Some Features of Black Carbon Aerosols Connected with Regional Climate Over Pristine Environment

The authors report the results of aethalometer black carbon(BC)aerosol measurements carried out over a rural(pristine)site,Panchgaon,Haryana State,India during the winter months of 2021-2022 and 2022-2023.They are compared with collocated and concurrent observations from the Air Quality Monitoring Station(AQMS),which provides synchronous air pollution and surface meteorological parameters.Secular variations in BC mass concentration are studied and explained with variations in local meteorological parameters.The biomass burning fire count retrievals from NASA-NOAA VIIRS satellite,and backward airmass trajectories from NOAA-ERL HYSPLIT Model analysis have also been utilized to explain the findings.They reveal that the north-west Indian region contributes maximum to the BC mass concentration over the study site during the study period.Moreover,the observed BC mass concentrations corroborate the synchronous fire count,primary and secondary pollutant concentrations.The results were found to aid the development of mitigation methods to achieve a sustainable climate system.

Influence of Meteorology on Particulate Matter (PM) and Vice-Versa over Two Indian Metropolitan Cities

This present study addresses the relationship between Particulate Matter (PM) and meteorological parameters over two metropolitan cities in India (Delhi and Pune) together with the Potential sources contribution function (PSCF) in order to understand the role of the transport on the variability of PM for a period of one year. To examine the variations of PM, over different time scales (diurnal and seasonal), at different observational locations, diurnal scales, are shown that maximum values of standard deviations (SD) are found in early hours of morning around 10AM, and later hours in the night over Delhi, however, the maximum values of SD are found in the morning hours around 8 to 10 AM over Pune. The relationship between PM and meteorological parameters is studied and explains a positive relationship between wind speed and planetary boundary layer height (PBLH), with a PM. Also, analyses on the Potential source contributions function (PSCF) over Delhi show that higher source contributions are observed during months of November, December and January over the region of Indo Gangetic Plain (IGP) plane north and Eastward of Delhi. Similarly, over Pune, most of the time, the source contribution in terms of pollution in Pune is coming from the south-east and eastern part of India, except in the winter season in the months of (December, January, and February). This analysis clearly suggests that the orography is played a pivotal role over the variations of PM over Pune.

Lidar Measurements of Aerosols in the Tropical Atmosphere

Measurements of atmospheric aerosols and trace gases using the laser radar (lidar) techniques, have been in progress since 1985 at the Indian Institute of Tropical Meteorology, Pune (18°32'N, 73°51'E, 559 m AMSL), India. These observations carried out during nighttime in the lower atmosphere (up to 5.5 km AGL), employing an Argon ion / Helium-Neon lidar provided information on the nature, size, concentration and other characteristics of the constituents present in the tropical atmosphere. The time-height variations in aerosol concentration and associated layer structure exhibit marked differences between the post-sunset and pre-sunrise periods besides their seasonal variation with maximum concentration during pre-monsoon / winter and minimum concentration during monsoon months. These observations also revealed the influence of the terrain of the experimental site and some selected meteorological parameters on the aerosol vertical distributions. The special observations of aerosol vertical profiles obtained in the nighttime atmospheric boundary layer during October 1986 through September 1989 showed that the most probable occurrence of mixing depth lies between 450 and 550 m, and the multiple stably stratified aerosol layers present above the mixing depth with maximum frequency of occurrence at around 750 m. This information on nighttime mixing depth / stable layer derived from lidar aerosol observations showed good agreement with the height of the ground-based shear layer / elevated layer observed by the simultaneously operated sodar at the lidar site.

Application of X-band Polarimetric Phased-array Radars in Quantitative Precipitation Estimation

The performance of different quantitative precipitation estimation(QPE) relationships is examined using the polarimetric variables from the X-band polarimetric phased-array radars in Guangzhou,China.Three QPE approaches,namely,R(ZH),R(ZH,ZDR) and R(KDP),are developed for horizontal reflectivity,differential reflectivity and specific phase shift rate,respectively.The estimation parameters are determined by fitting the relationships to the observed radar variables using the T-matrix method.The QPE relationships were examined using the data of four heavy precipitation events in southern China.The examination shows that the R(ZH) approach performs better for the precipitation rate less than 5 mm h-1, and R(KDP) is better for the rate higher than 5 mm h-1, while R(ZH,ZDR) has the worst performance.An adaptive approach is developed by taking the advantages of both R(ZH) and R(KDP) approaches to improve the QPE accuracy.

