Search

We examine the application of ensemble Kalman filter algorithms to the smoothing problem in high-dimensional geophysical prediction systems. The goal of smoothing is to make optimal estimates of the geophysical system state making best use of observations taken before, at, and after the analysis time. We begin by reviewing the underlying probabilistic theory, along with a discussion how to implement a smoother using an ensemble Kalman filter algorithm. The novel contribution of this paper is the investigation of various key issues regarding the application of ensemble Kalman filters to smoothing using a series of Observing System Simulation Experiments in both a Lorenz 1996 model and an Atmospheric General Circulation Model. The results demonstrate the impacts of non-linearities, ensemble size, observational network configuration and covariance localization. The Atmospheric General Circulation model results demonstrate that the ensemble Kalman smoother (EnKS) can be successfully applied to high-dimensional estimation problems and that covariance localization plays a critical role in its success. The results of this paper provide a foundation of understanding which will be useful in future applications of EnKS algorithms. [ABSTRACT FROM AUTHOR]

This paper considers the use of an ensemble Kalman filter to correct satellite radiance observations for state dependent biases. Our approach is to use state-space augmentation to estimate satellite biases as part of the ensemble data assimilation procedure. We illustrate our approach by applying it to a particular ensemble scheme—the local ensemble transform Kalman filter (LETKF)—to assimilate simulated biased atmospheric infrared sounder brightness temperature observations from 15 channels on the simplified parameterizations, primitive-equation dynamics (SPEEDY) model. The scheme we present successfully reduces both the observation bias and analysis error in perfect-model simulations. [ABSTRACT FROM AUTHOR]

In this paper, we attempt to divide the global divergent field at the upper troposphere in contributions from the Hadley, Walker and monsoon circulations, using a monthly mean velocity potential field at 200-hPa level. First, the zonal mean of the velocity potential is analysed to represent the Hadley circulation. The deviation from the zonal mean is then divided into its annual mean and the seasonal cycle parts, which are considered to represent the Walker and monsoon circulations, respectively. The intensities of each circulation are measured by their peaks in the velocity potential field separated in each component. According to this separation, the mean intensities of the Walker, monsoon and Hadley circulations appear to be 120: 60: 40 (× 105 m2 s−1) in January and 120: 90: 45 (×105 m2 s−1) in July, respectively. Based on this simple definition, interannual variabilities of each circulation are then examined quantitatively using the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. The time series of the intensity of the Walker circulation coincides with the Southern Oscillation index (SOI), and the intensity has weakened in recent decades. That of the Hadley circulation indicates intensifying trend in boreal winter. Finally, the same analysis is applied for the model atmosphere by the Meteorological Research Institute (MRI) coupled atmosphere–ocean general circulation model (CGCM1) with a gradual increase in CO2 at a compound rate of 1% yr−1 for 150 yr. It is shown that the Hadley circulation intensifies by 40% and the monsoon circulation decays by 20% in boreal summer when the global warming has occurred in a century later. The result demonstrates that the proposed simple separation of the tropical circulation in the Walker, monsoon and Hadley components is useful, although it is not rigorous, for the initial assessment of the model response to the global warming. [ABSTRACT FROM AUTHOR]

This paper aims at characterising the impact of the atmospheric variability on the aerosol burden and residence time in the Arctic region. For this purpose, a global simulation using an emissions inventory from the year 2000 is performed for the period 2000-2005. The model thus describes a 6-yr evolution of sulphate, black carbon (BC) and mineral dust, whose variability is driven by the atmosphere only. Our simulation is validated, thanks to comparisons with surface observations. The aerosol residence time takes minimum values in fall: 4 d for sulphate and 8 d for BC and dust. It takes maximum values in June: 10 d for sulphate and 16 d for BC and dust. However, from one spring to another, it can vary by about 50% for sulphate, 40% for BC and 100% for dust, depending on the atmospheric variability. In June, sulphate, BC and dust burden averaged over the Arctic region reach respectively maximums of 1.9 mg[S]m-2, 0.2 mgm-2 and 6mgm-2, characteristic of the so-called Arctic haze. From one year to another, these values can vary by 20% for sulphate, 10% for BC and 60% for dust. [ABSTRACT FROM AUTHOR]

Understanding and forecasting the evolution of geophysical fluids is a major scientific and societal challenge. Forecasting algorithms should take into account all the available information on the considered dynamic system. The variational data assimilation (VDA) technique combines all these informations in an optimality system (O.S.) in a consistent way to reconstruct the model inputs. VDA is currently used by the major meteorological centres. During the last two decades about 30 satellites were launched to improve the knowledge of the atmosphere and of the oceans. They continuously provide a huge amount of data that are still underused by numerical forecast systems. In particular, the dynamic evolution of certain meteorological or oceanic features (such as eddies, fronts, etc.) that the human vision may easily detect is not optimally taken into account in realistic applications of VDA. Image Assimilation in VDA framework can be performed using ‘pseudo-observation’ techniques: they provide apparent velocity fields, which are assimilated as classical observations. These measurements are obtained by certain external procedures, which are decoupled with the considered dynamic system. In this paper, we suggest a more consistent approach, which directly incorporates image sequences into the O.S. [ABSTRACT FROM AUTHOR]

Response function models are often used to represent the behaviour of complex, high order global carbon cycle (GCC) and climate models in applications which require short model run times. Although apparently black-box, these response function models need not necessarily be entirely opaque, but instead may also convey useful insights into the properties of the parent model or process. By exploiting a transfer function (TF) framework to analyse the Lenton GCC model, this paper attempts to demonstrate that response function representations of GCC models can sometimes also provide structural information on the parent model from which they are identified and calibrated. We take a fifth-order TF identified from the impulse response of the Lenton model atmospheric burden, and decompose this to show how it can be re-expresses in a generic five-box form in sympathy with the structure of the parent model. [ABSTRACT FROM AUTHOR]

The complexity of the laws of dynamics governing 3-D atmospheric flows associated with incomplete and noisy observations make the recovery of atmospheric dynamics from satellite image sequences very difficult. In this paper, we address the challenging problem of estimating physical sound and time-consistent horizontal motion fields at various atmospheric depths for a whole image sequence. Based on a vertical decomposition of the atmosphere, we propose a dynamically consistent atmospheric motion estimator relying on a multilayer dynamic model. This estimator is based on a weak constraint variational data assimilation scheme and is applied on noisy and incomplete pressure difference observations derived from satellite images. The dynamic model is a simplified vorticity-divergence form of a multilayer shallow-water model. Average horizontal motion fields are estimated for each layer. The performance of the proposed technique is assessed using synthetic examples and using real world meteorological satellite image sequences. In particular, it is shown that the estimator enables exploiting fine spatio-temporal image structures and succeeds in characterizing motion at small spatial scales. [ABSTRACT FROM AUTHOR]

