CALIPSO Data Research Articles

Characteristics of cirrus clouds in the tropical lower stratosphere

A unique type of cloud in the tropical lower stratosphere, which we call “stratospheric cirrus”, is described in this study. Stratospheric cirrus clouds are generally detached from overshooting deep convection and are much smaller than subvisual cirrus often observed near the tropical tropopause. We analyzed two cases of stratospheric cirrus in the tropical and subtropical lower stratosphere captured by the space-borne lidar, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Both cases occurred 2–3 hours after the most active phase of the nearby convective cloud clusters. Case 1 has a double-layer structure above the cold point height (CPH); the CPH and two cloud top heights are, respectively, 17.8, 18.9, and 19.9km. Case 2 has a single cloud layer where CPH and the cloud top height are, respectively, 16.5 and 18.7km. The mode radius and ice water content of the stratospheric cirrus clouds are estimated to be 4–10μm and 0.2–0.8mg/m3 based on the radar-lidar method and consideration of the cloud particle terminal velocity. Comparisons with previous numerical model simulation studies suggest that the double-layer stratospheric cirrus clouds are likely from an overshooting plume, pushed up into the stratosphere in an overshoot when warm stratospheric air is inhomogeneously mixed with cold overshooting air. The single-layer stratospheric cirrus cloud is associated with some non-negligible wind shear, so it could be a jumping cirrus cloud, although we cannot rule out the possibility that it came from an overshooting plume because of the similarity in cloud characteristics and morphology between the two cases. Guided by the case studies, an automatic algorithm was developed to select stratospheric cirrus clouds for global survey and statistical analysis. A total of four years of CALIPSO and space-borne cloud radar (CloudSat) data were analyzed. Statistical analysis suggests that stratospheric cirrus clouds occur on the order of 3.0×103 times a year between 30 °S and 30 °N. Many of the stratospheric cirrus clouds are found in the pre-monsoon season in the South and Southeast Asia, where convection is deep and intense.

WRF-chem sensitivity to vertical resolution during a saharan dust event

The Saharan dust event that occurred between the 22nd and 30th of June 2012 influenced the atmospheric radiative properties over North Africa, the Iberian Peninsula, the Western Mediterranean basin, extending its effects to France and Southern England. This event is well documented in satellite imagery, as well as on the air quality stations over the Iberian Peninsula and the AERONET NASA network. In order to assess the effect of the model vertical resolution on the extinction coefficient fields, as a proxy to the particulate matter concentrations in the atmosphere, the WRF-Chem model was applied during this period over a mother domain with a resolution of 18km, covering Europe and North Africa. To this end five model setups differing in the number of vertical levels were tested. Model skills were evaluated by comparing the model results with CALIPSO and EARLINET LIDAR data. Results show that the model is able to simulate the higher level aerosol transport but it is susceptible to the vertical resolution used. This is due to the thickness of the transport layers which is, eventually, thinner than the vertical resolution of the model. When comparing model results to the observed vertical profiles, it becomes evident that the broad features of the extinction coefficient profile are generally reproduced in all model configurations, but finer details are captured only by the higher resolution simulations.

Evaluation of cloud properties in the NCEP CFSv2 model and its linkage with Indian summer monsoon

Cloud fraction, which varies greatly among general circulation models, plays a crucial role in simulation of Indian summer monsoon rainfall (ISMR). The NCEP Climate Forecast System version 2 (CFSv2) model is evaluated in terms of its simulation of cloud fraction, cloud condensate, outgoing longwave radiation (OLR), and tropospheric temperature (TT). Biases in these simulated quantities are computed using observations from CALIPSO and reanalysis data from MERRA. It is shown that CFSv2 underestimates (overestimates) high- (mid-) level clouds. The cloud condensate is also examined to see its impact on different types of clouds. The upper-level cloud condensate is underestimated, particularly during the summer monsoon period, which leads to a cold TT and a dry precipitation bias. The unrealistically weak TT gradient between ocean and land is responsible for the underestimation of ISMR. The model-simulated OLR is overestimated which depicts the weaker convective activity. A large underestimate of precipitable water is also seen along the cross-equatorial flow and particularly over the Indian land region collocated with a dry precipitation bias. The linkages among cloud microphysical, thermodynamical, and dynamical processes are identified here. Thus, this study highlights the importance of cloud properties, a major cause of uncertainty in CFSv2, and also proposes a pathway for improvements in its simulation of the Indian summer monsoon.

