Space and Atmospheric Science Area

The Space and Atmospheric Science research group in NESAC is devoted in conducting research to understand the atmospheric processes prevalent over the region through observation and modeling. The group also provides services related to disaster management support for floods, severe storms, lightning, etc, and providing meteorological data for different applications. Characterizing the major drivers of climate change and improving the short and medium range weather forecasting over North Eastern region (NER) of India are other key activities of the group. The centre is developing a Space and Atmospheric science research hub by procuring a series of equipments to study the aerosols, trace gases, solar radiation, upper atmosphere, atmospheric boundary layer, monsoon system, severe storms and lightning, etc. The emphasis is on developing a regional facility to conduct and promote research on Atmospheric and Space science in collaboration with the academic institutes and other research organizations. The major research areas of the group are mentioned below:


MWR at NESAC campus

Diurnal and seasonal variation of black carbon over Umiam

Aerosol and Radiation

Aerosols are the suspended solid or liquid particles in the atmosphere and are one of the major drivers of climate change. While natural aerosols are present everywhere, anthropogenic aerosols have variable concentration in atmosphere. NER of India, particularly the Brahmaputra valley is one of the highest aerosol concentrated area in India due to its geographical location. NESAC works towards scientific understanding of the optical, physical, dynamical and radiative processes responsible for the climatic impact of aerosols over NER of India. The main objectives include (a) development of a primary aerosol database over the NER; (b) characterization of optical and physical properties of aerosols; (c) temporal and spatial mapping of aerosols over the region (d) estimate the spatio-temporal variation of aerosol radiative forcing; (e) assimilation of local database in regional climate models for the assessment of potential climatic impact and; (f) take up studies on satellite based aerosol retrieval from Indian satellites. The activities in this area are done primarily under the national project, Aerosol Radiative Forcing over India (ARFI), coordinated by Space Physics Laboratory, Thiruvananthapuram

Data from several surface based instruments (Multi wavelength radiometer, Sunphotometer, Aethalometer, Nephelometer, Electric low pressure impactor, Microaeth, etc) and satellite derived aerosol products are used to characterize the aerosol. Continuous data from three fixed observatories (at NESAC, Umiam, Meghalaya; Tawang, Arunachal Pradesh; and Lachung, Sikkim) are used for the purpose. Additionally, land campaigns are also conducted to collect short term data over different locations over NER of India. Three such campaigns have been conducted along the East-West and North-South corridor of the NE region and also along the Northern Arunachal Pradesh


Land campaign track in NER

Spectral AOD along the campaign track

Atmospheric boundary layer Physics and Dynamics

The atmospheric boundary layer (ABL) is the lowest part of the atmosphere and its behavior is directly influenced by its contact with a planetary surface. The ABL plays an important role in modulating local weather and climate. The study of spatial and temporal characteristics of ABL parameters is very important to understand the mixing processes in the ABL, transport of mass, momentum and energy between the surface layer and free troposphere as well as air quality prediction and improvement of the atmospheric model. Mountainous terrain like the NER of India, with its pronounced steep slopes and complex topographic features, produces an intrinsic spatial inhomogeneity in the boundary layer response to surface forcing, making the process more complex

Several studies have been taken up to understand the surface-air interaction and exchange processes, energy and radiation balance of the Earth-atmosphere system, ABL and its coupling with free-troposphere, etc. Main objective of the activities are to improve the understanding and parameterization of the ABL processes in numerical models, diurnal evolution of ABL and its role in pollutant dispersal, atmospheric turbulence, surface roughness, hydrological processes, etc. The activities are carried out under the national project on Network of Observatories for Boundary Layer Experiments (NOBLE) of ISRO Geosphere Biosphere program. Data from several instruments like, SOund Detection And Ranging (SODAR), Automatic Weather Station (AWS), 31 meter Meteorological Tower equipped with 3D Sonic anemometer (CSAT3) and Pisharoty sonde (launched using hydrogen gas filled balloons) are used. To investigate the ABL evolution over a complex terrain and valley, 15 days land campaign was conducted during Feb-march, 2015. More than 120 Dr Pisharoty sonde and Dr Graw sonde were launched simultaneously from Guwahati and NESAC, Umiam to study the diurnal variation of katabatic and anabatic wind flow along the Brahmaputra valley.

Atmospheric Chemistry

The studies on Atmospheric chemistry are focused on characterization of major trace gases, understanding the chemical process of generation and dissipation of these gases, trace gas transport modeling, understanding the interaction between the atmospheric parameters and the trace gases, etc. Although the trace gases are found in very small quantity in atmosphere, they play a major in atmospheric heating by absorbing outgoing long wave radiation from the earth's surface and thus contributes to global warming. Besides contributing to the green house effect and contributing to global warming, presence of these gases in higher amount at surface level is extremely bad for human health and have adverse effect on biosphere. Except few trace gases like the ozone, majority of trace gases are originated from fossil fuel burning at industrial establishments, from vehicles, biomass burning, etc. Looking into the severity of the situation government has also initiated few programs like National Ambient Air Quality Measurement (NAAQS) and Air quality Index (AQI) to create awareness. Atmospheric science lab at NESAC is equipped with trace gas analyzers for measuring surface level concentration of SO2, CO, NOx , O3, CH4 and non methane hydrocarbons. Along with the in-situ measurement, satellite data are also taken into account to study the long term pattern of trace gases and their impact on environment. Forecasting of trace gas concentration using numerical models like WRF-CHEM and REGCM are also taken up.


