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Possibilities of the usage of the total electron content in a low-latitude zone

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): O.A. Maltseva, N.S. Mozhaeva

Abstract

Last years, the small quantity of ionosondes at low latitudes could not give a sufficient picture of behavior of the ionosphere in these areas. Now, reception of experimental data, their analysis and detection of total electron content (TEC) variations at low latitudes are an actual problem. When moving from describing the state of the ionosphere using vertical sounding parameters to describing using TEC, it is important to identify similarities and differences in their behavior in order to assess the possibilities of using TEC. This paper carries out research on four ways of TEC usage in low-latitude zone: (1) research of climatological peculiarities of the TEC behavior, (2) validation of up-to-date TEC models, (3) foF2 calculation according to observational TEC, and (4) peculiarities of TEC behavior during geomagnetic disturbances. Results for station Hainan show the following. 1. In addition to previous investigation it is shown, that the empirical global and local models of TEC provide the values close to observational ones, however climatological features of TEC behavior described by various models may still differ from each other and from the experimental data showing in this case TEC maxima of diurnal variation in the afternoons, seasonal variations in March and October, some slight winter anomaly. 2. In contrast to previous investigation it is shown that the closest to the experimental values of TEC are provided by the IRI-Plas model, while this model overestimates values, and the model NeQuick underestimates values compared to the observational ones. 3. For the first time, the ionospheric equivalent slab thickness τ, which plays the role of the coefficient of proportionality between TEC and NmF2, was compared for the IRI, IRI-Plas, NeQuick models with the experimental median τ(med) and it was shown, that the usage of observational TEC data and τ(med) for calculation of critical frequencies foF2 allows improving correspondence with experimental data by 1.2–2 times compared to the models. 4. Comparison of foF2 and TEC behavior has a particular importance during disturbances. Using the example of 15 strong magnetic storms (Dst < −50 nT), it was shown that, despite its global nature, the details of the TEC response strongly depend on the region. So, the peculiarities of δTEC in comparison with the mid-latitude region are the predominance of the positive phase, and a smaller value of response. The synchronism of variations δTEC and δfoF2 was very high, although there are cases of mismatch. Using the median τ(med) allows determining foF2 during disturbances and filling data gaps.

Statistical features of TEC and ionospheric scintillation over the low latitude of China

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): L. Xu, J. Cheng, J.S. Xu

Abstract

In this paper, a new index is established which is defined by the standard deviation of total electron content (TEC) fluctuation and denoted by the symbol σtec. It is demonstrated that the index σtec is equivalent to the phase scintillation index and can serve as an indicator of the strength of the phase scintillation. The receiver transiently loses lock on the signal, leading to cycle slips and jumps in the TEC time series. In order to obtain continuous TEC data in the situation of the disturbed ionosphere, a batch processing method is developed to detect and correct cycle slip. Based on the methods mentioned above, we investigate the statistical features of the phase scintillations and cycle slips by means of the data from a scintillation observation network in the south-central region of China during 2012–2015. The results show that the variations of phase scintillation occurrences with local time and season display very similar features to those of the cycle slip occurrences, implying that cycle slips are closely related to phase scintillations. Phase scintillations occur mainly during the night, most frequently before midnight and seldom in the daytime. It is found that phase scintillations occur mainly in equinox months but seldom in solstice months in the crest of the ionization equatorial anomaly and its adjacent regions, and an equinoctial asymmetry that phase scintillations occur more frequently in Spring than in Autumn is also found. Besides, a comparison of the TEC fluctuation index (σtec) and amplitude scintillation index (S4) indicates that there is close relation between the σtec and S4, indicating the co-existence of large and small scale irregularities in equatorial irregularity structures.

