|
India’s Southwest Monsoon Rain Evaporates Below Clouds
A recent study by the Indian Institute of Tropical Meteorology (IITM), Pune, reveals that about 25% of India’s Southwest monsoon rain mass evaporates mid-air before reaching the ground. The study gathers primary measurements over the northern Western Ghats and Pune, and reports large day-to-day variation in below-cloud evaporation.
IITM Study on Below-Cloud Evaporation of Southwest Monsoon Rain:
| Dimension | Key Details |
|---|---|
| Authority | The study is conducted by the Indian Institute of Tropical Meteorology (IITM), Pune. |
| Core finding | Approximately 25% of India’s monsoon rain mass evaporates mid-air before reaching the ground. |
| Regional focus and season | Primary measurements are gathered over the northern Western Ghats and Pune during the Southwest monsoon season. |
| Quantitative range of daily evaporation | The mid-air evaporation rate ranges from 4% to 61% depending on ambient weather conditions. |
| Atmospheric drivers | The mid-air loss is dictated primarily by localised atmospheric factors such as ambient temperature, heat, and dry air. |
| Isotopic principle used | When water evaporates, lighter water molecules escape first, leaving the falling raindrop enriched with heavier hydrogen and oxygen isotopes. |
| Sampling and instrument | Researchers freeze and trap atmospheric vapor alongside surface rainwater, and analyse molecular signatures using a laser spectrometer. |
| Model used | Empirical isotopic data is fed into a below-cloud interaction model to track individual raindrops from the cloud base to the surface. |
| Global comparison values cited | Satellite data measures tropical trade-wind evaporation at around 20%, Zurich averages 40% during cold fronts, and Barbados can witness up to 63% of rain vanishing mid-air. |
| India-specific factors cited | The larger size of Indian monsoon drops and higher local humidity help shield India’s rain from disappearing faster. |