Investigation of Three-Dimensional Evolution of East Asian Dust Storm by Modeling and Remote Sensing Measurements

The three-dimensional evolution of an East Asian dust storm during 23–26 April 2009 was investigated by utilizing a regional air quality model system (RAQMS) and satellite measurements. This severe dust storm hit Mt. Tai in east China with daily mean PM10concentration reaching 1400 μg/m3and the model captured the PM10variation reasonably well. Modeled spatial distributions of AOD and vertical profiles of aerosol extinction coefficient during the dust storm were compared with MODIS and CALIPSO data, demonstrating that RAQMS was able to reproduce the 3D structure and the evolution of the dust storm reasonably well. During early days of the dust storm, daily mean dust-induced AOD exceeded 2.0 over dust source regions (the Gobi desert and the Taklamakan desert) and was in a range of 1.2–1.8 over the North China Plain, accounting for about 98% and up to 90% of total AOD over corresponding areas, respectively. The top of the dust storm reached about 8 km over east China, with high dust concentration locating at around 40°N. Dust aerosol below 2 km was transported southeastward off the Gobi desert while dust above 2 km was transported out of China along 40°–45°N.

English

Large volumes of Saharan dust particles are transported each year from northern Africa to the Americas, through Atlantic Ocean, reaching during the northern hemisphere summer the Wider Caribbean and Cuba in particular. Since the installation in October 2008 of a sun photometer type CIMEL CE-318, operated by Atmospheric Optics Group of Camaguey, numerous Saharan dust events have been registered. The most significant events for this AERONET measurement site were registered during July 2009. The highest AOD value with a magnitude greater than 0.6 was reported on July 6. The longest event for this period occurred between 15 and 20 July, with maximum AOD values above of 0.6. Measurement performed with lidar aboard CALIPSO satellite, for coincident measurement on July 19, distant 22.6 km to west of sun photometer site, provide information about the space-temporal distribution of this event. The AOD registered values of 0.35 and 0.32 for both, CALIPSO and MODIS, respectively, have equal magnitude than CIMEL measurement for the same day. The intercomparison between instruments, with different measurement principles, has corroborated its complementarity. CALIPSO, MODIS and AERONET data available at global scale are used, in conjunction with transport models and backtrajectories, for investigating the Saharan dust plume dispersion.

Surface matters: limitations of CALIPSO V3 aerosol typing in coastal regions

Abstract. In the CALIPSO data analysis, surface type (land/ocean) is used to augment the aerosol characterization. However, this surface-dependent aerosol typing prohibits a correct classification of marine aerosol over land that is advected from ocean to land. This might result in a systematic overestimation of the particle extinction coefficient and of the aerosol optical thickness (AOT) of up to a factor of 3.5 over land in coastal areas. We present a long-term comparison of CALIPSO and ground-based lidar observations of the aerosol conditions in the coastal environment of southern South America (Punta Arenas, Chile, 53° S), performed in December 2009–April 2010. Punta Arenas is almost entirely influenced by marine particles throughout the year, indicated by a rather low AOT of 0.02–0.04. However, we found an unexpectedly high fraction of continental aerosol in the aerosol types inferred by means of CALIOP observations and, correspondingly, too high values of particle extinction. Similar features of the CALIOP data analysis are presented for four other coastal areas around the world. Since CALIOP data serve as important input for global climate models, the influence of this systematic error was estimated by means of simplified radiative-transfer calculations.