Ionospheric Es layer scintillation characteristics studied with Hilbert-Huang transform

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): S.-Y. Su, L.-C. Tsai, C.H. Liu, C. Nayak, R. Caton, K. Groves

Abstract

A coincident event of daytime ionospheric Es layer scintillation observations is analyzed with the Hilbert-Huang transform (HHT) to study its layer structure. One of the coincident observations is made by a radio beacon passing through the Es layer at a slant angle received by the SCINDA (Scintillation Decision Aide) receivers located at southern Taiwan. The data indicates that the Es layer consists of scattering blocks of  ∼ 650 to 970 m in size as revealed in the dominant components of the HHT analysis. The time shift in the two spaced receiving antennas implies that the daytime E region westward drift is about 36 m/s. On the other hand, the same Es layer is observed by the radio occultation (RO) experiment with the L1 signal from the Global Positioning System (GPS) satellites to the FORMOSAT-3/Constellation-Observing-System-for-Meteorology (FS-3/COSMIC) satellites. The GPS L1 signal passes through the Es layer horizontally. The observed signal variations reveal a dense slab structure that blocks the L1 signal to cause a diffraction pattern. The slab thickness in the vertical direction is about 780 m. The HHT analyses of the coincident observations thus conclude that the observed daytime Es layer has a vertical dense slab structure and patches of scattering blocks in the horizontal structure.

The dependence of four-peak longitudinal structure of the tropical electric field on the processes in the lower atmosphere and geomagnetic field configuration

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): V.V. Klimenko, M.V. Klimenko, F.S. Bessarab, T.V. Sukhodolov, E.V. Rozanov

Abstract

In this article, we estimate the influence of the atmospheric-ionospheric interaction and the differences in the location of the geographic and geomagnetic poles on the longitudinal variability of the ionospheric electric field in the vicinity of the geomagnetic equator. For the study, we applied the upper atmosphere model (GSM TIP) and the recently created entire atmosphere model (EAGLE). The simulation results confirm that the four-peak structure of the longitudinal variation and the pre-reversal enhancement of the eastward electric field at the equator are caused by the atmosphere-ionosphere coupling. The role of F-region dynamo in the formation of pre-reversal enhancement of the eastward electric field is beyond the scope of this paper. These structures appear during the minimum of solar activity periods and are formed by the longitudinal variations of the horizontal thermospheric wind and the Pedersen conductivity arising from the action of the mesospheric tides. During solar activity minimum periods, the difference in the locations of geographic and geomagnetic poles leads to some complication and smoothing of the obtained picture of longitudinal variations in the electric field. We suggest that mesospheric tides have a significant effect on the longitudinal variation of the Pedersen conductivity, while the longitudinal variation of the Hall conductivity is mainly determined by the mismatch of geographic and geomagnetic poles. The amplitudes of the equatorial electric field longitudinal variations are three to four times smaller than the amplitudes of their diurnal variations, however, they can have a significant impact on the spatial distribution of the electron density in the F region of the low-latitude ionosphere.

Statistics of spread F characteristics across different sectors and IRI 2016 prediction

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): A.O. Afolayan, J.S. Mandeep, M. Abdullah, S.M. Buhari

Abstract

The occurrence of the plasma irregularity and the related scintillation have been extensively investigated as a result of the impact on radio signal propagation. This study focused on the equatorial spread F (ESF) occurrence using ionogram data and IRI prediction taken across different longitude sectors, including the Jicamarca, Fortaleza, Ilorin, Chumphon and Kwajalein ionosonde stations. We have briefly discussed the varying range type spread F (RSF) occurrence features across these stations such as the duration, onset time and seasonal asymmetry. The largest seasonal average of the RSF occurrence percentage was recorded at the Ilorin station during the low solar activity, while the occurrence rate at the Chumphon and Kwajalein stations increases significantly with the solar flux intensity. Furthermore, we presented a comparative analysis of the observed RSF occurrence rate and the IRI model prediction. The result exhibited a significant error percentage across these longitudes. The IRI could not reproduce significant features such as the delayed RSF onset at the Kwajalein station during June solstice or the equinox asymmetry in the RSF occurrence across these longitudes. Surprisingly, the IRI model also performed poorly at the Brazilian longitude. These observations highlight the strong dynamic nature of the RSF features across the different regions. Hence, an extensive dataset of the RSF occurrence distribution selected with cognizance for the longitudinal pattern of the major factors controlling the phenomenon is considered necessary for the further improvement of the empirical model.

