CALIPSO Observations Research Articles

An improved geolocation methodology for spaceborne radar and lidar systems

Abstract. Geolocation and co-registration methodologies are essential for the accurate interpretation of observations from spaceborne remote sensors. In preparations for the Earth Cloud Aerosol and Radiation Explorer (EarthCARE), here, we refine the definition of these techniques and present various examples of geolocation assessments. The geolocation methods build upon earlier work; however, they introduce several improvements that have increased the reliability of the geolocation accuracy. The EarthCARE active-sensor geolocation methods use coastlines and significant elevation gradients in both statistical and numerical ways. The effectiveness of the proposed geolocation methods was tested using the extensive record of CloudSat and CALIPSO observations. The EarthCARE active-sensor geolocation methods were effective in identifying and correcting a short period of CloudSat observations when the star tracker was not operating properly. In addition, the geolocation methods were able to reproduce the excellent geolocation record of the CloudSat and CALIPSO missions.

Comparison of the polluted dust plume and natural dust air mass in a spring dust event in Beijing 2023

The occurrence of extreme weather events is becoming more frequent due to global climate change. A long-lasting dust outbreak in the spring of 2023 was triggered by Mongolia cyclones and cold fronts in the dust source areas. In this study, we illustrate the spatial distribution, the transport path of the dust and its influence on the air quality of downstream cities utilizing ground-based and space-borne measurements. Results indicate a more complicated pollution, coexisting of polluted dust stage S1 and pure dust stage S2. In S1, the aerosol was characterized by a dual-layer vertical structure—high extinction coefficient of nearly 1.0 km−1 with a low particle depolarized ratio (PDR) of < 0.1 under 500 m, and a small extinction coefficient of 0.3 km−1 with a high PDR of 0.15 above 500 m. Then the intrusion of the Mongolian cyclone carried new dust plumes on 10 March, suggesting the onset of pure dust period S2. The source transition was also confirmed by the MODIS, CALIPSO and Hysplit observations. The pure Asian dust evolved rapidly with one thickening layer and distributed homogeneously in the boundary layer. The PDR increased significantly to the peak of 0.35 and resulted in the peak PM10 value of > 1300 µg/m3. PM10 positively correlated with trace gases in S1 while varying inversely with the pollution gases in S2. The results help to shed light on the classification of different types of dust and also be useful in developing an effective strategy to forecast air pollution in downstream areas.

Vertical structure, genesis and annual cycle of double ITCZ over tropical oceans derived from a decade of CloudSat and CALIPSO observations

Vertical structure, genesis and annual cycle of double ITCZ over tropical oceans derived from a decade of CloudSat and CALIPSO observations

Global characteristics of cloud macro-physical properties from active satellite remote sensing

Based on the products of joint CloudSat and CALIPSO observations from 2006 to 2017, this study investigates the global cloud macro-physical characteristics, including the spatial differences in cloud height, cloud thickness, cloud type, and cloud phase, along with the spatial-temporal variations and the land-sea discrepancy of the cloud vertical structure variables according to the study areas. The results show that the cloud frequency is higher over oceans than over land globally, but the opposite is true for cloud systems with more than two layers. Seasonal variability of global-average total cloud fraction is small, but large among different latitudinal bands. The global spatial distributions of cloud top height (CTH) and cloud base height (CBH) are similar, showing larger cloud heights over the land than over the ocean. The low clouds are mostly located in the central subtropical region, with CTH among 2.5–7.5 km, While the high clouds are mainly distributed in the equatorial region with CTH about 10–15 km. Meanwhile, the regional and seasonal variability of cloud geometric thickness (CGT) in all study areas are small, and the average thickness of higher clouds is slightly larger than that of lower clouds. By categorizing the clouds into eight types, it was found that the frequency of cirrus (Ci) and stratocumulus (Sc) is higher, followed by altocumulus (Ac), altostratus (As), nimbostratus (Ns) and cumulus (Cu), and the frequency of stratus (St) and deep convective clouds (DC) is the lowest. In addition, the occurrence frequency of clouds in phases was ranked from high to low as ice clouds, liquid clouds and mixed-phase clouds. Ice clouds are concentrated in the tropics and mid-latitudes, and located almost symmetrically around the equator during Mar-Apr-May (MAM) and Sep-Oct-Nov (SON). Liquid clouds are mainly distributed around 30°S and 30°N with large seasonal variability, and their frequency is higher over the ocean than over the land. Mixed-phase clouds are concentrated in the middle and high latitudes, with much less occurring in the equatorial regions.

