Satellite and ground detection of very dense smoke clouds produced on the islands of the Paraná river delta that affected a large region in Central Argentina

Intense fires were produced on the Paraná river delta islands, Argentina, during most part of 2008, by a combination of an exceptionally dry period and the farmers’ use of a fire land-cleaning technique. In April 2008, those fires significantly affected the nearby regions and their inhabitants, from Rosario city to Buenos Aires mega-city. In this work we present satellite as well as ground Aerosol Optical Depth (AOD) at 550 nm data obtained during the propagation of pollution clouds to the central zone of Argentina. The highest value (1.18) was registered at Buenos Aires by atmospheric remote sensing, using the satellite instrument MODIS/Terra on April 18th 2008 at 10:35 local time (= UT − 3 h). On the same day, ground air quality detectors also measured in this city the highest Total Suspended Particle (TSP) value of the month, 2.02 mg/m³. The AOD(550) daily variation at Rosario Astronomical Observatory, which is located near the Paraná riverside, was derived by combining solar ultraviolet erythemal irradiance data (measured with a YES biometre) with model calculations. On April 25th 2008, from 12:00 to 15:30 local time, a rather high and constant AOD(550) value was registered, with a mean value of (0.90 ± 0.21). Cities located on the side of the Rosario–Buenos Aires highway (San Nicolás, Baradero and San Pedro) were also affected, showing a mean AOD(550) between the Rosario and Buenos Aires values. The particulate matter was collected with gridded samplers placed on the Paraná river islands as well as at the Rosario Observatory. They were analysed with a Scanning Electron Microscope (SEM) and mainly showed a biological origin. Even if normally large particles travel small distances from the source, organic aerosol in the range of 40–100 μm and complex asymmetric structures were registered several kilometres away from the aerosol sources on the islands. Another event of intense UV index attenuation (98.6%) occurred on September 18th 2008, due to very dense smoke clouds that extended over the Rosario area for several hours. The clouds were driven away from the fires by East–northeast and East–southeast winds. The minimum value of this index measured around noon allows to derive a maximum AOD(550)_max = (3.65 ± 0.90) at 12:45 local time. Soot clouds extended over the Paraná river, transporting Burned Biomass Debris (BBD) that deposited on Rosario. In particular, burned leaves and small branches with dimensions of 1–20 cm were collected. The mean (BBD) particles deposited on the ground from 7:00 to 19:00 local time were (0.92 ± 0.20) BBD/(m² h).     

Signatures of the Sudden Stratospheric Warming events of January–February 2008 in Seoul,S. Korea

The period January–February 2008 was characterized by four Sudden Stratospheric Warmings (SSWs) in the Northern Hemisphere, of which the last warming, at the end of February 2008, was a major warming. A significant decrease in mesospheric water vapour (H₂O) of more than 2 ppmv (∼40%) was observed by the ground-based microwave (GBMW) radiometer in Seoul, S. Korea [37.3°N, 126.3°E] during the major SSW. A comparison with ground-based mesospheric H₂O observations from the mid-latitude station in Bern [46.9°N, 7°E] revealed an anticorrelation in the mesospheric H₂O data during the major SSW. In addition, prior to the major warming, strong periodic fluctuations were recorded in the Aura MLS vertical temperature distribution between 15 and 0.05 hPa at Seoul. The mesospheric temperature oscillation was found to have a period of ∼10–14 days with a persistency of 3–4 cycles.     

Studies of electron and ion temperatures at 500 km altitude during sunrise using Indian SROSS C2 satellite

Solar dependence of electron and ion temperatures (T_e and T_i) in the ionosphere is studied using RPA data onboard SROSS C2 at an altitude of ∼500 km and 77°E longitude during early morning hours (04:00–07:00 LT) for three solar activities: solar minimum, moderate and maximum during winter, summer and equinox months in 10°S–20°N geomagnetic latitude. In winter the morning overshoot phenomenon is observed around 06:00 LT (T_e enhances to ∼4000 K) during low-solar activity and to T_e ∼ 3800 K, during higher solar activity. In summer, it is observed around 05:30 LT, but the rate of T_e enhancement is higher during moderate solar activity (∼2700 K/hr) than the low-solar activity (∼1700 K/hr). During equinox, this phenomenon is delayed and is observed around 06:00 LT (∼4200 K) during all three activities.     

