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Geophysical Fluid Dynamics

Moist Geophysical Fluid Dynamics

Water, in its different phases, plays a significant role in shaping climate of the Earth. Apart from radiative impacts, the energy release associated with changes in phase of water has an intrinsic role in a variety of dynamical phenomena; for example, the Madden Julian Oscillation (MJO). One of our goals has been to construct and analyze minimal dynamically consistent models of moist geophysical fluid dynamics. Work in this direction includes, understanding scaling and structure formation in "moist turbulence”, the identification of a correspondence between the convectively coupled tropical waves, the MJO and large-scale gradients of tropical precipitable water, and based on this correspondence, the development of a plausible dynamical theory of large-scale, low-frequency, eastward and westward propagating tropical moist modes. We also explore low frequency variability in more complicated, albeit idealized aquaplanet general circulation models.

Geostrophic Turbulence and Mixing

Another long standing interest in our group concerns fundamental aspects of rotating and stratified turbulence. In particular, to develop an understanding of the relative importance of vertical and wave modes in mediating interscale energy transfer in a rotating and stratified fluid. We constructed a wave mode only model of stratified flows, performed a systematic examination of quasigeostrophic turbulence with a finite deformation scale with an emphasis on frequency and combined frequency-wavenumber analysis, shallow water turbulence and the emergence of superrotating states in both initial value and steady scenarios. We have also extended our analysis of spectra, intermittency and interscale energy and enstrophy transfer to oceanic settings. In particular, using altimetry data, analogous to the quasigeostrophic portion of the upper tropospheric Nastrom-Gage spectrum, we have elucidated the forward enstrophy transfer regime at scales between 200-100 km accompanied by a −3 scaling of the geostrophic kinetic energy. Ongoing work in this direction includes the analysis of in situ ADCP based currents to shed light on the relative roles of rotational and divergent modes in the surface kinetic energy of the Bay of Bengal.