Accounting for 3D radiative effects in MODIS aerosol retrievals near clouds using CALIPSO observations

Accounting for 3D radiative effects in MODIS aerosol retrievals near clouds using CALIPSO observations

The covariability between temperature inversions and aerosol vertical distribution over China

Temperature inversions (TI) have a unique impact on the regulation of aerosol distribution. However, it remains unclear the covariability of TI and aerosol vertical distribution. To address this issue, ten years CALIPSO observations and the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis system (ERA5) data from January 2008 to December 2017 across China were collected. The aim was to explore the relationship between TI and the aerosol vertical distribution. The characteristics of TI and aerosol vertical distribution have been analysed in the Taklimakan Desert (TD), North China (NC), South China (SC) and Sichuan Basin (SB). The results demonstrate that the frequency of TI, inversion strength (ΔT), and TI height (TIH) follow a similar seasonal pattern across the four areas. Specifically, they are highest in winter, followed by spring and autumn, and the least in summer. Notably, NC exhibits a significantly higher average frequency (10.3%) of TI during summertime compared to the other regions. This may be a result of the heating effect of the elevated black carbon aerosol on the upper atmosphere. Moreover, the observations demonstrate that aerosol optical depth (AOD) above the TIH in the four areas is greater during spring and summer months compared to autumn and winter. It indicates that there is an obvious aerosol high-level transport over the Chinese mainland in spring and summer. In winter months, most of the aerosols are located below the TIH. This phenomenon occurs due to the influence of a strong inversion layer and adverse atmospheric ventilation conditions. In addition, the average AOD below TIH increases with the ΔT increased in TD region, supporting the hypothesis that a strong inversion can suppress surface aerosols below the TI. Conversely, in NC and SC regions, the average AOD below (above) TIH decreases (increases) as the ΔT increases. It indicates that the strong atmospheric stability forms a more effective transmission channel, resulting in the accumulation of aerosols above TIH. These findings have important support for studying aerosol transport.

Multi‐Year CALIPSO Observations of Ubiquitous Elevated Aerosol Layer in the Free Troposphere Over South Asia: Sources and Formation Mechanism

AbstractThe vertical distribution of aerosols in the lower troposphere is critically important for assessing their impact on Earth's radiation budget and modulation of cloud microphysics. This study analyzed cloud‐free aerosol extinction coefficient (βext), aerosol subtypes, and particulate depolarization ratios obtained from CALIOP (Cloud‐Aerosol Lidar with Orthogonal Polarization) over the six regions of India during 2008–2018. We investigated unprecedented climatology of the physical and optical characteristics of elevated aerosol layers (EALs) along with their source and formation mechanism. The key findings include: (a) EALs over the Indian region were persistent between 4 and 6 km during all seasons, (b) geometrical layer thickness of EALs increased up to 36.7% and 25% from the annual mean during summer and fall seasons, respectively, compared to that of spring and winter, (c) dust and polluted dust accounted for up to 50%–80% from near‐surface to 6 km and up to 80%–90% of the EALs between 4 and 6 km, respectively for all the seasons and regions, (d) we anticipated that locally confined recirculation coupled with stratified stable layer capped within turbulent layers could be a possible mechanism of formation of stratified EALs between 4 and 6 km during winter‐spring‐fall, while in summer, vertical transport of pollutants from the PBL to mid‐troposphere due to enhanced deep convection served as a key formation mechanism of the EALs, (e) the second Modern‐Era Retrospective analysis for Research and Applications Global Modeling Initiative model reasonably simulated the shape and vertical gradient of βext with significant differences in magnitude below 4 km; however, it fails to reproduce EALs for all seasons and regions during the study period.

