JP4.8
Investigating the Role of Land-Atmosphere Interactions and the Desert Feedback Mechanism During the Active and Break Phases of the Monsoon Using MM5 and ARPS
Sam Chiao, Harvard University, Cambridge, MA; and A. P. Barros
Cumulative monsoon rainfall east of the Aravalli range in Northern India is three times higher on average than in the regions to the west often afflicted by major drought. It has been found that space-time variability patterns in cloudiness fields consistent with a hypothesis relating ocean-land-atmosphere feedbacks and the active and break phases of the monsoon. During the active phases of the monsoon, southeasterly depressions from the Bay of Bengal (BoB) propagate over northern India, maintaining sustained convergence of moist available energy east of the Aravalli range. Drier air originating from the Arabian Sea in the Western Indian Ocean (WIO) is constrained to the west. Accordingly, the active phase of the monsoon would be maintained via a positive feedback mechanism of land-atmosphere interactions. Increased rainfall in the east leads to an increase in soil moisture conditions, increase in surface latent heating due to increase in evapotranspiration, increase in CAPE (Convective Available Potential Energy), intensification of convective activity and increased rainfall over the region. Cooling periods in the BoB lead to a decrease in moisture convergence over the continent, weakening of the regional circulation east of the Aravalli range, thus allowing ventilation of the central portion of the Madhya Pradesh through penetration of westerly dry air and decrease of available soil moisture. Therefore, the break phase of the monsoon would be maintained by a negative feedback mechanism of land-atmosphere interactions. Increased ventilation by dry westerly flow leads to a decrease of soil moisture that is not replenished, which leads to a decrease in evapotranspiration and surface latent heating, lower CAPE, weakening of convective activity and leading to less rainfall.
In this study, we investigate this hypothesis using two regional scale models, the Penn State/NCAR MM5 and the Advanced Regional Prediction System (ARPS) model to simulate active and break phases of the monsoon at 30 and 10 km resolution over the Indian subcontinent. As a means of validating these simulations, we rely on concurrent hydrometeorological ground based and satellite observations. Analysis of thermodynamic and dynamic fields simulated by the models for a variety of land-use/land-cover change scenarios will show the role of land-atmosphere interactions in controlling the persistence of the different phases of the monsoon, and how the Thar Desert in NW India provides a barrier to the eastward propagation of convective activity.
Joint Poster Session 4, Land-Atmosphere Interactions Posters (Joint with the 15th Symp. on Global Change and Climate Variations and 18th Conf. on Hydrology; Hall 4AB)
Tuesday, 13 January 2004, 9:45 AM-9:45 AM, Hall 4AB
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