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Background, Aim, and Scope: The present study is an attempt to examine some of the probable causes of the unusually low tropospheric column ozone observed over eastern India during the exceptional drought event in July 2002., Method: We examined horizontal wind and omega (vertical velocity) anomalies over the Indian region to understand the large-scale dynamical processes which prevailed in July 2002. We also examined anomalies in tropospheric carbon monoxide (CO), an important ozone precursor, and observed low CO mixing ratio in the free troposphere in 2002 over eastern India., Results and Discussion: It was found that instead of a normal large-scale ascent, the air was descending in the middle and lower troposphere over a vast part of India. This configuration was apparently responsible for the less convective upwelling of precursors and likely caused less photochemical ozone formation in the free troposphere over eastern India in July 2002., Conclusion: The insight gained from this case study will hopefully provide a better understanding of the process controlling the distribution of the tropospheric ozone over the Indian region.

Vertical profiles of carbon monoxide (CO) and ozone retrieved from Tropospheric Emission Spectrometer have been analyzed during two super cyclone systems Mala and Sidr. Super cyclones Mala and Sidr traversed the Bay of Bengal (BOB) region on April 24-29, 2006 and November 12-16, 2007 respectively. The CO and ozone plume is observed as a strong enhancement of these pollutants in the upper troposphere over the BOB, indicating deep convective transport. Longitude-height cross-section of these pollutants shows vertical transport to the upper troposphere. CO mixing ratio ~90 ppb is observed near the 146-mb level during the cyclone Mala and near 316 mb during the cyclone Sidr. Ozone mixing ratio ~60-100 ppb is observed near the 316-mb level during both the cyclones. Analysis of National Centers for Environmental Prediction (NCEP) reanalysis vertical winds (omega) confirms vertical transport in the BOB.

Abstract: To investigate the effects of decadal solar variability on ozone and temperature in the mesosphere of the Northern tropics, data obtained from the Halogen Occultation Experiment (HALOE) aboard Upper Atmospheric Research Satellite (UARS) during the period 1992–2005 are analyzed using a multifunctional regression model. The inferred annual-mean solar signal in ozone is found to be insignificant in the lower mesosphere whereas it is of the order of 5%/100sfu in the upper mesosphere. Seasonal variation of ozone response to solar variability indicates a strong positive response (22–30%/100sfu) during summer and autumn between 5E-3 and 0.01mb pressure levels (∼80–85km). The annual mean temperature response is found to be of the order of 0.5–1K/100sfu. Significant positive temperature response is observed during winter and autumn in the lower mesosphere and during summer and spring in the upper mesosphere. Results obtained in the present study are also compared with the results obtained by other workers. [Copyright &y& Elsevier]

The Model for Ozone and Related chemical Tracers-2 (MOZART-2) is used to examine the evolution of pollutant O3 in the upper troposphere over the Indian region. Vertical profiles of ozone mixing ratio retrieved from Microwave Limb Sounder (MLS) aboard Earth Observing System (EOS) AURA satellite for the period 2005-2009 and Tropospheric Emission Spectrometer (TES) aboard (EOS) AURA for the period 2006-2007 has been analyzed. The satellite observations reveal the evidence of downward propagation of ozone (100-200 ppb) due to stratospheric intrusion during the winter and pre-monsoon seasons. The regular feature of enhancement of ozone in the upper troposphere over India is presented. Results obtained by the MOZART-2 simulations (for years 2000-2005) confirm the observations and indicate stratospheric intrusion of O3 during winter and pre-monsoon seasons. Observed enhanced O3 mixing ratio in the upper troposphere is explained by, variation of Potential Vorticity (PV), tropopause pressure, relative humidity and CO-O3 correlation. [ABSTRACT FROM AUTHOR]

To investigate the effects of decadal solar variability in ozone, data obtained from the Halogen Occultation Experiment (HALOE) onboard Upper Atmospheric Research Satellite (UARS) during the period 1992-2004 have been analysed using a multifunctional regression model. Solar effects on ozone are analysed over the 0-30˚ N and 0-30˚ S belts. The solar effect on ozone is found to be significant in most of the stratosphere (2 ± 1.1 to 4 ± 1.6%/100 sfu). It is negligible in the lower mesosphere whereas it is of the order of 5%/100 sfu in the upper mesosphere. These observed results are in reasonable agreement with model simulations. Results indicate a hemispheric symmetry in the tropics. Results obtained in the present study are also compared with the results obtained by other workers. [ABSTRACT FROM AUTHOR]

Spatiotemporal variation of Semi-Annual Oscillation (SAO) in temperature and ozone over the tropical-subtropical belts (40° N-40° S) was studied using Microwave Limb Sounder data for the period 1992-1999. Wavelet analysis followed by cross-wavelet analysis was performed to study interannual variations in amplitude and phases of SAO and to determine the definite relationship between them. Latitude-height cross-sections of amplitudes of temperature and ozone SAO exhibit a peak near the Equator. The peak in amplitude of temperature SAO is at a higher altitude (ca 2 hPa) than that in ozone SAO (ca 6 hPa). The peak in amplitude of ozone SAO is almost symmetrical around the Equator but, in temperature SAO, it is asymmetrical around the Equator. The phase structure reveals that the temperature SAO descends faster than the ozone SAO. Cross-wavelet analysis shows an antiphase relation between the amplitude of the temperature and ozone SAO in the upper stratospheric region, whereas an in-phase relation exists in the lower stratospheric region. [ABSTRACT FROM AUTHOR]