Large Scale Aspects of India-China Summer Monsoon Rainfall

This study investigates the dominant modes of variability in monthly and seasonal rainfall over the India-China region mainly through Empirical Orthogonal Function (EOF) analysis. The EOFs have shown that whereas the rainfall over India varies as one coherent zone, that over China varies in east-west oriented bands. The influence of this banded structure extends well into India.Relationship of rainfall with large scale parameters such as the subtropical ridge over the Indian and the western Pacific regions, Southern Oscillation, the Northern Hemispheric surface air temperature and stratospheric winds have also been investigated. These results show that the rainfall over the area around 40°N, 110°E over China is highly related with rainfall over India. The subtropical ridge over the Indian region is an important predictor over India as well an over the northern China region. '

An overview of studies of observed climate change in the Hindu Kush Himalayan (HKH) region

The Hindu Kush Himalayan (HKH hereafter) region is characterized by mountainous environments and a variety of regional climatic conditions. High-altitude regions in the HKH have the recent warming amplifications, especially during the global warming hiatus period. The rapid warming cause solid state water (snow, ice, glacier, and permafrost) to shrink, leading to increase in meltwater and there have been found more frequent incidences of flash floods, landslides, livestock diseases, and other disasters in the HKH region. Increasing awareness of climate change over the HKH region is reached a consensus. Meanwhile, the HKH region is often referred to as the water towers of Asia as many highaltitude regions store its water in the form of snow and/or glacier, feeding ten major large rivers in Asia. Therefore, the impacts of climate change on water availability in these river basins have huge influences on the livelihood of large number of population, especially in downstream regions. However, the scarcity of basic hydro-meteorological observations particularly in high-altitude regions of HKH limits rigorous analysis of climate change. Most studies used reanalysis data and/or model-reconstructed products to explore the spatial and temporal characteristics of hydro-meteorological processes, especially for extreme events. In this study, we review recent climate change in the HKH region, and the scientific challenges and research recommendations are suggested for this high-altitude area.

NUMERICAL SIMULATION OF SSTA IMPACTS UPON THE INTERDECADAL VARIATION OF THE CROSS-EQUATORIAL FLOWS IN EASTERN HEMISPHERE

Impacts of regional sea surface temperature(SST)anomalies on the interdecadal variation of the cross-equatorial flows(CEFs)in Eastern Hemisphere are studied using numerical simulations with a global atmospheric circulation model(NCAR CAM3)driven with 1950-2000 monthly SSTs in different marine areas(the globe,extratropics,tropics,tropical Indian Ocean-Pacific,and tropical Pacific)and ERA-40reanalysis data.Results show that all simulations,except the one driven with extratropical SSTs,can simulate the interdecadal strengthening of CEFs around Somali,120oE,and 150oE that occurred in the midand late-1970s.Among those simulated CEFs,the interdecadal variability in Somali and its interdecadal relationship with the East Asian summer monsoon are in better agreement with the observations,suggesting that changes in the SSTs of tropical oceans,especially the tropical Pacific,play a crucial role in the interdecadal variability of CEFs in Somali.The interdecadal change of CEFs in Somali is highly associated with the interdecadal variation of tropical Pacific SST.As the interdecadal warmer(colder)SST happens in the tropical Pacific,a"sandwich"pattern of SST anomalies,i.e."+,-,+"("-,+,-"),will occur in the eastern tropical Pacific from north to south with a pair of anomalous anticyclone(cyclone)at the lower troposphere;the pair links to another pair of anomalous cyclone(anticyclone)in the tropical Indian Ocean through an atmospheric bridge,and thus strengthens(weakens)the CEFs in Somali.

