Premium
The effect of horizontal resolution on Indian monsoon depressions in the Met Office NWP model
Author(s) -
Hunt Kieran M.R.,
Turner Andrew G.
Publication year - 2017
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.3030
Subject(s) - climatology , numerical weather prediction , troposphere , environmental science , diurnal cycle , monsoon , horizontal resolution , meteorology , tropical cyclone , atmospheric sciences , geology , geography
Monsoon depressions are synoptic‐scale features that are responsible for a significant fraction of the rain over northern India during the summer monsoon season, and therefore it is important to quantify their structure and behaviour in numerical weather prediction (NWP) models. It is known that increasing model resolution is strongly correlated with improved forecasts in the short term and global circulation in the longer term, as well as better representation of tropical cyclones; here, we explore the sensitivity of depressions to changes in resolution using the Met Office Unified Model. Seven NWP case‐studies of depressions from 2013 to 2015 were run at eight resolutions corresponding to equatorial grid spacing of between 16 and 208 km, and compared with data for the same events from Tropical Rainfall Measuring Mission (TRMM) and ERA‐Interim reanalysis. We found that, at the low‐resolution end of the spectrum, increases in resolution led to improvements in the composite structure, but with diminishing returns; that is to say, the improvements in forecast track and structure become smaller. The model also persistently overestimated the depression intensity, in particular the wind speed and the warm core aloft–with the source appearing to originate in the mid‐troposphere. The sensitivity of the diurnal cycle to resolution was also explored: the stratiform component was found to be very well represented by the model, whereas the convective component was described quite poorly. Improvement in most components of structure with increasing model resolution were marginal beyond N320 (63 km) and N512 (39 km) for dynamic and thermodynamic fields respectively.