Abstract: Spatiotemporal variations of the quasi-biennial oscillation (QBO) in temperature and ozone over the tropical–subtropical belts (40°N–40°S) have been studied using Microwave Limb Sounder data for the period 1992–1999. Wavelet analysis has been performed to study inter-annual variations in amplitude and phases of the QBO. Latitude-height cross-sections of the amplitudes of temperature and ozone QBO exhibit a double-peak structure near the equator. Phase structure reveals that the temperature QBO descended faster than the ozone QBO. Cross-wavelet analysis shows an anti-phase relation between the amplitudes of the temperature and ozone QBO in the upper stratospheric region, whereas in-phase relation exists in the middle stratospheric region. [Copyright &y& Elsevier]

Latitude-altitude structure of ozone QBO over the tropical-subtropical stratosphere (40° S–40° N) has been explored by analyzing Microwave Limb Sounder (MLS) aboard Upper Atmospheric Research Satellite (UARS) data for the period 1992–1999 using the multifunctional regression model. The inferred ozone QBO shows two maxima located at 22 hPa and 10 hPa with coefficient of 2–3% per 10 m/s centered at the equator. The equatorial maxima are out of phase with each other. Subtropics exhibit two peak structure near 14 hPa but of opposite sign to that of equatorial maximum near 10 hPa. Over the equatorial region, positive (zonal winds westerly) coefficients overlay negative (zonal winds easterlies) coefficients which descend with time. A pattern of equatorial maximum and two subtropical minima appears in the months December to February near 10 hpa and it propagates upward with progression of seasons. Equatorial QBO is seasonally asynchronous while subtropical QBO is seasonally synchronous. [ABSTRACT FROM AUTHOR]

Abstract: Temperature and ozone trends in the stratosphere are investigated using Halogen Occultation Experiment (HALOE) aboard Upper Atmospheric Research Satellite (UARS) observations for the period 1992–2004, over the tropics of Northern Hemisphere (0–30°N). The regression analysis of temperature time series indicates a significant annual cooling trend of 1–3K/decade in the free stratosphere. A cooling trend of ∼2±0.6K/decade near 25km which increases with altitude to reach a maximum around 35km and then decreases to 1±1.1K/decade near stratopause is computed. The observed maximum cooling trend near 35km may be viewed with caution due to the change over of temperature from National Centre for Environmental Prediction (NCEP) reanalysis data to HALOE instrument. A statistically significant decreasing ozone trend in the lower stratosphere is also obtained which becomes negligible above 40km. Attempt has been made to compute the seasonal trend components in both temperature and ozone. Seasonal distribution of temperature trends shows a maximum cooling during winter. The largest negative ozone trend is found during autumn with a peak (8–10% per decade) near 30km. [Copyright &y& Elsevier]

In this work, we compare for the first time different anthropogenic NO X emission inventories and examine the associate variation in simulated surface ozone (O 3 ) in India. Six anthropogenic NO X emission inventories namely Emission Database for Global Atmospheric Research (EDGAR), Intercontinental Chemical Transport Experiment-Phase B (INTEX-B), Regional Emission Inventory in Asia (REAS), MACCity, Indian National Emission Inventory (India_NOx), and Top-Down NO X emission inventory for India (Top-Down) are included in the comparison. We include these emission inventories in regional chemical transport model WRF-Chem to simulate tropospheric column NO 2 and surface O 3 mixing ratios for the month of summer (15-March to 15-April) and winter (December) in 2005. Predicted tropospheric column NO 2 using different NO X emission inventory are evaluated with the OMI satellite observations. All emission inventories show similar spatial features, however uncertainty in NO X emissions distribution is about 20–50% over rural regions and about 60–160% over the major point sources. Compared to OMI, the largest bias in simulated tropospheric NO 2 columns is seen in the REAS (−243.0 ± 338.8 × 10 13 molecules cm −2 ) emission inventory, followed by EDGAR (−199.1 ± 272.2 × 10 13 molecules cm −2 ), MACCity (−150.5 ± 236.3 × 10 13 molecules cm −2 ), INTEX-B (−96.8 ± 199.5 × 10 13 molecules cm −2 ), India_NOx (−87.7 ± 159.9 × 10 13 molecules cm −2 ) and Top-Down (−30.8 ± 69.6 × 10 13 molecules cm −2 ) inventories during winter. Simulations using different NO X emission inventories produces maximum deviation in daytime 8-h averaged O 3 of the order of 9–17 ppb (15–40%) in summer and 3–12 ppb (5–25%) in winter over most of the land area. The simulation suggests that choice of NO X emission inventories have significant effect on surface O 3 concentration for air quality studies over India. [ABSTRACT FROM AUTHOR]