Observations of NO_2 and O_3 during Thunderstorm Activity Using Visible Spectroscopy

Simultaneous observations for the total column densities of NO2,O3 and H2O were carried on using the portable Spectrometer (438-450 nm and 400-450 nm) and the visible Spectrometer (544.4-628 nm) during premonsoon thunderstorms and embedded hail storm activity at Pune (18°32'N & 73°51'E),India.These observations confirm the fact that there is an increase in O3 and NO2 column densities during thunderstorms.The increase in O3 was observed following onset of thunderstorm,while the increase in NO2 was observed only after the thunder flashes occur.This implies that the production mechanisms for O3 and NO2 in thunderstorm are different.The observed column density of NO,value (1 to 3×1017molecules cm-2) during thunderstorm activity is 10 to 30 times higher than the value (1×10th molecules cm-2) of a normal day total column density.The spectrometric observations and observations of thunder flashes by electric field meter showed that 6.4×1025molecules/flash of NO2 are produced.The increased to-oil column density of ozone during thunderstorm period is 1.2 times higher than normal (clear) day ozone concentration.The multiple scattering in the clouds is estimated from H2O and O2 absorption bands in the visible spectral region Considering this effect the calculated amount of ozone added in the global atmosphere due to thunderstorm activity is 0.26 to 0 52 DU,and the annual production of ozone due to thunderstorm activity is of the order of 4.02×10 molecules/year The annual NO2 production may be of the order of 2.02×1035molecules/year.

Tropical Stratospheric Circulation and Monsoon Rainfall

Interannual variability of both SW monsoon (June-September) and NE monsoon (October-December) rainfall over subdivisions of Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu have been examined in relation to monthly zonal wind anomaly for 10 hPa, 30 hPa and 50 hPa at Balboa (9°N, 80°W) for the 29 year period (1958-1986). Correlations of zonal wind anomalies to SW monsoon rainfall (r = 0.57, significant at 1% level) is highest with the longer lead time (August of the previous year) at 10 hPa level suggesting some predictive value for Coastal Andhra Pradesh. The probabilities estimated from the contingency table reveal non-occurrence of flood during easterly wind anomalies and near non-occurrence of drought during westerly anomalies for August of the previous year at 10 hPa which provides information for forecasting of performance of SW monsoon over Coastal Andhra Pradesh. However, NE monsoon has a weak relationship with zonal wind anomalies of 10 hPa, 30 hPa and 50 hPa for Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu.Tracks of the SW monsoon storms and depressions in association with the stratospheric wind were also examined to couple with the fluctuations in SW monsoon rainfall. It is noted that easterly / westerly wind at 10 hPa, in some manner, suppresses / enhances monsoon storms and depressions activity affecting their tracks.

Seasonal and Interdecadal Variations of Heat Transport over the Northern Hemisphere

Using NCEP/NCAR reanalysis data, variations of heat transport in the Northern Hemisphere were studied. It was found that there are interdecadal variations in heat transport from middle latitudes to higher latitudes. The variations of interdecadal heat transport over longitudes around 120°E are out of phase with those over around 90°E and over the Northeastern Pacific. The seasonal variations of heat transport were also discussed. It was found that most heat is transported in the lower layer of the troposphere from middle latitudes to higher latitudes. Over around 120°E and over around 120°W, the seasonal and interannual variations of heat transport across 32.5°N are apparent and in phase.

Diurnal Evolution of Urban Heat Island and Its Impact on Air Quality by Using Ground Observations (SAFAR) over New Delhi

The paper presents a study of urban heat island (UHI) intensity and its impact on air quality by using the System of Air Quality Forecasting and Research (SAFAR) network observations over Delhi during the clear sky month of December of 2013 and 2015. It is found that in the month of December 2013 and 2015 the UHI shows a peak in late evening around 20:00 hrs. The concentration of PM2.5 shows a bimodal peak in the month of December of both the years 2013 and 2015 which is due to the enhanced anthropogenic activity during the traffic hours. The formation of UHI during the late evening traffic hours is due to the enhancement in the concentration of PM2.5 due to the enhanced anthropogenic activity with higher ground heat flux and lower PBLH and wind speed which leads to both the years 2013 and 2015 during the month of December. It is also found that UHI intensity shows a positive correlation (r = 0.57) with PM2.5 concentration and a negative correlation (r = -0.40) with wind speed and the PM2.5 concentration also shows a negative correlation (r = -0.57) with wind speed during December 2013. Whereas during December 2015 it has found that UHI intensity has a positive correlation (r = 0.65) with PM2.5 concentration and a negative correlation (r = -0.45) with wind speed and the PM2.5 concentration also shows a negative correlation (r = -0.57) with wind speed.

