Feed aggregator

Single station modelling and comparison with ionosonde foF2 over Karachi from 1983 to 2007

Publication date: Available online 20 June 2019

Source: Advances in Space Research

Author(s): Muhammmad Ayyaz Ameen, Mehak Abdul Jabbar, Ghulam Murtaza, Farrukh Chishtie, Tong Xu, Weimin Zhen, Muhammad Atiq, Muneeza Salman Ali

Abstract

In this study, we develop a single station model (SSM) based upon derived solar radio flux (F10.7P) using ionosonde foF2 data over Karachi (24.95°N, 67.14°E) over a period of 1983–2007. The station is positioned at the northern Equatorial Ionization Anomaly (EIA) crest region. For the development of this SSM, six regression models are proposed which can be categorised as (i) sunspot number (R) against foF2, (ii) R and geomagnetic index (Ap) against foF2 and (iii) current and prior month indices against foF2. This is an initial study based on a large set of ground observations of foF2 over Karachi. A significant saturation between foF2 against R at daytime is observed in all the months for the entire dataset. Analysis shows that the local statistical models are better than International Reference Ionosphere (IRI-2016) which has least accuracy with higher Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) in comparison to the local models. The developed SSM is in good agreement with observations with lower RMSE and MAE values as compared to the mentioned local models. Based on this validation, our SSM is used to forecast and compare ionosonde foF2 over Sonmiani (25.19°N, 66.74°E) showing a standard deviation of 0.4956 MHz from the observed data supporting our error assessments for the year 2018 while IRI-2016 for the same shows standard deviation as 1.1088 MHz. On the basis of our results, it is proposed that IRI may make use of F10.7P for predicting foF2.

Features of downshifted maximum spectra during a dual-pump ionospheric heating experiment

Publication date: Available online 20 June 2019

Source: Advances in Space Research

Author(s): Libin Lv, Zhensen Wu, Qingliang Li, Shuji Hao, Guanglin Ma, JuTao Yang, Jian Ding, Jian Wu

Abstract

An ionospheric heating experiment was conducted using the dual-pump mode at the EISCAT/HEATING facility in Tromsø, Norway. Some new features were found in the downshifted maximum (DM) component of the stimulated electromagnetic emission (SEE) spectra. During the experiment, the DM1 generated by pump 1 was enhanced under the action of pump 2 with the peak intensity being increased by ∼4.8–9.8 dB to achieve maximum value, when the frequency of pump 2 was 4.100 MHz. The gyro resonance at the upper hybrid altitude played an important role in this phenomenon. It was also observed that the development time of DM2 generated by pump 2 was greatly shorter than that of DM1 due to the precondition provided by the artificial field-aligned irregularities (AFAIs) stimulated by pump 1. Additionally, the frequency offset and peak intensity of the DM1 spectrum showed a significant negative correlation, where the correlation coefficient reached a value of −0.91.

Nonlinear dependence study of ionospheric F2 layer critical frequency with respect to the solar activity indices using the mutual information method

Publication date: Available online 20 June 2019

Source: Advances in Space Research

Author(s): Hongmei Bai, Feng Feng, Jian Wang, Taosuo Wu

Abstract

This paper analyzes the dependence of the ionospheric F2 layer critical frequency, foF2, on two widely used solar activity indices (12-month running mean of the sunspot number (R12) and the solar radio flux of 10.7 cm wavelength (F10.712)) by using mutual information method at the ionospheric station of Darwin (geographic 12.4°S, 131.5°E) in Australia. The results show that the foF2 have different responses to R12 and F10.712 in different solar activity years. In the high and low solar activity years, the foF2 is more dependent on R12 rather than F10.712. In the moderate solar activity years, the foF2 is more dependent on F10.712 rather than R12. We further verify the effectiveness of the mutual information on the selection of the solar activity index by developing the prediction models of the foF2. Additionally, the results are compared against the International Reference Ionosphere (IRI) model. The data of training period used in the model is from 1998 to 2015, except 2000, 2009 and 2013. Data for 2000, 2009 and 2013 are used to validate the prediction accuracy, for high, low and moderate solar activity years, respectively. The results demonstrate that the favorable prediction results can be obtained when the solar activity index with large mutual information is used as the input variable of the foF2 prediction model. The proposed method not only can quantitatively analyze the nonlinear relationship between the foF2 and solar activity indices but also provides an effective way of selecting the solar activity indices for the foF2 prediction.

