While satellites have vastly improved India’s understanding of the monsoon rains that periodically devastate the Indian subcontinent – as they have in 2007 – much about them still remains a mystery, which is why researchers at the Indian Space Research Organi

(ISRO) are eager to get the Indo-French MeghaTropiques satellite into orbit.

The monsoon that brings rain during June to September is crucial for the largely agriculture-based economy of India. But trying to make predictions about the amount of rain

always had been something of a gamble. The advent of satellites changed that, claim J. Srinivasan, an atmospheric scientist at the Indian Institute of Science in Bangalore, and P.C. Joshi of the Space Applications Centre in Ahmedabad.

In a report in the July 25 issue of Current Science, published by the Indian Academy of Sciences in Bangalore, the authors say that satellite data have made a “large impact” on short-term forecasting of Indian monsoons and helped in understanding the processes that influence its year-to-year variation.

However, while data from satellites helped crack some of the monsoon’s mysteries – like the date of onset – there are still many unknowns about the monsoon processes, ISRO scientists say. “That is why ISRO has attached great importance to this project,” says C.B.S. Dutt,

member secretary of the MeghaTropiques joint working group at ISRO headquarters.

Currently scheduled to be launched in the middle of 2009, MeghaTropiques will “vastly improve our understanding of the monsoon leading to better forecasts,” Dutt



“For instance we have not understood the cloud systems, particularly the water vapor content and the heat energy that drives the monsoon,” Dutt

told Space News Aug.

2. Thanks to satellites, scientists now know that the monsoon, after the onset, is

driven largely by the heat released into the air as water vapor in the clouds changes

into rain drops, but

a lack of precise data on water vapor and the energy available for driving the monsoon had hampered their ability to make correct forecasts.

“What our Insat

satellite gives is snapshots of the clouds and the direction of their travel, but little information about cloud microphysics or the water content,”

Joshi said


“The Megha-Tropiques spacecraft will plug this gap in knowledge because this satellite actually looks into the cloud structure,” he said, noting that MeghaTropiques will have a

microwave radiometer and a microwave humidity profiler. “Once we plug the data from these sensors into our numerical weather prediction model, we can make better forecasts,” Joshi said.

P. Goswami, another monsoon modeler at the Centre for Mathematical Modeling and Computer Simulation, says he is “excited” about the potential of MeghaTropiques.

The satellite’s name is a mixture of Sanskrit and French. “Megha” means clouds in Sanskrit, while “tropiques” translates as tropics in French. Dutt said the satellite will target the tropical belt between 23 degrees North and 23 degrees south of the equator, which gets the maximum amount of solar heating. By measuring water content and the energy budget Megha-Tropiques “can enhance our understanding of the tropical weather system as a whole and definitely provide better insights into our monsoon,” Dutt said.

In their

July 25 article,

Joshi and



data obtained from satellites over

the last 40 years “has altered our perception about factors responsible for monsoon rainfall.” Before the advent of satellites, this energy available for driving the monsoon circulation had to be guessed from ground-based observations, the authors said. But this guessing game ended after NASA launched three Earth Radiation Budget Experiment (ERBE) satellites in the 1980s “that provided an accurate estimate of the total solar radiation reflected and infrared radiation emitted by the

Earth-atmosphere system.”

By enabling scientists to measure the radiation budget of the

Earth directly from space, the ERBE data “has fundamentally altered our understanding of the roles played by the oceans, water vapor, and radiation budget on the strength of the monsoon,” the report said.

But that data has not been adequate to develop climate models that predict the year-to-year variation in the strength and pattern of rainfall, Joshi and


“A dramatic improvement in the accuracy of prediction by climate models will occur if and only if more satellite data is obtained about the temporal evolution of cloud systems in the tropics,” the authors state in their article.

They conclude that satellites should be able collect data from the cloud systems during their “birth, growth and demise.”

Joshi said the Megha-Tropiques mission will do exactly that because it will be launched in an orbit that is inclined 20 degrees to the equatorial plane and has the right sensors.