Pepler, A.S., L.V. Alexander, J.P. Evans and S.C. Sherwood
Journal of Geophysical Research: Atmospheres, 122, 9173-9184, doi: 10.1002/2017JD027345, 2017.
The east coast of Australia has a relatively high frequency of midlatitude cyclones, locally known
as East Coast Lows (ECLs), which can cause severe weather including widespread flooding and coastal
erosion. The elevated topography close to the east coast has been hypothesized to play a role in both the
genesis and impacts of cyclones in this region, but existing studies have been limited to case studies of
individual events. In this paper we present the results from two 20 year simulations over the Australian region
using the Weather Research and Forecasting Model and assess the results from removing all topography in
the region on both mean atmospheric circulation and ECL frequency. Removing topography results in an
increase in sea level pressure to the south of Australia and an increase in moisture flux convergence and
rainfall near the east coast, as well as a decrease in potential vorticity to the north of the ECL region. This
results in a change in the spatial distribution of cyclones, with a 37% decrease in the frequency of cyclones
that develop to the south of the ECL region but a 20% increase in cyclones near the east coast. This results in
little overall change in the frequency of ECLs
and suggests that coarse topography is unlikely to be responsible for the difficulties in simulating coastal
cyclones in global climate models.
Figure 3. Changes in average circulation patterns in 1990–2009 when topography was removed: (a) MSLP (hPa), (b) 200 hPa geopotential height (m), (c) average
500–1000 hPa horizontal moisture flux (vectors) and divergence (contours), (d) 800 hPa and 250 hPa winds (m/s), (e) average precipitation (%), and (f) 500 hPa
potential vorticity (PVU). The dashed lines indicate statistical significance at the 5% level using a t test on annual data, while a grey line in the bottom figures shows
the eastern seaboard region used for calculating rainfall anomalies.