Observed linkages between the northern annular mode/North Atlantic Oscillation, cloud incidence, and cloud radiative forcing

AbstractThe signature of the northern annular mode/North Atlantic Oscillation (NAM/NAO) in the vertical and horizontal distribution of tropospheric cloudiness is investigated in CloudSat and CALIPSO data from June 2006 to April 2011. During the Northern Hemisphere winter, the positive polarity of the NAM/NAO is marked by increases in zonally averaged cloud incidence north of ~60°N, decreases between ~25 and 50°N, and increases in the subtropics. The tripolar‐like anomalies in cloud incidence associated with the NAM/NAO are largest over the North Atlantic Ocean basin/Middle East and are physically consistent with the NAM/NAO‐related anomalies in vertical motion. Importantly, the NAM/NAO‐related anomalies in tropospheric cloud incidence lead to significant top of atmosphere cloud radiative forcing anomalies that are comparable in amplitude to those associated with the NAM/NAO‐related temperature anomalies. The results provide observational evidence that the most prominent pattern of Northern Hemisphere climate variability is significantly linked to variations in cloud radiative forcing. Implications for two‐way feedback between extratropical dynamics and cloud radiative forcing are discussed.

Physical and optical properties of aerosols in a free tropospheric environment: Results from long-term observations over western trans-Himalayas

Simultaneous and collocated estimates of near-surface mass concentration of black carbon (BC), number size distribution (NSD) and total number concentration (NT) of composite aerosols, columnar spectral aerosol optical depth (AOD) and local meteorological parameters were made from Aug 2009 to July 2012 at the high altitude (4520 m amsl), remote location Hanle in western trans-Himalayas. Even though all the aerosol parameters remain quite low, large annual variations are seen in the monthly mean values of BC (25 ng m−3–181 ng m−3), total number concentrations of composite aerosols (628 cm−3–1500 cm−3) and AOD (0.05–0.16). Size segregated correlation analysis reveals that the BC mass contributes significantly to the size range of 200–400 nm of the submicron aerosol size spectra. The diurnal variation of BC mostly has been dampened; yet seems to be prominent during spring, showing the presence of weak boundary layer dynamics. In contrast, the diurnal fluctuations in total number concentration have been mostly controlled by the new particle formation events, leading to bursts of large concentrations of ultrafine particles, which subsequently undergo coagulation. Spectral dependence of AOD also shows large monthly variations, with the Angstrom exponent varying from ∼0.52 to 1.3, with a mean value of ∼0.95 ± 0.21. The vertical distribution of extinction coefficients, obtained from CALIPSO data, indicates the presence of elevated aerosol layers, attributed mainly to the influence of long range transport of aerosols from the west Asian and Indian desert region.

Multi-year observations of the spatial and vertical distribution of aerosols and the genesis of abnormal variations in aerosol loading over the Arabian Sea during Asian summer monsoon season

Intense aerosol plumes engulf a vast region of the Arabian Sea during the Asian summer monsoon season (ASM: June–September). The largest value of aerosol optical depth (AOD) at 550nm in this region generally occurs in July when the mean AOD attains its annual peak value of >0.8. However, the AOD over this region is abnormally large during the ASM in some years, especially during the June–July period. Long term satellite observations using MODIS reveal that the largest AOD during the 11-year period of March 2000–February 2011 occurred in June 2008 with a regional mean AOD of 1.1, which was ~97% larger than that of the corresponding long term mean value in June and ~49% larger than that in July. The availability of CALIPSO data since June 2006 provides a unique opportunity to quantify the role of continental aerosols transported from the West Asian desert regions in the genesis of the above abnormality over the Arabian Sea. We examine the spatial and vertical distributions of aerosols over the Arabian Sea and adjoining continents using multi-year data from MODIS and CALIPSO and explore the genesis of the above abnormal enhancement in AOD. The observed anomalies in AOD are substantially larger than that can be attributed to changes in wind-generated sea salt aerosols. The CALIPSO observations show that the anomalous enhancement in aerosol loading over the Arabian Sea during June 2008 was primarily caused by an enhancement in aerosol abundance in the altitude range of ~1–4km with a distinctly large volume depolarization ratio of >0.25, clearly indicating the dominance of highly non-spherical mineral dust. Although the aerosol loading over the Arabian Sea during the ASM is observed to be mainly caused by the mineral dust transported from the West Asian Deserts at northwest of the Arabian Sea, the abnormal enhancement in the observed AOD during June 2008 was primarily caused by a distinct increase in dust storms over the northern continents and subsequent transport into the Arabian Sea.