Trace gas alayzers at NESAC

Variation of trace gases over Umiam

Numerical Weather Forecasting

North Eastern Region of India is vulnerable to various kinds of weather-induced natural hazards such as Flood, Landslides, Severe storms, Lightning, Cyclone. The NER of India suffers huge loss of lives and revenue due to the devastation brought by these extreme events. Early warnings of these events are vital for this region. Numerical Weather prediction (NWP) model is a powerful tool that is being used globally for early warning of weather events. NWP models are mathematical models that represent the evolution of atmospheric systems as accurate as possible depending on the precise analysis of the atmospheric state.

The Weather Research and Forecasting (WRF) model is used at NESAC to conduct research for improvement of short and medium range weather forecast over NER of India. The model is run using a high performance computing (HPC) facility available at NESAC. The model is configured with three nested domains with resolutions varying from 27 km to 3 km. Background error statistics for this region is generated using NMC method.


Flowchart of operational NWP model run at NESAC

HPC at NESAC

The potential of NWP models depend on the initial conditions employed for integrating the model. Observational data must be modified in a dynamically consistent fashion in order to obtain a suitable set for model initialization. Such processes are called Data Assimilation (DA). Constant efforts are being made to upgrade the quality of initial condition using various DA techniques such as 3DVAR, 4DVAR, Hybrid ETKF-3DVAR. Observed data from AWS stations, Radiosonde, GFS-Prepbufr and Satellites are used for data assimilation. As in situ measurements are not well distributed spatially, satellite plays an important role for this region. Radiances, wind data from satellites such as INSAT-3D, SCATSAT-1, AMSU, HIRS, MHS are assimilated in the model. Several experiments are done with Hybrid: Hybrid-50, where 50% weight is given to each static and ensemble based background error covariance (BEC) and Hybrid-75 where 75% weight is given to ensemble based BEC


A typical WRF model rainfall forecast

Comparison of 3DVAR, Hybrid-50, Hybrid-75

Model validation is done by comparing daily accumulated WRF rainfall with respect to AWS rainfall data and GPM IMERG (GPM-MS) rainfall product available at 0.1 x 0.1 degree resolution and temporal resolution of 30 min. The validation strategy entails the estimation of the performance metrics such as Bias, RMSD, ETS, Statistically Significant (p<0.05) Pearson's Correlation Coefficient (CC). Other meteorological parameters are compared with NCEP reanalysis, Era interim data, ASCAT Wind. WRF generated Rainfall data has been used since 2010 by NESAC hydrology team for Flood Early Warning System (FLEWS) project to operationally forecast flood over different flood prone river basins in NER

Severe Weather Nowcasting Services

Severe weather events like severe storms, lightning, intense rainfall, etc are very common over the NER of India. In India, each year lightning alone kills more than 2,500 people and it ranks first in terms of killing among all the natural calamities (Report of National Crime Record Bureau, India). The NER of India is also no different. With the constantly increasing use of electronic devices in the industrial and domestic sphere, the vulnerability to lightning damages is growing in leaps and bounds. Lightning is often associated with gusting winds, intense rainfall, hails, etc

NESAC has developed a methodology for nowcasting of severe thunderstorms by integrating data from weather stations, Doppler weather radars, satellites, and numerical weather prediction models. A thunderstorm potential map is prepared for entire NER of India, indicating the areas where thunderstorm development is expected within next three hours from the time of issue of the forecast. The forecast is made available through NESAC website and also are directly communicated to the concerned stakeholders in each state of NER of India


Lightning climatology over India for March-April-May months (based on LIS data)

Thunderstorm potential map over NER

Thunderstorm event over NER as seen from DWR

NESAC has also initiated research to provide location based lightning warning services. The data from lightning detectors from different network over NER of India are used and assimilated is numerical weather prediction models to provide location specific lightning as well as severe weather warning with an actionable lead time

Improving the surface observational network over NER of India

NESAC with support from ISRO, has been putting maximum effort to improve the surface based meteorological observations over the NER of India. Towards this 118 numbers of automatic Weather Stations (AWS) and one S-band Doppler Weather Radar (DWR) has been installed in NER of India. The AWS records hourly data on rainfall, wind speed, wind direction, atmospheric pressure, relative humidity, temperature and Sun shine duration. The data is stored in a local data logger in addition to transmitting to meteorological and oceanographic satellite data archival centre (MOSDAC), Space Applications Centre, Ahmedabad and put in their web site (http://mosdac.gov.in). The data from these AWS are being extensively used by Agriculture departments, water resource departments, etc. of state governments


Automatic Weather Station Network in NER

An installed AWS

The first polarimetric S-band radar in India is installed at Sohra (Cherrapunjee), Meghalaya. The radar provides continuous data on rainfall and wind over a circular area having radius of 300 km with the radar at the centre. The data from the radar is made available in real time through India Meteorological Department and MOSDAC websites. The data from the DWR are used primarily for the nowcasting of severe thunderstorms and operational forecasting by IMD and Indian Air Force (IAF)


The DWR at Sohra (Cherrapunjee)

Hon'ble PM of India dedicating the DWR to nation

A typical Max Z product from the DWR

Z vertical cut product developed by NESAC