The possibility of estimating the height of the ionospheric inhomogeneities based on TEC variations maps obtained from dense GPS network

Publication date: Available online 19 June 2019

Source: Advances in Space Research

Author(s): Grzegorz Nykiel, Yevgen Zanimonskiy, Aleksander Koloskov, Mariusz Figurski

Abstract

A state of the ionosphere can be effectively studied using electromagnetic signals received from global navigation satellite systems (GNSS). Utilization of the dual frequency observations allows estimating values of the total electron content (TEC). They can be used for a number of scientific studies such as detection and monitoring of traveling ionospheric disturbances or plasma bubbles. Moreover, maps of TEC variations allow to classify ionospheric heterogeneities and to evaluate their parameters. However, most of the research describes ionospheric parameters only in 2D space and time. In this paper, we focus on the determination of the height of the ionospheric inhomogeneities. We used a dense network of GPS receivers to obtain the sequences of TEC variation maps for different heights of the ionospheric layer. For each satellite observed above 70°, we constructed separate sets of maps. For each ionospheric height, the cross-correlation function between maps corresponding to different satellites was calculated. The biggest cross-correlation coefficient value determines the height of the ionospheric irregularities. This paper describes the methodology and the results obtained for a geomagnetic storm on St. Patrick’s Day in March 2013. We have found that in quiet geomagnetic conditions the ionospheric irregularities are localized predominantly within the interval 180–220 km close to the maximum of the ionospheric F2 layer. In disturbed conditions, the height of their localization was increased up to several hundreds of kilometers. These estimations correspond to the changes in the slab thickness of the ionosphere.

Impact of GPS receiver antenna GRAPHIC residual variations on single-frequency orbit determination of LEO satellites

Publication date: Available online 19 June 2019

Source: Advances in Space Research

Author(s): Kai Shao, Defeng Gu, Xiao Chang, Bin Yi, Zhengming Wang

Abstract

Single-frequency (SF) precise orbit determination (POD) using space-borne Global Positioning System (GPS) measurements is a prerequisite for the success of many low-cost small/micro low Earth orbit (LEO) satellite missions. The first-order ionospheric effects are usually eliminated by group and phase ionospheric correction (GRAPHIC) combinations. GPS receiver antenna GRAPHIC residual variations (GRVs) are important systematic error sources in SF orbit determination. Azimuth and elevation dependent GRVs are estimated and obtained based on the GRAPHIC combination residuals in an in-flight calibration. One month of data from GRACE-A, GRACE-B, CHAMP and HY-2A satellites is used to assess the potential of receiver antenna GRVs in SF orbit determination. It is the first time to study the impact of receiver antenna GRVs on SF orbit determination for different LEO satellites, which exhibit different altitudes and data qualities. The impact of receiver antenna GRVs on SF orbit determination is significant. The use of in-flight determined receiver antenna GRVs leads to a better consistency between SF and dual-frequency POD solutions. The improvements are more obvious for GRACE-A and CHAMP satellites, whose receiver antenna GRV patterns demonstrate clear characteristics of systematic deviations. After correcting the receiver antenna GRVs, the root-mean-square of satellite laser ranging validation residuals are 3.11 cm, 2.31 cm, 2.86 cm and 5.29 cm for GRACE-A, GRACE-B, CHAMP and HY-2A satellites, respectively, which are reduced by 11.1%, 4.6%, 14.6% and 4.7%, respectively. At last, a set of a priori GDV corrections of GPS transmitter antennas are used in SF orbit determination and its effects on receiver antenna GRVs estimation and SF orbit determination are analyzed. Applying these corrections can slightly improve the SF orbit quality of GRACE-A satellite.