Polarization pattern of low and mid-frequency magnetic pulsations in the polar cap: A comprehensive analysis at Terra Nova Bay (Antarctica)

The polarization pattern of ULF pulsations (f ≈ 1–100 mHz) at Terra Nova Bay (Antarctica, CGM λ ∼ 80°) has been determined for the entire 2003, soon after the solar maximum. A comparison with the results of previous investigations, conducted at the same station close to the solar minimum (1994–96), allows to focus common elements and major differences among different frequency bands which persist through the entire solar cycle. Basically, between f ∼ 1.5 and 5 mHz, the day can be divided into four sectors with alternate polarizations. The local time and latitudinal dependence of the observed pattern can be tentatively interpreted in terms of a latitude of resonant field lines reaching λ ∼ 80° in the noon sector; on the other hand, resonance effects of lower latitude field lines can be clearly identified also far from the noon meridian when the station moves into the deep polar cap. Moreover, in the morning sector the resonance region would extend to lower latitudes than in the evening sector. The proposed profile of the resonant region can interpret also the results obtained at other cusp/auroral stations and appears consistent with that one inferred in the northern hemisphere at smaller latitudes. The resonance region progressively shifts toward lower latitude with increasing frequency; correspondingly, the four-sector pattern progressively disappears at TNB. Above f ∼ 20 mHz, the experimental observations might suggest an additional contribution from Sunward propagating waves, possibly via the magnetotail lobes.     

Seasonal variability of atmospheric aerosol over the North Indian region during 2005–2009

The Indo-Gangetic basin (IGB) extends 2000 km in length along NW–SE and has 400 km width, in the north the basin is bounded by towering Himalaya. High aerosol optical depth (AOD) is observed over the IGB throughout the year. The Himalaya restricts the transport of aerosols across Tibet and China. We have used ground based Kanpur and Gandhi College Aerosol Robotic Network (AERONET) stations and Multiangle Imaging SpectroRadiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) Terra level-3 AOD products for the years 2005–2009 to study the variability of aerosol over the Indo-Gangetic (IG) plains. An increase in both satellite-derived as well as ground observed aerosol loading during 2005–2009 has been found over major cities located in the IG plains. The correlation coefficients between AERONET and MISR data are found to be 0.70, 0.36 0.82, in contrast the correlation coefficients between AERONET and MODIS 0.49, 0.68, and 0.43, respectively during summer, winter and monsoon seasons. The AOD estimation using MISR is found to be close to AERONET data during summer and monsoon seasons, in contrast MODIS estimation is better during winter season.     

Status of the GAMMA-400 project

The preliminary design of the new space gamma-ray telescope GAMMA-400 for the energy range 100 MeV–3 TeV is presented. The angular resolution of the instrument, 1–2° at E_γ ∼ 100 MeV and ∼0.01° at E_γ > 100 GeV, its energy resolution ∼1% at E_γ > 100 GeV, and the proton rejection factor ∼10⁶ are optimized to address a broad range of science topics, such as search for signatures of dark matter, studies of Galactic and extragalactic gamma-ray sources, Galactic and extragalactic diffuse emission, gamma-ray bursts, as well as high-precision measurements of spectra of cosmic-ray electrons, positrons, and nuclei.     

Satellite derived aerosol optical depth climatology over Bangalore,India

Climatological aerosol optical depths (AOD) over Bangalore, India have been examined to bring out the temporal heterogeneity in columnar aerosol characteristics. AOD values at 550 nm derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard NASA’s Terra and Aqua satellites, for the period of 2002–2011 have been analyzed (independently) for the purpose. Frequency distributions of the AOD values are examined to infer the monthly mean values. Monthly and seasonal variations of AOD are investigated in the light of regional synoptic meteorology. Climatological monthly and seasonal mean Terra and Aqua AOD values exhibited similar temporal variation patterns. Monthly mean AOD values increased from January, peaks during May and thereafter (except for a secondary peak during July) fall off to reach a minimum during December. Monsoon season recorded the highest climatological seasonal mean AOD, while winter season recorded the lowest. AOD values show an overall increasing trend on a yearly basis, which was found mainly due to sustained increase in the seasonal averaged AOD during summer. The results obtained in the present study are compared with that of the earlier studies over the same location and also with AOD over various other Indian locations. Finally, the radiative and climatic impacts are discussed.     

