Elsa Cattani

East Africa experienced in the 2001–11 time period some of the worst drought events to date, culminating in the high-impact drought of 2010/11. Long-term monitoring of precipitation is thus essential, and satellite-based precipitation products can help in coping with the relatively sparse rain gauge ground networks of this area of the world. However, the complex topography and the marked geographic variability of precipitation in the region make precipitation retrieval from satellites problematic and product validation and intercomparison necessary. Six state-of-the-art monthly satellite precipitation products over East Africa during the 2001–09 time frame are evaluated. Eight areas (clusters) are identified by investigating the precipitation seasonality through the Global Precipitation Climatology Centre (GPCC) climatological gauge data. Seasonality was fully reproduced by satellite data in each of the GPCC-identified clusters. Not surprisingly, complex terrain (mountain regions in particular) represents a challenge for satellite precipitation estimates, as demonstrated by the standard deviations of the six-product ensemble. A further confirmation comes from the comparison between satellite estimates and rain gauge measurements as a function of terrain elevation. The 3B42 product performs best, although the satellite–gauge comparative analysis was not completely independent since a few of the products include a rain gauge bias correction.

Improvements of the 183-WSL retrieval method allow to better describe the precipitating clouds as to rain distribution, type and amount. The 183-WSL method is physically based on the water vapor absorption band at 18331 GHz and retrieves the rain rates upon discriminating the convective/stratiform characteristics of the observed precipitation. The current version of the retrieval scheme was upgraded with a

Multi-spectral data from the MODerate resolution Imaging Spectroradiometer (MODI S) onboard the Terra spacecraft are used to derive cloud optical thickness and effective particle radius using the algorithm of Nakajima and Nakajima (1995). Microphysical cloud properties are retrieved during strong aerosol events from biomass burning to better understand the actual effects of cloud-aerosol interactions. Rosenfeld (1999) observations have shown not

East Africa experienced in the 2001 -2011 time period some of the worst drought events to date, culminated with the high-impact drought in 2010-2011. The frequency and impacts of these extreme events require a continuous monitoring of precipitation, as a key variable for the inclusion of these phenomena in regional climatological studies and their timely forecast. Satellite precipitation products are particularly necessary in the region to enhance the observational capabilities limited sparse rain-gauge networks. Nevertheless, East Africa is characterized by a complex topography and highly varying climatic conditions ranging from the wetter mountainous regions to the arid lowlands with different precipitation seasonality, which can greatly affect the quality of satellite rainfall estimations. It is thus of utmost importance a satellite product validation and inter-comparison in order to assess their reliability and delimit the application domain. The monthly accumulated precipitatio...

Multi-spectral data from the MODerate resolution Imaging Spectroradiometer (MODIS) onboard the Terra spacecraft are used to derive cloud optical thickness and effective particle radius using the algorithm of Nakajima and Nakajima (1995). Microphysical cloud properties are retrieved during strong aerosol events from biomass burning to better understand the actual effects of cloud-aerosol interactions. Rosenfeld (1999) observations have shown not only that cloud microphysical properties are affected by the presence of smoke aerosols from burning vegetation but also that precipitation can be consequently suppressed. A key step for the understanding of these effects is the comparison of the retrieved cloud parameters with independent sources. In the present work the retrieved quantities (Costa et al., 2004) are compared with space and time coincident cloud optical thickness and effective particle radius from the MODIS official cloud product (King et al., 1998) and intensive measurement ...

The sensors in the infrared, near infrared and visible of polar orbiting and geostationary satellites have entered a new era where the number of channels and the data availability is greater than ever. The use of data from these channels is not anymore confined to the attribution of rainfall levels to cloud top brightness temperature fields as an indirect way of estimating precipitation at the ground. Channels at 1.6, 2.1 and 3.7 µm provide insights into cloud and precipitation formation mechanisms that are uniquely observed at these wavelengths. A perspective on the most recent advances in satellite cloud multispectral studies will be presented with special emphasis on