From CloudSat‐CALIPSO to EarthCare: Evolution of the DARDAR cloud classification and its comparison to airborne radar‐lidar observations

This paper presents the implementation of a new version of the DARDAR (radar lidar) classification derived from CloudSat and CALIPSO data. The resulting target classification called DARDAR v2 is compared to the first version called DARDAR v1. Overall DARDAR v1 reports more cloud or rain pixels than DARDAR v2. In the low troposphere this is because v1 detects too many liquid cloud pixels, and in the higher troposphere this is because v2 is more restrictive in lidar detection than v1. Nevertheless, the spatial distribution of different types of hydrometeors show similar patterns in both classifications. The French airborne Radar‐Lidar (RALI) platform carries a CloudSat/CALIPSO instrument configuration (lidar at a wavelength of 532nm and a 95GHz cloud radar) as well as an EarthCare instrument configuration (high spectral resolution lidar at 355nm and a 95GHz Doppler cloud radar). It therefore represents an ideal go‐between for A‐Train and EarthCare. The DARDAR v2 classification algorithm is adapted to RALI data for A‐Train overpasses during dedicated airborne field experiments using the lidar at 532nm and the radar Doppler measurements. The results from the RALI classification are compared with the DARDAR v2 classification to identify where the classification should still be interpreted with caution. Finally, the RALI classification algorithm with lidar at 532nm is adapted to RALI with high spectral resolution lidar data at 355nm in preparation for EarthCare.

The signature of the stratospheric Brewer‒Dobson circulation in tropospheric clouds

The signature of the stratospheric Brewer‒Dobson circulation (BDC) in tropospheric cloudiness is investigated in CloudSat and CALIPSO data from June 2006 through April 2011. During the Northern Hemisphere winter, periods of enhanced stratospheric wave driving are associated with increased cloud incidence in the tropical tropopause transition layer (TTL) juxtaposed against decreased cloud incidence in the Arctic troposphere. The results are consistent with the physical linkages between (1) the BDC and near‒tropopause temperature and (2) near‒tropopause temperature and upper tropospheric cloud incidence. The key finding of the work is that changes in the stratospheric circulation not only influence cloud amounts in the troposphere but also that they do so in a coupled manner that links climate variability in the Arctic and upper tropical troposphere. The results provide a pathway through which stratospheric processes influence tropospheric climate that is in addition to stratosphere/troposphere dynamical coupling.

Absorption characteristics of aerosols over the northwestern region of India: Distinct seasonal signatures of biomass burning aerosols and mineral dust

Continuous measurements of aerosol black carbon (BC) mass concentrations made over a period of 3 years from a semi-arid, near-coastal, remote and sparsely inhabited location along with satellite-based data of aerosol absorption index, optical depth and extinction profiles in western India are used to characterize the distinct nature of aerosols near the surface and in the free troposphere and their seasonality. Despite being far remote and sparsely inhabited, significant levels of BC are observed in the ambient during winter (1.45 ± 0.71 μg m−3) attributed to biomass burning aerosols, advected to the site from the north and west; while during summer the concentrations are far reduced (0.23 ± 0.11 μg m−3) and represent the apparent background concentrations. The spectral absorption coefficients suggest the BC during summer be mostly of fossil fuel combustions. The strong convective boundary layer dynamics produces significant diurnal variation during winter and modulates to a lesser extent the seasonal variation. Examination of aerosol (absorption) index from OMI data for the study period showed a seasonal pattern that is almost opposite to that seen at the surface; with high aerosol index in summer, showing a significant difference between the surface and columnar aerosol types in summer. MISR and MODIS-derived columnar AOD follow the OMI pattern. Analysis of the vertical profiles of aerosol extinction and volume depolarization ratio (VDR), derived from CALIPSO data indicates the presence of strong dust layers with VDR ∼ 0.3 in the altitude region 4–6 km, contributing to the high aerosol index in the OMI data, while the surface measurements show absorptive properties representing fossil fuel BC aerosols.

