Presentation on theme: "Characterisation of Aerosols over Indo- Gangetic Basin during Winter Season By Hiren Jethva Ph.D. Student Centre for Atmospheric & Oceanic Sciences Indian."— Presentation transcript:
Characterisation of Aerosols over Indo- Gangetic Basin during Winter Season By Hiren Jethva Ph.D. Student Centre for Atmospheric & Oceanic Sciences Indian Institute of Science Bangalore-12
Plan of Talk Why Aerosol Study??? Introduction & Data Specifications Satellite and In-situ observations AERONET Vs. MODIS Discussion Conclusions
Why Aerosol Study ??? Aerosols are tiny particles of liquid and solids suspended in the atmosphere. It plays a vital role in the earth's atmosphere through its ability to alter the radiation budget by scattering and absorption of incoming shortwave and outgoing longwave radiation. It is believed to be a major source of uncertainty in weather and climate prediction models due to its complex interaction with incoming shortwave and outgoing longwave radiation. In the present industrial era, aerosols become prime concern for causing air pollution and health related diseases.
Introduction In the recent past, the issue has been raised regarding the persistent and widespread air pollution over Indo-Gangetic basin during winter season. Human activities (biomass burning) in this region have been blamed for causing high air pollution. In the present study, the efforts has been made to characterize the aerosols over Indo-Gangetic basin using different data sources. The comparison of satellite retrieved products (MODIS) with in-situ measurements has been carried out to evaluate the performance of satellite retrieval. The possible reasons for the discrepancy between satellite retrieval and in-situ measurements has been discussed.
AERONET Technical Specification Ground-based aerosol measurement network Goal Assessment of aerosol optical properties and validation of satellite retrievals of aerosol properties
AERONET Technical Specification Standard Sunphotometer (CIMEL : 7 CE 318N VBS5) Polarized Sunphotometer (CIMEL CE 318N VPS8) Advanced Sunphotometer (CIMEL CE 318N EBS9) Aerosol Parameters (340 nm, 380 nm, 440 nm, 500 nm, 670 nm, 870nm, 1020 nm) Aerosol Optical Depth Abs. AOD Angstrom Exponent Single Scattering Albedo Aerosol Volume Size Distribution
Aerosol Number Size Distribution: Log-normal distribution Single-scattering Albedo:
MODIS Technical Specification Orbit: 705 km, 10:30 a.m. descending node (Terra) 1:30 p.m. ascending node (Aqua), sun-synchronous, near-polar, circular, cross track Swath Dimensions: 2330 km (cross track) by 10 km (along track at nadir) Spectral Bands : 36 Spatial Resolution: 250 m (bands 1-2) 500 m (bands 3-7) 1000 m (bands 8-36) Design Life: 6 years Moderate Resolution Imaging Spectroradiometer
We use data (1ºx1º) retrieved from first 7 spectral bands that are dedicated to Aerosol properties retrieval 1. AOD 2. Angstrom Exponent
Satellite Evidence of Aerosol Loading A large Aerosol Optical Depth (AOD) over Indo-Gangetic region as well over Bangladesh and north of Bay of Bengal from satellite MODIS. 4 th Dec 2001
14 Jan 2002
High AOD (550 nm) over Thar Desert and Punjab (High Mass Concentration and Low Ang. Exp. 0.3) that decreases in SE direction Ang. Exp. About 1.2 has been observed over southern edge of Himalaya Monthly Climatology from MODIS
Punjab Kanpur Aerosol Fine Fraction Mode
Satellite Observations A high Aerosol Optical Depth and Mass Concentration over Thar Desert, Punjab and Indo-Gangetic basin. A belt of high AOD ( ) moves from NW direction to SE from Oct to Jan period. Angstrom Exponent of 1.2 on southern edge of Himalaya and not over Indo-Gangetic basin!!! In-Situ Measurements ???
AERONET Observations Persistent high Aerosol Optical Depth (>0.5). Angstrom Exponent varies between 1 and 1.5 through out winter season!!!
Nov 2001 AOD Ang. Exp.
AOD Ang. Exp. Dec 2001
Nov 2002 AOD Ang. Exp.
A large difference in magnitude of Angstrom Exponent between AERONET and MODIS. Why ??? AOD at shorter wavelength (470 nm) is found to be higher in AERONET than in MODIS. AERONET MODIS
Single-scattering Albedo Fine Coarse Total Lower single-scattering albedo (coarse particles) during winter season. Internal Aerosol Mixing ???
Aerosol Volume Size Distribution Bi-modal Aerosol Size Distribution
Basis: The presence of UV absorbing particles reduces the spectral dependence of top of the atmosphere radiance from pure molecular atmosphere ( dependence) Advantages: Low surface reflectivity in UV spectrum Retrieve absorbing aerosols (dust and BC) A quarter of century data (from 1979 to present) Disadvantages: Low resolution (1.25 x 1 degree) Sub-pixel cloud contamination AI does not have physical meaning TOMS Aerosol Index
Dust episodes are well resolved but not biomass burning!
Monthly Climatology Winter
Monthly Climatology Summer
Monthly Climatology Monsoon
NCEP Monthly Wind Vector 850 mb
Satellite Retrieval of Aerosol Properties Satellite measured spectral radiance Filtering of aerosol back-scattered signal by estimating surface reflection Create a Look-Up tables with assumed (expected) aerosol models Pre-radiative transfer calculations for assumed (expected) aerosol models Match the satellite measured spectral radiances with Look-Up table Retrieval of Aerosol Model
Dark Target Approach Short wave surface reflection Vs mid-IR surface reflection
Assumed Regions of Aerosol Models in MODIS Retrieval
Conclusions A belt of aerosol loading has been observed over Indo-Gangetic basin through out the winter season from satellite MODIS images. In-situ measurements (AERONET) confirm high aerosol opacity over Kanpur station. The angstrom exponent is found to be underestimated by MODIS algorithm due to lower optical depth at shorter wavelength (470 nm). Coarser particles induces lower single-scattering albedo that gives the hint of internal aerosol mixing. Bi-modal aerosol volume size distribution indicates the presence of sub- micron as well as larger size particles over Kanpur station. TOMS Aerosol Index found to be a strong indicator of dust events and not biomass burning.
The persistent wind pattern in the basin may be responsible for widespread of aerosols. The inappropriate aerosol models and uncertainty in surface reflection estimation are believed to be the possible reason for the discrepancy between MODIS and AERONET