ABSTRACT The algorithm 183-WSL (Laviola and Levizzani 2008) exploits variations in emitted radiation within the water vapor absorption band at 183.31 GHz due to the extinction by rain drops for the estimation of rainfall rates over ocean and land surfaces. The 183-WSL retrieval scheme infers rain types on the basis of signal extinction associated to the presence of different hydrometeor states. Icy hydrometeors, which generally scatter more at high frequencies, are linked to higher rain rates. At the same time the signal depression due to absorption by liquid rain drops, which is typically lower than the scattering signal by ice crystals, is suitable to derive the lighter rain rates. Previous comparisons with other techniques have demonstrated the robustness of the 183-WSL results with respect to different precipitating events mainly at mid-latitudes. The present challenge of our research is to validate the 183-WSL algorithm results at higher latitudes. Some case studies are proposed located over Northern Europe covering different seasonal rain events. Precipitation formed at latitudes higher than 50 degrees is layered within the first kilometers of the atmosphere and generally structured as large stratified clouds with icy particles aloft. Rain rates associated with these stratiform systems are normally light and persistent and the formation of snowflake aggregates is quite common. On the other hand, during the summer season large scale systems and long time precipitation can generate floods and intense run-off. The goal of this work is to emphasize the capability of the 183-WSL algorithm to discern multi-seasonal different rain types when compared with rain rates derived from radar networks considered as ground truth. Moreover, a suite of microphysical parameters will be retrieved from the Meteosat Second Generation (MSG) Spinning Enhanced Visible and InfraRed Imager (SEVIRI) and employed to characterize the observed precipitation and better understand the retrieval results within the water vapor opaque frequencies.

The load of tropospheric aerosol from natural and anthropogenic sources is of crucial importance for the determination of the Earth radiative balance and the prediction of climate changes. The nadir- viewing spectrometers (AATSR, MERIS, and SCIAMACHY) onboard the ENVISAT-1 platform, to be launched mid 2001, will be independently operated and are conceived for different atmospheric studies. The spatial overlap of

METEOSAT Second Generation (MSG) Spinning Enhanced Visible and Infrared Imager (SEVIRI) channels in the visible (VIS), near infrared (NIR) and thermal infrared (IR) open up new possibilities for cloud top structure studies from the microphysical, radiative and dynamical perspectives. Studies such as those of Levizzani and Setvák (1996) have indicated the existence of unexpected features on top of deep convection that could only be detected using satellite sensors: plumes of small ice crystals, rotational features and wave patterns. Several of these features are yet to be explained in their overall complexity since cloud dynamics and microphysics are involved at the same time. Deep convection is also being reconsidered as a very powerful engine for troposphere-to-stratosphere water vapor exchanges. Simulations of the optical properties of randomly oriented ice crystal particles on top of deep convective clouds are presented. Computations are based on a combined Mie and Huygens theory...

In a previous work the relationship between rain area delineation by microwave (MW) channels of the Advanced Microwave Scanning Radiometer (AMSR-E) and the multi- spectral cloud field characterization by the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products was analyzed. Only a small percentage of water clouds were detected as raining by the operational AMSR-E algorithm (< 1%), while 27% of ice clouds were classified raining. The analysis, carried out for a period of 15 summer days in 2007 over the Mediterranean, showed a clear positive correlation for ice clouds between rain intensity and cloud optical thickness, and the presence of a sort of threshold for rain initiation at an optical thickness of 40. No clear relationship was found between cloud top effective radius and rain intensity. An analogous statistical analysis for the same period is now proposed by exploiting the cloud field parameters derived from the Advanced Very High Resolution Radiometer (AVHRR...

The interest in aerosol observations from satellite passive instrument is steadily increasing as a result of the better understanding of the key role played by aerosols within the climate system. Satellite instruments supply global observations for establishing the aerosol ...

A methodology for the retrieval of cloud properties from multi-spectral satellite measurements was developed and its application to measurements from the MODerate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua spacecrafts was shown by ...

Clouds are certainly the major factor regulating the Earth radiation budget. Special attention has been dedicated in the last few years to the cloud interaction with aerosol particles through modelling studies, in situ measurements and remote sensing techniques. The alterations ...