Elsevier

Atmospheric Research

Volume 196, 1 November 2017, Pages 83-96
Atmospheric Research

Association of atmospheric pollution and instability indices: A detailed investigation over an Indian urban metropolis

https://doi.org/10.1016/j.atmosres.2017.04.033Get rights and content

Highlights

  • Effect of air pollutants on severe convection has been studied over urban metropolis.

  • Pollutants (NO2, SO2, BC and PM2.5) inhibit the severe convective growth over India.

  • KLURT index is newly proposed to predict severe convective events over urban region.

  • KLURT has a prediction efficiency of 75%, false alarm of 35% with 1 h lead time.

  • This study provides totally new concept to measure and predict severe thunderstorms.

Abstract

Convection has a significant role in maintaining the atmospheric dynamics and thermodynamics, particularly in the tropical regions during pre-monsoon season, which may be due to the changing patterns in atmospheric instability and pollution. A critical analysis is done on the variability of instability indices and their significant signature to meteorological parameters and atmospheric pollution over Indian region in the warming atmosphere during 2005–2015. The present study represents that the solid as well as gaseous pollutants, in combination, produce a damping force in suppressing convective activities over the eastern coastal regions of India. A significant anti-correlation (r ~  0.6 to − 0.8) between instability parameters [Convective Available Potential Energy (CAPE) and Lifted Index (LI)] and atmospheric pollutants [gaseous (NO2 and SO2) and solid (BC and PM2.5)] has been obtained in the eastern coastal regions on a long-term basis. To improve the level of agreement between pollution and instability, a unitless and dimensionless index called KLURT index has been introduced, which provides correlation (r) value as high as ~ 0.6. On a real time basis, KLURT index is found to be useful as an effective precursor of thunderstorm events. The final part of this study indicates a prediction technique using KLURT index which gives a high prediction efficacy of 75%, low FAR value, extremely good BS 0.06, an excellent bias (~ 0.96) and a good lead time of 1 h for a threshold value of 12.5 in terms of predicting intense convections at the urban location, Kolkata. Thus, the present study provides an appropriate means to manifest convection as a function of changing anthropogenic factors both in long and short-term basis with high correlation values and provides significant efficacy in predicting severe weather, thereby demonstrating the usefulness of this hypothesis in various socio-economic aspects especially at the current tropical urban location.

Section snippets

List of acronyms

CAPEConvective Available Potential Energy
LILifted Index
NO2nitrogen dioxide
SO2sulphur dioxide
BCblack carbon
PM2.5particulate matter (size < 2.5 μm)
FARfalse alarm rate
BSBrier score
COcarbon monoxide
NWPnumerical weather prediction
PPMperfect prognostic method
RPG-HATPRORadiometer Physics GmbH-Humidity and Temperature Profiler
KIK-Index
TTITotal Totals Index
NCEPNational Center for Environmental Prediction
VWSHvertical wind shear
ULWSupper-level wind shear
LLWSlow-level wind shear
SSTsea surface

Experimental set-up and dataset used

Meteorological parameters and instability indices have been taken by a ground based Dicke radiometer (RPG-HATPRO) stationed at the rooftop of Institute of Radio Physics and Electronics, University of Calcutta, located at Kolkata (22°32′N, 88°20′E), India for the present study. It measures brightness temperatures at two frequency bands which are then converted to several atmospheric parameters using suitable retrieval methodologies (Chakraborty and Maitra, 2016). Table 1 indicates the brief

Variation of atmospheric instability parameters over the Indian sub-continent

Three factors emerge as important ingredients for strong convective development. They are moisture content, atmospheric instability and sufficient lifting force. As mentioned earlier, the atmospheric instability mainly refers to an irregularity in atmospheric temperature lapse rate profiles leading to localized air heating and intense updrafts on the onset of severe convective events. Saha et al. (2014) showed that the thunderstorm frequency has reduced at Kolkata in the past decade. In lieu of

Conclusions

The decrease in the CAPE, KI, TTI and increase in LI are responsible for the decrease of severe thunderstorm events during the study period. There is a sole anti-correlation between the instability indices and wind speed, which also determines the increasing stability of the atmosphere during the past 16 years. Based on the physical significances of the three instability indices, a new simpler index, KLURT index, has been designed which will be a pre-cursor for any convective phenomena and will

Acknowledgements

U.S. thankfully acknowledges the financial assistance provided by University Grants Commission (UGC), New Delhi, India, under the scheme of Dr. D.S. Kothari Post-Doctoral Fellowship (No. F.4-2/2006(BSR)/ES/15-16/0022). This work has also been partly supported under the collaboration of Banaras Hindu University, Varanasi and University of Calcutta, Kolkata. The authors acknowledge with thanks the West Bengal Pollution Control Board, Kolkata for providing us continuous pollution chart for our

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