Synergetic retrieval of terrestrial AOD from MODIS images of twin satellites Terra and Aqua

Aerosol optical depth (AOD) is one of the most important indicators of atmospheric pollution. It can be retrieved from satellite imagery using several established methods, such as the dark dense vegetation method and the deep blue algorithm. All of these methods require estimation of surface reflectance prior to retrieval, and are applicable to a certain pre-designated type of surface cover. Such limitations can be overcome by using a synergetic method of retrieval proposed in this study. This innovative method is based on the fact that the ratio K of surface reflectance at different angles/geometries is independent of wavelength as reported by Flowerdew and Haigh (1995). An atmospheric radiative transfer model was then established and resolved with the assistance of the ratio K obtained from two Moderate Resolution Imaging Spectroradiometer (MODIS) spectral bands acquired from the twin satellites of Terra and Aqua whose overpass is separated by three hours. This synergetic method of retrieval was tested with 20 pairs of MODIS images. The retrieved AOD was validated against the ground observed AOD at the Taihu station of the AErosol RObotic NETwork (AERONET). It is found that they are correlated with the observations at a coefficient of 0.828 at 0.47 μm and 0.921 at 0.66 μm wavelengths. The retrieved AOD has a mean relative error of 25.47% at 0.47 μm and 24.3% at 0.66 μm. Of the 20 samples, 15 and 17 fall within two standard error of the line based observed AOD data on the ground at the 0.47 μm and 0.66 μm, respectively. These results indicate that this synergetic method can be used to reliably retrieve AOD from the twin satellites MODIS images, namely Terra and Aqua. It is not necessary to determine surface reflectance first.     

Jovian periodicities (∼10 h, ∼40 min) on Ulysses’ Distant Jupiter Encounter observations around the Halloween CIR events

We analyzed data from four different instruments (HI-SCALE, URAP, SWOOPS, VHM/FGM) onboard Ulysses spacecraft (s/c) and we searched for possible evidence of Jovian emissions when the s/c approached Jupiter during the times of Halloween events (closest time approach/position to Jupiter: February 5, 2004/R = 1683 R_J,θ = ∼49°). In particular, we analyzed extensively the low energy ion measurements obtained by the HI-SCALE experiment in order to examine whether low energy ion/electron emissions show a symmetry, and whether they are observed at north high latitudes upstream from the jovian bow shock, as is known to occur in the region upstream from the south bow shock as well ( Marhavilas et al., 2001). We studied the period from October 2003 to March 2004, as Ulysses moved at distances 0.8–1.2 AU from the planet at north Jovicentric latitudes <75°, and we present here an example of characteristic Jovian periodicities in the measurements around a CIR observed by Ulysses on days ∼348–349/2003 (R = 1894 R_J,θ = 72°). We show that Ulysses observed low energy ion (∼0.055–4.7 MeV) and electron (>∼40 keV) flux and/or spectral modulation with the Jupiter rotation period (∼10 h) as well as variations with the same period in solar wind parameters, radio and magnetic field directional data. In addition, characteristic strong ∼40 min periodic variations were found superimposed on the ∼10 h ion spectral modulation. Both the ∼10 h and ∼40 min ion periodicities in HI-SCALE measurements were present in several cases during the whole period examined (October 2003 to March 2004) and were found to be more evident during some special conditions, for instance during enhanced fluxes around the start (forward shock) and the end (reverse shock) of CIRs. We infer that the Jovian magnetosphere was triggered by the impact of the CIRs, after the Halloween events, and it was (a) a principal source of forward and reverse shock-associated ion flux structures and (b) the cause of generation of ∼10 h quasi-periodic magnetic field and plasma modulation observed by Ulysses at those times.     

