sons, Ltd and ERP Environment. [ABSTRACT FROM AUTHOR]

The character of the atmospheric general circulation during summer-season droughts over Eastern Europe/Western Russia and North America during the late twentieth and early twenty first century is examined here. A criterion to examine atmospheric drought events that encompassed the summer season (an important part of the growing season) was used to determine which years were driest, using precipitation, evaporation, and areal coverage. The relationship between drought and the character of the atmosphere, using the Dzerzeevsky weather and climatic classification scheme, atmospheric blocking, teleconnections, and information entropy, was used to study the atmospheric dynamics. The National Centers for Environmental Prediction (NCEP) re-analyses dataset archived at the National Center for Atmospheric Research (NCAR) in Boulder, CO, USA, is used to examine the synoptic character and calculate the dynamic quantities for these dry events. The results demonstrate that extreme droughts over North America are associated with a long warm and dry period of weather and the development of a moderate ridge over the Central USA driven by surface processes. These were more common in the late 20th century. Extreme droughts over Eastern Europe and Western Russia are driven by the occurrence of prolonged blocking episodes, as well as surface processes, and have become more common during the 21st century. [ABSTRACT FROM AUTHOR]

The diurnal mode of the Asian summer monsoon during active and break periods is studied using four versions of the Florida State University (FSU) global spectral model (GSM). These versions differ in the formulation of cloud parameterization schemes in the model. Observational-based estimates show that there exists a divergent circulation at 200 hPa over the Asian monsoon region in the diurnal time scale that peaks at 1200 local solar time (LST) during break monsoon and at 1800 LST during active monsoon. A circulation in the opposite direction is seen near the surface. This circulation loop is completed by vertical ascending/descending motion over the monsoon domain and its surroundings. This study shows that global models have large phase and amplitude errors for the 200-hPa velocity potential and vertical pressure velocity over the monsoon region and its surroundings. Construction of a multimodel superensemble could reduce these errors substantially out to five days in advance. This was on account of assigning differential weights to the member models based on their past performance. This study also uses a unified cloud parameterization scheme that inherits the idea of a multimodel superensemble for combining member model forecasts. The advantage of this model is that it is an integrated part of the GSM and thus can improve the forecasts of other parameters as well through improved cloud cover. It was seen that this scheme had a larger impact on forecasting the diurnal cycle of cloud cover and precipitation of the Asian summer monsoon compared to circulation. The authors show that the diurnal circulation contributes to about 10% of the rate of change of total kinetic energy of the monsoon. Therefore, forecasting this pronounced diurnal mode has important implications for the energetics of the Asian summer monsoon. [ABSTRACT FROM AUTHOR]

The study of climate changes in India and search for robust evidences are issues of concern specially when it is known that poor people are very vulnerable to climate changes. Due to the vast size of India and its complex geography, climate in this part of the globe has large spatial and temporal variations. Important weather events affecting India are floods and droughts, monsoon depressions and cyclones, heat waves, cold waves, prolonged fog and snowfall. Results of this comprehensive study based on observed data and model reanalyzed fields indicate that in the last century, the atmospheric surface temperature in India has enhanced by about 1 and 1.1°C during winter and post-monsoon months respectively. Also decrease in the minimum temperature during summer monsoon and its increase during post-monsoon months have created a large difference of about 0.8°C in the seasonal temperature anomalies which may bring about seasonal asymmetry and hence changes in atmospheric circulation. Opposite phases of increase and decrease in the minimum temperatures in the southern and northern regions of India respectively have been noticed in the interannual variability. In north India, the minimum temperature shows sharp decrease of its magnitude between 1955 and 1972 and then sharp increase till date. But in south India, the minimum temperature has a steady increase. The sea surface temperatures (SST) of Arabian Sea and Bay of Bengal also show increasing trend. Observations indicate occurrence of more extreme temperature events in the east coast of India in the recent past. During summer monsoon months, there is a decreasing (increasing) trend in the frequency of depressions (low pressure areas). In the last century the frequency of occurrence of cyclonic storms shows increasing trend in the month of November. In addition there is increase in the number of severe cyclonic storms crossing Indian Coast. Analysis of rainfall amount during different seasons indicate decreasing tendency in the summer monsoon rainfall over Indian landmass and increasing trend in the rainfall during pre-monsoon and post-monsoon months. [ABSTRACT FROM AUTHOR]

Focuses on topics related to zonal indices as related to the winter climate in East Asia. Three basic zonal currents in the general circulation of the atmosphere; Computation for local zonal indices; Frequency of indices; Relationship between zonal indices and centers of action.

The article reports on the physical climatology of Amchitka Island, Alaska. It states that the extreme variability of surface-wind directions at Amchitka is a result of a high incidence of migratory pressure systems. It also mentions that fog is dominant during the summer months because the water warms more slowly than the air that flows over it. It also forwards that frequent migratory storms and the marine influence of the Pacific Ocean to the south and the Bering Sea to the north are the main factors influencing the weather and climate of this island.

The article focuses on the mean climate and variability of idealized aqua-planet. It could be noted that the identification of controlling mechanisms behind climate and climate variability is very difficult due to innumerable drivers acting on time scales. The researchers at the Massachusetts Institute of Technology started to use the information and knowledge encoded in climate models to explore the climate of highly idealized world. The partition of heat transport between atmosphere and ocean is the same as the present climate.