The spatial and temporal gradients in atmospheric CO2 contain signatures of carbon fluxes, and as part of inverse studies, these signatures have been combined with atmospheric models to infer carbon sources and sinks. However, such studies have yet to yield finer-scale, regional fluxes over the continent that can be linked to ecosystem processes and ground-based observations. The reasons for this gap are twofold: lack of atmospheric observations over the continent and model deficiencies in interpreting such observations. This paper describes a series of intensive atmospheric sampling field programmes designed as pilot experiments to bridge the observational gap over the continent and to help test and develop models to interpret these observations. We summarize recent results emerging from this work, outlining the role of the intensive atmospheric programmes in collecting CO2 data in both the vertical and horizontal dimensions. These data: (1) quantitatively establish the spatial variability of CO2 and the associated errors from neglecting this variability in models; (2) directly measure regional carbon fluxes from airmass-following experiments and (3) challenge models to reduce and account for uncertainties in atmospheric transport. We conclude with a look towards the future, outlining ways in which intensive atmospheric sampling can contribute towards advancing carbon science. [ABSTRACT FROM AUTHOR]

A 4-D implementation of an observation space variational data assimilation system is under development at the Marine Meteorology Division of the Naval Research Laboratory (NRL). The system is an extension of the current US Navy 3-D operational data assimilation system, the NRL Atmospheric Variational Data Assimilation System (NAVDAS). The new system, NAVDAS-AR, where AR stands for accelerated representer, is similar in many respects to the European Centre for Medium-Range Weather Forecasts (ECMWF) 4DVAR system. However, NAVDAS-AR is based on a weak constraint observation space, while the ECMWF system is based on a strong constraint model space. In this paper the formulation of NAVDAS-AR is described in detail and preliminary results with a perfect model assumption and comparisons with the operational NAVDAS are presented. [ABSTRACT FROM AUTHOR]

The lack of a firm relationship between wind speed (U10) and gas transfer velocity (k) is considered to be one of the factors that hinders accurate quantification of interannual variations of ocean–atmosphere CO2 fluxes. In this paper the interannual variations ofkof using four differentk– U10 parametrizations are examined using wind speed data from the NCEP/NCAR reanalysis project. The extent to which interannual variations are faithfully reproduced in the NCEP/NCAR data is also investigated. This is carried out through comparison with QuikSCAT data. Compared with 4 yr of QuikSCAT data, NCEP/NCAR data reproduce interannualkvariations, although the absolute magnitude ofkis underestimated. Interannualkvariation shows great sensitivity to selection ofk– U10 parametrization, and in the Westerlies it changes by a factor of three depending onk– U10 parametrization. Use of monthly mean winds speeds leads to overestimation of interannualkvariations compared withkvariations computed using 6-hourly wind speeds and the appropriatek– U10 parametrization. Even though the effect of changingk– U10 parametrization is large enough to be an issue that needs to be considered when computing interannual air–sea CO2 flux variations through combining estimates ofkwith data for the air–sea CO2 gradient, it is not sufficient to bridge the gap between such estimates and estimates based on analyses of atmospheric oxygen, CO2 andδ13C data. Finally it is shown that the ambiguity in the relationship between wind speed andkintroduces an uncertainty in interannual flux variations comparable to a bias of interannualΔ pCO2 variations of at most±5μatm. [ABSTRACT FROM AUTHOR]

abstract This paper presents the results of a simulation with a mechanistic terrestrial ecosystem model, focusing on the atmosphere–biosphere exchange and stable isotope composition of carbon. The simulation was performed from 1953 to 1999 on the basis of observed climate data and atmospheric carbon dioxide (CO2 ) concentration and stable carbon isotope ratio (δ13 C). The model, termed Sim-CYCLE, captures carbon dynamics from photosynthetic assimilation to microbial decomposition, including seasonal and interannual variability. Photosynthetic discrimination effect on δ13 C was considered at three levels: (1) leaf-level fractionation, (2) canopy-level CO2 recycling and (3) continent-level C3 /C4 pattern. The 47-yr simulation estimated that the average gross CO2 flux was 121 Pg C yr-1 , and that the average photosynthetic δ13 C discrimination coefficient (Δ) was 18.2%. A sensitivity analysis indicated that the estimated Δ depends heavily on the parameterization of stomatal conductance and C3 /C4 composition. In spite of their small biomass, C4 plants contributed considerably to the biospheric productivity and belowground carbon supply. The estimated net CO2 and isotopic exchange of the terrestrial ecosystems corresponded, at least qualitatively, with observed atmospheric CO2 and its δ13 C seasonal patterns in the Northern Hemisphere. The gross CO2 fluxes of photosynthesis and respiration indicated a wide range of interannual variability, which was in a sufficient magnitude to induce anomalies in the atmospheric CO2 growth rate. The estimated Δ showed a wide range of latitudinal and longitudinal variations and seasonal oscillation, but little interannual change. However, during the 47-yr period, the estimated δ13 C of carbon pools decreased by 0.3%, while the δ13 C of atmospheric CO2 decreased by 0.7%. These results carry implications for the application of a top-down approach, i.e. the double-deconvolution method, to inferring the global terrestrial CO2 budget. [ABSTRACT FROM AUTHOR]

We study the evolution of finite perturbations in the Lorenz ‘96 model, a meteorological toy model of the atmosphere. The initial perturbations are chosen to be aligned along different dynamic vectors: bred, Lyapunov, and singular vectors. Using a particular vector determines not only the amplification rate of the perturbation but also the spatial structure of the perturbation and its stability under the evolution of the flow. The evolution of perturbations is systematically studied by means of the so-called mean-variance of logarithms diagram that provides in a very compact way the basic information to analyse the spatial structure. We discuss the corresponding advantages of using those different vectors for preparing initial perturbations to be used in ensemble prediction systems, focusing on key properties: dynamic adaptation to the flow, robustness, equivalence between members of the ensemble, etc. Among all the vectors considered here, the so-called characteristic Lyapunov vectors are possibly optimal, in the sense that they are both perfectly adapted to the flow and extremely robust. [ABSTRACT FROM AUTHOR]

A narrow line of convective showers was observed over southern England on 18 July 2005 during the Convective Storm Initiation Project (CSIP). The showers formed behind a cold front (CF), beneath two apparently descending dry layers (i.e. sloping so that they descended relative to the instruments observing them). The lowermost dry layer was associated with a tropopause fold from a depression, which formed 2 d earlier from a breaking Rossby wave, located northwest of the UK. The uppermost dry layer had fragmented from the original streamer due to rotation around the depression (This rotation was also responsible for the observations of apparent descent—ascent would otherwise be seen behind a CF). The lowermost dry layer descended over the UK and overran higher air beneath it, resulting in potential instability. Combined with a surface convergence line (which triggered the convection but had less impact on the convective available potential energy than the potential instability), convection was forced up to 5.5 km where the uppermost dry layer capped it. The period when convection was possible was very short, thus explaining the narrowness of the shower band. Convective Storm Initiation Project observations and model data are presented to illustrate the unique processes in this case. [ABSTRACT FROM AUTHOR]

