The purpose of the International Global Precipitation Measurement (GPM) Program is to develop a next-generation space-based measuring system which can fulfill the requirements for frequent, global, and accurate precipitation measurements. The associated GPM Mission is being developed as an international collaboration of space agencies, weather and hydrometeorological forecast services, research institutions, and individual scientists. The design and development of the GPM Mission is an outgrowth of valuable knowledge and published findings enabled by the Tropical Rainfall Measurement Mission (TRMM). From the TRMM experience, it was recognized that the GPM Mission must consist of a mixed nonsunsynchronous and sunsynchronous orbiting satellite constellation in order to have the capability to provide physically based retrievals on a global basis, with ~3-h sampling assured at any given Earth coordinate ~90% of the time. The heart of the GPM constellation is the Core satellite, under joint development by NASA and the Japan Aerospace Exploration Agency (JAXA), which will carry a dual frequency Ku/Kaband precipitation radar (PR) and a high-resolution, multichannel passive microwave (PMW) rain radiometer. The core is required to serve as the calibration reference system and the fundamental microphysics probe to enable an integrated measuring system made up of additional constellationsupport satellites, each carrying at a minimum some type of PMW radiometer. In this article the background, planning, design, and implementation of the GPM is described.

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The mass of African dust present over the western Mediterranean during a transport episode from northwestern Africa, which occurred in early July 1985, is estimated using a desert aerosol model, an Earth‐atmosphere radiative transfer model and Meteosat visible channel data from 4 days running. Dust pixels are selected from Meteosat images, and their aerosol optical thickness is retrieved. A proportionality factor between aerosol optical thickness and atmospheric columnar aerosol loading is computed and applied to the dust pixels. The total mass of atmospheric particles over the basin is obtained by interpolation and spatial integration. The maximum aerosol optical thickness is 1.8. The maximum aerosol columnar loading is evaluated to be 2.3 g m−2. The integrated mass of particles present at a given time is estimated to raise up to about 0.6 × 1012 g at the maximum and the total mass of dust exported from Africa to be of the order of 1012 g. The method is carefully evaluated and uncertainties are discussed, with particular emphasis on the relationship between atmospheric dust mass and aerosol optical depth. The overall uncertainty on the total mass is roughly a factor ±3. In the absence of clouds it appears that the major uncertainty results from the lack of knowledge of the actual mass‐size distribution of suspended dust particles, pointing out the lack of relevant data on particles larger than 10 μm in diameter. A simple calculation based on results from both computations and simultaneous field measurements yields a net transfer velocity of particles from the dust layer of approximately 1 cm s−1.

The elements associated with mineral aerosol particles exhibit, in the Western Mediterranean, sporadic but intense concentration peaks. Twenty dust events were recorded during a one-year sampling period with their frequency being maximum in spring and summer. Threedimensional air-mass trajectories as well as satellite imagery (Meteosat II) show that all these events are associated with transport of so~l dust from Africa. Three principal source-regions have been distinguished by using air-mass trajectories. Each of them seems to be characterized also by the chemical composition of the dust collected in Corsica. Moreover, the emissions and transport of dust particles from these various source-regions were found to occur during different times of the year. This has been explained by the seasonal atmospheric circulation patterns over North Africa and the Western Mediterranean.Finally, total deposition measurements show that such dust transport events control a large fraction of the yearly atmospheric deposition of mineral aerosol particles to the Western Mediterranean. One single deposition event of short duration was found to account for 30% of the total annual flux for elements such as Si and Al. 227 M. Leinen and M. Sarnthein (eds.), Paleoclimatology and Paleometeorology: Modern and Past Patterns olGlobal Atmospheric Transport, 227-252.

[1] The aim of this paper is to characterize the deep convective systems over the Indian Ocean during Indian Ocean Experiment (INDOEX) and their relationship to cloudiness and to the Upper Tropospheric Humidity (UTH) of their environment together with the relevant longwave radiation fields. Multisatellite analyses are performed (Meteosat, Scanner for Radiation Budget (ScaRaB), and Special Sensor Microwave Imager (SSM/I)) to measure these environmental parameters. The use of Meteosat water vapor (WV) channel appears very efficient not only for estimating UTH but also for separating high level cloudiness, including thin cirrus, from clear sky and low clouds. The Meteosat infrared (IR) and WV channels are also used for correlating Meteosat and ScaRaB measurements, allowing to retrieve continuously the longwave radiative flux. The longwave flux is used to compute the cloud radiative forcing as well as the clear-sky greenhouse effect. Spatial relationships between upper level cloudiness and UTH are established. A strong positive linear relationship is found suggesting a local moistening of the upper troposphere by convection. The temporal analysis reveals that during the active phase of the intraseasonal oscillation, the longwave cloud radiative forcing reaches a mean value up to 40 W m À2 over a large region in the open ocean, while the average clear-sky greenhouse effect is in excess of 180 W m À2 . These radiative parameters are strongly correlated with the upper level cloudiness and upper level moisture, respectively. The temporal variability of UTH explains up to 80% of the greenhouse effect variability. The structure of the convective cloud systems is then studied. The observed population of systems spans a wide spectrum of area from 100 to 1,000,000 km 2 . The contribution to the high level cloudiness of the systems with a strong vertical development is dominant. These systems, with at least one convective cell reaching the highest levels (below 210 K), present indices of overshooting tops and are the most horizontally extended. The largest system exhibits an average longwave radiative forcing of around 100 W m À2. Their contribution to the cloud forcing over the Indian Ocean is overwhelming. The spatial and temporal variability of the systems is finally related to the UTH and to the clear-sky greenhouse effect. Strong correlations are found indicating that these organized convective systems at mesoscale play a leading role in the Indian Ocean climate. The analysis suggests that deeper convection is associated with larger cloud desks with larger cloud radiative forcing. It is also associated with a moister upper troposphere and a larger clear-sky greenhouse effect. These two effects would provide a positive feedback on the surface conditions.

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The diurnal cycle of clouds over the western equatorial Pacific region (15ЊS-15ЊN, 130ЊE-180Њ) is studied analyzing hourly GMS-4 infrared brightness temperature images during the intensive observation period (Nov 1992-Feb 1993) of TOGA COARE. Although the area studied is essentially (93%) oceanic, differences of diurnal behavior of the clouds are noticed over different ocean subareas, depending both on the general circulation conditions and on the vicinity of landmasses. This study focuses on the effects of New Guinea and other major islands on the diurnal cycle within the surrounding ocean areas, as for example, the TOGA COARE Intensive Flux Array. The major observable feature of the influence of land is the presence of a diurnal, rather than semidiurnal, average cycle of cloudiness with a high day-today repetitivity. The signal is observed up to 600 km off the coast of New Guinea and it is characterized by a variable phase propagating at an average speed of about 15 m s Ϫ1. For smaller islands, the effect extends over a distance approximately comparable to their size. The genesis of the propagating cloud systems is assumed as due to the low-level convergence between the largescale flow and a possible land breeze. This conceptual model has been previously proposed to explain a similar signal observed offshore of Borneo. Within this framework, the influence of the large-scale circulation on the intensity and spatial organization of the propagating cloud systems is discussed. The diurnal signal vanishes when the expected convergence is weaker or when overshadowed by large-scale disturbances crossing over the considered area. In the first 3 months of the period such disturbances are nearly always cloud clusters accompanying the active phase of the Madden-Julian oscillation. Finally it is shown that the small islands in the TOGA COARE domain can corrupt the ''oceanic'' signal by as much as 10% of the diurnal cycle.