Satellite based analysis of fire–carbon monoxide relationships from forest and agricultural residue burning (2003–2011)

Carbon monoxide (CO) is an important greenhouse gas that is emitted during the incomplete combustion of biomass burning. In this study, we assessed the Measurements Of Pollution In the Troposphere (MOPITT) CO retrievals from two different biomass burning regions, fires in the evergreen forests of Northeast India and agriculture residue fires, Punjab, India. We analyzed long-term trends (2003–2011) in CO retrievals and fire–CO relationships including CO profiles at nine different atmospheric levels. Over a ten year period, the mean monthly CO for Northeast India ranged from 140.86 ppmv (−1σ) to 348.85 ppbv (+1σ) with a mean CO of 244.85 ppbv. We observed a clear increase in CO signal from February to March followed by a decrease in May coinciding with the fire signal. In Punjab, the mean monthly CO ranged from 158.21 ppbv (−1σ) to 286.40 ppbv (+1σ) with a mean CO of 222.30 ppbv. Comparison of mean CO during the peak fire months suggested relatively higher CO (439.06 ppbv) during March (evergreen forest burning) than October (194.83 ppbv) agricultural residue burning. We found MODIS fire radiative power (FRP) as a stronger predictor of surface CO signal than the fire counts in the evergreen forest fires. The segmented regression model fitted using nine years of FRP–CO data was useful in finding the FRP threshold impact on CO concentrations in the evergreen forests. To explain the low correlation between fires and MOPITT CO signal from the agricultural residue fires, we used the CALIPSO data to infer the smoke plume heights. Results suggested an average smoke plume height of 2.2 km during the peak biomass burning month from agricultural fires, compared to 4.61 km from evergreen forest fires. Overall, the MODIS FRP and CALIPSO data were useful in understanding the MOPITT CO sensitivity to fires.

The representation of tropical upper tropospheric water in EC Earth V2

Tropical upper tropospheric humidity, clouds, and ice water content, as well as outgoing longwave radiation (OLR), are evaluated in the climate model EC Earth with the aid of satellite retrievals. The Atmospheric Infrared Sounder and Microwave Limb Sounder together provide good coverage of relative humidity. EC Earth's relative humidity is in fair agreement with these observations. CloudSat and CALIPSO data are combined to provide cloud fractions estimates throughout the altitude region considered (500-100 hPa). EC Earth is found to overestimate the degree of cloud cover above 200 hPa and underestimate it below. Precipitating and non-precipitating EC Earth ice definitions are combined to form a complete ice water content. EC Earth's ice water content is below the uncertainty range of CloudSat above 250 hPa, but can be twice as high as CloudSat's estimate in the melting layer. CERES data show that the model underestimates the impact of clouds on OLR, on average with about 9 W m(-2). Regionally, EC Earth's outgoing longwave radiation can be similar to 20 W m(-2) higher than the observation. A comparison to ERA-Interim provides further perspectives on the model's performance. Limitations of the satellite observations are emphasised and their uncertainties are, throughout, considered in the analysis. Evaluating multiple model variables in parallel is a more ambitious approach than is customary.

Computation of Solar Radiative Fluxes by 1D and 3D Methods Using Cloudy Atmospheres Inferred from A-train Satellite Data.