The spatial and temporal gradients in atmospheric CO2 contain signatures of carbon fluxes, and as part of inverse studies, these signatures have been combined with atmospheric models to infer carbon sources and sinks. However, such studies have yet to yield finer-scale, regional fluxes over the continent that can be linked to ecosystem processes and ground-based observations. The reasons for this gap are twofold: lack of atmospheric observations over the continent and model deficiencies in interpreting such observations. This paper describes a series of intensive atmospheric sampling field programmes designed as pilot experiments to bridge the observational gap over the continent and to help test and develop models to interpret these observations. We summarize recent results emerging from this work, outlining the role of the intensive atmospheric programmes in collecting CO2 data in both the vertical and horizontal dimensions. These data: (1) quantitatively establish the spatial variability of CO2 and the associated errors from neglecting this variability in models; (2) directly measure regional carbon fluxes from airmass-following experiments and (3) challenge models to reduce and account for uncertainties in atmospheric transport. We conclude with a look towards the future, outlining ways in which intensive atmospheric sampling can contribute towards advancing carbon science. [ABSTRACT FROM AUTHOR]

NAVDAS-AR is the 4DVAR extension of the United States Navy's operational 3DVAR data assimilation system, NAVDAS (Naval Research Laboratory Atmospheric Variational Data Assimilation System), where AR stands for accelerated representer. Like NAVDAS, NAVDAS-AR is cast in observation space, and is an observation space formulation of the 4DVAR algorithm, in contrast to the European Centre for Medium-Range Weather Forecasts 4DVAR system, which is an analysis space algorithm. In this paper we show how an inner loop linear solution can be augmented by an outer loop iteration procedure that introduces non-linear effects in the form of a first-order Taylor series expansion. The non-linear problem is then solved iteratively as a sequence of linear problems. We show results of the outer loop strategy, where the first loop, the ‘linear’ solution, is modified in the second outer loop by both a Taylor series term in the calculation of the observation innovations, and a linearized form of the background model that is linearized about an analysis ‘trajectory’ from the solution of the first loop. We also show results of how the outer loop strategy allows better assimilation of observations of surface wind speed and precipitable water, compared to the operational NAVDAS. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the relationship between atmospheric predictability and the Pacific North American (PNA) pattern in a perfect model context using the Canadian Centre for Climate Modelling and Analysis general circulation model (GCM). Description of the GCM model; Relationship between the tropical sea surface temperature anomalies and the PNA pattern; Prediction spread of model experiments for different PNA phases.

The compensation between the meridional heat transports in the atmosphere and ocean is studied through a coupled model's water-hosing experiments. It is found that the atmospheric heat transport (AHT) change compensates the oceanic heat transport (OHT) change very well in the extratropics, while the former overcompensates the latter in the tropics. Similar to previous studies, the fresh water input in the high latitude Atlantic weakens the Atlantic meridional overturning circulation and thus the northward Atlantic OHT significantly, leading to a warming (cooling) in sea surface temperature in the Southern (Northern) Hemisphere and in turn a southward shift of atmospheric convection. This results in an enhanced Hadley Cell (HC) and stronger northward AHT, compensating the reduced Atlantic OHT. Meanwhile, the wind-driven Subtropical Cell in the Indo-Pacific oceans is enhanced in response to the HC change, increasing the northward OHT in the Indo-Pacific, which partly offsets the reduced OHT in the Atlantic. The response in the Indo-Pacific is responsible for the overcompensation of the AHT to the global OHT. The Held's mechanism works very well in the tropical Indo-Pacific in our experiments. This is substantially different from previous studies. [ABSTRACT FROM AUTHOR]

The high ice-covered topography of Greenland represents a significant barrier to atmospheric flow and, as a direct and indirect result, it plays a crucial role in the coupled climate system. The wind field over Greenland is important in diagnosing regional weather and climate, thereby providing information on the mass balance of the ice sheet as well as assisting in the interpretation of ice core data. Here, we identify a number of hitherto unrecognised features of the three-dimensional wind field over Greenland; including a 2500-km-long jet along the central ice sheet's western margin that extends from the surface into the middle-troposphere, as well as a similar but smaller scale and less intense feature along its eastern margin. We refer to these features as Greenland Plateau Jets. The jets are coupled to the downslope katabatic flow and we argue that they are maintained by the zonal temperature gradients associated with the strong temperature inversion over the central ice sheet. Their importance for Greenland's regional climate is discussed. [ABSTRACT FROM AUTHOR]

ABSTRACT We apply methods from extreme value theory to identify extreme events in high (termed EHOs) and low (termed ELOs) total ozone and to describe the distribution tails (i.e. very high and very low values) of five long-term European ground-based total ozone time series. The influence of these extreme events on observed mean values, long-term trends and changes is analysed. The results show a decrease in EHOs and an increase in ELOs during the last decades, and establish that the observed downward trend in column ozone during the 1970-1990s is strongly dominated by changes in the frequency of extreme events. Furthermore, it is shown that clear 'fingerprints' of atmospheric dynamics (NAO, ENSO) and chemistry [ozone depleting substances (ODSs), polar vortex ozone loss] can be found in the frequency distribution of ozone extremes, even if no attribution is possible from standard metrics (e.g. annual mean values). The analysis complements earlier analysis for the world's longest total ozone record at Arosa, Switzerland, confirming and revealing the strong influence of atmospheric dynamics on observed ozone changes. The results provide clear evidence that in addition to ODS, volcanic eruptions and strong/moderate ENSO and NAO events had significant influence on column ozone in the European sector. [ABSTRACT FROM AUTHOR]

BSTRACT The trends of terrestrial carbon exchange and their mechanistic drivers are key components in understanding how carbon reservoirs will respond to climate change. Here we show trends in seasonal non-fossil land-atmosphere carbon exchange from 1980 to 2008 using atmospheric CO [ABSTRACT FROM AUTHOR]

Measurements of H at the high-altitude site of Jungfraujoch, Switzerland are reported upon for the period of August, 2005-November, 2009. The time series consists of measurements that are primarily representative of free tropospheric background conditions. Highest background H mixing ratios were observed in May, while the lowest were observed in November. The mean seasonal H peak-to-trough amplitude of 21 parts per billion (ppb, 10 dry air mixing ratio) at Jungfraujoch was considerably less than at other stations at similar latitudes and the seasonal minimum in November was comparatively delayed. These differences are primarily attributed to a dampening and delay of the surface soil sink signal during its vertical propagation to the free troposphere. Excess (mixing ratio minus corresponding baseline value) H (ΔH) and excess CO (ΔCO) displayed no significant correlation. This lacking correlation is attributed to H removal by soil during transport to Jungfraujoch, thereby significantly altering the ΔH/ΔCO ratio from traffic combustion sources, which is the largest source of anthropogenic H influencing measurements at Jungfraujoch. [ABSTRACT FROM AUTHOR]

