Sink mechanism for significantly low level of ozone over the Arabian Sea during monsoon

Measurement of surface ozone over the Arabian Sea during the southwest monsoon season (June-September) of 2002 has shown an unusually low level of ozone with an overall average of 9 nmol/mol. Such a low level of ozone could not be explained by simulations using a three-dimensional chemistry transport model, Model for Ozone and Related Tracers (MOZART), which accounts for the known processes of advective transport and includes a standard photochemical mechanism. Thus, for the Arabian Sea region, we propose for the first time that destruction of ozone by reactive halides released from sea salt aerosols is the sink mechanism which played a crucial role in ensuring the significantly low ozone level over the Arabian Sea. Theoretical calculations constrained by observations have shown that, on average, ozone losses due to catalytic action of halogens and due to photolysis plus chemical reaction amount to 2.15 nmol mol-1d-1 and 4.64 nmol mol-1d-1, respectively

radiative forcing of carbonaceous aerosols over two urban environments in northern india

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Variations in Mass of the PM 10 , PM 2.5 and PM 1 during the Monsoon and the Winter at New Delhi

ABSTRACT PM 10 , PM 2.5 and PM 1 mass concentrations have been measured at Delhi (28°35'N; 77°12'E) during the August to December 2007. The running mean of PM 10 , PM 2.5 and PM 1 data shows large variations. The PM 10 , PM 2.5 and PM 1 were ranged from 20 to 180 g/m 3 during the monsoon and from 100 to 500 g/m 3 during the winter (up to 1200 g/m 3 in November due to Deepavali fireworks). For the same running mean cycles, higher mass concentrations in the PM 10 , PM 2.5 and PM 1 were corresponded with peaks in the relative humidity and lower levels linked to peaks in the ambient temperature. The evolutions of PM 10 , PM 2.5 and PM 1 concentrations after the elapsed times are simulated with mean mass scavenging coefficients. These evolution patterns clearly show the difference in washout of PM 10 with impaction scavenging relative to those for PM 2.5 and PM 1 particles over different rainfall durations. Air-mass pathways traced with HYSPLIT model over the study area illustrates the nature of PM 10 , PM 2.5 and PM 1 levels with monsoon and winter airmass circulations over Delhi

Radiative Forcing of Black Carbon over Delhi

The radiative effects of black carbon (BC) aerosols over New Delhi, the capital city of India, for the period August 2010–July 2011, have been investigated using Santa Barbara DISTORT Atmospheric Radiative Transfer (SBDART) model in the present paper. The monthly mean BC concentrations in Delhi, an urban location, vary in between 15.935 ± 2.06 μg m−3 (December 2010)–2.44 ± 0.58 μg m−3 (July 2011). The highest value for monthly mean BC forcing has been found to be in November 2010 (66.10 ± 6.86 Wm−2) and the lowest in July 2011 (23 ± 3.89 Wm−2). Being the host city for the XIX Commonwealth Games (CWG-2010), government of Delhi set up a plan to reduce emissions of air pollutants during Games, from 03 October to 14 October, 2010. But opposite to the expectations, the emission controls implemented were not sufficient to reduce the pollutants like black carbon (BC), and therefore relatively a high value of BC radiative forcing (44.36 ± 2.4) was observed during the month of October 2010

Fractal dimensions of convective clouds around Delhi

189-192The results of the fractal analysis of convective clouds, observed within 100 km around Delhi during the summer (April to June) season of 1977 are presented. The study is based on the radar observations made with the help of a high power X-band radar. A total number of 397 radar echoes of convective clouds having areas between 4 and 984 km2 were analyzed for studying the relation between their perimeter (P) and area (A). A scatter plot of log P versus log A showed that there is a consistency of relation between the perimeter and the area of the cloud echoes for the entire range of the echo areas. The least square estimate of the fractal dimension (D) of the cloud echo perimeters has been found to be 1.42 with correlation coefficient of 0.994. This is in good agreement with the value D=1.35 arrived by S Lovejoy [Science (USA), 216 (1982) 185] for tropical clouds observed over the Indian ocean

A radar study of vertical growth and decay of convective clouds and associated variations of surface rainfall rate

