NATIONAL CENTRE FOR MEDIUM RANGE WEATHER FORECASTING

MINISTRY OF EARTH SCIENCES, GOVERNMENT OF INDIA

IMDAA 1-Hourly Single Level Dataset



Atmospheric Reanalysis data

A reanalysis is a high-quality climate-data product produced by assimilating long time series of observations with a consistent and state-of-the-art numerical weather prediction (NWP) model and data assimilation (DA) system to represent the best estimate of the state of the atmosphere. Reanalysis datasets have extensively been used for studying major global, hemispheric climatic patterns, trends, oscillations and teleconnections etc., during the last two decades. However, for regional/local synoptic and mesoscale processes, the grid resolution of present day global reanalyses, in the order of tens of kilometers, is not adequate. These reanalysis products limit the analysis of regional-scale phenomena. Hence there is a need for regional reanalysis using high resolution regional models.

What is IMDAA?

The Indian Monsoon Data Assimilation and Analysis reanalysis (IMDAA) is a regional atmospheric reanalysis over the Indian subcontinent. The IMDAA is the result of collaboration among the Met Office (MO), U.K, National Centre for Medium Range Weather Forecasting (NCMRWF), India and the India Meteorological Department (IMD) with funding from the National Monsoon Mission (NMM) project of the Ministry of Earth Sciences, Government of India. The reanalysis runs are carried out using high resolution (12km) mesoscale version of the Met Office Unified Model (UM) from 1979 to 2018, to span the era of modern meteorological satellites.

The IMDAA System

The IMDAA system is based on the Met Office four-dimensional variational assimilation scheme(4DVAR) and its Unified Model (UM). The system uses an intermittent data assimilation cycle. The model domain extends wider than the Indian subcontinent so as to include areas important for the development of Indian monsoon.

Horizontal grid resolution of the reanalysis model is 12 km (0.12°x0.12°) and it has 63vertical levels reaching to a height of approximately 40km. Lateral boundary conditions for the reanalysis run are taken from the global reanalysis ERA-Interim. Sea surface temperature is specified from the Hadley Centre Ice and Sea Surface Temperature dataset version 2 (HadISST2). Soil moisture analysis produced by the Extended Kalman Filter (EKF) based land data assimilation system, is used to update the soil moisture fields in every assimilation cycle.

Table 1: Details of IMDAA atmospheric, surface and subsurface fields available at different temporal resolutions.

(Note IMDAA-Like products:*3 hourly; #not available; Multi-level products are available only at 18 pressure levels.)

VariablesUnitsLevelStatistic
Relative Humidity%Entire AtmosphereInstantaneous (3 hourly)
TemperatureKEntire AtmosphereInstantaneous (3 hourly)
U-Component of Windm s-1Entire AtmosphereInstantaneous (3 hourly)
V-Component of Wind m s-1Entire AtmosphereInstantaneous (3 hourly)
W-Component of Wind m s-1Entire AtmosphereInstantaneous (3 hourly)
Relative Humidity%2 m above groundInstantaneous (hourly)
Temperature K2 m above groundInstantaneous (hourly)
Visibilitym2 m above groundInstantaneous (hourly)
U-Component of Wind m s-110 m above groundInstantaneous (hourly)
V-Component of Wind m s-110 m above groundInstantaneous (hourly)
Wind Speed (Gust)m s-110 m Above GroundInstantaneous (hourly)*
U-Component of Wind m s-150 m above groundInstantaneous (hourly)
V-Component of Windm s-150 m above groundInstantaneous (hourly)
Planetary Boundary Layer Height mAbove GroundInstantaneous (hourly)*
Evaporation Rate From Canopy kg m-2 s-1SurfaceAverage (hourly)*
Evaporation Rate From Open Sea kg m-2 s-1SurfaceAverage (hourly)#
Evaporation Rate From Soil Surfacekg m-2 s-1SurfaceAverage (hourly)*
Convective Rain Ratekg m-2 s-1SurfaceAverage (hourly)
Large Scale Rain Ratekg m-2SurfaceAverage (hourly)
Convective Snowfall Rate m s-1SurfaceAverage (hourly)
Large-Scale Snowfall Rate m s-1SurfaceAverage (hourly)
Convective Snow Amount kg m-2SurfaceAccumulation (hourly)
Large-Scale Snow Amountkg m-2SurfaceAccumulation (hourly)
Water Equivalent of Accumulated Snow Depth kg m-2SurfaceAccumulation (hourly)
Convective Water Precipitation kg m-2SurfaceAccumulation (hourly)
Large Scale Water Precipitation (Non-Convective)kg m-2SurfaceAccumulation (hourly)
Total Precipitation kg m-2SurfaceAccumulation (hourly)
Cloud BasemAbove ground levelInstantaneous (hourly)#
Very Low Cloud Cover %Atmosphere ColumnInstantaneous (hourly)
Low Cloud Cover %Atmosphere ColumnInstantaneous (hourly)
Medium Cloud Cover %Atmosphere ColumnInstantaneous (hourly)
High Cloud Cover %Atmosphere ColumnInstantaneous (hourly)
Total Cloud Cover Assuming Random Overlap%Atmosphere ColumnInstantaneous (hourly)
Downward Long-Wave Radiation FluxW m-2SurfaceAverage (hourly)*
Downward Short-Wave Radiation Flux W m-2SurfaceAverage (hourly)*
Downward Short-Wave Radiation FluxW m-2Top of AtmosphereAverage (hourly)*
Net Long-Wave Radiation Flux W m-2SurfaceAverage (hourly)*
Net Long-Wave Radiation Flux W m-2Top of AtmosphereAverage (hourly)*
Net Short Wave Radiation FluxW m-2SurfaceAverage (hourly)*
Net Short Wave Radiation Flux W m-2Top of AtmosphereAverage (hourly)*
Sensible Heat Net Flux W m-2SurfaceAverage (hourly)*
Latent Heat Net Flux W m-2SurfaceAverage (hourly)*
Water Runoff kg m-2Sub SurfaceAverage (hourly)#
Water Runoff Rate kg m-2s-1Sub Surface Average (hourly)#
Upward Water Ratekg m-2 s-1SurfaceAverage (hourly)#
Surface Temperature (skin) KSurfaceInstantaneous (hourly)*
Surface Pressure PaSurfaceInstantaneous (hourly)
Mean Sea Level Pressure PaMean Sea LevelInstantaneous (hourly)
Surface Roughness mSurfaceInstantaneous (hourly)*
0-0.1 m below ground Column-Integrated Soil Moisturekg m-2SoilInstantaneous (hourly)
0.1-0.35 m below ground Column-Integrated Soil Moisture kg m-2SoilInstantaneous (hourly)
0.35-1 m below ground Column-Integrated Soil Moisture kg m-2SoilInstantaneous (hourly)
1-3 m below ground Column-Integrated Soil Moisture kg m-2SoilInstantaneous (hourly)
Soil Temperature (0-0.1 m below ground)KSoilInstantaneous (hourly)
Soil Temperature (0.1-0.35 m below ground) KSoilInstantaneous (hourly)
Soil Temperature (0.35-1 m below ground)KSoilInstantaneous (hourly)
Soil Temperature (1-3 m below ground)KSoilInstantaneous (hourly)