Radiative Energy Budget Research Articles

Daily Radiation Budget of the Baltic Sea Surface from Satellite Data

Abstract Recently developed system for assessment of radiation budget for the Baltic Sea has been presented and verified. The system utilizes data from various sources: satellite, model and in situ measurements. It has been developed within the SatBałtyk project (Satellite Monitoring of the Baltic Sea Environment - www.satbaltyk.eu) where the energy radiation budget is one of the key element. The SatBałtyk system generates daily maps of the all components of radiation budget on every day basis. We show the scheme of making daily maps, applied algorithms and empirical data collection within the system. An empirical verification of the system has been carried out based on empirical data collected on the oil rig placed on the Baltic Sea. This verification concerned all the components of the surface radiation budget. The average daily NET products are estimated with statistical error ca. 13 Wm-2. The biggest absolute statistical error is for LWd component and equals 14 Wm-2. The relative error in relation to the average annual values for whole Baltic is the biggest for SWu and reaches 25%. All estimated components have correlation coefficient above 0.91.

Radiative heating and cooling in the middle and lower atmosphere of Venus and responses to atmospheric and spectroscopic parameter variations

A sophisticated radiative transfer model that considers absorption, emission, and multiple scattering by gaseous and particulate constituents over the broad spectral range 0.125–1000µm is applied to calculate radiative fluxes and temperature change rates in the middle and lower atmosphere of Venus (0–100km). Responses of these quantities to spectroscopic and atmospheric parameter variations are examined in great detail. Spectroscopic parameter studies include the definition of an optimum spectral grid for monochromatic calculations as well as comparisons for different input data with respect to spectral line databases, continuum absorption, line shape factors, and solar irradiance spectra. Atmospheric parameter studies are based on distinct variations of an initial model data set. Analyses of actual variations of the radiative energy budget using atmospheric features that have been recently retrieved from Venus Express data will be subject of a subsequent paper.The calculated cooling (heating) rates are very reliable at altitudes below 95 (85)km with maximum uncertainties of about 0.25K/day. Heating uncertainties may reach 3–5K/day at 100km. Using equivalent Planck radiation as solar insolation source in place of measured spectra is not recommended. Cooling rates strongly respond to variations of atmospheric thermal structure, while heating rates are less sensitive. The influence of mesospheric minor gas variations is small, but may become more important near the cloud base and in case of episodic SO2 boosts. Responses to cloud mode 1 particle abundance changes are weak, but variations of other mode parameters (abundances, cloud top and base altitudes) may significantly alter radiative temperature change rates up to 50% in Venus' lower mesosphere and upper troposphere.A new model for the unknown UV absorber for two altitude domains is proposed. It is not directly linked to cloud particle modes and permits an investigation of radiative effects regardless of the absorbers’s chemical composition. A globally averaged Bond albedo of Venus of 0.763 is inferred in accordance with previous results. Considering the gaseous UV absorbers SO2 and CO2 shortward of 0.32µm, the globally averaged deposited solar net flux at the top of atmosphere (TOA) and the outgoing thermal net flux differ by only 1.5Wm−2 around the mean value of 159Wm−2 for the selected initial atmospheric model. Global radiative equilibrium can be achieved by moderate adjustments of cloud mode and UV absorber abundances. Half of the TOA solar net flux is absorbed by atmospheric constituents at altitudes above 63km. Consideration of the unknown UV absorber provides about 50% more heating at 68km compared with a neglect of this opacity source. Less than 5% of the incident flux reaches the surface. There is a broad net cooling region between 70 and 80km with a strong increase of cooling toward the poles. A net radiative temperature change rate gradient is also observed at 65km where heating occurs at low latitudes. At altitudes above 80km, net heating dominates the low and mid latitudes, while net cooling prevails at high latitudes leading to a dominant global average net heating that has to be balanced by dynamical processes to maintain the observed thermal structure. The results of energy balance response analyses will serve as reference for ongoing investigations and provide a profound data base to improve the understanding of radiative forcing of atmospheric dynamical processes.