Competition Between Radiative and Seeding Effects of Overlying Clouds on Underlying Marine Stratocumulus

AbstractOverlying cloud can affect the radiative and precipitation features of underlying cloud via its radiative and seeding effects. Using 4 years of CALIPSO and CloudSat observations, this study demonstrates that overlying clouds usually suppress the vertical development of underlying stratocumulus (Sc) by their radiative effect, thus reducing the precipitation, cloud liquid water path and thickness of Sc on a global scale. The radiative effect intensity increases with increasing optical depth (COD) of overlying cloud and decreasing cloud distance between cloud layers. By dividing the overlying clouds into seeder and non‐seeder groups, we find that seeding by overlying clouds can partly or even totally offset the precipitation suppression caused by their radiative effect. The net effect on precipitation of Sc switches from suppression to enhancement when COD of overlying cloud exceeds 0.16. This finding indicates that the competition between radiative and seeding effects of overlying cloud should be considered in cloud‐precipitation interaction.

Impact of atmospheric thermodynamic structures and aerosol radiation feedback on winter regional persistent heavy particulate pollution in the Sichuan-Chongqing region, China

Potential relationships among heavy air pollution, weather conditions, and meteorological effects are unclear and require further investigation, especially for areas with complex terrains, such as the Sichuan Basin (SCB), one of the most polluted regions in China. In this study, air pollution in the SCB was examined and 18 regional persistent heavy pollution events (RPHEs) were identified for the winters of 2014–2018. The average persistent period of the RPHEs was 8.89 days, and the number of affected cities was 17. Based on ground-based observations, CALIPSO satellite data, reanalysis data, and backward trajectory calculations, the synergistic effects of the thermodynamic structures, synoptic circulations and the radiative feedback of aerosols on the formation of RPHEs were revealed. The results can be summarized as follows: (1) An abnormal warming center, attributing to the warm southerly advection in the upper layer and the cold air dammed by the topography near the surface, always presented around 800–700 hPa to form a deep stable layer. (2) The diurnal variations in vertical motions triggered by the thermodynamic structures could regulate the pollution episodes. During the daytime, pollutants accumulated rapidly and thoroughly mixed under the control of sinking airflow from 800 hPa layer to the ground. At night, pollutants sometimes slowly diffused when weak ascending airflow appeared. (3) Forced by the stable layer and topography of the Tibetan Plateau, the local circulation was confined within SCB, resulting in the intensive mixing of local emissions and transport pollutants from other regions. This situation could be maintained for a long time with stable synoptic circulation in winter, leading to the formation of RPHEs. (4) The pollution episodes were featured with multi-layer pollutants above SCB according to the CALIPSO observations, including the local anthropogenic aerosols near the surface, dust aerosols originating from the Taklamakan Desert, and biomass burning aerosols from Southeast Asia. Solar absorption aerosols, including black carbon and dust above the region, could cause meteorological feedback, making the vertical layer more stable and enhancing the persistence and intensity of the pollution episodes. This study highlights the appreciable effects of synoptic circulations on the vertical thermodynamic structures of the atmosphere and air quality, and raises the understanding of the environmental and climate impacts of RPHEs in complex terrains.

An Overview of Aerosol Properties in Clear and Cloudy Sky Based on CALIPSO Observations

AbstractA full understanding of the climatological properties of aerosols is an important step towards characterizing their effects on climate. Utilizing the observations from Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations, we study cloud‐free and cloudy aerosol properties with attention on aerosol and cloud layer relative vertical positions. On a global scale, the cloud‐free aerosols account for about 56% of all detected aerosols with a mean optical depth () and mean uncertainty of 0.135 ± 0.047. The cloudy aerosols, accounting for 44%, have a larger and larger mean uncertainty of 0.143 ± 0.074 compared to the cloud‐free aerosols. The above‐cloud aerosols (∼4%), primarily composed of elevated smoke, dust/volcanic ash and polluted dust, have a much smaller of (0.056 ± 0.038). The below‐cloud aerosols (∼21%) have ∼ 0.165 0.087. The below‐cloud and cloud‐free aerosols show close probability density distributions and similar aerosol types, indicating that cloud‐free aerosol climatologies from passive sensors are likely representative of all‐sky conditions. In addition, about 27% of the detected aerosol profiles are found to have cloud layers vertically connected to the detected aerosol layers. The lidar backscatter profiles of these aerosols have larger median values than the cloud‐free, above‐cloud and below‐cloud aerosols. The seasonal variations of the cloud‐free and the cloudy aerosols significantly vary with regions. Our results imply that quantifying the impact of clouds, particularly cirrus due to the wide coverage of cirrus‐aerosol overlap, on aerosol direct radiative effect is crucial to assess aerosols' roles in the Earth‐climate system.

