Dj. Stensrud et Jl. Anderson, Is midlatitude convection an active or a passive player in producing global circulation patterns?, J CLIMATE, 14(10), 2001, pp. 2222-2237
The ability of persistent midlatitude convective regions to influence hemis
pheric circulation patterns during the Northern Hemisphere summer is invest
igated. Global rainfall data over a 15-yr period indicate anomalously large
July total rainfalls occurred over mesoscale-sized, midlatitude regions of
North America and/or Southeast Asia during the years of 1987, 1991, 1992,
and 1993. The anomalous 200-hPa vorticity patterns for these same years are
suggestive of Rossby wave trains emanating from the regions of anomalous r
ainfall in the midlatitudes.
Results from an analysis of an 11-yr mean monthly 200-hPa July wind field i
ndicate that, in the climatological mean, Rossby waveguides are present tha
t could assist in developing a large-scale response from mesoscale-sized re
gions of persistent convection in the midlatitudes. This hypothesis is test
ed using a barotropic model linearized about the 200-hPa July time-mean flo
w and forced by the observed divergence anomalies. The model results are in
qualitative agreement in the observed July vorticity anomalies for the fou
r years investigated. Model results forced by observed tropical forcings fo
r the same years do not demonstrate any significant influence on the midlat
itude circulation. It is argued that persistent midlatitude convective regi
ons may play a role in the development, maintenance, and dissipation of the
large-scale circulations that help to support the convective regions.