On the field validation of α-μ fading coefficients estimator based on the autocorrelation function for ionospheric amplitude scintillation

Publication date: Available online 18 June 2019

Source: Advances in Space Research

Author(s): Leonardo Marini-Pereira, Kelias de Oliveira, Lucas A. Salles, Alison de O. Moraes, Eurico R. de Paula, Marcio Tadeu de Assis Honorato Muella, Waldecir J. Perrella

Abstract

The ionosphere in low-latitude regions has intense dynamics with great variability – not only spatially but also temporally. The most critical effect found in the low-latitude region is the scintillation in phase and amplitude due to plasma bubble occurrence in the ionospheric layer. To augmentation systems like GBAS or SBAS, designed to provide Category-I (CAT I) precision approach service in low-visibility conditions, plasma bubbles can compromise the performance requirements for air navigation precision approach in a way that the service provided by the system is considered unviable. In practical terms, this is the main reason why the Brazilian Department of Airspace Control (DECEA) still has not implemented any augmentation system in Brazil. Scintillation may lead to loss of signal lock of the affected satellite. In this context, a better understanding of the scintillation pattern and its statistical properties gain particular relevance, once this is the most concerning issue for the performance of any GNSS receiver in low-latitude regions especially in the context of augmentation systems for air navigation. Previous works validated the use of the α-μ distribution to characterize amplitude scintillation. The present work is concerned with proposing a new method for the estimation of the α-μ coefficients based on the α-μ autocorrelation function. The method is validated using field data and comparing the results from empirical autocorrelation function with the results obtained from the moment-based estimator. Additionally, the efficiency of the method is proven by analyzing measurements of Level-Crossing Rate (LCR) and Average Fading Duration (AFD) with their respective theoretical formulation.

The Spörer minimum was deep

Publication date: Available online 17 June 2019

Source: Advances in Space Research

Author(s): M.G. Ogurtsov

Abstract

Seventeen reconstructions of past solar activity, based on cosmogenic isotope and auroral data, were analyzed for the time interval CE 1402–1850 covering three prolonged periods of weak solar activity – the Spoerer, Maunder and Dalton minima. The information contained in these proxies has been generalized and sunspot number reconstructed. It was shown that from the point of view of solar paleoastrophysics the Spoerer minimum (15th–16th centuries) was a prolonged (ca 140 years) period of very quiet Sun with a mean solar activity level lower than that during the minimum of Maunder.

Changes of space weather and space climate at Earth orbit: An update

Publication date: Available online 13 June 2019

Source: Advances in Space Research

Author(s): H.S. Ahluwalia

Abstract

We present an update of the changes in space weather/space climate at Earth orbit using sunspot number (SSN) timeline (1700–2018), geomagnetic indices aa/Ap, solar polar magnetic field, interplanetary magnetic field (IMF) and galactic cosmic ray (GCR) flux in the stratosphere at high latitudes. The Cycle 24 is close to solar minimum, expected in 2020. The baseline of aa index increases monotonically from 1900 to 1986 and declines steeply afterwards, solar polar magnetic field decreases systematically for the last three cycles (22–24) as do SSNs at cycle peaks. Livingston and Penn (2009) note a long term weakening of maximum magnetic field in sunspots since 1992. They expect SSNs for the Cycle 25 to peak at 7 (a steep decline in solar activity) leading to Maunder-like minimum, in contrast to prediction of several colleagues of a Dalton minimum. The North-South asymmetry in solar polar field is pronounced for the decay phase of cycles 23, 24, itseems to change sign after the Cycle 21. GCR flux in the stratosphere is greater that in 1965 and increasing, pointing to an enhanced radiation exposure in future for the passengers on transpolar flights, the astronauts on the space station as well as those travelling to and staying on the Moon and the Mars on prolonged missions; the assets in space would have to be hardened for safety from increased radiation. We speculate about the connection between the Earth climate and changes in solar activity, inferring that the science of the Earth climate change is not settled yet.

High energy interactions of cosmic rays

Publication date: Available online 12 June 2019

Source: Advances in Space Research

Author(s): Sergey Ostapchenko

Abstract

A discussion of a number of important topics related to modeling of high energy cosmic ray interactions is presented. Special attention is devoted to novel theoretical approaches employed in event generators of hadronic interactions and to the impact of experimental data from the Large Hadron Collider (LHC). In relation to studies of ultra-high energy cosmic rays (UHECRs), differences between various predictions for basic characteristics of UHECR-induced extensive air showers in the atmosphere are analyzed and traced down to differences in the respective treatments of hadronic interactions. Possibilities to discriminate between the alternative approaches, based on LHC and UHECR data, are demonstrated and the relation to UHECR primary composition is outlined. Finally, in relation to direct studies of charged cosmic rays, potential improvements of the treatment of cosmic ray interactions at low and intermediate energies are discussed.

