The ion–aerosol interactions from the ion mobility and aerosol particle size distribution measurements on January 17 and February 18, 2005 at Maitri,Antarctica – A case study

A case study for the ion–aerosol interactions is presented from the simultaneous measurements of mobility spectra of atmospheric ions in the mobility range of 2.29 to 2.98 × 10^− 4 cm² V^− 1 s^-1^{-1}(diameter range 0.41–109 nm) and of size distribution of atmospheric aerosol particles in the size ranges of 4.4–700 nm and 500–20,000 nm diameters made at Maitri (70°45^′52^{′ ′}S, 11°44^′2.7^{′ ′}E; 130 m above mean sea level), Antarctica, on two days January 17 and February 18, 2005, with contrasting meteorological conditions. In contrast to January 17, on February 18, winds were stronger from the morning to noon and lower from the noon to evening, atmospheric pressure was lower, cloudiness was more, the land surface remained snow-covered after a blizzard on February 16 and 17 and the airmass over Maitri, descended from an altitude of ~3 km after an excursion over ocean. On these days mobility spectra showed two modes, corresponding to intermediate ions and light large ions and an indication of additional one/two maxima for small/cluster ions and heavy large ions. The small ions generated by cosmic rays, and the nucleation mode particles generated probably by photochemical reactions grew in size by condensation of volatile trace gases on them and produced the cluster and intermediate ion modes and the Aitken particle mode in ion/particle spectra. Particles in the size range of 9–26 nm have been estimated to grow at the rate of 1.9 nm h^− 1 on February 18, 2005. Both, ions and aerosol particles show bimodal size distributions in the 16–107 nm size range, and comparison of the two size distributions suggests the formation of multiple charged ions. Attachment of small ions to particles in this bimodal distribution of Aitken particles together with the formation of multiple charged ions are proposed to result in the light and heavy large ion modes. Growth of the nucleation mode particles on February 18, 2005 is associated with the passage of the airmass over ocean. In contrast, though the ion size distributions were not much different, the aerosol size distributions did not show a dominant peak for the formation and growth of nucleation mode particles on January 17. More measurements are needed before the conclusion of this case study is generalized.     

Volatile properties of atmospheric aerosols during nucleation events at Pune,India

Continuous measurements of aerosol size distributions in the mid-point diameter range 20.5–500 nm were made from October 2005 to March 2006 at Pune (18°32′N, 73°51′E), India using Scanning Mobility Particle Sizer (SMPS). Volatilities of atmospheric aerosols were also measured at 40°, 125°, 175°, 300° and 350°C temperatures with Thermodenuder–SMPS coupled system to determine aerosol volatile fractions. Aerosols in nucleated, CCN and accumulated modes are characterized from the measured percentage of particles volatized at 40°, 125°, 175°, 300° and 350°C temperatures. Averaged monthly aerosol concentration is at its maximum in November and gradually decreases to its minimum at the end of March. The diurnal variations of aerosol concentrations gradually decrease in the night and in early morning hours (0400–0800 hr). However, concentration attains minimum in its variations in the noon (1400–1600 hr) due to higher ventilation factor (product of mixing height and wind speed). The half an hour averaged diurnal variation of aerosol number concentration shows about 5 to 10-fold increase despite the ventilation factor at higher side before 1200 hr. This sudden increase in aerosol concentrations is linked with prevailing conditions for nucleation bursts. The measurement of volatile fraction of ambient aerosols reveals that there are large number of highly volatile particles in the Aitken mode in the morning hours and these volatile fractions of aerosols at temperatures <150°C are of ammonium chloride and ammonium sulfate, acetic and formic acids.     

