Solar cycle 24 from December 2008 to December 2019 had an unusual progression and was the weakest cycle in a century, providing an ideal scenario to study perceivable effect of wave forcing from lower atmosphere. This study examines the... more
Solar cycle 24 from December 2008 to December 2019 had an unusual progression and was the weakest cycle in a century, providing an ideal scenario to study perceivable effect of wave forcing from lower atmosphere. This study examines the ionospheric response to meteorological phenomenon of sudden stratospheric warming (SSW) during solar cycle 24 (Arctic winter 2008/2009 to 2018/2019) using Global Positioning System‐derived total electron content (VTEC) and its deviation from monthly median (ΔVTEC) for four longitudinal chains. Each chain comprises eight stations, covering varied latitudes in both hemispheres. A longitude‐ and latitude‐dependent response of VTEC is observed within ∼3 weeks of peak polar stratospheric temperature anomaly (ΔTmax), with maximum variations seen for low‐latitude stations at American and Australian‐East Asian sectors. It is seen that variations during minor warming events are comparable or at times even larger than during major warming events. These responses increase with an increase in solar activity, with major SSW events primarily seen during moderate and low solar activity periods and minor SSW during high solar activity period. Under similar ionizing conditions, a quite similar ionospheric response is observed irrespective of ΔTmax and of SSW type (major or minor); however, under similar SSW strength, no prominent pattern in ionospheric response is observed. Latitude‐dependent semidiurnal ionospheric behavior is observed for only a few events. This vertical coupling between lower and upper atmosphere during SSW is predominantly influenced by 13–16 days periodicities in VTEC, along with other periodicities of 9, 7, 5, and 3 days.
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The devastating flood episode (16–17 June 2013) at Kedarnath (Uttrakhand, India), caused a huge loss of lives and loss of physical/material wealth. To understand this catastrophic event, rainfall/convective data and associated climate... more
The devastating flood episode (16–17 June 2013) at Kedarnath (Uttrakhand, India), caused a huge loss of lives and loss of physical/material wealth. To understand this catastrophic event, rainfall/convective data and associated climate meteorological parameters are investigated. A low-pressure zone with very high cloud cover (60–90 %) and relative humidity (70–100 %), associated with low (< 4 m s<sup>−1</sup>) wind velocity, are observed over the Kedarnath region during 15–17 June. The cause of this disaster seems to be heavy and continuous rainfall, associated with snowmelt and the overflooding/collapse of Chorabari Lake, located upstream. Monsoon advancement was much faster than usual, due to the presence of the convectively active phase of the Madden–Julian oscillation.
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Climate is among the most important natural resources for all living beings. The main external and internal driver for climate change is variability of the Sun. The Sun is the ultimate source of the energy on the Earth and play a key role... more
Climate is among the most important natural resources for all living beings. The main external and internal driver for climate change is variability of the Sun. The Sun is the ultimate source of the energy on the Earth and play a key role in its climate change. What is still not known and needs to be found is the extent to which these variations in solar behavior affect the total energy that the Sun emits. The small variation in the solar irradiance and changes in its spectral distribution leads to a large variation in climate. An attempt has been made to report the present understanding of the solar variability and its consequences on the variability of solar irradiance which exhibits 11-year cyclic variation and modulation on higher time scale. Galactic Cosmic Rays (GCR) reaching the Earth's atmosphere is modulated by the solar wind and geomagnetic field, which also exhibit 11-year cyclic variation. In the present paper, we have reviewed our current understanding on physics of...