Seasonal to sub-seasonal variations of the Asian Tropopause Aerosols Layer affected by the deep convection, surface pollutants and precipitation

The Asian Tropopause Aerosols Layer (ATAL) refers to an accumulation of aerosols in the upper troposphere and lower stratosphere during boreal summer over Asia, which has a fundamental impact on the monsoon system and climate change. In this study, we primarily analyze the seasonal to sub-seasonal variations of the ATAL and the factors potentially influencing those variations based on MERRA2 reanalysis. The ability of the reanalysis to reproduce the ATAL is well validated by CALIPSO observations from May to October 2016. The results reveal that the ATAL has a synchronous spatiotemporal pattern with the development and movement of the Asian Summer Monsoon. Significant enhancement of ATAL intensity is found during the prevailing monsoon period of July–August, with two maxima centered over South Asia and the Arabian Peninsula. Owing to the fluctuations of deep convection, the ATAL shows an episodic variation on a timescale of 7–12 days. Attribution analysis indicates that deep convection dominates the variability of the ATAL with a contribution of 62.7%, followed by a contribution of 36.6% from surface pollutants. The impact of precipitation is limited. The ATAL further shows a clear diurnal variation: the peak of ATAL intensity occurs from 17:30 to 23:30 local time (LT), when the deep convection becomes strongest; the minimum ATAL intensity occurs around 8:30 LT owing to the weakened deep convection and photochemical reactions in clouds. The aerosol components of the ATAL show different spatiotemporal patterns and imply that black carbon and organic carbon come mainly from India, whereas sulfate comes mainly from China during the prevailing monsoon period.

Tropospheric and stratospheric wildfire smoke profiling with lidar: mass, surface area, CCN, and INP retrieval

Abstract. We present retrievals of tropospheric and stratospheric height profiles of particle mass, volume, surface area, and number concentrations in the case of wildfire smoke layers as well as estimates of smoke-related cloud condensation nuclei (CCN) and ice-nucleating particle (INP) concentrations from backscatter lidar measurements on the ground and in space. Conversion factors used to convert the optical measurements into microphysical properties play a central role in the data analysis, in addition to estimates of the smoke extinction-to-backscatter ratios required to obtain smoke extinction coefficients. The set of needed conversion parameters for wildfire smoke is derived from AERONET observations of major smoke events, e.g., in western Canada in August 2017, California in September 2020, and southeastern Australia in January–February 2020 as well as from AERONET long-term observations of smoke in the Amazon region, southern Africa, and Southeast Asia. The new smoke analysis scheme is applied to CALIPSO observations of tropospheric smoke plumes over the United States in September 2020 and to ground-based lidar observation in Punta Arenas, in southern Chile, in aged Australian smoke layers in the stratosphere in January 2020. These case studies show the potential of spaceborne and ground-based lidars to document large-scale and long-lasting wildfire smoke events in detail and thus to provide valuable information for climate, cloud, and air chemistry modeling efforts performed to investigate the role of wildfire smoke in the atmospheric system.

Examining Cloud Macrophysical Changes over the Pacific for 2007–2017 Using CALIPSO, CloudSat, and MODIS Observations

