6.1 Partitioning between deep and shallow convection in MPAS.
Fowler, Laura D., and Mary C. Barth, Mesoscale & Microscale Meteorology Laboratory, National Center for Atmospheric Research
The impact on
moist processes of a variable-resolution mesh over the Tropical Pacific Ocean
is used to analyze the partitioning between shallow and deep convection in two
scale-aware convection schemes implemented in the Model for Prediction Across
Scales (MPAS). The first convection scheme is the Grell and Freitas (GF, 2014)
scheme which comprises separate formulations of deep and shallow convection.
The second convection scheme is the Multi-Scale Kain Fritsch (MSKF; Alapaty et
al. 2014) scheme which more simply distinguishes between shallow and deep
convection as functions of the cloud depth.
Each convection scheme is used in two 31-day experiments for December 2015. The
first simulation employs a 30-km uniform resolution mesh, while the second
simulation uses a 30-6 km variable resolution mesh where the refined grid is
located over the warmest sea-surface temperatures in the Western Tropical
Pacific Ocean.
Results show that because GF and MSKF assume that shallow convective clouds do
not precipitate, the formation of precipitation in deep convective updrafts
contributes a major part to increased simulated precipitation compared to TRMM
Precipitation Analysis data in the uniform resolution experiments. In the
variable resolution experiments, decreased deep convection over the refined
area of the mesh produces increased relative humidity and excess grid-scale
precipitation.
Results indicate that the GF convection scheme strongly overestimates the cloud
liquid water path (LWP) compared to CERES data and to the MPAS experiments
using the MSKF convection scheme, due to increased mixing from shallow
convection. The GF and MSKF convection schemes yield similar cloud ice path
(IWP) along the Inter-Tropical Convergence Zone and Western Pacific warm pool.