A comparison of low pressure system statistics derived from a high resolution NWP output and three re-analysis products over the Southern Ocean
P. Uotila, A.B. Pezza, A.H. Lynch, K. Keay, and J.J. Cassano
2009, Journal of Geophysical Research, 114, D17105, doi:10.1029/2008JD011583.
We compare low pressure system statistics derived from the Antarctic
Mesoscale Prediction System (AMPS) and NCEP, NCEP2 and JRA25 re-analysis
products using an automatic cyclone tracking scheme. Comparisons are based
on the 2001-2007 period. Since AMPS model spatial and temporal resolutions
are much higher than the ones of the re-analyses, this study provides a
valuable insight of the ability of numerical models to simulate low pressure
systems with an increasing resolution.
Results based on AMPS data agree relatively well with re-analyses based
results when looking at the seasonal variability and spatial patterns of low
pressure system properties over large scales. Results dier systematically
close to the Antarctic ice sheet, where the horizontal resolution is
important in resolving the continental topography. This appears as lower
AMPS system densities and smaller system sizes close to the Antarctic coast.
Results differ most during winter when especially the correct
parametrization of surface energy balance is crucial over the sea-ice
covered ocean. AMPS data show more small systems at around and south of 60
degrees S in the Antarctic Circumpolar Trough, where re-analyses display
fewer systems of larger size. Earlier studies of cyclonic systems over the Southern Ocean show that there is a spectrum of atmospheric systems, where
small synoptic systems merge into mesoscale lows. Accordingly a high
resolution model setup with appropriate physics parametrization, like AMPS,
is required to generate small systems. This study highlights that when new
data become available it is important to update low pressure system
statistics to gain a better understanding of high latitude processes over
intermediate scales. |
216 UCB