Human conversion of natural ecosystems to croplands modifies not only the exchange of water and energy between the surface and the atmosphere, but also carbon fluxes. To investigate the impacts of crops on carbon fluxes and resulting atmospheric CO concentrations in the mid-continent region of the United States, we coupled a crop-specific phenology and physiology scheme for corn, soybean and wheat to the coupled ecosystem-atmosphere model SiB3-RAMS. Using SiBcrop-RAMS improved carbon fluxes at the local scale and had regional impacts, decreasing the spring uptake and increasing the summer uptake over the mid-continent. The altered fluxes changed the mid-continent atmospheric CO concentration field at 120 m compared to simulations without crops: concentrations increased in May and decreased >20 ppm during July and August, summer diurnal cycle amplitudes increased, synoptic variability correlations improved and the gradient across the mid-continent region increased. These effects combined to reduce the squared differences between the model and high-precision tower CO concentrations by 20%. Synoptic transport of the large-scale N-S gradient caused significant day-to-day variability in concentration differences measured between the towers. This simulation study shows that carbon exchange between crops and the atmosphere significantly impacts regional CO fluxes and concentrations. [ABSTRACT FROM AUTHOR]

The variability of satellite retrieved precipitation and freshwater flux from the ‘Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data’ (HOAPS) is assessed with special emphasis on the ‘North Atlantic Oscillation’ (NAO). To cover also land areas, a novel combination of the satellite derived precipitation climatology with the rain gauge based ‘Full Data Reanalysis Product Version 4’, of the ‘Global Precipitation Climatology Centre’ (GPCC) is used. This yields unique high-resolution, quasi-global precipitation fields compiled from two independent data sources. Over the ocean, the response of the freshwater balance and the related parameters to the NAO is investigated for the first time by using a purely satellite based data set. A strong dependence of precipitation patterns to the state of the NAO is found. On synoptic scale this is in accordance with earlier findings by other satellite based and reanalysis products. Furthermore, the consistency of the combined HOAPS-3/GPCC data set allows also detailed regional analyses of precipitation patterns. The response of HOAPS-3 freshwater flux to the NAO is dominated by precipitation at mid and high latitudes, while for the subtropical regions the feedback of the evaporation is stronger. [ABSTRACT FROM AUTHOR]

Global high-precision atmospheric Δ14CO2 records covering the last two decades are presented, and evaluated in terms of changing (radio)carbon sources and sinks, using the coarse-grid carbon cycle model GRACE. Dedicated simulations of global trends and interhemispheric differences with respect to atmospheric CO2 as well as δ13CO2 and Δ14CO2, are shown to be in good agreement with the available observations (1940–2008). While until the 1990s the decreasing trend of Δ14CO2 was governed by equilibration of the atmospheric bomb 14C perturbation with the oceans and terrestrial biosphere, the largest perturbation today are emissions of 14C-free fossil fuel CO2. This source presently depletes global atmospheric Δ14CO2 by 12–14‰ yr−1, which is partially compensated by 14CO2 release from the biosphere, industrial 14C emissions and natural 14C production. Fossil fuel emissions also drive the changing north–south gradient, showing lower Δ14C in the northern hemisphere only since 2002. The fossil fuel-induced north–south (and also troposphere–stratosphere) Δ14CO2 gradient today also drives the tropospheric Δ14CO2 seasonality through variations of air mass exchange between these atmospheric compartments. Neither the observed temporal trend nor the Δ14CO2 north–south gradient may constrain global fossil fuel CO2 emissions to better than 25%, due to large uncertainties in other components of the (radio)carbon cycle. [ABSTRACT FROM AUTHOR]

The performance of an atmospherically forced ocean general circulation model (OGCM) in simulating daily and monthly sea surface temperature (SST) is examined during the historical El Niño Southern Oscillation (ENSO) events during the time period 1993–2003. For this purpose, we use the HYbrid Coordinate Ocean Model (HYCOM) configured for the North Pacific north of 20°S at a resolution of ≈9 km. There is no assimilation of (or relaxation to) SST data and no date-specific assimilation of any data type. The ability of the model in simulating temporal variations of SST anomalies is discussed by comparing model results with two satellite-based SST products. The HYCOM simulation gives a basin-averaged monthly mean bias of 0.3 °C and rms difference of 0.6 °C over the North Pacific Ocean during 1993–2003. While the model is able to simulate SST anomalies with mean biases in comparison to observations during most of the ENSO events, limitations in the accuracy of atmospheric forcing (specifically, net short-wave radiation) have some influence on the accuracy of simulations. This is specifically demonstrated during the 1998 transition period from El Niño to La Niña, when a record large SST drop of occurred in the eastern equatorial Pacific Ocean. [ABSTRACT FROM AUTHOR]

Recent loss of summer sea ice in the Arctic is directly connected to shifts in northern wind patterns in the following autumn, which has the potential of altering the heat budget at the cold end of the global heat engine. With continuing loss of summer sea ice to less than 20% of its climatological mean over the next decades, we anticipate increased modification of atmospheric circulation patterns. While a shift to a more meridional atmospheric climate pattern, the Arctic Dipole (AD), over the last decade contributed to recent reductions in summer Arctic sea ice extent, the increase in late summer open water area is, in turn, directly contributing to a modification of large scale atmospheric circulation patterns through the additional heat stored in the Arctic Ocean and released to the atmosphere during the autumn season. Extensive regions in the Arctic during late autumn beginning in 2002 have surface air temperature anomalies of greater than 3 °C and temperature anomalies above 850 hPa of 1 °C. These temperatures contribute to an increase in the 1000–500 hPa thickness field in every recent year with reduced sea ice cover. While gradients in this thickness field can be considered a baroclinic contribution to the flow field from loss of sea ice, atmospheric circulation also has a more variable barotropic contribution. Thus, reduction in sea ice has a direct connection to increased thickness fields in every year, but not necessarily to the sea level pressure (SLP) fields. Compositing wind fields for late autumn 2002–2008 helps to highlight the baroclinic contribution; for the years with diminished sea ice cover there were composite anomalous tropospheric easterly winds of ∼1.4 m s–1, relative to climatological easterly winds near the surface and upper tropospheric westerlies of ∼3 m s–1. Loss of summer sea ice is supported by decadal shifts in atmospheric climate patterns. A persistent positive Arctic Oscillation pattern in late autumn (OND) during 1988–1994 and in winter (JFM) during 1989–1997 shifted to more interannual variability in the following years. An anomalous meridional wind pattern with high SLP on the North American side of the Arctic—the AD pattern, shifted from primarily small interannual variability to a persistent phase during spring (AMJ) beginning in 1997 (except for 2006) and extending to summer (JAS) beginning in 2005. [ABSTRACT FROM AUTHOR]