Estimating Actual Transpiration of Apple Trees Based on Infrared Thermometry

AbstractA method was developed based on the radiative properties and energy budget of a single apple leaf to calculate the actual transpiration (T) of apple trees. The model uses canopy temperature (Tc), air temperature (Ta) measured in the orchard, and other meteorological data from a local weather station as inputs. The model was applied to two scenarios, as follows: (1) well-watered, young Fuji apple trees in the 2007 and 2008 growing seasons; and (2) older apple trees, bearing little fruit in the 2013 growing season. Simulated transpiration rates at both scenarios were compared with Penman-Monteith (PM) model predictions corrected by regionally adjusted crop coefficients, i.e., values of ETc. In 2007 and 2008, a linear regression analysis of the relationship between daily mean transpiration (Tavg) and ETc revealed that they better agreed on warm and dry days (correlation coefficient R2=0.57, slope=1.16, and intercept=0.4) than during cold and humid periods (R2=0.48, slope=0.69, and intercept=2.3). Com...

Size-dependent wet removal of black carbon in Canadian biomass burning plumes

Abstract. Wet deposition is the dominant mechanism for removing black carbon (BC) from the atmosphere and is key in determining its atmospheric lifetime, vertical gradient and global transport. Despite the importance of BC in the climate system, especially in terms of its ability to modulate the radiative energy budget, there are few quantitative case studies of wet removal in ambient environments. We present a case study of BC wet removal by examining aerosol size distributions and BC coating properties sampled in three Canadian boreal biomass burning plumes, one of which passed through a precipitating cloud. This depleted the majority of the plume's BC mass, and the largest and most coated BC-containing particles were found to be preferentially removed, suggesting that nucleation scavenging was likely the dominant mechanism. Calculated single-scattering albedo (SSA) showed little variation, as a large number of non-BC particles were also present in the precipitation-affected plume. The remaining BC cores were smaller than those observed in previous studies of BC in post-precipitation outflow over Asia, possibly due to the thick coating by hydrophilic compounds associated with the Canadian biomass burning particles. This study provides measurements of BC size, mixing state and removal efficiency to constrain model parameterisations of BC wet removal in biomass burning regions, which will help to reduce uncertainty in radiative forcing calculations.

Physical Properties of High-Level Cloud over Land and Ocean from CloudSat–CALIPSO Data

Abstract Unlike other cloud types, high-level clouds play an important role, often imposing a warming effect, in the earth–atmosphere radiative energy budget. In this paper, macro- and microphysical characteristics of cirrus clouds, such as their occurrence frequency, geometric scale, water content, and particle size, over northern China (land area, herein called the L area) and the Pacific Ocean (ocean area, herein the O area) are analyzed and compared based on CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) products from 1 January 2007 to 31 December 2010. Over both areas, statistical analysis shows that cirrus occurrence approached 33% in summer whereas it was only ~10% in winter, >50% of cirrus cloud thicknesses were in the range of ~(0.25–1.5) km, there were >98% ice particles in high-level clouds, and temperature had a closer linear relationship with ice effective radius (IER) than height. Also, the seasonal difference of this linear relationship is minor over both land and ocean. Comparisons reveal that the mean occurrence frequency, mean cloud thickness, range of cloud-base and cloud-top height, IER, and ice water content of cirrus in summer were generally greater in winter, and greater over the O area than over the L area. However, the relationship between IER and temperature over land is close to that over ocean.

Quantifying the respective roles of aerosols and clouds in the strong brightening since the early 2000s over the Iberian Peninsula

AbstractThe contribution of clouds and aerosols to the decadal variations of downward surface shortwave radiation (SSR) is a current controversial topic. This study proposes a method, which is based on surface‐based SSR measurements, aerosol observations, and radiative transfer simulations (in cloud‐free and cloud‐ and aerosol‐free scenarios), to evaluate cloud‐aerosol (CARE), cloud (CRE), and aerosol (ARE) radiative effects. This method is applied to quantify the role played by, separately, clouds and aerosols on the intense brightening of the SSR observed in the Iberian Peninsula. Clouds and Earth's Radiation Energy Budget System (CERES) and surface‐based data exhibit an increase in SSR between 2003 and 2012, exceeding +10 W m−2 over this period for some areas of the peninsula. The calculations are performed for three surface‐based sites: Barcelona and Valladolid (Spain), and Évora (Portugal). Ranges in monthly values of CARE, CRE, and ARE are (−80, −20), (−60, −20), and (−30, 0), respectively (in W m−2). The average trends for the analyzed period of CARE, CRE, and ARE are +7, +5, and +2 W m−2 per decade, respectively. Overall, three fourths of the SSR trend is explained by clouds, while the other one fourth is related to aerosol changes. The SSR trends explained by the clouds and aerosol radiative effects are in line with the observed reductions in total cloud cover and aerosol load (both at the surface and in the whole atmospheric column). Furthermore, the CRE values are compared against CERES data showing good agreement between both data series, although some discrepancies are observed in their trends.