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

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

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.

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

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

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.

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

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

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.

Chemical physics of D and E layers of the ionosphere

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

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.

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

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

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: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

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.

Advanced meteor radar observations of mesospheric dynamics during 2017 minor SSW over the tropical region

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): S. Eswaraiah, M. Venkat Ratnam, Yong Ha Kim, Kondapalli Niranjan Kumar, G. Venkata Chalapathi, L. Ramanajaneyulu, Jaewook Lee, P. Vishnu Prasanth, K. Thyagarajan, S.V.B. Rao

Abstract

The observations of the advanced meteor radar at the Indian tropical station Tirupati (13.63°N, 79.4°E) have been used to investigate the effects of the 2017 minor Sudden Stratospheric Warming (SSW) on the tropical mesosphere and lower thermosphere (MLT). The episodic minor warmings were observed in February 2017 with the gain of ∼40 K in the polar stratospheric temperature (PST), followed by a weakening of the eastward wind by 27 m/s. The observations show the large temporal variations in the zonal wind at 75–80 km during the SSW. We report the occurrence of 14–16 day waves in the MLT zonal wind during SSW and the secondary waves (2–7 days) in the meridional wind after SSW. A large enhancement (∼30 m/s) is observed in the amplitude of the semi-diurnal tide (SDT) during the SSW. The present results are similar to those observed during the major SSW. Therefore, the present results stress that the studies of minor SSW on the tropical MLT dynamics must be important.

Turbopause range measured by the method of the artificial periodic irregularities

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): A.V. Tolmacheva, N.V. Bakhmetieva, G.I. Grigoriev, M.N. Egerev

Abstract

A new opportunity for estimating the level of the turbopause is presented. It is based on the method of determining atmospheric parameters using artificial periodic irregularities of the ionospheric plasma (the API techniques). The obtained data show the presence of variations of the level of the turbopause. Experiments were carried out using SURA heating facility (56.1°N, 46.1°E) for API creation. Above the observation point the turbopause region occupies the altitude interval between 94 and 106 km. There are changes in the level of the turbopause during the day: in the evening hours the turbopause level can go down. Temporal variations of the turbopause level are observed. They are compared with variations in the atmospheric parameters at these heights.

Observation of mesospheric wave using collocated OH airglow temperature and radar wind measurements over Indian low latitude

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): R.N. Ghodpage, Alok Taori, O.B. Gurav, P.T. Patil, S. Gurubaran, Devendraa Siingh, G.P. Naniwadekar

Abstract

We analyzed the mesospheric winds and temperature data for investigating the waves scaling from the period of few hours to several hours (and few days) based on the airglow observations at Kolhapur (16.8°N, 74.2°E, 10.6°N dip. lat.). The data presented in this study are collected using medium frequency radar and Multispectral Scanning Photometer at low latitude station Kolhapur. We scrutinized the wind and temperature relation of these waves for the observed period from January to May 2011. The data of 56 clear nights were collected and out of which 22 nights of data shows a conspicuous wavelike features. The nocturnal variability reveals the prominent wave signatures with a period which range from 7 to 12 h (h) as a dominant nocturnal wave. The presence of quasi 2.8–4 days waves with significant amplitudes is also detected. The comparison of the winds and temperatures suggests the temperature waves to be near in phase with meridional wind component and a time delayed relation with the zonal wind component.