This study used realistic representations of cloudy atmospheres to assess errors in solar flux estimates associated with 1D radiative transfer models. A scene construction algorithm, developed for the EarthCARE mission, was applied to CloudSat, CALIPSO and MODIS satellite data thus producing 3D cloudy atmospheres measuring 61 km wide by 14,000 km long at 1 km grid-spacing. Broadband solar fluxes and radiances were then computed by a Monte Carlo photon transfer model run in both full 3D and 1D independent column approximation modes. Results were averaged into 1,303 (50 km)2 domains. For domains with total cloud fractions A c < 0.7 top-of-atmosphere (TOA) albedos tend to be largest for 3D transfer with differences increasing with solar zenith angle. Differences are largest for A c > 0.7 and characterized by small bias yet large random errors. Regardless of A c, differences between 3D and 1D transfer rarely exceed ±30 W m−2 for net TOA and surface fluxes and ±10 W m−2 for atmospheric absorption. Horizontal fluxes through domain sides depend on A c with ∼20% of cases exceeding ±30 W m−2; the largest values occur for A c > 0.7. Conversely, heating rate differences rarely exceed ±20%. As a cursory test of TOA radiative closure, fluxes produced by the 3D model were averaged up to (20 km)2 and compared to values measured by CERES. While relatively little attention was paid to optical properties of ice crystals and surfaces, and aerosols were neglected entirely, ∼30% of the differences between 3D model estimates and measurements fall within ±10 W m−2; this is the target agreement set for EarthCARE. This, coupled with the aforementioned comparison between 3D and 1D transfer, leads to the recommendation that EarthCARE employ a 3D transport model when attempting TOA radiative closure.

The effects of atmospheric waves on the amounts of polar stratospheric clouds

Abstract. A quantitative analysis on the relationship between atmospheric waves and polar stratospheric clouds (PSCs) in the 2008 austral winter and the 2007/2008 boreal winter is made using CALIPSO, COSMIC and Aura MLS observation data and reanalysis data. A longitude-time section of the frequency of PSC occurrence in the Southern Hemisphere indicates that PSC frequency is not regionally uniform and that high PSC frequency regions propagate eastward at different speeds from the background zonal wind. These features suggest a significant influence of atmospheric waves on PSC behavior. Next, three temperature thresholds for PSC existence are calculated using HNO3 and H2O mixing ratios. Among the three, the TSTS (a threshold for super cooled ternary solution)-based estimates of PSC frequency accord best with the observations in terms of the amount, spatial and temporal variation, in particular, for the latitude ranges of 55° S–70° S and 55° N–85° N. Moreover, the effects of planetary waves, synoptic-scale waves and gravity waves on PSC areal extent are separately examined using the TSTS-based PSC estimates. The latitude range of 55° S–70° S is analyzed because the TSTS-based estimates are not consistent with observations at higher latitudes (&lt;75° S) above 18 km, and PSCs in lower latitudes are more important to the ozone depletion because of the earlier arrival of solar radiation in spring. It is shown that nearly 100% of PSCs between 55° S and 70° S at altitudes of 16–24 km are formed by temperature modulation, which is influenced by planetary waves during winter. Although the effects of synoptic-scale waves on PSCs are limited, around an altitude of 12 km more than 60% of the total PSC areal extent is formed by synoptic-scale waves. The effects of gravity waves on PSC areal extent are not large in the latitude range of 55° S–70° S. However, at higher latitudes, gravity waves act to increase PSC areal extent at an altitude of 15 km by about 30% in September. Similar analyses are performed for the Northern Hemisphere. It is shown that almost all PSCs observed in the Northern Hemisphere are attributable to low temperature anomalies associated with planetary waves.

Comparisons and analyses of aircraft and satellite observations for wintertime mixed-phase clouds

[1] This work presents a study of midlevel, mixed-phase clouds using satellite (remote sensing) and aircraft (in situ) observations. In this study, we analyze coincident multisatellite and in situ aircraft measurements of three mixed-phase cloud cases during an intensive field experiment (C3VP/CLEX-10) to better understand the microphysics and radiative properties and provide a foundation for the improvement of the satellite retrieval algorithms for these clouds. For the selected cases, various aspects observed from different instruments are presented and compared for these clouds. It is found that many areas in the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud phase product classified as “unknown” are more appropriately classified as “mixed phase” based on CloudSat and CALIPSO data as well as C3VP/CLEX-10 aircraft measurements. The aircraft measurements show that a significant amount of supercooled liquid water exists at or near cloud top at very low temperatures for these midlevel, mixed-phase clouds, contrary to the assumptions used in the CloudSat retrieval algorithms. The spatial distribution of liquid water content and ice water content and other cloud properties are examined for both the satellite remote sensing and in situ probe measurements. CloudSat and airborne radar reflectivity data are also compared through a structure function analysis. Radiative transfer simulations based on the aircraft and satellite observations indicate the importance of proper assignment of cloud phase within retrieval algorithms and numerical models, which use similar assumptions.