Changes in concentration and size distribution of aerosols during fog over the south Indian Ocean

Measurements of the concentration and size distribution of aerosol particles in the size-ranges of 0.5–20 μm and 16–700 nm diameters were made during six fog episodes over the south Indian Ocean. Observations show that concentrations of particles of all sizes start decreasing 1–2 hours before the occurrence of fog. This decrease is more prominent for coarse particles of >1 μm diameter and continues until 10–20 minutes before the onset of fog when particle concentrations in all size ranges rapidly increase by one/two orders of magnitude in ∼20 minutes. Thereafter, concentrations of particles of all sizes gradually decrease until the dissipation of fog. After the fog dissipation, concentrations of coarse mode particles rapidly increase and restore to their pre-fog levels but concentrations of the Aitken mode particles decrease slowly and reach their pre-fog levels only after 1–2 hours. The net effect of fog is to change the bimodal size distributions of aerosols with a coarse mode at 1.0 μm and an accumulation mode at 40–60 nm to a power law size distribution. It is proposed that the preferential growth and sedimentation of the coarse mode hygroscopic particles in the initial phase cause a large decrease in the aerosol surface area. As a result, the low vapour pressure gases which were initially being used for the growth of coarse mode particles, now accelerate the growth rates of the accumulation and Aitken mode particles.     

Velocity of small-scale auroral ionospheric current systems over Indian Antarctic station Maitri

The Indian Antarctic station Maitri (geog. 70‡45’S, 11‡45’E, geom. 66‡.03S, 53‡.21E) occupies a sub-auroral location during magnetically quiet conditions(Σκρ < 10), but attains an auroral position when the auroral oval shifts equatorwards with increasing strength of magnetic disturbance. At the latter times, triangulation with 3 fluxgate magnetometers located at the vertices of a suitable triangle provides a means of monitoring mobile auroral ionospheric current systems over Maitri. The spacing between the magnetometers is typically kept at 75–200 km, keeping in mind the scale-sizes of ∼ 100 km for these mobile current systems. This work reports the results of two triangulation experiments carried out around Maitri in January 1992 and January 1995, both during Antarctic summer. The velocities estimated for pulsations of the Pc4 and Pc5 type were about 0.59 km/sec in the direction 102‡.7 east of due north, in the first case, and about 1–3 km/sec in the second case in the east-west direction. While several magnetometer arrays exist in the northern auroral regions (e.g., the Alberta array in Canada, the Alaskan array in the U.S. and the IMS Scandinavian array), there is no report in literature of triangulation through arrays in Antarctica, except for a one-day study by Neudegget al 1995 for ULF pulsations of the Pc1 and Pc2 type. The velocities obtained for the Pi3 type of irregular pulsations over Antarctica in the present study tally well with those obtained for northern auroral locations.     

Retrieval of stratospheric O3 and NO2 vertical profiles using zenith scattered light observations

Daily zenith scattered light intensity observations were carried out in the morning twilight hours using home-made UV-visible spectrometer over the tropical station Pune (18‡31′, 73‡51′) for the years 2000–2003. These observations are obtained in the spectral range 462–498 nm for the solar zenith angles (SZAs) varying from 87‡ to 91.5‡. An algorithm has been developed to retrieve vertical profiles of ozone (O₃) and nitrogen dioxide (NO₂) from ground-based measurements using the Chahine iteration method. This retrieval method has been checked using measured and recalculated slant column densities (SCDs) and they are found to be well matching. O₃ and NO₂ vertical profiles have been retrieved using a set of their air mass factors (AMFs) and SCDs measured over a range of 87–91.5‡ SZA during the morning. The vertical profiles obtained by this method are compared with Umkehr profiles and ozonesondes and they are found to be in good agreement. The bulk of the column density is found near layer 20–25 km. Daily total column densities (TCDs) of O₃ and NO₂ along with their stratospheric and tropospheric counterparts are derived using their vertical profiles for the period 2000–2003. The total column, stratospheric column and tropospheric column amounts of both trace gases are found to be maximum in summer and minimum in the winter season. Increasing trend is found in column density of NO₂ in stratospheric, tropospheric and surface layers, but no trend is observed in O₃ columns for above layers during the period 2000–2003     

New particle formation by ion-induced nucleation during dissipation stage of thunderstorm

A case of new particle formation observed during dissipation stage of a thunderstorm at a tropical station, Pune, India on 3 June 2008 is reported. The flash rate and rainfall intensity increased as high as 110 flashes per 5 minutes and 150 mm hour^− 1 respectively during the active stage of thunderstorm, and then gradually decreased during the dissipation stage. The number concentration of particles in the size range of 10–100 nm sharply increased from 350 particles cm^− 3 to ∼8000 particles cm^− 3 during the dissipation stage of a thunderstorm and grew to larger diameter subsequently. Observations suggest that the atmospheric conditions such as (i) reduced background aerosol concentration after heavy rain, (ii) high humidity condition, and (iii) increased ion concentration during the dissipation stage by corona discharges, favoured generation of new particles by ion-induced nucleation (IIN). Observations also suggest that generation of unipolar ions by corona discharges may be more favourable for IIN and subsequent growth of the particles.     

