MEGHA-TROPIQUES is a space mission designed to study convective systems, focusing on the analysis of water cycle with water vapour distribution and transport, convective systems life cycle and energy exchanges in the tropical belt. The tropical areas are where the most intensive energy exchanges take place: radiative exchanges, heat exchanges, transport of components and energy through dynamic processes. The main purposes of the mission is to build a tropical data set in order to support climate prediction studies, climate and whether models validation, over tropical areas. The mission will also provide relevant data for global Earth climate understanding because tropical processes may also affect the global climate.
The science objectives have been divided in three categories:
- To collect a long-term set of measurements with a good time sampling and coverage over tropical latitudes. A better understanding of these processes is expected related to large tropical convective systems and their life cycle.
- To improve the determination of water and energy budgets at various time-space scales.
- To obtain meaningful statistics on the conditions in which tropical convective systems are formed and evolve, analyzing the way they interact with the general circulation of the atmosphere, studying the inter-annual and inter-seasonal variations and diurnal cycle of the systems. It should help the scientists to improve parametrization inside climate and meteorological models and assimilation of data related to convective system in forecasts models.
The final objective of the mission is to enhance our understanding of the impacts of these convective systems on the tropical climate and improve our abilities to predict them at different time-space scales.
For more information, visit the scientific team website.
Megha-Tropiques is part of the GPM constellation (Global Precipitation Monitoring) with NASA, JAXA, NOAA and EUMETSAT to obtain rainfall estimates in slightly deffered time, digital weather forecast and monitoring of tropical storm evolution. Thanks to its specific coverage of the tropical area, Megha-Tropiques has significantly contributed to this international cooperation.
The originality of the mission lies in the orbit: the tropical belt, 23°N to 23°S at an altitude of 866 km. The cycle is seven days and the revisit is every three to more than five times per day.
An ideal time sampling would be one measurement every 2 hours. However, realistic orbital constraints do not allow this kind of sampling over the whole intertropical band. Then the minimum sampling requirement has been defined as:
- at least three measurements per day over the whole tropical zone, with possibly more over the zone between 10° to 20° (up to five with the chosen orbit of 20° inclination)
- successive observations at less than two hours interval during limited periods.
The spatial resolution is constrained by the size of the systems to be observed and the size of the observations used for statistics. The smallest details are related to the convective precipitation field, with a size of individual convective cell of about 10 km.
The statistics on a 1° x 1° grid include more than 100 pixels. The water vapour must also be observed with this resolution.
For other parameters regarding clouds and radiation, the resolution can be relaxed to 40 km, which implies 5 to 10 pixels per 1° x 1° grid. Thus we can determine the following requirements:
- a 10 km horizontal resolution for convective cells and water vapour
- a 40 km horizontal resolution for radiative budget and other cloud parameters.