Solar cycle and latitude dependence of high-beta suprathermal plasma conditions in interplanetary space between 1.3 and 5.4 AU

The analysis of energetic particles and magnetic field measurements from the Ulysses spacecraft has shown that in a series of events, the energy density contained in the suprathermal tail particle distribution is comparable to or larger than that of the magnetic field, creating conditions of high-beta plasma. In this work we analyze periods of high-beta suprathermal plasma occurrences (β_ep > 1) in interplanetary space, using the ratio (β_ep) of the energetic particle (20 keV to ∼5 MeV) and magnetic field energy densities from measurements covering the entire Ulysses mission lifetime (1990–2009) in order to reveal new or to reconfirm some recently defined interesting characteristics. The main key-results of the work are summarized as follows: (i) we verify that high-beta events are detected within well identified regions corresponding mainly to the vicinity of shock surfaces and magnetic structures, and associated with energetic particle intensity enhancements due to (a) reacceleration at shock-fronts and (b) unusually large magnetic field depressions. (ii) We define three considerable features for the high-beta events, concentrated on the next points: (a) there is an appreciable solar-activity influence on the high-beta events, during the maximum and middle solar-cycle phase, (b) the annual peak magnitude and the number of occurrences of high events are well correlated with the sunspot number, (c) the high-beta suprathermal plasma events present a spatial distribution in heliographic latitudes (HL) up to ∼±80°, and a specific important concentration on the low (−25° ? HL < −6°, 6° < HL ? 25°) and median (−45° ? HL < −25°, 25° < HL ? 45°) latitudes. We also reconfirm by a statistical analysis the results of Marhavilas and Sarris (2011), that the high-beta suprathermal plasma (β_ep > 1) events are characterized by a very large parameter β_ep (up to 1732.5), a great total duration (406 days) and a large percentage of the Ulysses-mission lifetime (which is equal to 6.34% of the total duration with usable measurements, and 11.3% of the duration in presence of suprathermal particles events).     

Thermally evolved gas analysis (TEGA) of hyperarid soils doped with microorganisms from the Atacama Desert in southern Peru: Implications for the Phoenix mission

TEGA, one of several instruments on board of the Phoenix Lander, performed differential scanning calorimetry and evolved gas analysis of soil samples and ice, collected from the surface and subsurface at a northern landing site on Mars. TEGA is a combination of a high temperature furnace and a mass spectrometer (MS) that was used to analyze samples delivered to the instrument via a robotic arm. The samples were heated at a programmed ramp rate up to 1000 °C. The power required for heating can be carefully and continuously monitored (scanning calorimetry). The evolved gases generated during the process can be analyzed with the evolved gas analyzer (a magnetic sector mass spectrometer) in order to determine the composition of gases released as a function of temperature. Our laboratory has developed a sample characterization method using a pyrolyzer integrated to a quadrupole mass spectrometer to support the interpretations of TEGA data. Here we examine the evolved gas properties of six types of hyperarid soils from the Pampas de La Joya in southern Peru (a possible analog to Mars), to which we have added with microorganisms (Salmonella typhimurium, Micrococcus luteus, and Candida albicans) in order to investigate the effect of the soil matrix on the TEGA response. Between 20 and 40 mg of soil, with or without ∼5 mg of lyophilized microorganism biomass (dry weight), were placed in the pyrolyzer and heated from room temperature to 1200 °C in 1 h at a heating rate of 20 °C/min. The volatiles released were transferred to a MS using helium as a carrier gas. The quadrupole MS was ran in scan mode from 10 to 200 m/z. In addition, ∼20 mg of each microorganism without a soil matrix were analyzed. As expected, there were significant differences in the gases released from microorganism samples with or without a soil matrix, under similar heating conditions. Furthermore, samples from the most arid environments had significant differences compared with less arid soils. Organic carbon released in the form of CO₂ (ion 44 m/z) from microorganisms evolved at temperatures of ∼326.0 ± 19.5 °C, showing characteristic patterns for each one. Others ions such as 41, 78 and 91 m/z were also found. Interestingly, during the thermal process, the release of CO₂ increased and ions previously found disappeared, demonstrating a high-oxidant activity in the soil matrix when it was subjected to high temperature. Finally, samples of soil show CO₂ evolved up to 650 °C consistent with thermal decomposition of carbonates. These results indicate that organics mixed with these hyperarid soils are oxidized to CO₂. Our results suggest the existence of at least two types of oxidants in these soils, a thermolabile oxidant which is highly oxidative and other thermostable oxidant which has a minor oxidative activity and that survives the heat-treatment. Furthermore, we find that the interaction of biomass added to soil samples gives a different set of breakdown gases than organics resident in the soil. The nature of oxidant(s) present in the soils from Pampas de La Joya is still unknown.     