Geographical gradients in boreal forest albedo and structure in Finland

Land surface albedo is an essential climate variable controlling the planetary radiative energy budget, yet it is still among the main uncertainties of the radiation budget in the current climate modeling. To date, albedo satellite products have not been linked to extensive forest inventory data sets due to the lack of ground reference data. Here, we used comprehensive and detailed maps of forest inventory variables to couple forest structure and MODIS albedo products for both winter and summer conditions. We investigated how the relationships between forest variables and albedo change seasonally and along latitudinal gradients in the forest biomes of Finland between 60° and 70° N. We observed an increase in forest albedo with increasing latitude in winter but not in summer. Also, relationships between forest variables and the black-sky albedo or directional–hemispherical reflectance (DHR) at different latitudes were tighter in winter than in summer, especially for forest biomass. Summer albedo was only weakly correlated with the traditional inventory variables. Our findings suggest that the relationships between forest variables and DHR depend on latitude.

The optical properties and longwave radiative forcing in the lateral boundary of cirrus cloud

AbstractThrough observations from the Cloud‐Aerosol Lidar with Orthogonal Polarization onboard the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation, we detected a common feature of narrow and subvisible lateral boundary layer in cirrus cloud. In this layer the lidar backscatter, the depolarization ratio, the ice water content, the effective radius of ice particles, and the cloud optical depth all decrease sharply toward the cloud edge. In general, the width of this layer (6.4 ± 3.1 km over land) decreases with increasing ambient temperature. The estimated longwave radiative forcing associated with the layer is about 10 W/m2. Due to its extremely small optical depth (less than 0.3), such lateral boundary layer may be missed by conventional satellite passive optical sensors. As a consequence, the mentioned radiative forcing has not been credited with its deserved share in the Earth's radiative energy budget.

Radiative energy budget reveals high photosynthetic efficiency in symbiont-bearing corals

The light field on coral reefs varies in intensity and spectral composition, and is the key regulating factor for phototrophic reef organisms, for example scleractinian corals harbouring microalgal symbionts. However, the actual efficiency of light utilization in corals and the mechanisms affecting the radiative energy budget of corals are underexplored. We present the first balanced light energy budget for a symbiont-bearing coral based on a fine-scale study of the microenvironmental photobiology of the massive coral Montastrea curta. The majority (more than 96%) of the absorbed light energy was dissipated as heat, whereas the proportion of the absorbed light energy used in photosynthesis was approximately 4.0% under an irradiance of 640 µmol photons m(-2) s(-1). With increasing irradiance, the proportion of heat dissipation increased at the expense of photosynthesis. Despite such low energy efficiency, we found a high photosynthetic efficiency of the microalgal symbionts showing high gross photosynthesis rates and quantum efficiencies (QEs) of approximately 0.1 O2 photon(-1) approaching theoretical limits under moderate irradiance levels. Corals thus appear as highly efficient light collectors with optical properties enabling light distribution over the corallite/tissue microstructural canopy that enables a high photosynthetic QE of their photosynthetic microalgae in hospite.

All-Sky Surface Radiation and Clear-Sky Surface Energy Budgets: Summer to Freeze-Up in the Western Maritime Arctic

The 2009 ArcticNet expedition was a field campaign in the Amundsen Gulf–eastern Beaufort Sea region from mid-July to the beginning of November aboard the CCGS Amundsen that provided an opportunity to describe the all-sky surface radiation and the clear-sky surface energy budgets from summer to freeze-up in the data sparse western maritime Arctic. Because the fractional area of open water was generally larger than the fractional area of ice floes, the net radiation at the water surface controlled the radiation budget. Because the water albedo is much less than the albedo of the ice floes, the extent and duration of open water in summer is an important albedo feedback mechanism. From summer to freeze-up, the net all-sky shortwave radiation declined steadily as the solar angle lowered, while coincidently the net all-sky longwave radiation became increasingly negative. The all-sky net surface radiation switched from positive in summer to negative during the freeze-up period. From summer to freeze-up, both upward and downward turbulent heat fluxes occurred. In summer, a positive surface energy budget residual contributed to the melting of ice floes and/or to the warming of the Arctic Ocean's mixed layer. During the freeze-up period, with temperatures below approximately −5°C, the residuals were mainly negative suggesting that heat loss from the ocean's mixed layer and heat released by the phase change of water were significant components of the energy budget's residual.