We developed an efficient retrospective optimal interpolation (ROI) algorithm by which we can avoid the overlap of model integration periods, which appears in the procedure of evolving a previous analysis error covariance. If the fixed-lag Kalman smoother (FLKS) is used to determine the analysis state at the beginning of the fixed analysis window as is done for ROI, the FLKS can be considered a suboptimal version of the efficient ROI when the involved model is non-linear and has no errors. We confirm that the efficient ROI analyses are more accurate than the FLKS analyses with the increase of the analysis window size. Nevertheless, the computation costs for implementing efficient ROI are almost the same as those for FLKS. Additionally, the reduced-rank version of the efficient ROI is developed based on the accuracy-saturation property. From the experiments using Lorenz 3-variable model, it is confirmed that the non-linearity of numerical model, which becomes stronger with the increase of the analysis window size, makes the analysis of efficient ROI more accurate than that of FLKS. Our Lorenz 40-variable experiments show that the average analysis error of the efficient ROI is smaller than that of the FLKS for an analysis window size of up to 4 d. However, the efficient ROI and the FLKS requires almost the same costs for computation. From the results of Lorenz 40-variable model experiments, it is suggested that, by using the reduced-rank formulation of the efficient ROI, we can obtain the suboptimal analysis more cost-effectively rather than FLKS. [ABSTRACT FROM AUTHOR]

The evolution of identical twin errors from an atmospheric general circulation model is studied in the linear range (small errors) through intermediate times and the approach to saturation. Between forecast day 1 and 7, the normalized error variance in the tropics is similar to that at higher latitudes. After that, tropical errors grow more slowly. The predictability time τ taken for tropical errors to reach half their saturation values is larger than that for mid-latitudes, especially for the planetary waves, thus implying greater potential predictability in the tropics. The discrepancy between mid-latitude and tropical τ is more pronounced at 850 hPa than at 200 hPa, is largest for the planetary waves, and is more pronounced for errors arising from wave phase differences (than from wave amplitude differences). The spectra of the error in 200 hPa zonal wind show that for forecast times up to about 5 d, the tropical error peaks at much shorter scales than the mid-latitude errors, but that subsequently tropical and mid-latitude error spectra look increasingly similar. The difference between upper and lower level tropical τ may be due to the greater influence of mid-latitudes at the upper levels. [ABSTRACT FROM AUTHOR]

An idealised two-basin model is used to investigate the impact of the wind field on the heat exchange between the ocean basins. The scalar potential of the divergent component of the horizontal heat flux is computed, which gives a ‘coarse-grained’ image of the surface heat flux that captures the large-scale structure of the horizontal heat transport. Further the non-divergent component is examined, as well as the meridional heat transport and the temperature–latitude overturning stream function. A sensitivity analysis examines the heat transport response to changes in wind stress at different latitudes. The results are compared with results from an eddy-permitting global circulation model. The westerly wind stress over the Southern Ocean has two effects: a local reduction of the surface heat loss in response to the equatorward surface Ekman drift, and a global re-routing of the heat export from the Indo-Pacific. Without wind forcing, the Indo-Pacific heat export is released to the atmosphere in the Southern Ocean, and the net heat transport in the southern Atlantic is southward. With wind forcing, the Indo-Pacific export enters the Atlantic through the Aghulas and is released in the Northern Hemisphere. The easterlies enhance the poleward heat transport in both basins. [ABSTRACT FROM AUTHOR]

Atmospheric N2O concentration was observed in the Pacific for the period 1991–2006, using commercial container ships sailing between Japan and North America and between Japan and Australia or New Zealand. The N2O concentration showed a secular increase and interannual variations at all sampling locations, but a seasonal cycle was detectable only at northern high latitudes. The annual mean N2O concentration showed little longitudinal variations (within ± 0.3 ppb) in the northern Pacific, but showed a clear north-south gradient of about 0.8 ppb, with higher values in the Northern Hemisphere. The annual mean N2O was also characterized by especially high values at 30°N due to strong local N2O emissions and by a steep latitudinal decrease from the equator to 20°S due to the suppression of interhemispheric exchange of air by the South Pacific Convergence Zone. The N2O growth rate showed an interannual variation with a period of about 3 yr (high-values in 1999 and 2000), with a delayed eastward and poleward phase propagation in the northern and western Pacific, respectively. The interannual variations of the N2O growth rate and soil water showed a good correlation, suggesting that the N2O emission from soils have an important causative role in the atmospheric N2O variation. [ABSTRACT FROM AUTHOR]

A high-resolution (1.67 km) ensemble transform (ET)-based meso-scale modelling system utilizing urbanization and sea surface temperature (SST) perturbations is used to examine characteristics of sea breeze/heat island interactions and atmospheric transport and dispersion for Tokyo. The ensemble displays a positive spread–skill relationship, with the addition of urban perturbations enabling the ensemble variance to distinguish a larger range of forecast error variances. Two synoptic regimes are simulated. For a pre-frontal period (stronger synoptic flow), there is less variability among ensemble members in the strength of the urban heat island and its interaction with the sea breeze front. During the post-frontal time period, the sea breeze frontal position is very sensitive to the details of the urban representation, with horizontal frontal variation covering the width of the urban centre (∼30 km) and displaying significant impacts on the development and strength of the heat island. Moreover, the dosage values of a tracer released at offshore and urban sites have considerable variability among ensemble members in response to small-scale features such as coastally upwelled water, enhanced anthropogenic heating and variations in building heights. Realistic variations in SST (i.e. warm Tokyo Bay or local upwelling) produce subtle sea breeze variations that dramatically impact tracer distributions. [ABSTRACT FROM AUTHOR]

In atmospheric data assimilation (DA), observations over a 6–12-h time window are used to estimate the state. Non-adaptive moderation or localization functions are widely used in ensemble DA to reduce the amplitude of spurious ensemble correlations. These functions are inappropriate (1) if true error correlation functions move a comparable distance to the localization length scale over the time window and/or (2) if the widths of true error correlation functions are highly flow dependent. A method for generating localization functions that move with the true error correlation functions and that also adapt to the width of the true error correlation function is given. The method uses ensemble correlations raised to a power (ECO-RAP). A gallery of periodic one-dimensional error models is used to show how the method uses error propagation information and error correlation width information retained by powers of raw ensemble correlations to propagate and adaptively adjust the width of the localization function. It is found that ECO-RAP localization outperforms non-adaptive localization when the true errors are propagating or the error correlation length scale is varying and is as good as non-adaptive localization when such variations in error covariance structure are absent. [ABSTRACT FROM AUTHOR]