Evaluation of ice cloud representation in the ECMWF and UK Met Office models using CloudSat and CALIPSO data

AbstractIce cloud representation in general circulation models remains a challenging task, due to the lack of accurate observations and the complexity of microphysical processes. In this article, we evaluate the ice water content (IWC) and ice cloud fraction statistical distributions from the numerical weather prediction models of the European Centre for Medium‐Range Weather Forecasts (ECMWF) and the UK Met Office, exploiting the synergy between the CloudSat radar and CALIPSO lidar. Using the last three weeks of July 2006, we analyse the global ice cloud occurrence as a function of temperature and latitude and show that the models capture the main geographical and temperature‐dependent distributions, but overestimate the ice cloud occurrence in the Tropics in the temperature range from −60 °C to −20 °C and in the Antarctic for temperatures higher than −20 °C, but underestimate ice cloud occurrence at very low temperatures. A global statistical comparison of the occurrence of grid‐box mean IWC at different temperatures shows that both the mean and range of IWC increases with increasing temperature. Globally, the models capture most of the IWC variability in the temperature range between −60 °C and −5 °C, and also reproduce the observed latitudinal dependencies in the IWC distribution due to different meteorological regimes. Two versions of the ECMWF model are assessed. The recent operational version with a diagnostic representation of precipitating snow and mixed‐phase ice cloud fails to represent the IWC distribution in the −20 °C to 0 °C range, but a new version with prognostic variables for liquid water, ice and snow is much closer to the observed distribution. The comparison of models and observations provides a much‐needed analysis of the vertical distribution of IWC across the globe, highlighting the ability of the models to reproduce much of the observed variability as well as the deficiencies where further improvements are required. Copyright © 2011 Royal Meteorological Society and British Crown Copyright, the Met Office

Cross-Comparison of MODIS and CloudSat Data as a Tool to Validate Local Cloud Cover Masks

This paper presents a cross-comparison of the data acquired by the MODIS and CloudSat sensors in order to understand the limit of the developed cloud-mask algorithm and to provide a quantitative validation assessment of cloud masks by using exclusively remotely sensed data. The analysis has been carried out by comparing both the intermediate levels of the cloud mask such as the brightness temperatures and the reflectance values for different channels, and the cloud mask itself with the cloud profiles as measured by the CloudSat sensor. The comparison between MODIS cloud tests and the CloudSat profiles indicates an agreement with hit rates (H) and Hanssen-Kuiper Skill Score (KSS) varying between 0.7 and 1.0 and 0.4 and 1.0, respectively. In this case, the low values of H and KSS are found due to the limitation of CloudSat to detect low clouds. The comparison between the cloud mask and the CloudSat profile determines H and KSS values between 0.6 and 1, except for one case. The CloudSat profile has also been compared with the Standard MODIS cloud mask in order to understand the improvement obtained in the use of local adapted thresholds. A comparison of MODIS and CALIPSO data is also presented.

Regional and vertical distribution of semitransparent cirrus clouds over the tropical Indian region derived from CALIPSO data

Monthly mean spatial and vertical distributions of the frequency of occurrence ( F STC) of semitransparent cirrus (STC) and their physical and optical properties over the Indian region are investigated using multiyear CALIPSO data. Over the Bay of Bengal (BoB), F STC above the lapse-rate tropopause is >30% during the summer monsoon season, most of which has optical depth <0.03. Based on spatial variations of the observed STC properties away from deep convective regions, we propose that the presence of high-altitude clouds below STCs over the BoB and Indian regions during summer monsoon reduces dissipation of STCs, resulting in their longer lifetime (∼1–2 days).