Intraseasonal Monsoon Phase Transitions Viewed from Remote Sensing Observations and Reanalysis Data Sets

In this study we examine the transitions in the monsoon phases (onset, active, break and the withdrawal) during an entire monsoon season. This makes use of a host of observational tools that come from satellites and surface based measurements. Among these we make use of GPM and TRMM satellites for precipitation estimates, the vertical structure of rain, hydrometeors and cloud types from TRMM and CLOUDSAT data sets. The details we present for the monsoon phases include typical rainfall distributions, cloud distributions including horizontal and vertical structures with cloud heights. Among several reanalysis based fields that are covered here include moisture fluxes and moisture convergences, evolution of moist static energy, the mapping of intraseasonal oscillations and the total winds during these phases, the details of energy exchanges between the rotational and the divergent kinetic energy and the transitions of soil moisture. The above fields show rather sharp transitions from one phase of the monsoon to the next. During the onset phase we illustrate vertical structures with tall cumulonimbus clouds that extend out to 16km, the active phase is dominated by alto stratus and nimbostratus type clouds that are somewhat shallower. In general we noted an absence of such clouds during the break and the withdrawal phases. Those structures were consistent in a number of derived fields such as the moisture convergence, moisture transports and the energy conversions among the rotational and the divergent winds and the corresponding phases of the intraseasonal oscillations. The three dimensional back trajectories were also analyzed to answer the question, where do the parcels come from that ended up over Indian region during these phases of the monsoon.