Detection of aerosol pollution sources during sandstorms in Northwestern China using remote sensed and model simulated data

The present paper has used a comprehensive approach to study atmosphere pollution sources including the study of vertical distribution characteristics, the epicenters of occurrence and transport of atmospheric aerosol in North-West China under intensive dust storm registered in all cities of the region in April 2014. To achieve this goal, the remote sensing data using Moderate Resolution Imaging Spectroradiometer satellite (MODIS) as well as model-simulated data, were used, which facilitate tracking the sources, routes, and spatial extent of dust storms. The results of the study have shown strong territory pollution with aerosol during sandstorm. According to ground-based air quality monitoring stations data, concentrations of PM₁₀ and PM_2.5 exceeded 400?μg/m³ and 150?μg/m³, respectively, the ratio PM_2.5/PM₁₀ being within the range of 0.123–0.661. According to MODIS/Terra Collection 6 Level-2 aerosol products data and the Deep Blue algorithm data, the aerosol optical depth (AOD) at 550?nm in the pollution epicenter was within 0.75–1. The vertical distribution of aerosols indicates that the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) 532?nm total attenuates backscatter coefficient ranges from 0.01 to 0.0001?km^?1?×?sr^?1 with the distribution of the main types of aerosols in the troposphere of the region within 0–12.5?km, where the most severe aerosol contamination is observed in the lower troposphere (at 3–6?km). According to satellite sounding and model-simulated data, the sources of pollution are the deserted regions of Northern and Northwestern China.     

Quantifying the role of solar radiative forcing over the 20th century

The 20th century temperature anomaly record is reproduced using an energy balance model, with a diffusive deep ocean. The model takes into account all the standard radiative forcings, and in addition the possibility of a non-thermal solar component. The model is parameterized and then optimized to produce the most likely values for the climate parameters and radiative forcings which reproduce the 20th century global warming. We find that the best fit is obtained with a negligible net feedback. We also show that a non-thermal solar component is necessarily present, indicating that the total solar contribution to the 20th century global warming, of ΔT_solar = 0.27 ± 0.07 °C, is much larger than can be expected from variation in the total solar irradiance alone. However, we also find that the largest contribution to the 20th century warming comes from anthropogenic sources, with ΔT_man = 0.42 ± 0.11 °C.     

A comparison of different regression models for downscaling Landsat and MODIS land surface temperature images over heterogeneous landscape