AbstractCloud macrophysical changes over the Pacific from 2007 to 2017 are examined by combining CALIOP and CloudSat (CALCS) active-sensor measurements, and these are compared with MODIS passive-sensor observations. Both CALCS and MODIS capture well-known features of cloud changes over the Pacific associated with meteorological conditions during El Niño-Southern Oscillation (ENSO) events. For example, mid (cloud tops at 3–10 km) and high (cloud tops at 10–18 km) cloud amounts increase with relative humidity (RH) anomalies. However, a better correlation is obtained between CALCS cloud volume and RH anomalies, confirming more accurate CALCS cloud boundaries than MODIS. Both CALCS and MODIS show that low cloud (cloud tops at 0–3 km) amounts increase with EIS and decrease with SST over the eastern Pacific, consistent with earlier studies. It is also further shown that the low cloud amounts do not increase with positive EIS anomalies if SST anomalies are positive. While similar features are found between CALCS and MODIS low cloud anomalies, differences also exist. First, compared to CALCS, MODIS shows stronger anti-correlation between low and mid/high cloud anomalies over the central and western Pacific, which is largely due to the limitation in detecting overlapping clouds from passive MODIS measurements. Second, compared to CALCS, MODIS shows smaller impacts of mid and high clouds on the low troposphere (&lt; 3 km). The differences are due to the underestimation of MODIS cloud layer thicknesses of mid and high clouds.

A complex aerosol transport event over Europe during the 2017 Storm Ophelia in CAMS forecast systems: analysis and evaluation

Abstract. In mid-October 2017 Storm Ophelia crossed over western coastal Europe, inducing the combined transport of Saharan dust and Iberian biomass burning aerosols over several European areas. In this study we assess the performance of the Copernicus Atmosphere Monitoring Service (CAMS) forecast systems during this complex aerosol transport event and the potential benefits that data assimilation and regional models could bring. To this end, CAMS global and regional forecast data are analysed and compared against observations from passive (MODIS: Moderate Resolution Imaging Spectroradiometer aboard Terra and Aqua) and active (CALIOP/CALIPSO: Cloud-Aerosol LIdar with Orthogonal Polarization aboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite sensors and ground-based measurements (EMEP: European Monitoring and Evaluation Programme). The analysis of the CAMS global forecast indicates that dust and smoke aerosols, discretely located on the warm and cold fronts of Ophelia, respectively, were affecting the aerosol atmospheric composition over Europe during the passage of the Storm. The observed MODIS aerosol optical depth (AOD) values are satisfactorily reproduced by the CAMS global forecast system, with a correlation coefficient of 0.77 and a fractional gross error (FGE) of 0.4. The comparison with a CAMS global control simulation not including data assimilation indicates a significant improvement in the bias due to data assimilation implementation, as the FGE decreases by 32 %. The qualitative evaluation of the IFS (Integrated Forecast System) dominant-aerosol type and location against the CALIPSO observations overall reveals a good agreement. Regarding the footprint on air quality, both CAMS global and regional forecast systems are generally able to reproduce the observed signal of increase in surface particulate matter concentrations. The regional component performs better in terms of bias and temporal variability, with the correlation deteriorating over forecast time. Yet, both products exhibit inconsistencies on the quantitative and temporal representation of the observed surface particulate matter enhancements, stressing the need for further development of the air quality forecast systems for even more accurate and timely support of citizens and policy-makers.

Evaluation of AIRS Cloud Phase Classification over the Arctic Ocean against Combined CloudSat–CALIPSO Observations

AbstractCloud phase retrievals from the Atmospheric Infrared Sounder (AIRS) are evaluated against combinedCloudSat–CALIPSO(CCL) observations using four years of data (2007–10) over the Arctic Ocean. AIRS cloud phase is evaluated over sea ice and open ocean separately using collocated CCL and AIRS fields of view (FOVs). In addition, AIRS and CCL cloud phase occurrences are evaluated seasonally, zonally, and with respect to total column water vapor (TCWV) and the temperature difference between 1000 and 300 hPa (ΔT1000−300). Last, collocated MODIS cloud information is implemented in a 1-month case study to assess the relationship between AIRS and CCL phase decisions, cloud cover, and cloud phase throughout the AIRS FOV. Depending on the surface type, AIRS classification skill for single-layer ice and liquid-phase clouds is over the ranges of 85%–95% and 22%–32%, respectively. Most unknown and liquid AIRS phase classifications correspond to mixed-phase clouds. AIRS ice-phase relative occurrence is biased low relative to CCL. However, the liquid-phase relative occurrence is similar between the two instruments. When compared with the CCL climatology, AIRS accurately represents the seasonal cycle of liquid and ice cloud phase across the Arctic as well as the relationship between cloud phase and TCWV and ΔT1000−300regime in some cases. The more heterogeneous the MODIS cloud macrophysical properties within an AIRS FOV are, the more likely it is that the AIRS FOV is classified as unknown phase.