Comparison of IRI-2016 model-predictions of F2-layer peak density height options with the ionosonde-derived hmF2 at the equatorial station during different phases of solar cycle

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): O.S. Oyekola

Abstract

We have investigated the performance of 2016 International Reference Ionosphere (IRI) at equatorial Ouagadougou (12.4°N, 358.5°E; dip latitude: 1.5°N), Burkina Faso station, using 4 years 5 months of hourly monthly median M(3000)F2 values from January to May 1986 and from January 1987 to December 1990 using Shimazaki (1955) analysis technique. The deduced values of hmF2 are compared with the predictions of the three global IRI-2016 hmF2 model options for four different levels of solar activity with yearly averaged solar flux intensity F10.7 value of 85, 140, 214 and 190, corresponding to a year of 1987 solar minimum, 1988 moderate solar activity, 1989 very high solar activity and 1990 solar maximum, respectively. We find that the three IRI-hmF2 models: SHU-2015, AMTB-2013, and BSE-1979 reproduce the diurnal features of ionosonde-based hmF2 fairly well, showing daytime maximum and the prominent evening peak, except for solar cycle minimum where such feature is absent in Bilitza et al. (1979) and weakly expressed in Shubin (2015) hmF2 models. The magnitudes of the evening peaks in hmF2 for both data and models essentially correlate with solar activity but the occurrence times are independent of the phases of the solar cycle for all models. On average, the dayside maximum occurs between about noon and 1400 LT for both ionosonde-derived hmF2 and IRI models with typical values of 430 and 420 km, while the prominent evening peak in hmF2 occurs between about 1800–1900 LT with characteristic values of 390–450 km. We observed SHU-2015 persistently occur at about 1800 LT with a lower magnitude compared to ionosonde-based hmF2, the digisonde-based hmF2 model (AMTB), and Bilitza et al. (1979) model. We also show that SHU-2015 is consistently and significantly lower in values that the ionosonde hmF2, AMTB-2013 and BSE-1979 models. SHU-2015 deviates from data by about 2 times during low and median solar activity years but diverges by about 3–4 times during very and high solar maximum. Quantitative analyses indicate that the average absolute discrepancy between ionosonde-derived hmF2 and IRI model is 15%, 5.2% and 5.8% for SHU-2015, AMTB-2013, and BSE-1979, respectively. SHU-2015 model root-mean-squared error (RMSE) varies strongly with increasing solar activity with magnitudes roughly within the range ∼41–74 km, whereas AMBT-2013 and BSE-1979 RMSE vary between ∼19–36 km and ∼25–27 km, correspondingly. BSE-1979 RMSE does not exhibit any dependence on solar activity, while AMBT-2013 RMSE appears to decrease with an increase in solar activity. In contrast, SHU-2015 mean-relative-deviation (MRD) increases dramatically with increasing solar activity with values between ∼10–16%. AMTB-2013 and BSE-1979 both indicate a slight decrease with increasing solar activity, with values ranging between ∼3.3–8.9% and ∼4.8–6.7%, respectively. On the basis of evidence provided in this work, we conclude that AMTB-2013 and BSE-1979 have higher accuracy than SHU-2015. Although the hmF2 calculated from ionograms and from empirical formula of Shimazaki could differ rather substantially from the real hmF2 values, especially in the equatorial region. The results of this study show that the AMTB-2013 and BSE-1979 models describes better the hmF2 obtained from the M(3000)F2 values, consequently, we recommend AMTB-2013 and BSE-1979 for equatorial region over West African longitude sector.