How well do the current state-of-the-art CMIP5 models characterise the climatology of the East Asian winter monsoon?

Previous studies have revealed some common biases in coupled general circulation model's simulations of the East Asian (EA) winter monsoon (EAWM), including colder surface air temperature and more winter precipitation over the EA region. In this study, we exam- ined 41 fully coupled atmosphere-ocean models from fifth phase of the Coupled Model Intercomparison Project (CMIP5), which will be widely used in the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC), and address whether the current state-of-the-art CMIP5 models can characterise the climatology of the East Asian winter monsoon. We also compared the results with the models from third phase of CMIP, which was exten- sively used in the fourth assessment report of the IPCC. The results show that the cold surface air temperature (SAT) bias is lessened and the precipitation amount decreased with the current CMIP5 models. Moreover, the CMIP5 models performbetter at predicting surface winds and high-level jet streams than the CMIP3 models. More- over, CMIP5 models show more model consistency in most EAWM parameters, and the interannual variability of the SAT is closer to the observations. We also examined the change in the radiation energy budget in the CMIP5 models and compared with CMIP3 models. Although the improvements are significant, deficiencies still exist in the simulation of the EAWM, e.g., the stronger EA major trough and the stronger zonal sea level pressure gradient.

Infrared radiative transfer in atmospheres of Earth-like planets around F, G, K, and M stars

Context. Clouds play an important role in the radiative transfer of planetary atmospheres because of the influence they have on the different molecular signatures through scattering and absorption processes. Furthermore, they are important modulators of the radiative energy budget affecting surface and atmospheric temperatures.Aims. We present a detailed study of the thermal emission of cloud-covered planets orbiting F-, G-, K-, and M-type stars. These Earth-like planets include planets with the same gravity and total irradiation as Earth, but can differ significantly in the upper atmosphere. The impact of single-layered clouds is analyzed to determine what information on the atmosphere may be lost or gained. The planetary spectra are studied at different instrument resolutions and compared to previously calculated low-resolution spectra.Methods. A line-by-line molecular absorption model coupled with a multiple scattering radiative transfer solver was used to calculate the spectra of cloud-covered planets. The atmospheric profiles used in the radiation calculations were obtained with a radiative-convective climate model combined with a parametric cloud description.Results. In the high-resolution flux spectra, clouds changed the intensities and shapes of the bands of CO2 , N2 O, H2 O, CH4 , and O3 . Some of these bands turned out to be highly reduced by the presence of clouds, which causes difficulties for their detection. The most affected spectral bands resulted for the planet orbiting the F-type star. Clouds could lead to false negative interpretations for the different molecular species investigated. However, at low resolution, clouds were found to be crucial for detecting some of the molecular bands that could not be distinguished in the cloud-free atmospheres. The CO2 bands were found to be less affected by clouds. Radiation sources were visualized with weighting functions at high resolution.Conclusions. Knowledge of the atmospheric temperature profile is essential for estimating the composition and important for avoiding false negative detection of biomarkers, in both cloudy and clear-sky conditions. In particular, a pronounced temperature contrast between the ozone layer and surface or cloud is needed to detect the molecule. Fortunately, the CO2 bands allow temperature estimation from the upper stratosphere down to the troposphere even in the presence of clouds.

