S. L. Jain

On some aspects of tropospheric ozone variability over the Indo-Gangetic (IG) basin, India

To study tropospheric ozone variability over the Indo-Gangetic (IG) basin, monthly tropospheric ozone residual (TOR) data has been analysed for the 1979–2004 period. Tropospheric column ozone has been observed to have a maximum during late summer (48 ± 4.1 DU) and a minimum during late winter (30 ± 4.2 DU) over the IG basin. The amplitude of the seasonal cycle has been observed to be comparatively larger over the western part of the IG region (∼51 ± 2.3 DU) than over the central (∼47 ± 3.2 DU) and eastern parts (∼47 ± 3.2 DU) of the region. Similarly, the seasonal variation in tropospheric ozone has been observed to be comparatively larger over the western part of the IG region (∼22 DU) than over the central (∼18 DU) and eastern parts (∼17 DU) of the region. The difference in tropospheric ozone amount over the eastern and western parts of the IG region also shows seasonal variation with a large difference (up to 4 DU) during the monsoon season. The monsoon system plays an important role in the seasonal variation of the tropospheric ozone over the different parts of the IG region.

Global distribution of tropospheric ozone and its precursors: a view from space

Satellite-borne tropospheric ozone measurements obtained from the tropospheric ozone residual (TOR) method, CO from the MOPITT (at 850 hPa level) measurements and NO2 from the SCIAMACHY measurements for the three-year period 2003–2005 have been utilized to examine the distribution of the pollutant sources and long-range transport on a global scale. Elevated tropospheric ozone columns have been observed over regions of high NO2 and CO concentrations in the northern and southern hemispheres. High levels of the tropospheric ozone column have been observed below about 5°S in the vicinity of the biomass burning regions and extend from continents out over the Atlantic during October. The seasonal distribution of tropospheric O3 and its precursors in the southern hemisphere shows the strong correlation with the seasonal variation of biomass burning in Africa and South America. Northern hemisphere summer shows the widespread ozone and CO pollution throughout the middle latitudes. The inter-hemispheric gradient of ozone and CO found to be decreased during October. Large-scale transport of the ozone and CO over the Atlantic and Pacific Oceans has been clearly identified. Strong inter-continental transport has been observed to occur from west to east along with the mid-latitude winds in the northern hemisphere.

Depolarization ratio measurement using single photomultiplier tube in micropulse lidar

The conventional dual polarization micropulse lidar uses two separate photomultiplier tubes (PMT) to detect both the copolarized and cross-polarized beam. The prominent sources of error in the depolarization ratio measurement are mismatch in PMT, improper selection of discriminator threshold and unequal PMT high voltage. In the present work a technique for the measurement of lidar depolarization ratio using only one PMT sensor has been developed. The same PMT detects both copolarized and cross-polarized lidar backscatter. A stepper motor is used along with the mirrors to bring both the received polarization signals over the PMT window. Application of the same PMT minimizes the error caused in the depolarization ratio measurement due to error in photon counting of an individual channel. The design description of this technique along with the preliminary results depicting its functionality has been mentioned in this article.

Tropospheric ozone variability over the Indian coastline and adjacent land and sea

A tropospheric ozone variability study is carried out to investigate the spatial and temporal distribution over the coastline of the Indian peninsula and adjacent land and sea using NASA Langley Tropospheric Ozone Residual data set for the period 1979–2005. A strong seasonal cycle has been observed with large variation (∼ 55%) over the upper eastern coast, followed by the upper and lower western coast, compared to the lower eastern coast (∼ 33%). A negative gradient in ozone concentration is observed along eastern and western coasts during summer (slope ∼ –0.78 and –0.65) and a positive gradient (slope ∼ 0.16 and 0.21) during winter. The same is observed over the adjacent land and sea along the coastline with slight variation. This change in gradient can be attributed to the anthropogenic emission of precursor gases that reinforce localized photochemical production of ozone. In addition, topography, transport, seasonality of emission of precursor gases and the solar insolation cycle play a vital role.

Observations and model calculations of direct solar UV irradiances in the Schirmacher region of east Antarctica

Measurements of direct UV irradiances (using a MICROTOPS II Sunphotometer) carried out from a high‐latitude site, Antarctica are presented. The instantaneous irradiances at 305±0.9, 312±0.9 and 320±1.0 nm during a no‐ozone‐hole (13 December 2004) and an ozone‐hole (4 October 2004) period have been observed to be about 0.031, 0.150 and 0.299 W m−2 and 0.010, 0.049 and 0.102 W m−2, respectively at local noontime. The observations of the direct UV irradiances at 305±0.9, 312±0.9 and 320±1.0 nm are compared with tropospheric ultraviolet visible (TUV) radiation transfer model calculations. The model estimate shows that, during the ozone‐hole period, a loss of ozone of the order of 44% leads to an increase in irradiance of the order of 410%, 90% and 25% at 305±0.9, 312±0.9 and 320±1.0 nm, respectively. The relationship between change in UV irradiance due to a change in column ozone is obtained using a TUV model and irradiances thus estimated from this relationship are found to compare well with the observed irradiances.

Comparative study of the total ozone column over Maitri, Antarctica during 1997, 2002 and 2003

The total ozone (TOZ) column was measured using a Microtop Sun‐photometer at Maitri (70° 45′ S, 11° 44′ E), Antarctica during the 16th, 21st and 22nd Indian Scientific Expedition to Antarctic. A comparative study of the TOZ column at Maitri, Antarctica was made to understand the behaviour of the ozone hole. The observations showed a direct relationship between the stratospheric temperature anomaly and year‐to‐year variation in TOZ. The minimum TOZ observed at Maitri, Antarctica during spring was 135 DU (Dobson unit), 185 DU and 126 DU in 1997, 2002 and 2003, respectively. The ozone hole in 2003 was much deeper and had a longer duration. The observations showed that chemical loss of ozone over Maitri during the ozone hole period in 2003 was increased by 18.6% when compared with 1997 and 42% when compared with 2002. The observations at Maitri also showed an event of major stratospheric warming along with surface warming during 2002. A temporary sudden rise in the TOZ column before the recovery period (days 300–315) was also observed and found to be overlapping in all the observational years.