Cloud Condensation Nuclei over the Bay of Bengal during the Indian Summer Monsoon

The first measurements of cloud condensation nuclei （CCN） at five supersaturations were carried out onboard the research vessel ＂Sagar Kanya＂ （cruise SK-296） from the south to the head-bay of the Bay of Bengal as part of the Continental Tropical Convergence Zone （CTCZ） Project during the Indian summer monsoon of 2012. In this paper, we assess the diurnal variation in CCN distributions at supersaturations from 0.2% to 1% （in steps of 0.2%） and the power-law fit at supersaturation of 1%. The diurnal pattern shows peaks in CCN concentration （NccN） at supersaturations from 0.2% to 1% between 0600 and 0700 LST （local standard time, UTC＋0530）, with relatively low concentrations between 1200 and 1400 LST, followed by a peak at around 1800 LST. The power-law fit for the CCN distribution at different supersaturation levels relates the empirical exponent （k） of supersaturation （%） and the Nccy at a supersaturation of 1%. The Nccy at a supersaturation of 0.4% is observed to vary from 702 cm-3 to 1289 cm-3, with a mean of 961 ＋ 161 cm-3 （95% confidence interval）, representing the CCN activity of marine air masses. Whereas, the mean Nccy of 1628 ＋ 193 cm-3 at a supersaturation of 1% is higher than anticipated for the marine background. When the number of CCN spectra is 1293, the value of k is 0.57 ± 0.03 （99% confidence interval） and its probability distribution shows cumulative counts significant at k ≈ 0.55 ± 0.25. The results are found to be better at representing the features of the marine environment （103 cm-3 and k ≈ 0.5） and useful for validating CCN closure studies for Indian sea regions.

The Variability of the Interannual Oscillations of the Indian Summer Monsoon Rainfall

A new method of analysis namely, Singular Spectrum Analysis (SSA) is applied to the Indian Summer Monsoon (June-September) Rainfall (ISMR) series. The method is efficient in extracting the statistically significant oscillations with periods 2.8 and 2.3 year from the white noise of the ISMR series. The study shows that 2.8 / 2.3 year cycle captures the variability of the ISMR related to Southern Oscillation / Quasi Biennial Oscillation. The temporal structure of these oscillations show that these are in phase in extreme (excess and drought) monsoon conditions as well as in El Nino Southern Oscillation (ENSO) years. Both these oscillations show minimum variability during the period 1920-1940 and there is an increasing trend in the variability of these oscillations in the recent decades. The study enables to obtain pure signal consisting of reconstructed time series using these two Oscillations, from the original white noise series.

On the Spatio-Temporal Variations of the Tropopause Height over India and Indian Summer Monsoon Activity

The spatio-temporal variation of the tropopause height (TH) over the Indian region (5°N-35°N, 70°E-95°E) has been studied using monthly mean TH data, for 22-year period, 1965 to 1986. The study revealed that the stations south of 20° showed maximum TH in April / May and minimum in September. This variation in TH has been attributed to the corresponding variation of average sea surface temperature (SST) over ± 20° latitudinal belt over Indian Ocean, Arabian Sea and Bay of Bengal. Further the stations north of 20°N showed maximum in June and minimum in October/ November. This maximum in TH has primarily been attributed to the increased insolation and convection. Furthermore it is noticed that the anomaly of TH moved northwards during the period April to July.The interannual variability of the Indian Summer Monsoon Activity (ISMA) has been studied in relation to all India mean TH (at 12 GMT) for six months April through September. The composites of mean TH for good and bad monsoon years showed that all India mean TH is statistically higher in good monsoon years than in bad monsoon years. The relationship between ISMA and all India mean May TH has been studied using the contingency table. The study suggested that the forecast of ISMA could be prepared using mean May TH.

Signatures of a Universal Spectrum for Nonlinear Variability in Daily Columnar Total Ozone Content

Continuous periodogram analyses of sets of 50 to 364 daily mean atmospheric columnar total ozone content at19 globally representative stations indicate that the power spectra fOllow the universal inverse power law form of thestatistical normal distribution. The results are consistent with prediction of a cell dynamical system model for atmospheric flows extending up to the stratosphere and above. The unique quantification for nonlinear variability of dailyatmospheric total ozone implies predictability of the total pattern of fluctuations.