Smoke of extreme Australian bushfires observed in the stratosphere over Punta Arenas, Chile, in January 2020: optical thickness, lidar ratios, and depolarization ratios at 355 and 532 nm

Abstract. We present particle optical properties of stratospheric smoke layers observed with multiwavelength polarization Raman lidar over Punta Arenas (53.2∘ S, 70.9∘ W), Chile, at the southernmost tip of South America in January 2020. The smoke originated from the record-breaking bushfires in Australia. The stratospheric aerosol optical thickness reached values up to 0.85 at 532 nm in mid-January 2020. The main goal of this rapid communication letter is to provide first stratospheric measurements of smoke extinction-to-backscatter ratios (lidar ratios) and particle linear depolarization ratios at 355 and 532 nm wavelengths. These aerosol parameters are important input parameters in the analysis of spaceborne CALIPSO and Aeolus lidar observations of the Australian smoke spreading over large parts of the Southern Hemisphere in January and February 2020 up to heights of around 30 km. Lidar and depolarization ratios, simultaneously measured at 355 and 532 nm, are of key importance regarding the homogenization of the overall Aeolus (355 nm wavelength) and CALIPSO (532 nm wavelength) lidar data sets documenting the spread of the smoke and the decay of the stratospheric perturbation, which will be observable over the entire year of 2020. We found typical values and spectral dependencies of the lidar ratio and linear depolarization ratio for aged stratospheric smoke. At 355 nm, the lidar ratio and depolarization ratio ranged from 53 to 97 sr (mean 71 sr) and 0.2 to 0.26 (mean 0.23), respectively. At 532 nm, the lidar ratios were higher (75–112 sr, mean 97 sr) and the depolarization ratios were lower with values of 0.14–0.22 (mean 0.18). The determined depolarization ratios for aged Australian smoke are in very good agreement with respective ones for aged Canadian smoke, observed with lidar in stratospheric smoke layers over central Europe in the summer of 2017. The much higher 532 nm lidar ratios, however, indicate stronger absorption by the Australian smoke particles.

Measurements of light-absorbing impurities in snow over four glaciers on the Tibetan Plateau

Black carbon (BC), dust, and organic carbon (OC) aerosols, when deposited onto the surface of glaciers, can absorb light and decrease the snow albedo. These impurities in snow are referred to as ILAIs (i.e., insoluble light absorbing impurities). Atmospheric chemical models have been extensively used to simulate the transport and deposition of atmospheric aerosols in glacierized areas. However, systematic investigations of ILAIs in snowpack of glaciers on the Tibetan Plateau (TP) are rare. In this study, observations of ILAIs in snow and simulations of ILAIs of atmospheric aerosol at surface over four glaciers on the TP have been analyzed. Strong correlation between BC and dust was found in surface aged-snow, and their correlation significantly varied with snowpit depth. BC and OC concentrations in snowpit tended to decrease with depth. Significant differences of ILAI concentrations among depth intervals reflect their diverse hydrophilicities, physiochemical properties and post-depositional processes in snowpit, offering important observational constraints on the related processes. Monthly variation of atmospheric ILAIs at surface over glaciers is characterized by distinct spatial heterogeneity. The statistical results show higher ILAI concentrations in the summer of 2015 than 2014, which is in qualitative agreement with CALIPSO observations, likely reflecting the effects of inter-annual variation of summer monsoon on snow ILAI loadings. Optical attenuation (ATN) of BC is gradually decreased with depth of snowpit, whereas the trend of mass absorption cross-section (MAC) of BC throughout the profile of snowpit is opposite to that of ATN. The scanning electron microscopy (SEM) imaging demonstrates that calcium and silicon rich particles dominate over biological, quartz and flying ash particles in the cryoconite, providing additional constraints on the sources of dust-in-snow and can facilitate better understanding of the physicochemical properties and climatic effects of particles in the glacial cryoconite.