北极黄河站秋季气团传输影响下大气气溶胶数谱分布特征

2013 年9月在北极黄河站开展了气溶胶数谱（10~400nm）的短期观测实验。数浓度小时平均值主要出现在300~400cm^-3,平均值为350cm^-3,高于新奥尔松Zeppelin 全球大气本底站及环北极海洋大气7-9月航测报道的浓度。大气气溶胶的三个模态（核模态、爱根核模态和积聚模态）数浓度平均分别为35、122和193cm^-3。观测期间没有发生新粒子生成事件,平均数谱分布呈现双模态的分布特征,模态峰值分别出现在30nm和115nm,由积聚模态主导。平均数谱分布的几何中值粒径出现在约100~110nm。从单颗粒分析结果来看,观测期间黄河站地区大气气溶胶主要以海盐气溶胶为主,但是在来自挪威海域和北欧大陆的气团影响下,也观测到煤烟颗粒、富硫颗粒物和含碳颗粒物等人为气溶胶。     

Detection of marine aerosols with IRS P4-Ocean Colour Monitor

The atmospheric correction bands 7 and 8 (765nm and 865nm respectively) of the Indian Remote Sensing Satellite IRS P4-0CM (Ocean Colour Monitor) can be used for deriving aerosol optical depth (AOD) over the oceans. A retrieval algorithm has been developed which computes the AOD using band 7 data by treating the ocean surface as a dark background after removing the Rayleigh path radiance in the sensor-detected radiances. This algorithm has been used to detect marine aerosol distributions at different coastal and offshore locations around India. A comparison between OCM derived AOD and the NOAA operational AOD shows a correlation ∼0.92 while that between OCM derived AOD and the ground-based sun photometer measurements near the coast of Trivandrum shows a correlation of ∼0.90.     

Records of climatic changes and volcanic events in an ice core from Central Dronning Maud Land (East Antarctica) during the past century

The depth profiles of electrical conductance, δ¹⁸O,²¹⁰Pb and cosmogenic radio isotopes¹⁰Be and³⁶Cl have been measured in a 30 m ice core from east Antarctica near the Indian station, Dakshin Gangotri. Using²¹⁰Pb and δ¹⁸O, the mean annual accumulation rates have been calculated to be 20 and 21 cm of ice equivalent per year during the past ∼ 150 years. Using these acumulation rates, the volcanic event that occurred in 1815 AD, has been identified based on electrical conductance measurements. Based on δ¹⁸O measurements, the mean annual surface air temperatures (MASAT) data observed during the last 150 years indicates that the beginning of the 19th century was cooler by about 2‡ C than the recent past and the middle of 18th century. The fallout of cosmogenic radio isotope¹⁰Be compares reasonably well with those obtained on other stations (73‡ S to 90‡ S) from Antarctica and higher latitudes beyond 77‡N. The fallout of³⁶Cl calculated based on the present work agrees well with the mean global production rate estimated earlier by Lal and Peters (1967). The bomb pulse of³⁶Cl observed in Greenland is not observed in the present studies – a result which is puzzling and needs to be studied on neighbouring ice cores from the same region.     