On an analogy in the restricted and general three-body problems

Publication date: Available online 11 June 2019

Source: Advances in Space Research

Author(s): S.P. Sosnitskii

Abstract

It is shown that the approach proposed by the author in Sosnitskii (2017) to investigate the Lagrange stability of motions in the planar restricted three-body problem can also be applied to the planar case of the general three-body problem. In particular, we prove the Lagrange stability theorem, which is an analogue of Theorem 2 from Sosnitskii (2017).

Performance evaluation of the IRI 2016 and IRI-Plas 2017 models over central Asian mid-latitude regions in the descending phase of solar cycle 24

Publication date: Available online 11 June 2019

Source: Advances in Space Research

Author(s): Yekoye Asmare Tariku

Abstract

This paper scrutinizes the performance of the latest versions of the IRI model (IRI 2016 with NeQuick, IRI01-corr and IRI2001 options for the topside electron density) and the IRI extended to the plasmasphere (IRI-Plas 2017) models in the estimation of the Vertical TEC (VTEC) variation over the central Asian mid-latitude regions in the descending phase of solar cycle 24 (2014–2016). The GPS dual frequency receivers installed at Kurchatov, KRTV (geog 50.71°N, 78.62°E, Geom. 41.84°N), Khantau, SUMK (44.21°N, 74.00°E, Geom. 35.73°N), Talas, TALA (42.45°N, 72.21°E, Geom.34.13°N) and Kazarman, KAZA (41.38°N, 73.94°E, Geom.32.92°N) have been used to derive the estimate of the vertical TEC (GPS-VTEC) for the comparison of the monthly and seasonal performance of the models. The modelled VTEC values generally tend to be larger than the GPS-VTEC values during periods of high solar irradiance (daytime hours), with the highest overestimation being observed by IRI-Plas 2017 model followed by IRI 2016 model with the IRI2001 topside option. However, the differences between the models and between the models and the GPS-VTEC values become diminished as the solar irradiance decreases, with the highest underestimation being observed by the IRI 2016 model with NeQuick topside option. It has also been shown that the smallest root-mean-square deviations between the GPS-VTEC and modelled VTEC are observed generally in the June solstice months, showing that the models perform best during local summer. On the contrary, the largest root-mean-square deviations between the modelled VTEC and GPS-VTEC are observed during high solar irradiance on the surface of the Earth (especially in the time interval between 05:00 and 10:00 UT which corresponds to the daytime hours 10:00 and 15:00 LT), showing that the models perform poorly during high solar irradiance. In addition, both the IRI 2016 and IRI-Plas 2017 models show a progressive decline in VTEC during a negative storm, but do not adequately estimate the storm time VTEC variation.

Masers: Precision probes of molecular gas

Publication date: Available online 11 June 2019

Source: Advances in Space Research

Author(s): A.M.S. Richards, A. Sobolev, A. Baudry, F. Herpin, L. Decin, M.D. Gray, S. Etoka, E.M.L. Humphreys, W. Vlemmings

Abstract

Maser emission from water, methanol, silicon monoxide and other molecules can reach brightness temperatures ≫1010 K. Such observations can achieve sub-pc precision for discs around black holes or sub-au scale interactions in protostellar discs and the regions where evolved star winds reach escape velocity. Ultra-high resolution maser observations also provide photon statistics, for fundamental physics experiments. RadioAstron has shown the success – and limitations – of cm-wave maser observations on scales ≪1 mas with sparse baseline coverage. ALMA, APEX and earlier single dish searches have found a wealth of mm and sub-mm masers, some of which probably also attain high brightness temperatures. Masers are ideal for high-resolution observations throughout the radio regime and we need to consider the current lessons for the best observational strategies to meet specific science cases.