A statistics-based temporal filter algorithm to map spatiotemporally continuous shortwave albedo from MODIS data

Abstract. Land-surface albedo plays a critical role in the earth's radiant energy budget studies. Satellite remote sensing provides an effective approach to acquire regional and global albedo observations. Owing to cloud coverage, seasonal snow and sensor malfunctions, spatiotemporally continuous albedo datasets are often inaccessible. The Global LAnd Surface Satellite (GLASS) project aims at providing a suite of key land surface parameter datasets with high temporal resolution and high accuracy for a global change study. The GLASS preliminary albedo datasets are global daily land-surface albedo generated by an angular bin algorithm (Qu et al., 2013). Like other products, the GLASS preliminary albedo datasets are affected by large areas of missing data; beside, sharp fluctuations exist in the time series of the GLASS preliminary albedo due to data noise and algorithm uncertainties. Based on the Bayesian theory, a statistics-based temporal filter (STF) algorithm is proposed in this paper to fill data gaps, smooth albedo time series, and generate the GLASS final albedo product. The results of the STF algorithm are smooth and gapless albedo time series, with uncertainty estimations. The performance of the STF method was tested on one tile (H25V05) and three ground stations. Results show that the STF method has greatly improved the integrity and smoothness of the GLASS final albedo product. Seasonal trends in albedo are well depicted by the GLASS final albedo product. Compared with MODerate resolution Imaging Spectroradiometer (MODIS) product, the GLASS final albedo product has a higher temporal resolution and more competence in capturing the surface albedo variations. It is recommended that the quality flag should be always checked before using the GLASS final albedo product.

Modeling the South American regional smoke plume: aerosol optical depth variability and surface shortwave flux perturbation

Abstract. Intra-seasonal variability of smoke aerosol optical depth (AOD) and downwelling solar irradiance at the surface during the 2002 biomass burning season in South America was modeled using the Coupled Chemistry-Aerosol-Tracers Transport model with the Brazilian developments on the Regional Atmospheric Modeling System (CCATT-BRAMS). Measurements of total and fine mode fraction (FMF) AOD from the AErosol RObotic NETwork (AERONET) and solar irradiance at the surface from the Solar Radiation Network (SolRad-NET) were used to evaluate model results. In general, the major features associated with AOD evolution over the southern part of the Amazon basin and cerrado ecosystem are captured by the model. The main discrepancies were found for high aerosol loading events. In the northeastern portion of the Amazon basin the model systematically underestimated total AOD, as expected, since smoke contribution is not dominant as it is in the southern portion and emissions other than smoke were not considered in the simulation. Better agreement was obtained comparing the model results with observed FMF AOD, which pointed out the relevance of coarse mode aerosol emission in that region. Likewise, major discrepancies over cerrado during high AOD events were found to be associated with coarse mode aerosol omission in our model. The issue of high aerosol loading events in the southern part of the Amazon was related to difficulties in predicting the smoke AOD field, which was discussed in the context of emissions shortcomings. The Cuiabá cerrado site was the only one where the highest quality AERONET data were unavailable for both total and FMF AOD. Thus, lower quality data were used. Root-mean-square error (RMSE) between the model and observed FMF AOD decreased from 0.34 to 0.19 when extreme AOD events (FMF AOD550 nm ≥ 1.0) and Cuiabá were excluded from the analysis. Downward surface solar irradiance comparisons also followed similar trends when extreme AOD were excluded. This highlights the need to improve modelling of the regional smoke plume in order to enhance the accuracy of the radiative energy budget. An aerosol optical model based on the mean intensive properties of smoke from the southern part of the Amazon basin produced a radiative flux perturbation efficiency (RFPE) of −158 Wm−2/AOD550 nm at noon. This value falls between −154 Wm−2/AOD550 nm and −187 Wm−2/AOD550 nm, the range obtained when spatially varying optical models were considered. The 24 h average surface radiative flux perturbation over the biomass burning season varied from −55 Wm−2 close to smoke sources in the southern part of the Amazon basin and cerrado to −10 Wm−2 in remote regions of the southeast Brazilian coast.

Effect of spatial resolution on estimating surface albedo: A case study in Speulderbos forest in The Netherlands