Long-term measurements of fluxes of sensible heat ( H), latent heat ( LE) and carbon dioxide ( Fc) were made from December 2005 to August 2006 over an urban landscape in Helsinki, Finland using the direct micrometeorological eddy covariance technique. Three distinguished sectors of land-use cover (vegetation, roads and buildings) allowed comparisons of fluxes over different urban surfaces. The normalized standard deviation of wind and scalars as a function of atmospheric stability were typical for rough surfaces, as were turbulence spectra and cospectra. Footprint analysis was performed by a boundary-layer one and half-order closure model allowing for discrimination of surface and canopy sinks/sources and complex topography. Fluxes were analysed as average diurnal courses over winter, spring and summer periods. H exceeded LE reaching 300 W m–2 over urban and road surfaces in the summer and it was close to 100 W m–2 in the winter. LE was highest in the summer over vegetation cover attaining 150 W m–2. The emission rate of CO2 was high over road sector [20 μmol (m2s)–1][Correction added after online publication 16 Oct 2007: 30 μmol changed to 20 μmol] while in the vegetation sector it remained below 5 μmol (m2s)–1 and at summertime reached even −10 μmol(m2 s)−1[Correction added after online publication 16 Oct 2007: wording of sentence altered]. Effluxes from soil measured by chambers were 1–3 μmol (m2s)−1. Fc correlated with traffic density and a background non-vehicle flux was 1 μmol (m2s)−1[Correction added after online publication 16 Oct 2007: 2 μmol changed to 1 μmol]. [ABSTRACT FROM AUTHOR]

The accuracy and computational efficiency of a parallel computer implementation of the Local Ensemble Transform Kalman Filter (LETKF) data assimilation scheme on the model component of the 2004 version of the Global Forecast System (GFS) of the National Centers for Environmental Prediction (NCEP) is investigated. Numerical experiments are carried out at model resolution T62L28. All atmospheric observations that were operationally assimilated by NCEP in 2004, except for satellite radiances, are assimilated with the LETKF. The accuracy of the LETKF analyses is evaluated by comparing it to that of the Spectral Statistical Interpolation (SSI), which was the operational global data assimilation scheme of NCEP in 2004. For the selected set of observations, the LETKF analyses are more accurate than the SSI analyses in the Southern Hemisphere extratropics and are comparably accurate in the Northern Hemisphere extratropics and in the Tropics. The computational wall-clock times achieved on a Beowulf cluster of 3.6 GHz Xeon processors make our implementation of the LETKF on the NCEP GFS a widely applicable analysis-forecast system, especially for research purposes. For instance, the generation of four daily analyses at the resolution of the NCAR-NCEP reanalysis (T62L28) for a full season (90 d), using 40 processors, takes less than 4 d of wall-clock time. [ABSTRACT FROM AUTHOR]

The Dynamic State Index (DSI) basing on the Energy-Vorticity Theory is able to detect all non-stationary and diabatic processes in the atmosphere. It is shown for the first time that the index is practicable for diagnostic analysis of the synoptic scale, in particular on pressure levels, using the ERA-40 reanalysis data set from the European Centre for Medium-Range Weather Forecasts (ECMWF). To verify the practical value of the DSI as a parameter diagnosing atmospheric developments, the index is applied to the synoptic scale. In a global view two different north hemispheric winters and particularly two case studies concerning the winter storm ‘Lothar’ and hurricane ‘Andrew’ are presented. For analysing the storm structures, both DSI on pressure levels and three-dimensional views of DSI isosurfaces are utilized. The results of this study document that the magnitude of the index expresses the intensification and decaying of the observed vortices. Thereby, it draws conclusions from the steering mechanism of ‘Lothar’ and ‘Andrew’ by virtue of their different DSI structures. A main result for practical weather forecasts is the early visibility of cyclones in the DSI field compared to the pressure field. Furthermore, storm tracks and their intensity can be visualized using the index. [ABSTRACT FROM AUTHOR]

Due to the non-linearity of cloud–radiation interaction in general circulation models (GCMs), the time-mean cloud radiative forcing (CRF) is in general different from the CRF of time-mean clouds. This implies that a change in temporal cloud variability induces a change in radiative forcing even if there is no change in time-mean cloud properties. Here we investigate this variability contribution to CRF quantitatively in the National Center for Atmospheric Research Community Climate Model 3.6 GCM. In a reference run, the variability contribution is found to account for 35% of the global-mean climatological CRF. The variability contribution peaks in the mid-latitudes and is shown to be driven by synoptic eddy activity. In a climate change experiment, where the atmospheric CO2 is quadrupled, the change in cloud variability offsets 40% of the change in CRF due to the change in mean clouds. It is found that almost all of this effect is due to variability in cloud fraction rather than in cloud water content, and it is traced to the non-linearity introduced by the model's treatment of vertical cloud overlap. This study indicates the possibility of an eddy variability-climate feedback that has not been extensively studied and quantified in the past. [ABSTRACT FROM AUTHOR]

Recent observational work shows that three factors control the formation of deep convection over tropical oceans; the saturation fraction of the troposphere, surface moist entropy fluxes, and the strength of convective inhibition. A linearized, two-dimensional, non-rotating model of the tropical atmosphere is presented here which incorporates all of these factors into its convective closure in a simplified fashion. Two types of large-scale unstable modes develop in this model, a slowly propagating ‘moisture mode’ which is driven primarily by saturation fraction anomalies, and a convectively coupled ‘gravity mode’ which is governed by anomalies in convective inhibition caused by buoyancy variations just above the top of the planetary boundary layer. The gravity mode maps onto the equatorial Kelvin wave in the earth's atmosphere and the predicted propagation speed for this mode is close to the observed phase speed of convectively coupled equatorial Kelvin waves. For reasonable parameter values the growth rate peaks at zonal wavenumbers at which Kelvin waves exhibit the greatest spectral energy. The computed vertical structure matches that of observed Kelvin waves, but is produced by a simple sinusoidal vertical heating profile with half-wavelength equal to the depth of the troposphere. [ABSTRACT FROM AUTHOR]

The potential for tropical cyclogenesis in a given ocean basin during its active season has been represented by genesis potential indices, empirically determined functions of large-scale environmental variables which influence tropical cyclone (TC) genesis. Here we examine the ability of some of today's atmospheric climate models, forced with historical observed SST over a multidecadal hindcast period, to reproduce observed values and patterns of one such genesis potential index (GP), as well as whether the GP in a given model is a good predictor of the number of TCs generated by that model. The effect of the horizontal resolution of a climate model on its GP is explored. The five analysed models are capable of reproducing the observed seasonal phasing of GP in a given region, but most of them them have a higher GP than observed. Each model has its own unique relationship between climatological GP and climatological TC number; a larger climatological GP in one model compared to others does not imply that that model has a larger climatological number of TCs. The differences among the models in the climatology of TC number thus appear to be related primarily to differences in the dynamics of the simulated storms themselves, rather than to differences in the simulated large-scale environment for genesis. The correlation of interannual anomalies in GP and number of TCs in a given basin also differs significantly from one model to the next. Experiments using the ECHAM5 model at different horizontal resolutions indicate that as resolution increases, model GP also tends to increase. Most of this increase is realized between T42 and T63. [ABSTRACT FROM AUTHOR]

