During the Indoex experiment, a specific effort was done in LMD, France, for collecting the satellite data relevant to the region and period, and put them in a well conditioned data base. Meteosat-5 was moved by EUMETSAT over the Indian Ocean, and is the leading satellite for the studies presented here. METEOSAT allows the study and tracking of the convective systems and events, as well as estimation of the upper tropospheric humidity. Other satellite information on the water vapour in the atmosphere or precipitation come from microwave instruments as SSM/I or the instruments of TRMM. Concerning the radiative budget components, ScaRaB on the Russian satellite RESURS was providing outgoing radiative fluxes. All this information is combined here in order to study the fluctuations of convection at different time space scales and its relationship to environmental conditions such as humidity, sea surface temperature,...
The Megha-Tropiques satellite is devoted to the study of the atmospheric water cycle in the tropics and its relation to the radiative budget. It is aiming to study both the energy and water budget of the intertropical band and the life cycle of the convective complexes in the Tropics. The orbit of the satellite allows it to sample several times per day the zone from 23°N to 23°S, where most of the precipitation of the planet and large energy exchanges occur. The three instruments of the mission are a microwave imager, a microwave water vapor sounder and a radiative budget instrument. The launch of this mission by an Indian Rocket is foreseen in 2006-2007. It will hopefully coincide with the time frame of the Global Precipitation Mission, allowing to improve its tropical coverage.
CLOUDS is a project co-funded by the EC under FP-4, conducted by 12 European partners, also cooperating with NOAA/ETL. It is the mission study of a monitoring satellite to perform measurements necessary to describe cloud-radiation interaction in operational models for climate and long-term weather prediction. Complementary to missions for process study, CLOUDS addresses the monitoring aspect. As such, it has to comply with requirements of sufficiently frequent observing cycle, and operational sustainability. This prevents using active systems and leads to consider passive radiometry only, however exploiting as much as possible of the em spectrum, with more polarizations and more viewing geometries. The paper reports on the effort to demonstrate that, by these means, the main ingredients of the cloud-radiation interaction mechanism may be observed with sufficient accuracy. The optimal channels are determined. Clouds, aerosol radiation and precipitation are observed under identical geometry with in a range of the em spectrum spanning from 340 nm to 4.3 cm, i.e. over five orders of magnitudes, for a true multi- spectral approach.
Statistics of brightness temperatures from the water vapor (WV) band channel of Meteosat 2 (5.7-
7. 1pm) from July 1983 through July 1987 are analyzed. All measurements (clearor not) are used
to produce monthly and lOday averages. The ISCCP cloudiness retrieval is used to assess the
cloud influence on the monthly WV brightness temperatures. The regional repartition and the
interannual variations of different cloud types are compared with the global WV brightness
temperatures. The main problem is the scattered presence of very thin clouds. But generally
speaking, the warmest spots in monthly WV images are related with clear or low cloudy skies
while the coldest areas correspond to clouds whose top is above 440 hPa. To confirm these
results, a clear sky image has been synthetised using a cloud clearing algorithm. The WV
statistics are then used to characterize seasonal and interannual variations of both the ITCZ
(coldest spots) and the subtropical subsidence areas (warmest spots). Because the seasonal
variations of both phenomena are generally larger than their interannual changes, the seasonal
cycle of WV radiances is used to study relationships between the intensity and the extension of
the ITCZ compared to the dry subtropical areas. It is shown that, for the Meteosat sector, a wetter
subtropical high troposphere is associated with an enhanced activity of the JTCZ, and vive-versa.
This result seems to indicate a positive water vapor feedback in this particular region.
The tropical atmosphere plays a major role in the climate dynamics, through the influence of water vapor and clouds on the radiative budget of the Earth, and the release of latent heat in rainy systems. Present operational satellites do not allow reliable estimations of atmospheric water parameters, because they suffer from inappropriate instrumentation (geosynchronous) or from insufficient sampling (polar orbiters). TRMM is the only scheduled mission devoted to the tropics, but will still provide an insufficient sampling. Small satellites may alleviate these problems by placing several key passive instruments into appropriate orbits. TROPIQUES, studied by CNES, will carry two key instruments, one for radiative budget and one microwave imager. The orbit will have a low inclination (10 to 15 degree(s)), and the swath 2000 km, allowing repetitive cover of the equatorial band. The altitude will be at least 1000 km, due to microwave imager geometry constraints. The resolution will be relatively coarse, 40 km for the radiative budget instrument, 15 to 100 km for the microwave imager. TROPIQUES will be used in synergy with the polar platforms and geosynchronous satellites of the years 2000. It will provide a useful complementary system for the global study of our climate.
In order to get a better understanding of the influence of clouds on the Earth's energy budget, one needs a cloud classification taking into account cloud height, thickness, and cloud cover. The radiometer ScaRaB (scanner for radiation balance), launched in 1993, has in addition to the two broad-band channels (0.2 - 4 micrometers and 0.2 - 50 micrometers ) necessary for earth radiation budget (ERB) measurements, two narrow-band channels (0.5 - 0.7 micrometers and 10.5 - 12.5 micrometers ) in order to improve cloud detection. Most automatic cloud classifications have been developed with measurements of very good spatial resolution (200 m to 5 km). Earth radiation budget experiments, on the other hand, work at a spatial resolution of about 40 km (at nadir), and therefore we investigated a cloud classification algorithm adapted on this scale. The algorithm is based on the dynamic clustering method and uses co-located AVHRR-ERBE data, simulating the ScaRaB measurements. This cloud field classification is compared on one hand to results obtained by a well tested threshold algorithm using AVHRR (advanced very high resolution radiometer) measurements at reduced spatial resolution of 4 km and on the other hand to cloud parameters extracted from HIRS (high resolution infrared sounder)/MSU (microwave sounding unit) data. We find that classification of cloud fields is still possible at a resolution of 40 km, and by combining AVHRR, ERBE, and HIRS/MSU measurements one can undertake interesting studies on the influence of different cloud fields on the Earth radiation budget.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.