Land surface albedo is one of the most important parameters accountable for the planetary radiative energy budget. It is known that albedo varies in both space and time as a result of various natural processes and human interventions. Especially in forest ecosystems these variations are much more intense due to inherent canopy structural differences and anticipated seasonal changes. In such environments, estimation of spatially distributed surface albedo poses challenges in terms of capturing the spatial variability using a remotely sensed sensor with a finite field of view. This study investigated the stand level surface albedo variability of a patchwork forest in the central part of The Netherlands. The data used for the study included airborne and satellite imageries and tower-based solar radiation measurements acquired through a dedicated field campaign. The imageries were preprocessed and atmospherically corrected to obtain top of the canopy (TOC) reflectance. The TOC reflectance bands in the visible and near-infrared domain were integrated to estimate spatially distributed surface albedo while the tower-based radiation measurements in the solar-reflective region were used to obtain the temporal variation of surface albedo over a needleleaf forest canopy. The diurnal variation of surface albedo is consistent with the previous findings for needleleaf forest canopies. The spatial mean surface albedo values estimated from remote sensing data for needleleaf (pure Douglas fir), broadleaf (pure Beech) and mixed forest classes are 0.09, 0.13 and 0.11, respectively. Both visual characteristics and descriptive statistics indicate that with increased pixel size, the spatial variability of albedo progressively decreases. The semivariogram analysis was more insightful to perceive the nature and causes of albedo spatial variability in different forest classes in relation to sensor spatial resolution.

Parameterisation of sea and lake ice in numerical weather prediction models of the German Weather Service

ABSTRACTA bulk thermodynamic (no rheology) sea-ice parameterisation scheme for use in numerical weather prediction (NWP) is presented. The scheme is based on a self-similar parametric representation (assumed shape) of the evolving temperature profile within the ice and on the integral heat budget of the ice slab. The scheme carries ordinary differential equations (in time) for the ice surface temperature and the ice thickness. The proposed sea-ice scheme is implemented into the NWP models GME (global) and COSMO (limited-area) of the German Weather Service. In the present operational configuration, the horizontal distribution of the sea ice is governed by the data assimilation scheme, no fractional ice cover within the GME/COSMO grid box is considered, and the effect of snow above the ice is accounted for through an empirical temperature dependence of the ice surface albedo with respect to solar radiation. The lake ice is treated similarly to the sea ice, except that freeze-up and break-up of lakes occurs freely, independent of the data assimilation. The sea and lake ice schemes (the latter is a part of the fresh-water lake parameterisation scheme FLake) show a satisfactory performance in GME and COSMO. The ice characteristics are not overly sensitive to the details of the treatment of heat transfer through the ice layer. This justifies the use of a simplified but computationally efficient bulk approach to model the ice thermodynamics in NWP, where the ice surface temperature is a major concern whereas details of the temperature distribution within the ice are of secondary importance. In contrast to the details of the heat transfer through the ice, the cloud cover is of decisive importance for the ice temperature as it controls the radiation energy budget at the ice surface. This is particularly true for winter, when the long-wave radiation dominates the surface energy budget. During summer, the surface energy budget is also sensitive to the grid-box mean ice surface albedo with respect to solar radiation. Considering the crucial importance of the surface radiation budget, future efforts should go into the development of a refined formulation of the grid-box mean surface albedo, including the albedo of ice itself and the fractional ice cover. NWP models may also benefit from an explicit treatment of snow above the ice. As the results from single-column experiments suggest, a bulk snow parameterisation holds promise but improved formulations of the snow density and the snow temperature conductivity are required.

Estimation of radiative effect of a heavy dust storm over northwest China using Fu–Liou model and ground measurements

A heavy dust storm that occurred in Northwestern China during April 24–30 2010 was studied using observational data along with the Fu–Liou radiative transfer model. The dust storm was originated from Mongolia and affected more than 10 provinces of China. Our results showed that dust aerosols have a significant impact on the radiative energy budget. At Minqin (102.959°E, 38.607°N) and Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL, 104.13°E, 35.95°N) sites, the net radiative forcing (RF) ranged from 5.93 to 35.7Wm−2 at the top of the atmosphere (TOA), −6.3 to −30.94Wm−2 at surface, and 16.77 to 56.32Wm−2 in the atmosphere. The maximum net radiative heating rate reached 5.89K at 1.5km on 24 April at the Minqin station and 4.46K at 2.2km on 29 April at the SACOL station. Our results also indicated that the radiative effect of dust aerosols is affected by aerosol optical depth (AOD), single-scattering albedo (SSA) and surface albedo. Modifications of the radiative energy budget by dust aerosols may have important implications for atmospheric circulation and regional climate.