Effect of Counter-Gradient in the Computation of Turbulent Fluxes of Heat and Moisture in a Regional Model

The counter-gradient terms in the computations of turbulent fluxes of heat and moisture have been included in the PBL parameterization of a regional model for monsoon prediction. Results show that inclusion of counter-gradient terms has a marginal impact in the prediction of large scale monsoon circulation and rainfall rates.

Seasonal Variation of Urban Heat Island and Its Impact on Air-Quality Using SAFAR Observations at Delhi, India

This paper discussed the urban heat island (UHI) intensity and local air quality by using observational data of project of the System of Air Quality Forecasting and Research (SAFAR) over Delhi during the month of May and December 2013. It is found that UHI magnitudes ~2.2°C and ~1.5°C are formed at the evening traffic hours during May and December respectively. Also, intensity of UHI °C over daytime is referred as Urban Cool Island (UCI) during May and December. The diurnal PM2.5 concentration shows a bimodal pattern with peaks at morning and evening traffic hours during May and December. The planetary boundary layer height (PBLH) values show higher in magnitude during the daytime and lower in magnitude during the night-time. Whereas, the Ground Heat Flux values are lower during the daytime and higher during the night-time. The wind speed shows lower values during the UHI and higher magnitudes during the UCI formation hours. Concentration of PM2.5 and wind speed shows a strong negative correlation during May (r = -0.56, p = 0.002) and December (r = -0.57, p = 0.001) at C V Raman (CVR) site, however, high values in the concentration of PM2.5 during the low wind speed favour the condition for the formation of UCI. The regression analysis indicated that PM2.5 plays a significant role in the daytime cooling and nighttime warming over the urban areas during the low wind speed condition.

Aircraft Observations of Electrical Conductivity in Warm Clouds

Aircraft observations of electrical conductivity and cloud microphsical, dynamical and other electrical parameters were made in warm stratocumulus and cumulus clouds forming during the summer monsoon seasons (June-September) of 1983 and 1985 in the Deccan Plateau region, India. A Gerdien type cylindrical condenser was used for the measurement of electrical conductivity. The variations in the electrical conductivity are observed to be closely associated with the updrafts and downdrafts in the cloud, liquid water content, cloud droplet charge and corona discharge current. The value of electrical conductivity in warm clouds is found to be in the order of 10-12 ohm-1 m-1 which is two orders higher than that observed in clear-air at cloud-base levels in some regions by other investigators.Classical static electricity concepts predict reduced conductivity values inside clouds. Cloud electrical conductivity measurements, particularly in warm clouds are few and the results are contradictory. The recently identified mechanism of vertical mixing in clouds lends support to convective charge separation mechanism with inherent larger than clear-air values for cloud electrical conductivity and therefore consistent with the measurements reported herein.

Modelling of Indian Monsoon Rainfall Series by Univariate Box-Jenkins Type of Models

The time domain approach, i.e. Autoregressive (AR) processes, of time series analysis is applied to the monsoon rainfall series of India and its two major regions, viz. North-West India and Central India. Since the original time series shows no modelable structure due to the presence of high interannual variability, a 3-point running filter is applied before exploring and fitting appropriate stochastic models. Out of several parsimonious models fitted, AR(3) is found to be most suitable. The usefulness of this fitted model is validted on an independent datum of 18 years and some skill has been noted. These models therefore can be used for low skill higher lead time forecasts of monsoon. Further the forecasts produced through such models can be combined with other forecasts to increase the skill of monsoon forecasts.

Power and Cross-Spectra for the Turbulent Atmospheric Motion and Transports in the Domain of Wave Number Frequency Space: Theoretical Aspects

The study of large-scale atmospheric turbulence and transport processes is of vital importance in the general circulation of the atmosphere. The governing equations of the power and cross-spectra for the atmospheric motion and transports in the domain of wave number frequency space have been derived. The contributions of the nonlinear interactions of the atmospheric waves in velocity and temperature fields to the conversion of kinetic and potential energies and to the meridional transports of angular momentum and sensible heat in the atmosphere have been discussed.