Rapid determination of source parameters for the 2017 Mw 8.2 Mexico earthquake based on high-rate GPS data

Publication date: Available online 10 June 2019

Source: Advances in Space Research

Author(s): Yunfei Xiang, Jianping Yue, Dongjian Cai, Hao Wang

Abstract

Aiming to rapidly determine source parameters (i.e., static offset, seismic wave arrival, moment magnitude, and hypocentral location) for the Mexico 8.2 earthquake, the records of 7 high-rate GPS stations are utilized. Smoothness Priors Method (SPM) is introduced to rapidly extract the static offset from GPS displacement waveforms, and the result suggests this approach is feasible. The seismic wave arrival detection is carried out with the aid of S-transform, and the propagation velocity of seismic wave detected by most GPS stations are within 4–5 km/s, implying the seismic wave captured by GPS station may be S wave or surface wave. After that, an empirical regression model is adopted to characterize the moment magnitude for this earthquake, and this empirical formula can obtain reliable magnitude in comparison with the reference magnitude. The convergence time of average moment magnitude is 298 s, suggesting that a reliable and robust magnitude (Mw 8.37) can be estimated by the 7 GPS stations with about 298 s after earthquake occurrence. Considering the influence of the spatial distribution of GPS stations, 4 nearest GPS stations evenly distributed on both sides of the fault are selected to determine the warning-magnitude for the Earthquake Early Warning (EEW). A reliable and robust moment magnitude (Mw 8.2) can be estimated by the 4 stations with about 251 s, which is 57 s ahead of 7 stations. Finally, the coordinates of 6 GPS stations and corresponding seismic wave arrival time are utilized to determine the hypocentral location, and the latitude and longitude of estimated location is 14.925°N and 93.765°W, which is 17.9 km from the reference location. The results indicate that the source parameters required for EEW can be rapidly determined based on high-rate GPS displacement waveforms, and integrating real-time GPS into a joint EEW system will be crucial going forward.

Decomposition of geodetic time series: A combined simulated annealing algorithm and Kalman filter approach

Publication date: Available online 10 June 2019

Source: Advances in Space Research

Author(s): Feng Ming, Yuanxi Yang, Anmin Zeng, Bin Zhao

Abstract

In this paper we propose a network-based Kalman filter combined generalized simulated annealing algorithm approach to decompose a group of GPS position time series into secular trend, annual and semi-annual signals as well as noise components. This approach treats east, north and vertical components of the whole network separately and estimates network-average process-noise parameters to constrain the time variability of the seasonal signals and noise components. Each coordinate component for each station is modeled in state-space model (SSM) individually. The noise components are described as the combination of flicker noise (FN), random walk noise (RWN) and observation white noise (WN). Each component, except for the trend, is allowed to variate over the time, and their amplitudes are estimated by maximization of likelihood function using a generalized simulated annealing (GSA) algorithm. The proposed approach is applied to 10 reprocessed GPS position time series from the Tectonic and Environmental Observation Network of Mainland China (CMONOC II), and its output is compared with that of ordinary maximum likelihood estimation (MLE). The results show that the proposed approach is an effective tool for the decomposition of GPS position time series. Finally, the advantages and limitations of the proposed approach are also discussed.

Space VLBI: from first ideas to operational missions

Publication date: Available online 8 June 2019

Source: Advances in Space Research

Author(s): Leonid I. Gurvits

Abstract

The operational period of the first generation of dedicated Space VLBI (SVLBI) missions commenced in 1997 with the launch of the Japan-led mission VSOP/HALCA and is coming to closure in 2019 with the completion of in-flight operations of the Russia-led mission RadioAstron. They were preceded by the SVLBI demonstration experiment with the Tracking and Data Relay Satellite System (TDRSS) in 1986–1988. While the comprehensive lessons learned from the first demonstration experiment and two dedicated SVLBI missions are still awaiting thorough attention, several preliminary conclusions can be made. This paper addresses some issues of implementation of these missions as they progressed over four decades from the original SVLBI concepts to the operational status.

Chemical physics of D and E layers of the ionosphere

Publication date: Available online 7 June 2019

Source: Advances in Space Research

Author(s): V.V. Kuverova, S.O. Adamson, A.A. Berlin, V.L. Bychkov, A.V. Dmitriev, Y.A. Dyakov, L.V. Eppelbaum, G.V. Golubkov, A.A. Lushnikov, M.I. Manzhelii, A.N. Morozov, S.S. Nabiev, V.L. Shapovalov, A.V. Suvorova, M.G. Golubkov

Abstract

The main chemical reactions that lead to formation of the nonequilibrium two-temperature plasma and highly excited Rydberg complexes are considered. A special attention is given to l-mixing reaction responsible for the formation of quantum resonance properties for radio wave propagation medium. A detailed analysis of the influence of Rydberg states to the behavior of GPS signals in D and E layers of the ionosphere is presented. It is shown that the transition frequencies between the excited states of orbitally degenerate Rydberg complex are resonant with respect to the carrier frequencies of GPS. That is why these states are the main cause of the GPS signal distortion. The mechanism of GPS signal delay in D and E layers is also discussed.