Surface energy and radiation budget over a tropical station: An observational study

This study attempts to understand the variations in the radiation and surface energy budget parameters during days of occurrence and non occurrence of convective activity such as thunderstorms at Ranchi (23°25′N, 85°26′E), India using the special experimental data sets obtained during pre-monsoon month of May, 2008. For this purpose five continuous thunderstorm days (TD) of varying intensity, along with three non-thunderstorm days (NTD) preceding the TD are considered. Thunderstorms occurred at site are multi-cellular in nature. Change of wind direction and strong gusty winds are noticed in TD cases. Pre-dominant wind direction is south westerly for the TD; it is northwesterly during NTD. Sudden drop of air temperature and rise of relative humidity and rise/drop in atmospheric pressure is noticed during TD are found to be proportional to the intensity of thunderstorm event. More partitioning of net radiation (QN) is in to latent heat flux (QE) and the contribution of sensible heat flux (QH) and soil heat flux (QG) are same during TD. But in the NTD more partitioning of QN is in to QH followed by QG that of QE. Significant differences in radiation and energy budget components are noticed during TD and NTD events.

Investigation of direct radiative effects of aerosols in dust storm season over East Asia with an online coupled regional climate-chemistry-aerosol model

A new online coupled regional climate-chemistry-aerosol model (RIEMS-Chemaero) has been developed and applied to investigate direct radiative effects of dust aerosol and mixed aerosols over East Asia in March 2010, when an extremely intense dust storm on 19–22 March swept across almost the entire east China including the Pearl River Delta of south China, where little dust storm was observed before. The model results are evaluated against ground observation of PM10 concentration, aerosol optical depth (AOD) from both AERONET measurement and satellite retrieval (MODIS). The comparison demonstrates a good ability of RIEMS-Chemaero in reproducing major features of aerosol spatial distribution and temporal variation, as well as dust evolution during the dust storm period. However, the model tends to generally underpredict AOD at AERONET sites, with larger biases at urban sites than that at rural sites. Dust aerosols exerted a significant impact on radiation energy budget during the dust storm period, with the 4-day mean values of shortwave and longwave radiative forcings at the surface up to −90 W m−2 and +40 W m−2, respectively, over the Gobi desert. The monthly mean net dust radiative forcings at the surface ranged from −9 to −24 W m−2 over the dust source regions, and from −6 to −21 W m−2 over wide downwind areas including the middle and lower reaches of the Yellow River and the Yangtze River and the Yellow Sea. The net dust radiative forcing at TOA varied from near zero to +6.0 W m−2 in large areas of the continent. The monthly mean values of the net direct radiative forcings due to dust, non-dust aerosols and all aerosols (dust + sea salt + anthropogenic aerosols) averaged over the whole domain are estimated to be −3.9 W m−2, −5.6 W m−2 and −9.3 W m−2, respectively, at the surface, and to be +0.9 W m−2, −3.0 W m−2 and −2.0 W m−2, respectively, at TOA, indicating a light dust warming effect and an overall aerosol cooling effect in the springtime over East Asia. In east China, the net radiative forcings due to dust, non-dust aerosols and all aerosols at the surface are enhanced to −8.4 W m−2, −10.2 W m−2 and −18.0 W m−2, respectively, due to both the frequent dust influence and the intensive anthropogenic emissions in this region. The dust forcing accounts for about 42% of the total aerosol forcing at the surface in the domain, implying a potentially important role of mineral dust in radiation budget and regional climate. The semi-direct effect of dust aerosol tends to reduce cloud cover throughout the domain and it is partly responsible for the direct radiative forcings because of the feedbacks among aerosol, radiation, cloud and dynamics.

Combining satellite data and models to estimate cloud radiative effect at the surface and in the atmosphere

AbstractSatellite measurements and numerical forecast model reanalysis data are used to compute an updated estimate of the cloud radiative effect on the global multi‐annual mean radiative energy budget of the atmosphere and surface. The cloud radiative cooling effect through reflection of short wave radiation dominates over the long wave heating effect, resulting in a net cooling of the climate system of − 21 Wm−2. The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of − 53 Wm−2. Clouds impact long wave radiation by heating the moist tropical atmosphere (up to around 40 Wm−2 for global annual means) while enhancing the radiative cooling of the atmosphere over other regions, in particular higher latitudes and sub‐tropical marine stratocumulus regimes. While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night. The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed. Copyright © 2011 Royal Meteorological Society