Remotely sensed high spatial resolution thermal images are required for various applications in natural resource management. At present, availability of high spatial resolution (<200 m) thermal images are limited. The temporal resolution of such images is also low. Whereas, coarser spatial resolution (∼1000 m) thermal images with high revisiting capability (∼1 day) are freely available. To bridge this gap, present study attempts to downscale coarser spatial resolution thermal image to finer spatial resolution using relationships between land surface temperature (LST) and vegetation indices over a heterogeneous landscape of India. Five regression based models namely (i) Disaggregation of Radiometric Temperature (DisTrad), (ii) Temperature Sharpening (TsHARP), (iii) TsHARP with local variant, (iv) Least median square regression downscaling (LMS_DS) and (v) Pace regression downscaling (PR_DS) are applied to downscale LST of Landsat Thematic Mapper (TM) and Terra MODIS (Moderate Resolution Imaging Spectroradiometer) images. All the five models are first evaluated on Landsat image aggregated to 960 m resolution and downscaled to 480 m and 240 m resolution. The downscale accuracy is achieved using LMS_DS and PR_DS models at 240 m resolution at 0.61 °C and 0.75 °C respectively. MODIS data downscaled from 1000 m to 250 m spatial resolution results root mean square error (RMSE) of 1.43 °C and 1.62 °C for LMS_DS and PR_DS models, respectively. The LMS_DS model is less sensitive to outliers in heterogeneous landscape and provides higher accuracy when compared to other models. Downscaling model is found to be suitable for agricultural and vegetated landscapes up to a spatial resolution of 250 m but not applicable to water bodies, dry river bed sand sandy open areas.     

Interpretation of the SOHO/UVCS observations of two CME-driven shocks

We report on the analysis of two fast CME-driven shocks observed with the UltraViolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO). The first event, detected on 2002 March 22 at 4.1 R_⊙ with the UVCS slit placed in correspondence with the flank of the expanding CME surface, represents the highest UV detection of a shock obtained so far with the UVCS instrument in the corona. The second one, detected on 2002 July 23 at 1.6 R_⊙ with the UVCS slit placed in correspondence with the front of the expanding CME surface, shows an anomalous deficiency of ion heating with respect to what observed in previous CME/shocks observed by UVCS, possibly reflecting the effect of different coronal plasma conditions over the solar cycle. From the two different sets of observations we derived an estimate for the shock compression ratio X, which turns out to be X = 2.4 ± 0.2 and X = 2.2 ± 0.1, respectively, for the first and second event. Comparison between the two events provides complementary perspectives on the dynamical evolution of CME-driven shocks.     

Simulation of depth–dose distributions for various ions in polyethylene medium

Study of depth–dose distributions for intermediate energy ion beams in tissue-like media such as polyethylene (CH₂)_n provides a good platform for further improvements in the fields of hadrontherapy and space radiation shielding. The depth–dose distributions for ¹²C ions at various energies and for light and intermediate ion beams (³He, ¹⁶O, ²⁰Ne and ²⁸Si) as well as for heavy ions ⁵⁶Fe in polyethylene were estimated by using simulation toolkit: Geant4. Calculations were performed mainly by considering two different combinations of standard electromagnetic (EM), binary cascade (BIC), statistical multifragmentation (SMF) and Fermi breakup (FB) models. The energies of the ion beams were selected to achieve the Bragg peaks at predefined position (∼60 mm) and as per their availability. Variations of peak-to-entrance ratio (from 7.44 ± 0.05 to 8.87 ± 0.05), entrance dose (from 2.89 ± 0.01 to 203.71 ± 0.63 MeV/mm) and entrance stopping power (from 3.608 to 208.858 MeV/mm, calculated by SRIM) with atomic number (Z) were presented in a systematic manner. The better peak-to-entrance ratio and less entrance dose in the region Z = 2 to 8 (i.e. ³He to ¹⁶O) may provide the suitability of the ion beams for hadrontherapy.     

Probing the method of correcting Faraday rotation in vector magnetograms

By analyzing the vector magnetograms of Huairou Solar Observing Station (HSOS) taken at the line center (0.0 Å) and the line wing (−0.12 Å) of FeI λ5324.19 Å, we make an estimate of the measured errors in transversal azimuths (δ?) caused by Faraday rotation. Since many factors, such as the magnetic saturation and scattered light, can affect the measurement accuracy of the longitudinal magnetic field in the umbrae of sunspots, we limit our study in the region ∣B_z∣ < 800 G. The main mean azimuth rotations are about 4°, 6°, 7° and 9°, while ∣B_z∣ are in the ranges of 400–500 G, 500–600 G, 600–700 G and 700–800 G, respectively. Moreover, we find there is also an azimuth rotation of about 8° at the wavelength offset −0.12 Å of the line compared against a previous numerical simulation.     