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ABSTRACT With an aim to study the year-to-year changes in physical, optical, and radiative properties of polar aerosols, special observation campaigns were conducted during three consecutive summers of 2010, 2011 and 2012 over Ny-Ålesund... more
ABSTRACT With an aim to study the year-to-year changes in physical, optical, and radiative properties of polar aerosols, special observation campaigns were conducted during three consecutive summers of 2010, 2011 and 2012 over Ny-Ålesund (78.9°N, 11.9°E, 42 m AMSL), Arctic, employing a ground-based Multi-channel Solar-radiometer (MICROTOPS II Sun- photometer). In the present study, the columnar Aerosol Optical Depth (AOD) at λ = 500 nm and the Angstrom exponent (α) data sets are used to analyse the daily mean AOD and α by using a liner regression (best-fit) method. The results highlight that the columnar aerosol optical depth (mean AOD@500 nm for the study period) is 0.144 ± 0.05. Signature of secondary aerosol formation through marine sources based on variation in two wavelength AODs is also studied. These columnar AOD measurements over the study region are found to be in good agreement within experimental limitations with the synchronous MODIS satellite derived values. The 3 years’ α mean value is found to be 0.797 ± 0.328 within the range of 0.01–1.4. The frequency of occurrence and relative frequency histograms of α exhibited two modes centred at around 1.2 and 0.8. The primary and secondary modes reveal that the marine aerosols in the study region are mixed type, and they contribute about 44%, with the accumulation particles alone contributing about 31%. We found a close correspondence between aerosol optical properties and local meteorological conditions over the experimental location. The aerosol radiative forcing estimations revealed higher negative aerosol radiative forcing (indicating cooling) at Bottom-of-the-Atmosphere (BOA) and positive radiative forcing (indicating warming) in the Atmosphere (ATM) and Top-of-the-Atmosphere (TOA) during 2012 as compared to those obtained during 2010 and 2011, which is consistent with the observed AOD and α. The airmass back-trajectory model analysis also showed intrusion of anthropogenic aerosols from neighbouring regions into the study region, particularly during the year 2012.
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Analysis of monthly mean data of lightning and convective rain for the region 8° N - 35° N, 60° E - 120° E and for the period 1998-2010 show that lightning and convective rain are not significantly influenced by solar parameters such as... more
Analysis of monthly mean data of lightning and convective rain for the region 8° N - 35° N, 60° E - 120° E and for the period 1998-2010 show that lightning and convective rain are not significantly influenced by solar parameters such as sunspot number, total solar irradiance (TSI) and solar radio flux whereas CAPE anomaly and temperature anomaly have significant impact on the total lightning flash rate and convective rain during ENSO periods. Further no significant relation between cosmic ray flux and total lightning flash rate during La Nina period is obtained. On the other hand, for the El Nino period and for the total period, we get statistically some significant negative correlation between cosmic ray flux and total lightning flash rate. However, it is not possible to make any comment on the general relation between cosmic ray flux and total lightning flash rate due to contaminating global effects, regional effects and cloud microphysics. In the monthly variation of the paramete...
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Thunderstorms and the lightning that they produce are inherently interesting phenomena that have intrigued scientists and mankind in general for many years. The study of thunderstorms has rapidly advanced during the past century and many... more
Thunderstorms and the lightning that they produce are inherently interesting phenomena that have intrigued scientists and mankind in general for many years. The study of thunderstorms has rapidly advanced during the past century and many efforts have been made towards understanding lightning, thunderstorms and their consequences. Recent observations of optical phenomena above an active lightning discharge along with the availability of modern technology both for data collection and data analysis have renewed interest in the field of thunderstorms and their consequences in the biosphere. In this paper, we review the electrification processes of a thunderstorm, lightning processes and their association with global electric circuit and climate. The upward lightning discharge can cause sprites, elves, jets, etc. which are together called transient luminous events. Their morphological features and effects in the mesosphere are reviewed. The wide spectrum of electromagnetic waves generate...
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ABSTRACT While the formation of new atmospheric aerosol particles and their subsequent growth have been observed under diverse environmental conditions globally, such observations are very scarce over Indian subcontinent. Here, we present... more
ABSTRACT While the formation of new atmospheric aerosol particles and their subsequent growth have been observed under diverse environmental conditions globally, such observations are very scarce over Indian subcontinent. Here, we present the systematic analysis for new particle formation (NPF) from two distinct urban locations in India during April-May of two consecutive years. Particle size distributions were measured at Pune (18.53 degrees N, 73.85 degrees E) during 16 April-23 May, 2012 and at Kanpur (26.46 degrees N, 80.32 degrees E) during 16 April-23 May, 2013. The campaign mean total particle number concentration in the similar size range of 4-135 nm at Pune (12.2 x 10(3) cm(-3)) was higher than at Kanpur (7.9 x 10(3) cm(-3)), whereas the estimated total condensation sink (CS4-750) at Pune (16.2 x 10(-3) s(-1)) was lower than at Kanpur (33.3 x 10(-3) s(-1)). Despite lower particle number concentrations at Kanpur, larger particle sizes resulted in higher condensation sink than at Pune. The mean particle mode diameter at Kanpur was found larger by a factor of similar to 1.8 than at Pune. NPF events were observed commonly at both sites, with lower frequency at Kanpur (14%) than that at Pune (26%). The derived particle growth rates, GR, and the formation rates of 5 nm particles, J(5), ranged from 3.4 to 133 nm h(-1) and 0.4 to 13.9 cm(-3) s(-1), respectively, which are generally comparable to typical values reported in previous studies. Generally, the particle growth rates were found higher at Kanpur, whereas the formation rates were higher at Pune. It appears that the presence of pre-existing large particles at Kanpur than at Pune suppressed formation rates and favored particle growth. Overall, NPF occurred at lower condensation sink, lower RH, higher solar radiation, and higher temperature.
