Regional simulation of Indian summer monsoon intraseasonal oscillations at gray-zone resolution

Abstract

Abstract. Simulations of the Indian summer monsoon by the cloud-permitting Weather Research and Forecasting (WRF) model at gray-zone resolution are described in this study, with a particular emphasis on the model ability to capture the monsoon intraseasonal oscillations (MISOs). Five boreal summers are simulated from 2007 to 2011 using the ERA-Interim reanalysis as the lateral boundary forcing data. Our experimental setup relies on a horizontal grid spacing of 9 km to explicitly simulate deep convection without the use of cumulus parameterizations. When compared to simulations with coarser grid spacing (27 km) and using a cumulus scheme, the 9 km simulations reduce the biases in mean precipitation and produce more realistic low-frequency variability associated with MISOs. Results show that the model at the 9 km gray-zone resolution captures the salient features of the summer monsoon. The spatial distributions and temporal evolutions of monsoon rainfall in the WRF simulations verify qualitatively well against observations from the Tropical Rainfall Measurement Mission (TRMM), with regional maxima located over Western Ghats, central India, Himalaya foothills, and the west coast of Myanmar. The onset, breaks, and withdrawal of the summer monsoon in each year are also realistically captured by the model. The MISO-phase composites of monsoon rainfall, low-level wind, and precipitable water anomalies in the simulations also agree qualitatively with the observations. Both the simulations and observations show a northeastward propagation of the MISOs, with the intensification and weakening of the Somali Jet over the Arabian Sea during the active and break phases of the Indian summer monsoon.

Radiative Effects of Secondary Ice Enhancement in Coastal Antarctic Clouds

“…PolarWRF model options are detailed in supporting information S1 (Bigg, 1953;Bromwich et al, 2013;Chen et al, 2018;Dearden et al, 2016;Nakanishi & Niino, 2006;Prein et al, 2015). The model was run for 48 hr, to allow adequate time for spin up, at high spatial resolution.…”

Potential Impacts of Assimilating All-Sky Satellite Infrared Radiances on Convection-Permitting Analysis and Prediction of Tropical Convection

“…Their results show that the gray-zone resolution simulation was able to realistically replicate the general precipitation, circulation, thermodynamic, and radiation features of the October and November MJO events observed during DYNAMO. Subsequent work by Chen et al (2018b) showed that the gray-zone resolution simulation can capture the general features of atmospheric overturning across different scales well. Similar model setups have also been used to study the physical mechanisms of tropical convection (Zhang et al 2017;Chen et al 2018a,c;Chen and Zhang 2019).…”

Development and Evaluation of an Ensemble‐Based Data Assimilation System for Regional Reanalysis Over the Tibetan Plateau and Surrounding Regions

“…The same physical schemes were used in the D01 and D02, including the WRF Double-Moment 6class microphysics scheme (Lim & Hong, 2010), the longwave radiation scheme of Rapid Radiative Transfer Model for general circulation model applications (Iacono et al, 2008), the New Goddard shortwave radiation scheme (Chou & Suarez, 1999), the Monin-Obukhov similarity surface-layer scheme (Paulson, 1970) (Hong et al, 2006). No cumulus parameterization scheme was used in either of the model domains (D01 and D02), which follows Chen et al (2018). Note that the data assimilation method used by the WRF-EnKF system presented here is ensemble based, which is drastically different from those variational methods used for creating ERA-Interim and ERA5, the IFS Cycle 31r2 4DVAR and IFS Cycle 41r2 4DVAR (Hersbach & Dee, 2016), respectively, besides their differences in model, resolution, and physics parameterization schemes.…”