230-234The results of a radar study of vertical growth rates, decay rates and durations of convective clouds observed in Delhi region during April-August 1982 have been presented. The study relating to 22 cloud cases showed that the vertical growth rates of their radar echoes varied between 0.9 and 25.0 m s-1 and the decay rates varied between 0.9 and 8.7 m s-1. Average echo duration was found to be 50 min. Variations of the cloud-echo top height with time and the associated surface rainfall rate (cloud-echo intensity near ground level) have been found to be positively correlated

Relationship between lightning activity over peninsular India and sea surface temperature

This paper presents a study of spatiotemporal variation of lightning activity over Peninsular India (8° -22°N, 72°-88°E) by using monthly satellite-based lightning flash grid (1° × 1°) data for a period of 10 yr (1998-2007). The data are examined in terms of spatial, annual, and seasonal distribution of the lightning activity. It is found that lightning activity is higher over south Peninsular India and eastern India. On a seasonal time scale, the lightning activity shows two maxima - first in the month of May and then in the month of September. The lightning activity in the monsoon period is noticed to be considerable because of the occurrence of the low-level jet and increase in the monsoon break period. During the postmonsoon, the activity is mainly due to the presence of the convective nature of the disturbed weather during the northeast monsoon season over most parts of the east coast of south Peninsular India. The relationship between lightning activity over Peninsular India and sea surface temperature in the bordering seas (Arabian Sea and Bay of Bengal) is also examined. The results disclose a significant link between them

Characteristics of layer type radar echoes around Delhi

8-14Some characteristics of the precipitation echoes from layer type clouds in Delhi region have been studied using radar observations made during 1960-1962. The study showed that the height of the layer echoes first observed varied between 3.0 and 13.0 km. Mean height of the first observed layer echoes was about 8 km in summer (April-June), 10 km during monsoon (July-September) and 7 km during winter (November-March). The depth of these echoes have been found to be usually in the range 0.5-6.0 km and horizontal extensions varied between wide limits ranging from 12 to 200 km. Occurrence of layer echoes preceded by convective development has been found to be maximum during summer while melting band feature occurred more frequently during monsoon. Rainfall rate and liquid water content I layer clouds as well as the percentage contribution towards season’s rainfall from such clouds have also been estimated

Fractal dimensions of convective clouds around Delhi

1-6Clouds exhibit fractal structure over wide ranges of scale. Following the method suggested by Love-joy [Science (USA), 216 (1982) 185], fractal analysis of convective clouds, observed within 100 km around Delhi during the monsoon season (July-September) of 1977, has been carried out. The study is based on the radar observations collected with a high power 3-cm weather radar. A total number of 2568 radar echoes of convective clouds having areas between 4 and 7420 km2 were analyzed for studying the relationship between their perimeters (P) and areas (A). The analysis showed that the relationship between the above two echo parameters can well be represented by a formula P~AD/2, where D is described as the fractal dimension of the cloud echo perimeter. However, it was found that the two fractal dimensions of the perimeters are required to describe the above perimeter-area relationship applicable for the entire range of cloud echo area. That is, D=1.34 for cloud echoes having areas up to 600 km2 and D=1.79 for echoes having areas greater than 600 km2

Surface ozone measurements over Himalayan region and Delhi, North India

391-398Measurement of surface ozone concentration has been made at two Himalayan stations, Mohal (during 19-26 May 1999 and 20-25 May 2000) and Kothi (during 27 May –1 June 1999 and during 27-31 May 2000) and at Delhi (during 2-5 June 2000). The study reveals that the average concentration of ozone at Mohal was 19.1 ppb during May 1999 and 26.1 ppb during May 2000. At Kothi , the average concentrations were 42.7 ppb and 23.0 ppb, respectively, and it was 38.3 ppb at Delhi. Diurnal variation of ozone at Mohal indicated the dominance of photochemical production mechanisms in both the years. Lack of diurnal signal was seen at Kothi over the period of observation in 1999 which suggests that there may be transport of ozone in the region from upper level of the atmosphere. During observational period in 2000, a weak diurnal variation of O3 was observed. It suggests that apart from photochemical production of ozone, some other mechanisms also contribute considerably to the observed O3 concentration. At Delhi also, the diurnal variation showed the influence of temperature on O3 production. Variation of  O3 concentration with O3  concentration at previous hour, temperature, relative humidity at previous hour and wind speed at individual locations and years showed a good degree of association of O3 with these parameters