Aga Mrowiec

Isentropic analysis of convective motions.

Mesoscale convective systems (MCS) are groups of storms organized by the 
large-scale dynamics of the atmosphere. Strong updrafts and downdrafts 
within the convective organization lead to mass and moisture 
redistribution resulting in intense rainfall. Correct representation of 
all important aspects of organized mesoscale convection is crucial for 
current and future climate predictions. Strong convective motions 
generate gravity waves that are spatially and temporally co-located with 
them. Tropical convection is one of the most significant sources of 
non-orographic, multi-scale gravity waves. Large-scale atmospheric 
gravity waves are important for transport of momentum and energy, 
triggering new convection and mixing - among other things. However, 
within a vast spectrum of atmospheric gravity waves there are also 
small, reversible buoyant oscillations that do not contribute to the 
overall mass transport within the convective system and thus should be 
filtered out. When studying the convective and stratiform elements of an 
MCS it is difficult to extract wave-free signal. By sorting the 
convective motions based on entropy or equivalent potential temperature, 
which evolve on timescales that are much shorter than convectively 
driven small scale gravity waves, one can filter out most of the 
oscillations. This approach emphasizes the fact that the upward energy 
and entropy transports by convection are due to the combination of 
ascending air parcels with high energy and entropy and subsiding air 
parcels with lower energy and entropy, thus allowing to study averaged 
properties of updrafts and downdrafts. The use of this conditional 
averaging is also applied to other variables such as vertical velocity, 
temperature or relative humidity to obtain a detailed description of 
convective circulation. The mean diabatic tendencies from the three 
dimensional dynamic and thermodynamic fields can also be determined. 
This is an excellent method for model results analysis and model 
inter-comparison.