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Simultaneous measurements of the small, intermediate and large positive ions and air-Earth current density made at a coastal station, Maitri (70°45′52″S, 11°44′03″E, 130 m above sea level), at Antarctica during January–February 2005, are... more
Simultaneous measurements of the small, intermediate and large positive ions and air-Earth current density made at a coastal station, Maitri (70°45′52″S, 11°44′03″E, 130 m above sea level), at Antarctica during January–February 2005, are reported. Although small and large positive ion concentrations do not show any systematic diurnal variations, variations in them are almost similar to each other. On the other
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In the present study, the atmospheric electric field observations are reported at Gulmarg station, Kashmir (34°05′N; 74°42′E) for a period of 1 year: June 2019–May 2020. The observation site is situated in an area with high thunderstorm... more
In the present study, the atmospheric electric field observations are reported at Gulmarg station, Kashmir (34°05′N; 74°42′E) for a period of 1 year: June 2019–May 2020. The observation site is situated in an area with high thunderstorm activity and very high radon concentration. Diurnal characteristics of PG are explained with electrode effect under summer/dry surface conditions and evaporation effect under winter/wet surface conditions associated with sunrise. The latter effect is highly responsible for the diurnal peak of PG observed in afternoon (1300 LT) hours along with the water vapour pressure under low temperature. Similarly, excess positive charges found at the electrode layer shift the diurnal peak to an earlier time ~1000–1100 LT under turbulent exchange from the surface. Therefore, the annual mean curve is the resultant of these two effects that act in different seasons. In addition, the annual diurnal variation of the potential gradient is in agreement with some other continental stations having two maxima and higher values of PG during the winter months. The secondary diurnal maximum (2000 LT) is likely due to African thunderstorm activity being reflected strongly at our measurement site. Comparison of our results with Carnegie leads to a weak correlation between the two, which is due to the difference in the nature of observation sites, while a comparison with the observations of B N Raina (August 1970–October 1973) at the same observatory reveals a similar nature of PG variation. Finally, simple correlation plots of PG with meteorological parameters and radon concentration have been shown. The results indicate that radon concentration and meteorological parameters like temperature, relative humidity in addition to water vapour pressure are important local factors influencing the surface PG measurements at our site.
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Abstract The Microtops II ozonometer has been deployed to continuously measure the total column ozone (TCO), precipitable water content (PWC) and aerosol optical thickness (AOT) at Atigre village (16.74° N, 74.37° E, 604 m above sea... more
Abstract The Microtops II ozonometer has been deployed to continuously measure the total column ozone (TCO), precipitable water content (PWC) and aerosol optical thickness (AOT) at Atigre village (16.74° N, 74.37° E, 604 m above sea level, masl) located on the southeastern slope of Indian western Ghats. The Microtops II ozonometer measurements during the period from September 2017 to June 2018 were analyzed along with the retrieved products of Ozone Monitoring Instrument (OMI) and Moderate Resolution Imaging Spectroradiometer (MODIS) onboard NASA's Terra satellites and also the ERA-interim reanalysis model. We found that the TCO (or PWC) data from the OMI (or MODIS) and the ERA reanalysis model data products are in good agreement. The measurements showed strong seasonal variability such that TCO was lowest in the winter season but increased in the summer season, and both PWC and AOT were lowest in the post-monsoon season and increased in the summer season. In continuous ERA-interim reanalysis TCO observations, we found the three types of periodicities in the daily mean TCO as well as PWC (i) The weekly (7 days), (ii) quasi-biweekly (14 to 16 days), (iii) Madden Julian Oscillations (MJO) (30–60 days) oscillations. These oscillations depend on the periodic weather changes in the troposphere. We also observe that the average day to day variability in daily mean TCO observations in the observational period is about 1.4%, 1.1%, 2.62% in the Microtops II ozonometer, ERA-interim reanalysis, and OMI data respectively. We found the positive correlation between daily mean AOT and PWC in all seasons (except monsoon), which is maximum in the winter season, showing the hygroscopic nature of aerosols. The sources of water vapor and aerosol at our location are also studied using back-trajectory analysis.