NATIONAL CENTRE FOR MEDIUM RANGE WEATHER FORECASTING
MINISTRY OF EARTH SCIENCES, GOVERNMENT OF INDIA
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.
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 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.
(Note IMDAA-Like products:*3 hourly; #not available; Multi-level products are available only at 18 pressure levels.)
Variables | Units | Level | Statistic |
---|---|---|---|
Relative Humidity | % | Entire Atmosphere | Instantaneous (3 hourly) |
Temperature | K | Entire Atmosphere | Instantaneous (3 hourly) |
U-Component of Wind | m s-1 | Entire Atmosphere | Instantaneous (3 hourly) |
V-Component of Wind | m s-1 | Entire Atmosphere | Instantaneous (3 hourly) |
W-Component of Wind | m s-1 | Entire Atmosphere | Instantaneous (3 hourly) |
Relative Humidity | % | 2 m above ground | Instantaneous (hourly) |
Temperature | K | 2 m above ground | Instantaneous (hourly) |
Visibility | m | 2 m above ground | Instantaneous (hourly) |
U-Component of Wind | m s-1 | 10 m above ground | Instantaneous (hourly) |
V-Component of Wind | m s-1 | 10 m above ground | Instantaneous (hourly) |
Wind Speed (Gust) | m s-1 | 10 m Above Ground | Instantaneous (hourly)* |
U-Component of Wind | m s-1 | 50 m above ground | Instantaneous (hourly) |
V-Component of Wind | m s-1 | 50 m above ground | Instantaneous (hourly) |
Planetary Boundary Layer Height | m | Above Ground | Instantaneous (hourly)* |
Evaporation Rate From Canopy | kg m-2 s-1 | Surface | Average (hourly)* |
Evaporation Rate From Open Sea | kg m-2 s-1 | Surface | Average (hourly)# |
Evaporation Rate From Soil Surface | kg m-2 s-1 | Surface | Average (hourly)* |
Convective Rain Rate | kg m-2 s-1 | Surface | Average (hourly) |
Large Scale Rain Rate | kg m-2 | Surface | Average (hourly) |
Convective Snowfall Rate | m s-1 | Surface | Average (hourly) |
Large-Scale Snowfall Rate | m s-1 | Surface | Average (hourly) |
Convective Snow Amount | kg m-2 | Surface | Accumulation (hourly) |
Large-Scale Snow Amount | kg m-2 | Surface | Accumulation (hourly) |
Water Equivalent of Accumulated Snow Depth | kg m-2 | Surface | Accumulation (hourly) |
Convective Water Precipitation | kg m-2 | Surface | Accumulation (hourly) |
Large Scale Water Precipitation (Non-Convective) | kg m-2 | Surface | Accumulation (hourly) |
Total Precipitation | kg m-2 | Surface | Accumulation (hourly) |
Cloud Base | m | Above ground level | Instantaneous (hourly)# |
Very Low Cloud Cover | % | Atmosphere Column | Instantaneous (hourly) |
Low Cloud Cover | % | Atmosphere Column | Instantaneous (hourly) |
Medium Cloud Cover | % | Atmosphere Column | Instantaneous (hourly) |
High Cloud Cover | % | Atmosphere Column | Instantaneous (hourly) |
Total Cloud Cover Assuming Random Overlap | % | Atmosphere Column | Instantaneous (hourly) |
Downward Long-Wave Radiation Flux | W m-2 | Surface | Average (hourly)* |
Downward Short-Wave Radiation Flux | W m-2 | Surface | Average (hourly)* |
Downward Short-Wave Radiation Flux | W m-2 | Top of Atmosphere | Average (hourly)* |
Net Long-Wave Radiation Flux | W m-2 | Surface | Average (hourly)* |
Net Long-Wave Radiation Flux | W m-2 | Top of Atmosphere | Average (hourly)* |
Net Short Wave Radiation Flux | W m-2 | Surface | Average (hourly)* |
Net Short Wave Radiation Flux | W m-2 | Top of Atmosphere | Average (hourly)* |
Sensible Heat Net Flux | W m-2 | Surface | Average (hourly)* |
Latent Heat Net Flux | W m-2 | Surface | Average (hourly)* |
Water Runoff | kg m-2 | Sub Surface | Average (hourly)# |
Water Runoff Rate | kg m-2s-1 | Sub Surface | Average (hourly)# |
Upward Water Rate | kg m-2 s-1 | Surface | Average (hourly)# |
Surface Temperature (skin) | K | Surface | Instantaneous (hourly)* |
Surface Pressure | Pa | Surface | Instantaneous (hourly) |
Mean Sea Level Pressure | Pa | Mean Sea Level | Instantaneous (hourly) |
Surface Roughness | m | Surface | Instantaneous (hourly)* |
0-0.1 m below ground Column-Integrated Soil Moisture | kg m-2 | Soil | Instantaneous (hourly) |
0.1-0.35 m below ground Column-Integrated Soil Moisture | kg m-2 | Soil | Instantaneous (hourly) |
0.35-1 m below ground Column-Integrated Soil Moisture | kg m-2 | Soil | Instantaneous (hourly) |
1-3 m below ground Column-Integrated Soil Moisture | kg m-2 | Soil | Instantaneous (hourly) |
Soil Temperature (0-0.1 m below ground) | K | Soil | Instantaneous (hourly) |
Soil Temperature (0.1-0.35 m below ground) | K | Soil | Instantaneous (hourly) |
Soil Temperature (0.35-1 m below ground) | K | Soil | Instantaneous (hourly) |
Soil Temperature (1-3 m below ground) | K | Soil | Instantaneous (hourly) |