Climatology of quasi-two day oscillations from GPS-derived total electron content during 1999–2015

Publication date: Available online 7 June 2019

Source: Advances in Space Research

Author(s): Fekadu Demissie Feleke, Gizaw Mengistu Tsidu, Gebregiorgis Abraha

Abstract

The paper presents the climatology of eastward- and westward-propagating quasi-2-day oscillations (QTDOs) with zonal wave numbers 1–4 using the global ionospheric total electron content (TEC) derived at the International GNSS Service (IGS) from the network of ground Global Positioning System (GPS) receivers. The climatologies of space-time spectra and amplitudes of QTDOs in TEC during 16 years from December to February (DJF) (1998/99–2014/15) and 17 years from June to August (JJA) (1999–2015) were investigated. The space-time spectra (spectral signature) and the mean amplitude of all wave modes (1–4) of QTDOs exhibit strong latitudinal, hemispheric, inter-annual and solar-cycle variations. Latitudinaly, strengths of the spectral signature and amplitude values diminish gradually from maxima at equatorial ionization anomaly (EIA) crest towards high latitude regions. The spectral signature amplify (weaken) in the solar maximum (minimum) periods. Likewise, the amplitudes of both the eastward- and westward-propagating QTDOs attain peak values during the maximum solar activity phases of the solar cycle. Seasonally, the spectral signature and amplitude values reveal summer amplification in both hemispheres as opposed to winter suppression. However, the spectral signatures (amplitudes) in the Southern Hemisphere summer are stronger (larger) than that in the Northern Hemisphere summer. Moreover, the spectral signatures and amplitudes associated with the westward-propagating oscillations are dominant over those propagating eastward. The hemispheric and latitudinal mean differences in the long-term mean daily values of amplitude of E1 (W1) QTDOs exhibit high values in the southern (northern) hemisphere near the December (June) solstices that follow the solar declination. The global spatial mean amplitudes of E1 and W1 QTDOs are significantly higher during DJF than in JJA throughout the period of study with a few exceptions revealing the annual anomaly phenomenon in TEC which is more notable during solar maxima. Moreover winter anomaly is distinctly captured in the northern hemisphere as reflected by higher amplitudes of E1 and W1 QTDOs in summer solstice (JJA) than in winter solstice (DJF) consistent with the antecedent understanding.

The nature and origins of the day-to-day variability in Earth’s surface magnetic field

Publication date: Available online 7 June 2019

Source: Advances in Space Research

Author(s): Jeffrey M. Forbes, Astrid Maute, Xiaoli Zhang

Abstract

Numerical experiments are performed with the National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) to reveal the characteristics and origins of daytime magnetic field variations on the ground (ΔB) at planetary-wave (PW) periods (2–20 days). Simulations are performed to separate the responses to forcing in the lower atmosphere from solar-magnetospheric forcing. Lower-atmosphere forcing is specified at the 97-km lower boundary of the TIE-GCM by NCAR's Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model (TIME-GCM), which itself is forced at 30 km by MERRA (Modern Era Retrospective-analysis for Research and Applications) outputs. Solar and magnetospheric inputs to the TIE-GCM are specified according to parameterizations based on F10.7 and Kp. The study focuses on latitudes 0°–65°N during October 1–31, 2009, when F10.7 (range 68–80), Kp (range 0–4), and Ap (range 0–13) are typical of quiet-time “weather”. Neutral dynamics in the dynamo region (ca. 100–150 km) during this period is dominated by winds due to PW modulated tides, where the PW include the quasi-6, 10 and 16-day westward-propagating normal modes with zonal wavenumber s = 1, and eastward-propagating ultra-fast Kelvin waves (UFKW) with s = −1 and periods between 2 and 5 days.