Estimation of the elastic Earth parameters (h2, l2) using SLR data

We present results for the global elastic parameters h₂ and l₂ derived from the analysis of Satellite Laser Ranging (SLR) data. SLR data for the two satellites LAGEOS 1 and LAGEOS 2 observed during 2.5 years from January 3, 2005 until July 1, 2007 with 18 globally distributed ground stations were analysed using different approaches. The analysis was done separately for the two satellites and approaches to estimate the two elastic parameters independently and together were performed. We do a sequential analysis and study the stability of the estimates as a function of length of the data set used. The adjusted final values for h₂ equal to 0.6151 ± 0.0008 and 0.6152 ± 0.0008, and those for l₂ equal to 0.0886 ± 0.0003 and 0.0881 ± 0.0003 for LAGEOS 1 and LAGEOS 2 tracking data are compared to other independently derived estimates. These parameters and their errors achieve stability at about the 24 and 27 month time interval for h₂ and l₂, respectively.     

Solar cycle effect on temporal and spatial variation of topside ion density measured by SROSS C2 and ROCSAT 1 over the Indian longitude sector

We investigated the diurnal, seasonal and latitudinal variations of ion density Ni over the Indian low and equatorial topside ionosphere within 17.5°S to 17.5°N magnetic latitudes by combining the data from SROSS C2 and ROCSAT 1 for the 9 year period from 1995 to 2003 during solar cycle 23. The diurnal maximum density is found in the local noon or in the afternoon hours and the minimum occurs in the pre sunrise hours. The density is higher during the equinoxes as compared to that in the June and December solstice. The local time spread of the daytime maximum ion density increases with increase in solar activity. A north south asymmetry with higher ion density over northern hemisphere in the June solstice and over southern hemisphere in December solstice has been observed in moderate and high solar activity years. The crest to crest distance increases with increase in solar flux. Ion density bears a nonlinear relationship with F_10.7 cm solar flux and EUV flux in general. The density increases linearly with solar flux up to ∼150 sfu (1 sfu = 10⁻²²Wm⁻²Hz⁻¹) and EUV flux up to ∼50 units (10⁹ photons cm⁻² s⁻¹). But beyond this the density saturates. Inverse saturation and linear relationship have been observed in some season or latitude also. Inter-comparison of the three solar activity indices F_10.7 cm flux, EUV flux and F_10.7P (= (F_10.7 + F_10.7A)/2, where F_10.7A is the 81 day running average value of F_10.7) shows that the ion density correlates better with F_10.7P and F_10.7 cm fluxes. The annual average daytime total ion density from 1995 to 2003 follows a hysteresis loop as the solar cycle reverses. The ion density at 500 km over the Indian longitude sector as obtained by the international reference ionosphere is in general lower than the measured densities during moderate and high solar activity years. In low solar activity years the model densities are equal or higher than measured densities. The IRI EIA peaks are symmetric (±10°) in equinox while densities are higher at 10°N in June solstice and at 10°S in the December solstice. The model density follows F_10.7 linearly up to about F_10.7 > ∼150 sfu and then saturates.     

Is there an abnormal enhancement of atmospheric aerosol before the 2008 Wenchuan earthquake?

There are extensive reports of ionospheric disturbances before the great 2008 Wenchuan earthquake, which are possibly explained by seismogenic electric field hypotheses linked with the aerosols injected in atmosphere. This paper attempts to investigate the possible change of atmospheric aerosol optical depth (AOD) associated with this earthquake by using MODIS data from both Terra and Aqua satellites. The result shows a clear enhancement of AOD along the Longmenshan faults 7 days before the quake, which is 1 day and 4 days earlier than the reported negative and positive ionospheric disturbances, respectively, and is 1 day earlier than or quasi-synchronism with other reported atmospheric anomalies including air temperature, outgoing longwave radiation and relative humidity. Particularly, the spatial distribution of AOD enhancement is very local and it is correlated well with the active faults and surface ruptures. We suggest that this unique enhancement could be associated with the Lithosphere–Atmosphere–Ionosphere coupling process during the preparation of the Wenchuan earthquake.