临安一次沙尘暴过程影响气溶胶物理化学特性演变的初步分析

文章利用2002年3月29日～4月4日在浙江临安大气本底污染监测站观测的气溶胶粒子质量谱、离子与元素成分的数据,结合TOMS卫星的气溶胶指数资料和轨迹模式,重点分析在北方沙尘暴输送影响期间临安气溶胶质量浓度尺度分布的演变特点以及气溶胶化学成分与不同空气来源的关系。初步分析结果显示,受北方沙尘暴天气影响,临安气溶胶质量浓度、离子、元素浓度有明显的尺度分布演变。这种演变与污染物来源和大气污染物的气粒转化有关。沙尘影响前和结束后临安地区气溶胶主要以细粒子为主(<2.1μm),峰值粒径0.65～2.1μm,而受北方地区的沙尘暴影响,峰值粒径偏移到2.1～3.3μm,且在7～11μm间出现另一个峰值,同时临安气溶胶粗粒子中矿物元素显著增加。从离子成分看,在整个观测期间SO^2-₄与NH⁺₄在细粒子段有很好的一致性,而SO^2-₄,NO^-₃与Ca²⁺在粗粒子段有很好的相关,尤其是沙尘影响期间NO^-₃与Ca²⁺有很好的对应关系,表现出较明显的表面非均相反应特征     

Airborne measurements of submicron aerosols across the coastline at Bhubaneswar during ICARB

Airborne measurements of the number concentration and size distribution of aerosols from 13 to 700 nm diameter have been made at four vertical levels across a coastline at Bhubaneswar (20°25′N, 85°83′E) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) programme conducted in March–April 2006. The measurements made during the constant-level flights at 0.5, 1, 2 and 3 km altitude levels extend ～100 km over land and ～150km over ocean. Aerosol number concentrations vary from 2200 to 4500 cm^?3 at 0.5 km level but are almost constant at ～ 6000 cm^?3 and ～ 800 cm^?3 at 2 and 3 km levels, respectively. At 1km level, aerosol number concentration shows a peak of 18,070 cm^?3 around the coastline. Most of the aerosol size distribution curves at 0.5 km and 1 km levels are monomodal with a maxima at 110nm diameter which shifts to 70 nm diameter at 2 and 3 km levels. However, at the peak at 1 km level, number concentration has a bimodal distribution with an additional maximum appearing in nucleation mode. It is proposed that this maxima in nucleation mode at 1 km level may be due to the formation and transport of new particles from coastal regions.     

Effect of relative humidity on the angular distribution of scattered light intensity for rural and urban aerosols

The change in atmospheric relative humidity affects the physical and optical properties of aerosol particles. It would be interesting to study the effect of an increase in relative humidity on the angular scattering of light by aerosols (by incorporating the changes due to it as the complex refractive index and the parameters of the size distribution function). In the present paper we have computed the angular scattering function for rural and urban aerosols, for light of wavelength 0.55 μn. The results obtained for these two models, representative of different environments, are interesting and show some discriminating features.     

Identification of a surface layer structure and analysis of humidity data in two weather situations at Jodhpur (26°18′N, 73°04′E), India,during MONTBLEX 1990

The Monsoon Trough Boundary Layer Experiment held in 1990 was a multi-institutional effort to probe the atmospheric boundary layer over the monsoon trough over northern India. For this experiment, four micrometeorological towers were set up at four different locations along the normal position of the trough. One such tower of 30m height was located at Jodhpur (26‡18′N, 73‡04′E), Rajasthan. The fast and slow response data available during the experiment have been used in the present study to determine a suitable layer-structure of the surface layer for evaluation of sensible heat flux using the multilayer hypothesis of Kramm (1989).     

Observations of the atmospheric surface layer parameters over a semi arid region during the solar eclipse of August 11th, 1999

This paper discusses the observations of the Atmospheric Surface Layer (ASL) parameters during the solar eclipse of August 11th, 1999. Intensive surface layer experiments were conducted at Ahmedabad (23‡21′N, 72‡36′E), the western part of India, which was close to the totality path. This rare event provided by nature is utilised to document the surface layer effects during the eclipse period using measurements of high frequency fluctuations of temperature, tri-axial wind components as well as mean parameters such as temperature, humidity, wind speed and subsoil temperature. Analysis showed that during the eclipse period, the turbulence parameters were affected leading to the suppression of the turbulence process, the main dynamic process in the atmospheric boundary layer, while the mean parameters showed variations within the natural variability of the observational period. The spectra of the wind components and temperature indicated decrease in spectral power by one order in magnitude during the eclipse period. The rate of dissipation of turbulent kinetic energy is found to decrease by more than one order during the eclipse period. The stability parameter showed a change from unstable to stable condition during the period of eclipse and back to unstable condition by the end of eclipse     

