Ch. Liu et al., Hierarchical modelling of tropical convective systems using explicit and parametrized approaches, Q J R METEO, 127(572), 2001, pp. 493-515
Citations number
31
Categorie Soggetti
Earth Sciences
Journal title
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY
Cloud systems observed during 1-7 September of GATE are examined in a hiera
rchical approach, namely: a two-dimensional cloud-resolving simulation usin
g a 2 km grid length; two- and three-dimensional simulations using the Kain
-Fritsch convective parametrization and 10, 15 and 25 km grid lengths; and
coarse-grid simulations without any convective parametrization. All simulat
ions are forced by the same objectively analysed time-varying large-scale a
dvection of temperature and moisture. The domain-mean winds are relaxed to
the observed wind profiles.
Both the cloud-resolving modelling and the lower-resolution modelling with
parametrized convection realize the three observed cloud system categories
(squall line, non-squall cluster and scattered convection) and transitions
among them. In particular, the well-organized fast-moving squall-type cloud
system observed on 4 September is realized in a three-dimensional experime
nt with parametrized convection. In contrast, the lower-resolution modellin
g without any convective parametrization fails to produce the squall-type c
onvective system during the weakly forced period but successfully represent
s the non-squall cluster during strong forcing. This lack of success is mos
tly attributed to convective triggering and the absence of resolved downdra
ught-enhanced surface fluxes. These issues are not as critical during stron
g large-scale forcing.
The observed evolutions of temperature, water vapour mixing ratio, precipit
ation and surface moisture flux are realized in all simulations. A common d
eficiency is the overprediction of upper-level relative humidity. The simul
ation with parametrized convection features a comparatively large low-level
water vapour mixing ratio, a surface and upper-level cold temperature bias
and a mid-tropospheric warm bias. This is mainly attributed to deficiencie
s in how the Kain-Fritsch scheme represents convective mass flux, detrainme
nt and entrainment by cumulus congestus.