An evaluation of the IRI-Plas-TEC for winter anomaly along the mid-latitude sector based on GIM-TEC and foF2 values

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): G.I. Gordiyenko, O.A. Maltseva, F. Arikan, A.F. Yakovets

Abstract

Total Electron Content (TEC) has become one of the most widely used observable parameters of the ionosphere. IRI-Plas is an empirical climatic model of the ionosphere and plasmasphere that extends up to GPS orbital height of 20,000 km. The purpose of the study is to reveal whether the winter anomaly (a phenomenon where the mid-latitude daytime NmF2 (or foF2) is greater in winter than in summer at approximately the same solar activity level) occurs in TEC over the Asian sector and how well it is “captured” by IRI-Plas. The study is based on GPS-TEC data derived from Global Ionospheric Maps (GIM-TEC) for January and July months of high (2000), low (2009) and moderate (2012) levels of solar activity. Ionosonde data recorded at a number of mid-latitude Russian and Kazakhstan ionospheric stations in winter and summer seasons for different levels of solar activity are used along with corresponding IRI-Plas calculations to illustrate some specific features of seasonal variations of the midlatitude ionosphere. A comparative study made between IRI-Plas-foF2 and ionosonde foF2 indicates that the IRI-Plas-foF2 variations are found to be in good agreement with the observations showing similar structures, similar magnitudes reflecting the winter anomaly in the diurnal variations. When the IRI-Plas-TEC values are examined for the difference between winter and summer seasons, it is found that their variations are mainly similar to those of IRI-Plas-foF2. Different from that of IRI-Plas-TEC, the winter anomaly in GIM-TEC is not so strong, appears for both high and moderate levels of solar activity, and it is more pronounced at higher latitudes. In low solar activity, the winter anomaly in GIM-TEC is almost absent at the region considered. Finally, the comparison of the IRI-Plas-TEC and GIM-TEC results for winter conditions show that the IRI-Plas-TEC values are significantly larger than those of daytime GIM-TEC at all locations of Russia and Kazakhstan and for all levels of solar activity that coincides with results of previous studies. However, unlike the previous studies, in summer solstice, IRI-Plas-TEC systematically underestimates the GIM-TEC values during high solar activity year and mostly overestimates them for low solar activity. In moderate solar activity year, IRI-Plas-TEC and GIM-TEC values are practically comparable. Thus, the IRI-Plas-TEC model represents the seasonal anomaly observed in foF2 in mid-latitude region for all levels of solar activity but there is a certain deviation from the behavior of GIM-TEC. One of the main reasons of this discrepancy may be the difference of the model Ne(h)-profile from a realistic profile in the upper ionosphere and plasmasphere, that demands additional updating of models for those upper atmosphere regions.

Signatures of substorm related overshielding electric field at equatorial latitudes under steady southward IMF Bz during main phase of magnetic storm

Publication date: 15 November 2019

Source: Advances in Space Research, Volume 64, Issue 10

Author(s): Bhaskara Veenadhari, Takashi Kikuchi, Sandeep Kumar, S. Tulasiram, D. Chakrabarty, Yusuke Ebihara, G.D. Reeves

Abstract

During the geomagnetic storm periods, the convection electric field penetrates promptly to equatorial latitudes, causing an eastward electric field in the dayside ionosphere. Occasionally, the polarity of the dayside ionospheric electric field is inverted when the Interplanetary Magnetic Field (IMF) turns northward. In this paper, interesting observations of the strong westward electric field in the day side equatorial latitudes are presented, as evidenced by strong Counter Electrojet (CEJ) at Indian and Japanese sectors under the steady southward IMF Bz. The westward electric field perturbations are quite large with CEJ amplitude of ∼−120 nT over the Indian sector (14–15 December 2006) and ∼−220 nT for Japanese sector (7–8 November 2004). The plausible mechanisms for the observed overshielding electric fields under steady southward IMF Bz have been investigated in light of the possible role of substorm activity. The clear signatures of substorm were observed at geosynchronous particle flux measurements from LANL (Los Alamos National Laboratory) satellite and associated with sudden decrease in AL index. The observed variations of asymmetric ring current shows the enhancement of Partial Ring Current (PRC) at the dusk sector further supporting the substorm onset during that period which will probably enhance the overshielding due to increased Region 2 Field-Aligned Currents (R2 FACs). The observations of such significantly large amplitudes of CEJ associated with the substorm related overshielding events are sparse and the results bring out the important role of substorm onset and the development of PRC in accordance with the R2 FACs during intense magnetic storms which alter the day time equatorial electric field perturbations.