Study of total column atmospheric aerosol optical depth,ozone and precipitable water content over Bay of Bengal during BOBMEX-99

The spatial and temporal variations in aerosols and precursor gases over oceanic regions have special importance in the estimation of radiative forcing parameters and thereby in the refinement of general circulation models. Extensive observations of the columnar aerosol optical depth (AOD), total column ozone (TCO) and precipitable water content (PWC) have been carried out using the on-line, multi-band solar radiometers onboard ORV Sagar Kanya (Cruise # SK 147B) over Bay of Bengal during 11th–28th August 1999. Aerosol optical and physical properties (optical depth and angstrom parameter) have been estimated at six wavelengths covering from UV to NIR (380–1020 nm) while TCO and PWC have been determined using the UV band around 300 nm and NIR band around 940 nm, respectively. Added, concurrent meteorological and satellite observations during this field phase of BOBMEX-99 have been utilized to investigate spectral-temporal variations of AOD, TCO and PWC in marine environment. The results indicate lower AODs (around 0.4 at characteristic wavelength of 500 nm) and size distributions with abundance of coarse-mode particles as compared to those aerosols of typical land origin. An interesting result that is found in the present study is the significant reduction in AOD at all wavelengths from initial to later part of observation period due to cloud-scavenging and rain-washout effects as well as signature of coastal aerosol loading. The clear-sky daytime diurnal variation of TCO shows gradual increase during post-sunrise hours, broad maximum during afternoon hours and gradual decrease during pre-sunset hours, which is considered to be due to photochemical reactions. The diurnal variation curve of PWC showed maximum (~ 4 cm) during morning hours and gradual decrease (~ 3.5 cm) towards evening hours, which are found to be greater as compared to typical values over land. Another interesting feature observed is that although the PWC values are very high, there was no proportionate or appreciable enhancement in AOD—a feature that can be utilized to infer composition of aerosols over the study region.     

Controls on porphyroblast size along a regional metamorphic field gradient

Garnet-bearing schists from the Waterville Formation of south-central Maine provide an opportunity to examine the factors governing porphyroblast size over a range of metamorphic grade. Three-dimensional sizes and locations for all garnet porphyroblasts were determined for three samples along the metamorphic field gradient spanning lowest garnet through sillimanite grade, using high-resolution X-ray computed tomography. Comparison of crystal size distributions to previous data sets obtained by stereological methods for the same samples reveals significant differences in mode, mean, and shape of the distributions. Quantitative textural analysis shows that the garnets in each rock crystallized in a diffusion-controlled nucleation and growth regime. In contrast to the typical observation of a correlation between porphyroblast size and position along a metamorphic field gradient, porphyroblast size of the lowest-grade specimen is intermediate between the high- and middle-grade specimens’ sizes. Mean porphyroblast size does not correlate with peak temperatures from garnet-biotite Fe-Mg exchange thermometry, nor is post-crystallization annealing (Ostwald Ripening) required to produce the observed textures, as was previously proposed for these rocks. Robust pseudosection calculations fail to reproduce the observed garnet core compositions for two specimens, suggesting that these calc-pelites experienced metasomatism. For each of these two specimens, Monte Carlo calculations suggest potential pre-metasomatism bulk compositions that replicate garnet core compositions. Pseudosection analyses allow the estimation of the critical temperatures for garnet growth: ∼481, ∼477, and ∼485°C for the lowest-garnet-zone, middle-garnet-zone, and sillimanite-zone specimens, respectively. Porphyroblast size appears to be determined in this case by a combination of the heating rate during garnet crystallization, the critical temperature for the garnet-forming reaction and the kinetics of nucleation. Numerical simulations of thermally accelerated, diffusion-controlled nucleation, and growth for the three samples closely match measured crystal size distributions. These observations and simulations suggest that previous hypotheses linking the garnet size primarily to the temperature at the onset of porphyroblast nucleation can only partially explain the observed textures. Also important in determining porphyroblast size are the heating rate and the distribution of favorable nucleation sites.     