Two-dimensional mineral dust radiative effect calculations from CALIPSO observations over Europe

Abstract. A demonstration study to examine the feasibility of retrieving dust radiative effects based on combined satellite data from MODIS (Moderate Resolution Imaging Spectroradiometer), CERES (Clouds and the Earth's Radiant Energy System) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar vertical profiles along their orbit is presented. The GAME (Global Atmospheric Model) radiative transfer model is used to estimate the shortwave and longwave dust radiative effects below the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite) orbit assuming an aerosol parameterization based on the CALIOP vertical distribution at a horizontal resolution of 5 km and additional AERONET (Aerosol Robotic Network) data. Two study cases are analyzed: a strong long-range transport mineral dust event (aerosol optical depth, AOD, of 0.52) that originated in the Sahara Desert and reached the United Kingdom and a weaker event (AOD = 0.16) that affected eastern Europe. The radiative fluxes obtained are first validated in terms of radiative efficiency at a single point with space–time colocated lidar ground-based measurements from EARLINET (European Aerosol Research Lidar Network) stations below the orbit. The methodology is then applied to the full orbit. The strong dependence of the radiative effects on the aerosol load (and to a lesser extent on the surface albedo) highlights the need for accurate AOD measurements for radiative studies. The calculated dust radiative effects and heating rates below the orbits are in good agreement with previous studies of mineral dust, with the radiative efficiency obtained at the surface ranging between −80.3 and −63.0 W m−2 for lower dust concentration event and −119.1 and −79.3 W m−2 for the strong event. Thus, results demonstrate the validity of the method presented here to retrieve 2-D accurate radiative properties with large spatial and temporal coverage.

Characteristics of Ice Clouds Over Mountain Regions Detected by CALIPSO and CloudSat Satellite Observations

AbstractThis study examines the characteristics of orographic ice clouds in steep mountain regions using 3 years of CloudSat and CALIPSO satellite products. A combination of radar and lidar cloud fraction data is used to identify ice cloud systems. Additionally, the retrieved ice water content (IWC) and ice number concentration (NI) are used to analyze the dominant ice cloud microphysics in convective‐ and cirrus‐type clouds. The analysis shows that temporally averaged values of the IWC and NI are larger in mountain regions than in land and ocean regions. For convective clouds over mountains, both the IWC and NI have larger values at atmospheric temperatures warmer than 250 K, suggesting a dominant role for the freezing of supercooled liquid water. For cirrus clouds over mountains, however, only the NI has larger values at atmospheric temperatures colder than 240 K, indicating the importance of homogeneous ice nucleation. These characteristics of ice‐phase clouds in terms of the IWC and NI in mountain regions are distinct, with a horizontal scale smaller than 300 km. This study suggests that it is useful to categorize ice clouds in mountain regions in addition to ocean and land regions to evaluate the microphysical properties (mass and number) of such ice clouds in atmospheric models.

The prospects for increasing the horizontal resolution of the Aeolus horizontal line‐of‐sight wind profiles

AbstractThis article evaluates the prospects for increasing the horizontal resolution of the Aeolus horizontal line‐of‐sight (HLOS) wind profiles at the expense of their accuracy. The evaluation is performed by combining a 10‐day atmosphere simulation by the ECMWF model at T3999 horizontal resolution with the CALIPSO observations of atmospheric composition as inputs to the Aeolus simulator. The validation shows that the ECMWF model represents the location and the vertical structure of the observed cloud systems well. At the nominal accumulation length of L ≈ 90 km (from the Aeolus measurement scale of ∼3 km), the Mie‐cloudy retrieval provides 1–4 times fewer observations than Rayleigh‐clear but the Mie‐cloudy HLOS winds have the highest quality with estimated error standard deviation of about 1 m/s in the troposphere and no bias. The experiments with reduced L reveal that neither the observation error standard deviation nor bias of the Mie‐cloudy winds are significantly affected when the accumulation length L varies in the range between 100 and 10 km. At the same time, the number of observations significantly increases as L reduces. This suggests that mesoscale NWP may profit from the Aeolus Mie‐cloudy HLOS profiles with the accumulation lengths as small as 10 km.