Simulating lightning NO production in CMAQv5.2: performance evaluations

Geoscientific Model Development - Mon, 10/21/2019 - 18:49
Simulating lightning NO production in CMAQv5.2: performance evaluations
Daiwen Kang, Kristen M. Foley, Rohit Mathur, Shawn J. Roselle, Kenneth E. Pickering, and Dale J. Allen
Geosci. Model Dev., 12, 4409–4424, https://doi.org/10.5194/gmd-12-4409-2019, 2019
This paper provides a comprehensive evaluation of the lightning production schemes in CMAQ as described in https://www.geosci-model-dev.net/12/3071/2019/gmd-12-3071-2019.html on model performance. The impact of lightning NOx from different schemes is evaluated in time and space using both ground–level network measurements and aloft (ozonesonde and aircraft) observations. These results provide users the benchmark model performance when the lightning NOx production schemes are applied.

ELIFAN, an algorithm for the estimation of cloud cover from sky imagers

Atmos.Meas.Tech. discussions - Mon, 10/21/2019 - 17:35
ELIFAN, an algorithm for the estimation of cloud cover from sky imagers
Marie Lothon, Paul Barnéoud, Omar Gabella, Fabienne Lohou, Solène Derrien, Sylvain Rondi, Marjolaine Chiriaco, Sophie Bastin, Jean-Charles Dupont, Martial Haeffelin, Jordi Badosa, Nicolas Pascal, and Nadège Montoux
Atmos. Meas. Tech., 12, 5519–5534, https://doi.org/10.5194/amt-12-5519-2019, 2019
In the context of an atmospheric network of instrumented sites equipped with sky cameras for cloud monitoring, we present an algorithm named ELIFAN, which aims to estimate the cloud cover amount from full-sky visible daytime images. ELIFAN is based on red-to-blue ratio thresholding applied on the image pixels and on the use of a blue-sky library. We present its principle and its performance and highlight the interest of combining several complementary instruments.

Evaluation of MOPITT Version 7 joint TIR–NIR XCO retrievals with TCCON

Atmos.Meas.Tech. discussions - Mon, 10/21/2019 - 17:35
Evaluation of MOPITT Version 7 joint TIR–NIR XCO retrievals with TCCON
Jacob K. Hedelius, Tai-Long He, Dylan B. A. Jones, Bianca C. Baier, Rebecca R. Buchholz, Martine De Mazière, Nicholas M. Deutscher, Manvendra K. Dubey, Dietrich G. Feist, David W. T. Griffith, Frank Hase, Laura T. Iraci, Pascal Jeseck, Matthäus Kiel, Rigel Kivi, Cheng Liu, Isamu Morino, Justus Notholt, Young-Suk Oh, Hirofumi Ohyama, David F. Pollard, Markus Rettinger, Sébastien Roche, Coleen M. Roehl, Matthias Schneider, Kei Shiomi, Kimberly Strong, Ralf Sussmann, Colm Sweeney, Yao Té, Osamu Uchino, Voltaire A. Velazco, Wei Wang, Thorsten Warneke, Paul O. Wennberg, Helen M. Worden, and Debra Wunch
Atmos. Meas. Tech., 12, 5547–5572, https://doi.org/10.5194/amt-12-5547-2019, 2019
We seek ways to improve the accuracy of column measurements of carbon monoxide (CO) – an important tracer of pollution – made from the MOPITT satellite instrument. We devise a filtering scheme which reduces the scatter and also eliminates bias among the MOPITT detectors. Compared to ground-based observations, MOPITT measurements are about 6 %–8 % higher. When MOPITT data are implemented in a global assimilation model, they tend to reduce the model mismatch with aircraft measurements.

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