IMF BY dependence of the extent of substorm westward electrojet

In this paper the duskward extension of the westward auroral electrojet is investigated for substorm intervals on the basis of magnetograms recorded at the Indian Antarctic station, Maitri. The database comprises three years from 1998–2000. Based on an initial study of the magnetograms, an arbitrary local time of 2030 MLT is fixed to define the early manifestation of the substorm westward electrojet. Using this criterion 12 substorms are identified and the possible causes examined. Many of these events are observed to be associated with a moderate to intense ring current. The hourly average of the GSM B_Y-component of the interplanetary magnetic field (IMF) for the hour preceding the substorm onset at Maitri is negative for most of the events. It is suggested that the azimuthal shift of the auroral electrojets in the southern hemisphere resulting from a negative B_Y-component of the IMF influences the extent of the substorm westward electrojet. This finding implies that the IMF may have a role in controlling the longitudinal extent of substorm occurrence.     

Geomagnetic activity control on VHF scintillations over an Indian low latitude station, Waltair (17.7‡N, 83.3‡E, 20‡N dip)

Using the data of amplitude scintillations recorded at 244 MHz from the geostationary satellite, FLEETSAT (73‡E) at a low latitude station, Waltair (17.7‡N, 83.3‡E, 20‡N dip), during the increasing sunspot activity period of 1997–2000, the effect of the geomagnetic storms on the occurrence of ionospheric scintillations has been studied. A total of 60 SC storms studied during this period, following the Aarons’ criterion, reveals that the local time of onset of the recovery phase of the geomagnetic storms play an important role in the generation or inhibition of the ionospheric irregularities. Out of the 60 storms studied, nearly 60 to 70% satisfied the categories I, II and III of Aarons’ criteria. However, in the remaining 30 to 40% of the cases, no consistent results were observed. Thus, there is a necessity for further investigation of the effect of geomagnetic storms on ionospheric irregularities, particularly with reference to the altitude variations of the F-layer (h’F) relating to the changes in the local electric fields.     

Below-thunderstorm rain scavenging of urban aerosols in the health hazardous modes

A very high number concentration of aerosols in urban locations has a wide impact on health and ecosystem. The evolutions of urban aerosol distributions at elapse-time 30 and 60 min are simulated at rainfall rates, 0.5 and 0.9 mm h⁻¹ applying scavenging coefficients to initial aerosols number concentrations (before rain). We show how thunderstorm rain scavenges number concentrations of urban aerosols in the ultrafine and fine modes. Elapsed-time evolutions of urban aerosols presented in this work show washout of about 50–60 and 70–80% number concentrations of particles in the diameter range 0.02 μm ≤ D _p  ≤ 0.1 μm after 30 and 60 min of thunderstorm rain when compared to initial number concentrations (before rain). Assuming 37 and 24% Sulfate and Organic Carbon particles in aerosol distributions in the urban environment and by applying scavenging coefficients to these initial number concentrations, elapse-time evolutions after 30 and 60 min of thunderstorm rain are presented in this work. The health impact is addressed in terms of depositions of particles within respiratory system by deposition fractions as a function of particle size. For D _p  ≤ 0.1 μm, 33 and 41% of initial number concentrations of Sulfate and Organic Carbon particles deposits within respiratory system. Whereas elapsed-time evolutions show 60 and 80% cleansing of initial number concentrations of Sulfate and Organic Carbon particles after 30 and 60 min of thunderstorm rain.     

Thermodynamic structure of the marine atmosphere over the region 80–87°E along 13°N during August (phase II) BOBMEX-99

Thermodynamic structure of the marine atmosphere in the region between 80 and 87‡E along 13‡N over the Bay of Bengal was studied using 13 high resolution radiosonde profiles from surface-400 hPa collected onboard ORV Sagar Kanya during the period 27th–30th August, during BOBMEX-99. Saturation point concept, mixing line analysis and conserved variable diagrams have been used to identify boundary layer characteristics such as air mass movement and stability of the atmosphere. The results showed relatively dry air near the ocean surface between 1000 and 950 hPa. This feature is confirmed by the conserved teta_v structure in this layer. Further, teta_v seldom showed any inversions in this region. The teta_e and teta_es profiles showed persistent low cloud layers between 900 and 700 hPa. The conserved variable diagrams (teta_e-q) showed the existence of double mixing line structures approximately at 950 and 700 hPa levels.