Tropical cyclones (TC) under different climate conditions in the Northern Hemisphere have been investigated with the Max Planck Institute (MPI) coupled (ECHAM5/MPI-OM) and atmosphere (ECHAM5) climate models. The intensity and size of the TC depend crucially on resolution with higher wind speed and smaller scales at the higher resolutions. The typical size of the TC is reduced by a factor of 2.3 from T63 to T319 using the distance of the maximum wind speed from the centre of the storm as a measure. The full three-dimensional structure of the storms becomes increasingly more realistic as the resolution is increased. For the T63 resolution, three ensemble runs are explored for the period 1860 until 2100 using the IPCC SRES scenario A1B and evaluated for three 30 yr periods at the end of the 19th, 20th and 21st century, respectively. While there is no significant change between the 19th and the 20th century, there is a considerable reduction in the number of the TC by some 20% in the 21st century, but no change in the number of the more intense storms. Reduction in the number of storms occurs in all regions. A single additional experiment at T213 resolution was run for the two latter 30-yr periods. The T213 is an atmospheric only experiment using the transient sea surface temperatures (SST) of the T63 resolution experiment. Also in this case, there is a reduction by some 10% in the number of simulated TC in the 21st century compared to the 20th century but a marked increase in the number of intense storms. The number of storms with maximum wind speeds greater than 50 m s−1 increases by a third. Most of the intensification takes place in the Eastern Pacific and in the Atlantic where also the number of storms more or less stays the same. We identify two competing processes effecting TC in a warmer climate. First, the increase in the static stability and the reduced vertical circulation is suggested to contribute to the reduction in the number of storms. Second, the increase in temperature and water vapour provide more energy for the storms so that when favourable conditions occur, the higher SST and higher specific humidity will contribute to more intense storms. As the maximum intensity depends crucially on resolution, this will require higher resolution to have its full effect. The distribution of storms between different regions does not, at first approximation, depend on the temperature itself but on the distribution of the SST anomalies and their influence on the atmospheric circulation. Two additional transient experiments at T319 resolution where run for 20 yr at the end of the 20th and 21st century, respectively, using the same conditions as in the T213 experiments. The results are consistent with the T213 study. The total number of TC were similar to the T213 experiment but were generally more intense. The change from the 20th to the 21st century was also similar with fewer TC in total but with more intense cyclones. [ABSTRACT FROM AUTHOR]

A technique called extended mosaic (EM) was designed to allow the subgrid scale interactions between the land surface and the atmosphere to extend vertically. EM addresses a limitation of previously existing techniques, and has been shown to have an important impact on the simulated climate in global models. The present work focuses on an observational validation of the climate characteristics of a general circulation model using EM, based on a set of 10-yr simulations with each of EM and the standard mosaic technique (M), driven by climatological sea surface temperatures. Model simulations using EM show improvements in many aspects of the mid-latitude climate and in wintertime air temperature over Alaska and Western Canada and in the pattern of the Australian monsoon precipitation over land. An example of a degradation in the EM simulation is the temperature over southern South America in wintertime. [ABSTRACT FROM AUTHOR]

The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is used to analyse the geographical and the seasonal characteristics of nitrate aerosol (ANO3) concentration distributions over East Asia. Three-dimensional concentrations in January, March, April, July and October of 2001 are simulated, and for the evaluation of model performances, the simulated values of wind direction, wind speed, temperature, specific humidity, nitric oxide (NO), nitrogen oxide (NO2), ANO3 and ammonium aerosol (ANH4) are compared with the observational data obtained onboard the P-3B aircraft during its four consecutive flights over the South China Sea, the East China Sea, the Yellow Sea and the water areas to the east of Japan conducted on 13, 17, 18 and 21 March 2001. The observed data are 5-min averaged and the model results with a 1-hour temporal resolution are interpolated to the aircraft location and time using trilinear interpolation. Comparison shows that the observed values exhibit strong temporo-spatial variations, and the model reproduces these variations reasonably well. The simulated values of wind direction, wind speed, temperature and specific humidity are generally in good agreement with the observed ones, their correlation coefficients reach 0.66, 0.94, 0.99 and 0.96, respectively. Comparison also shows that the average mixing ratios of modelled and observed NO, NO2, ANO3 and ANH4 agree reasonably well with each other, the correlation coefficient for ANO3 and ANH4 are larger than 0.8, but the simulated standard deviations are smaller than the observed one, and the correlation coefficient for NO and NO2 are 0.48 and 0.44. Analysis of horizontal distributions of monthly averaged ANO3 concentrations in the boundary layer indicates that the ANO3 mixing ratios have noticeable differences among the four seasons. Generally the concentrations are high in the winter, spring and fall and low in the summer, and seasonal variations are typically strongest over China and Japan. Highest concentrations are found over eastern China where emissions of nitrogen oxides and ammonia are high and long-range transport may cause elevated concentrations in remote areas under favourable meteorological conditions, but the seasonal variation in the ANO3 concentrations is heavily influenced by the changes in precipitation and temperature. [ABSTRACT FROM AUTHOR]

The Integrated Deposition Model (IDEM) was improved by incorporating a novel multilayer biochemical dry deposition module for gases. The aerosol and base cation deposition module was adopted from IDEM. For evaluation of primary and ecosystem productivity, carbon respiration schemes were included. The resulting Framework for Atmosphere-Canopy Exchange Modelling (FACEM) was then evaluated by the case studies presented here. First, results for deposition of SO x, NO y and NH x were compared with site observations, showing correlations of up to . Applicability for grid deposition calculations for these compounds was then evaluated for Europe. The model was clearly able to reproduce the elevated deposition near the important emission areas in Europe. Next, we compared the modelled CO2 fluxes with measurements from 26 European sites. Correlations of up to indicate good performance. To evaluate grid performance, the 2003 European heat wave was studied in a final case study, resulting in convincing correspondence with the observed productivity anomalies. [ABSTRACT FROM AUTHOR]

The sensible and latent heat fluxes, representatives of the physical exchange processes of energy and water between land and air, are the two crucial variables controlling the surface energy partitioning related to temperature and humidity. The net primary production (NPP), the major carbon flux exchange between vegetation and atmosphere, is of great importance for the terrestrial ecosystem carbon cycle. The fluxes are simulated by a two-way coupled model, Atmosphere-Vegetation Interaction Model-Global Ocean-Atmosphere-Land System Model (AVIM-GOALS) in which the surface physical and physiological processes are coupled with general circulation model (GCM), and the global spatial and temporal variation of the fluxes is studied. The simulated terrestrial surface physical fluxes are consistent with the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA40) in the global distribution, but the magnitudes are generally 20–40 W/m2 underestimated. The annual NPP agrees well with the International Geosphere Biosphere Programme (IGBP) NPP data except for the lower value in northern high latitudes. The surface physical fluxes, leaf area index (LAI) and NPP of the global mid-latitudes, especially between 30 °N–50 °N, show great variation in annual oscillation amplitudes. And all physical and biological fields in northern mid-latitudes have the largest seasonality with a high statistical significance of 99.9%. The seasonality of surface physical fluxes, LAI and NPP are highly correlated with each other. The meridional three-peak pattern of seasonal change emerges in northern mid-latitudes, which indicates the interaction of topographical gradient variation of surface fluxes and vegetation phenology on these three latitudinal belts. [ABSTRACT FROM AUTHOR]

