Assessment of Data Assimilation Approaches for the Simulation of a Monsoon Depression Over the Indian Monsoon Region

AbstractA high resolution regional reanalysis of the Indian Monsoon Data Assimilation and Analysis (IMDAA) project is made available to researchers for deeper understanding of the Indian monsoon and its variability. This 12 km resolution reanalysis covering the satellite-era from 1979 to 2018 using 4D-Var data assimilation method and the UK Met Unified Model is presently the highest resolution atmospheric reanalysis carried out for the Indian monsoon region. Conventional and satellite observations from different sources are used, including Indian surface and upper air observations, of which some were not used in any previous reanalyses. Various aspects of this reanalysis, like quality control and bias correction of observations, data assimilation system, land surface analysis, and verification of reanalysis products, are presented in this paper. Representation of important weather phenomena of each season over India in the IMDAA reanalysis verifies reasonably well against India Meteorological Department (IMD) observations and compares closely with ERA5. Salient features of the Indian summer monsoon are found to be well represented in the IMDAA reanalysis. Characteristics of major semi-permanent summer monsoon features (e.g., Low-level Jet and Tropical Easterly Jet) in IMDAA reanalysis are consistent with ERA5. The IMDAA reanalysis has captured the mean, inter-annual, and intra-seasonal variability of summer monsoon rainfall fairly well. IMDAA produces a slightly cooler winter and a hotter summer than the observations; the reverse for ERA5. IMDAA captured the fine-scale features associated with a notable heavy rainfall episode over complex terrain. In this study, the fine grid spacing nature of IMDAA is compromised due to the lack of comparable resolution observations for verification.

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Effects of Convection Representation and Model Resolution on Diurnal Precipitation Cycle Over the Indian Monsoon Region: Toward a Convection‐Permitting Regional Climate Simulation

Journal of Geophysical Research Atmospheres ◽

10.1029/2019jd032150 ◽

2020 ◽

Vol 125 (16) ◽

Cited By ~ 1

Author(s):

Rakesh Teja Konduru ◽

Hiroshi G. Takahashi

Keyword(s):

Indian Monsoon ◽

Regional Climate ◽

Climate Simulation ◽

Monsoon Region ◽

Model Resolution ◽

Regional Climate Simulation ◽

Indian Monsoon Region ◽

Precipitation Cycle

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Diurnal variability of the atmospheric boundary layer height over a tropical station in the Indian monsoon region

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-531-2017 ◽

2017 ◽

Vol 17 (1) ◽

pp. 531-549 ◽

Cited By ~ 14

Author(s):

Sanjay Kumar Mehta ◽

Madineni Venkat Ratnam ◽

Sukumarapillai V. Sunilkumar ◽

Daggumati Narayana Rao ◽

Boddapaty V. Krishna Murthy

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Diurnal Variation ◽

Indian Monsoon ◽

Winter Season ◽

Monsoon Region ◽

Diurnal Variability ◽

The Mean ◽

Indian Monsoon Region ◽

Tropical Station

Abstract. The diurnal variation of atmospheric boundary layer (ABL) height is studied using high-resolution radiosonde observations available at 3 h intervals for 3 days continuously from 34 intensive campaigns conducted during the period December 2010–March 2014 over a tropical station Gadanki (13.5° N, 79.2° E; 375 m), in the Indian monsoon region. The heights of the ABL during the different stages of its diurnal evolution, namely, the convective boundary layer (CBL), the stable boundary layer (SBL), and the residual layer (RL) are obtained to study the diurnal variabilities. A clear diurnal variation is observed in 9 campaigns out of the 34 campaigns. In 7 campaigns the SBL did not form in the entire day and in the remaining 18 campaigns the SBL formed intermittently. The SBL forms for 33–55 % of the time during nighttime and 9 and 25 % during the evening and morning hours, respectively. The mean SBL height is within 0.3 km above the surface which increases slightly just after midnight (02:00 IST) and remains almost constant until the morning. The mean CBL height is within 3.0 km above the surface, which generally increases from morning to evening. The mean RL height is within 2 km above the surface which generally decreases slowly as the night progresses. The diurnal variation of the ABL height over the Indian region is stronger during the pre-monsoon and weaker during winter season. The CBL is higher during the summer monsoon and lower during the winter season while the RL is higher during the winter season and lower during the summer season. During all the seasons, the ABL height peaks during the afternoon (∼ 14:00 IST) and remains elevated until evening (∼ 17:00 IST). The ABL suddenly collapses at 20:00 IST and increases slightly in the night. Interestingly, it is found that the low level clouds have an effect on the ABL height variability, but the deep convective clouds do not. The lifting condensation level (LCL) is generally found to occur below the ABL for the majority of the database and they are randomly related.

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