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Upcoming Seminar/Colloqium


Investigation of atmospheric Dynamics over central Himalayas using ST Radar and other observations

Speaker : Aditya Jaiswal
Affiliation : ARIES
Date & Time :
Venue : Auditorium
Abstract :

The central Himalayan region, being located at the subtropical latitudes experiences the interaction
of the tropical and extratropical weather systems. The complex and elevated orography of the
region substantially induces modifications in the weather often resulting in the frequent occurrence
of extreme weather episodes like cloud bursts, hailstorm etc. Therefore observations of
meteorological variables at finer spatial and temporal scales are essential for the improvement in
the forecast skill and simulation of the weather over this region. In the light of this, a Stratosphere
Troposphere Radar operating at 206.5 MHz has been installed at the high altitude site of Nainital
(~ 1.8 km amsl) to facilitate representative atmospheric dynamics of this region. The radar can
continuously provide the three dimensional structure of the wind field up to 20 km. The zonal,
meridional wind vectors, wind speed and wind direction from the radar have been validated and
found to be in good agreement against the conventional balloon borne GPS radiosonde derived

The high temporal and vertical resolution observations of the wind field has been utilized to
estimate to characterize the strength of turbulence in the free atmosphere. Turbulence parameters
viz. refractivity turbulence structure constant (Cn2), turbulent kinetic energy dissipation rates, eddy
diffusivity coefficient, inner and outer scale lengths of inertial subranges have been estimated and
their seasonal variability has been inferred. The seasonal median of Cn2 over the region varies form
10-15.5 to 10-19 m-2/3 over this region. The seasonal median of turbulent kinetic energy dissipation
rate and eddy diffusivity coefficient varies in the range of 10-2.5 10-4 m2s-3 and 10-0.7 to 10 m2s-1
respectively. Additionally, radar observations have been applied to monitor the integrated optical
turbulence parameters i.e ‘seeing’, isoplanatic angle, wavefront coherence time to aid the
astronomical observations at the site. The best median seeing has been observed in the winter and
post monsoon season varying from 0.4′′ to 0.6′′ respectively.

Attributes of the pre monsoon and summer monsoon deep convective systems were delineated
by observing the hailstorm and heavy rainfall episodes during these seasons. At least ten times
enhancement in the momentum flux exchange has been observed between upper troposphere and
lower stratosphere due to the triggering of gravity waves by the deep convective systems. The
results of these studies highlights the applications of the 200 MHz VHF radar in providing the
detailed insights into the microscale to mesoscale dynamics of the lower atmosphere.

About Speaker :

 Aditya Jaiswal is a Ph.D. student at ARIES and this is his pre-thesis submission talk.