The impact of increasing levels of carbon dioxide on stomatal conductance and surface ozone levels was investigated using a global three-dimensional general circulation model (GCM) coupled to an interactive land surface scheme and a chemistry model. Pre-industrial, present day and doubled present day levels of carbon dioxide were used. This approach was used to examine the sensitivity of modelled surface ozone levels to changes in stomatal conductance via dry deposition. A doubled level of carbon dioxide was found to increase surface ozone levels by between 2 and 8 ppb in all four seasons owing to reduced dry deposition fluxes, although the location and extent of the changes were very different between each season. No change in levels of nitrogen oxides (NO and NO2) was modelled. A similar experiment to examine the same effect on modelled pre-industrial ozone levels showed that the ozone levels over Europe were only slightly smaller (by 1–1.5 ppb) when the CO2 level was decreased from 369 ppm to 280 ppm. [ABSTRACT FROM AUTHOR]

The standard approach to predicting climate change, assessing its impacts and planning mitigation strategies tends to be compartmentalized, leading to inadequate or incomplete advice for climate policy. Climate models used for future global warming predictions and attribution of past changes generally consider only global climate drivers, ignoring local drivers, such as land use change and urban effects. Impacts studies are generally carried out in isolation from each other and hence ignore interactions between different impacts sectors, such as hydrology, natural ecosystems and agriculture. Feedbacks from impacts to climate change, which often involve land ecosystem-atmosphere interactions, are often neglected. This can result in representations of global changes that are at best inconsistent and at worst completely misleading. Moreover, a number of climate change mitigation strategies, such as carbon sequestration and biofuels involve changes in land ecosystems. In addition to affecting climate through the exchange of carbon with the atmosphere, these land ecosystem changes may affect climate change or its impacts through a variety of additional processes, such as surface albedo change or changes in the surface moisture budget. Failure to account for these may have consequences that are potentially at odds with the aims of climate change mitigation. [ABSTRACT FROM AUTHOR]

A vertically resolved linear model for large-scale motions in an equatorial non-rotating atmosphere is presented. Precipitation is forced by tropospheric precipitable water, cloud–radiation interactions (CRI), and wind-induced surface heat exchange (WISHE). The dynamics of the model are based on the assumption that the vertical heating profile has the shape of the first baroclinic mode. The vertical profiles of vertical velocity, temperature perturbation, etc. are calculated using an upward radiation boundary condition. The modelled modes are of three types: fast gravity waves that resemble adiabatic modes with the vertical wavelength twice the depth of the troposphere; convectively coupled gravity modes that are damped and move with a phase speed of ≈17 m s−1; and the unstable moisture mode. The value of the model is that under a single dynamical assumption it yields the observed phase speed for the convectively coupled gravity waves that map to Kelvin waves in the equatorial beta plane case while still producing the unstable moisture mode. However, the model lacks the precipitation physics needed to produce the observed destabilization of the gravity mode. [ABSTRACT FROM AUTHOR]

Stratiform precipitation over multiscale terrain is examined based on two-dimensional simulations of moist airflow past two-ridge terrain with a narrower ridge superposed on the windward slope of a wider ridge. It has been demonstrated that the narrower ridge could significantly modulate the precipitation intensity and distribution by inducing upslope ascent, leeside descent, and gravity waves. Three distinct flow regimes have been identified based on simulations, namely linear, non-linear, and blocking regimes. For low terrain, the wave response is primarily linear, and more precipitation occurs over the narrower ridge. Precipitation over the major ridge is much reduced by precipitation over the narrower ridge, which decreases the moisture flux that reaches the major ridge, and by leeside descent over the narrower ridge, which limits the horizontal dimension of the updraft zone over the major ridge. In the linear regime, the total precipitation produced by the two-ridge terrain and the corresponding wide smooth ridge is comparable. For terrain of moderate heights, the wave response is non-linear and oscillation occurs with updraft and precipitation maxima alternating between the upwind slopes of the two ridges, likely due to non-linear wave–wave interaction. Strong lee waves are produced in the lee of the first ridge due to non-linear amplification and could significantly enhance precipitation over the major ridge through directly increasing the condensation rate over the upwind slope of the major ridge and through generating snow above the freezing level. Correspondingly, precipitation rates over the two ridges become comparable and the total precipitation over the two-ridge terrain is considerably larger than over the corresponding reference ridge. For higher terrain, blocking becomes significant and precipitation over the first ridge tends to detach from the terrain and propagates upstream. Additional simulations indicate that the precipitation intensity and distribution are also sensitive to terrain geometry such as the ratio of the two ridge heights, the depth of the relative valley, and the distance between the two ridges. [ABSTRACT FROM AUTHOR]

During the period of July 8–13, 2002, we collected vertical profiles by aircraft of meteorological variables and atmospheric CO2 over the OBS (old black spruce) site located in Boreal Ecosystem Research and Monitoring Sites in Northern Saskatchewan, Canada. We have used the data from the morning and afternoon flights to calculate the regional daily afternoon CO2 flux for the days July 8–11. These daily fluxes were then compared to those obtained by the boundary layer budget method and by the eddy covariance measurements on the tower at the OBS site. We identified the importance of changes in the CO2 concentration by advection to the flux estimates. In addition, we provide arguments to suggest that subseasonal temporal averaging might not, at least in some cases, eliminate advective bias contribution to the flux estimates. Because the advective influence is large and highly directional, even on seasonal and interannual timescales, it is advisable that flux estimates based on CO2 concentration change at a site contain dynamic description of an air parcel transport history. [ABSTRACT FROM AUTHOR]

Atmospheric CO2 inversion studies infer surface sources and sinks from observations and models. These studies usually require determination of the fossil fuel component of the observation, which can be estimated using anthropogenic tracers such as CO. The objective of this study is to demonstrate a new CO tracer method that accounts for overlapping forest fire and photochemical CO influences, and to quantify several aspects of the uncertainty in the CO tracer technique. Photochemistry model results and observations from the International Consortium for Atmospheric Research on Transport and Transformation experiment are used to quantify changes in the fossil fuel CO2 prediction from the CO tracer method with and without the inclusion of CO from biomass burning and photochemistry. Although the chemical sources and sinks tend to offset each other, there are regions where the chemical reactions change fossil fuel CO2 predictions by up to ±4 ppm. Including biomass burning lowers fossil fuel CO2 by an average of 12 ppm in plumes heavily influenced by long-range transport of forest fire CO. An alternate fossil fuel CO2 calculation is done in a power plant plume using SO2 as a tracer, giving a change in 20 ppm from the CO method, indicative of uncertainty in the assumed CO:CO2 ratio. [ABSTRACT FROM AUTHOR]