Results and conclusions are as follows. PW-period perturbations in daytime ΔB at the ground are dominated by variability originating in the lower atmosphere. The only exception is the 45°–65° latitude regime around noon, where the ΔB variability due to lower atmospheric forcing exceeds that due to solar-magnetospheric forcing by only about 50%. Broadband zonally-symmetric oscillations also occur in ΔB due to dissipation of the tidal spectrum at PW periods in the E-region. These results raise the possibility that some level of contamination from the lower atmosphere may exist in magnetic indices such as ap, Kp, and Ap that are used as measures solar-magnetosphere-ionosphere coupling strength, under levels of geomagnetic activity similar to that characterizing October 2009. It is also found that variations in conductivities play a minor role compared with neutral winds in producing PW-period variations in ΔB, and that there is not a robust one-to-one correspondence between spectral peaks in ΔB and those in the neutral winds. Several factors contribute to this latter result, which are explained in the text.

Allsky airglow imaging observations from Hanle, Leh Ladakh, India: Image analyses and first results

Publication date: Available online 5 June 2019

Source: Advances in Space Research

Author(s): S. Mondal, A. Srivastava, V. Yadav, S. Sarkhel, M.V. Sunil Krishna, Yamini K. Rao, Vir Singh

Abstract

We have installed a multi-wavelength allsky airglow imager over the Indian Himalayan region at Hanle, Leh Ladakh, (32.7°N, 78.9°E; dip lat. ∼24.1°N). This is the first of its kind that is installed in the Himalayan region at an altitude of around 4200 m above the mean sea level. The high sensitive thermoelectrically cooled CCD based imager is equipped with two interference filters (557.7 nm and 630.0 nm with a bandwidth of 2 nm). The airglow imaging observations have been carried out during moonless nights since June 2018. This paper presents the detailed steps of the image processing techniques to transform the raw images into the geospatially-calibrated images and discusses the process for the estimation of gravity wave parameters (horizontal wavelength, apparent phase velocity and periodicities) from the processed images. In addition, we report a few interesting events like Ripple-type structures, gravity waves and mesospheric bores in the mesopshere and lower thermosphere (MLT) region and the plasma disturbances in the ionospheric F region observed for the first time over Hanle, Leh Ladakh.

A new method to estimate cloud effective radius using Meteosat Second Generation SEVIRI over Middle East

Publication date: 15 August 2019

Source: Advances in Space Research, Volume 64, Issue 4

Author(s): Mostafa Hadizadeh, Mehdi Rahnama, Mehdi Kamali, Mona Kazemi, Ali Mohammadi

Abstract

The cloud particle size distribution varies with height and the phase may change from water to mixed phase to ice through the vertical profile of the cloud, giving rise to different radiative characteristics. Researchers suggested an empirical equation for an approximation of the relation between cloud-particle effective radius and reflectance of channel IR3.7 for Advanced Very High Resolution Radiometer (AVHRR) and Multi-Functional Transport Satellite (MTSAT)-1R satellites. However, when we examined this empirical equation for MSG satellites, there was no correlation between the cloud particle effective radius and those from the Terra and Aqua/MODIS (Moderate Resolution Imaging Spectrometers) products. Given the fact that this relationship is empirical and not applicable for Meteosat satellites with 3.9 µm wavelength cloud properties, we need to introduce a new nonlinear equation that is independent from other cloud properties, to retrieve the cloud effective radius from MSG satellite over Middle East. Thus, in this study, a development of the mentioned method, based on a nonlinear regression model, was introduced to estimate the water/ice-cloud particle effective radius from the 3.9 µm wavelength reflectivity of the Meteosat Second Generation Indian Ocean Data Coverage (MSG-1(IODC)) satellite over the Middle East region. For this purpose, the LibRadTran radiative transfer model was used. This approach is almost independent from other cloud properties, which makes this relationship more efficient for retrieving a cloud’s effective radius. To evaluate this approach, the results have been compared to the effective-radius product of the MODIS on board the Terra and Aqua satellites, and cloud effective radius parameter from the MSG-1 satellite’s optimal cloud analysis (OCA) data. The average of correlation coefficient, standard deviation, and RMSE (root mean square error) of this retrieved algorithm method for 29 randomly selected case studies, in comparison to the corresponding MODIS product, are 0.93, 3.093, and 3.639, and compared with OCA product, 0.88, 4.015, and 4.51, respectively. Therefore, the results of analysis in the Middle East region show that the retrieved effective particle radius from Meteosat satellites corresponds strongly with MODIS data from the Terra and Aqua satellites, and also with the OCA products of the MSG-1. Furthermore, using the algorithm that is presented in this paper, a nonlinear regression relationship can be made for retrieving cloud effective radius in the intended place.

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