Journal of Atmospheric and Solar-Terrestrial Physics

Long term air ion monitoring in search of pre-earthquake signals

Tue, 04/02/2019 - 19:10

Publication date: May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 186

Author(s): Sheldon Warden, Tom Bleier, Karl Kappler

Abstract

Air ion concentrations at ground level have been measured both indoors and outdoors to address a wide variety of questions, such as estimating air quality or assessing the impact of ions on human health. While most studies rely on discrete measurements, other applications require continuous monitoring over extended periods of time. In this paper, we discuss the challenges posed by long term air ion monitoring within the frame of earthquake forecasting. We first provide a brief state of the art, outlining the main hypotheses advanced to explain anomalies in air ion concentrations that were reported prior to earthquakes, namely the p-hole theory and the radon exhalation theory. We then describe the array of Gerdien capacitors deployed by QuakeFinder in the US and abroad with the goal to identify pre-earthquake variations in air ion data: we discuss the characteristics of these instruments and derive the criticial mobility associated with their parallel-plate geometry. We then present the results of a Parallel Sensor Test (PST) during which positive and negative air ion counters were deployed side by side at increasing separation distances. This test provides insight about the sampling rate at which air ion concentrations should be measured with the QuakeFinder air ion counters.

The main processing steps applied to raw air ion data are then described. Particular emphasis is set on the unipolarity coefficient and how it may be used to identify faulty sensors. One of the key issues encountered while monitoring air ion concentrations for extended periods of time is the condensation forming on the electrodes due to increased relative humidity levels. It appears that the relative humidity working range provided by instruments manufacturers is not accurate for long term outdoors measurement and that sensors saturate at relative humidity values lower than the threshold advertised in the instrument specifications. We detail some of the strategies implemented to automatically reject data acquired during episodes of high relative humidity. Finally, we discuss the instrumental improvements that can be made to prevent moisture from forming on the plates of the Gerdien capacitors and that QuakeFinder plans to implement in the near future.

Oblique absorption effects of the <em>D</em> region during HF waves heating

Tue, 04/02/2019 - 19:10

Publication date: May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 186

Author(s): Qi Cheng, Li-xin Guo, Hui-min Li, Jiang-ting Li, Dan Zhang

Abstract

With the development of heating research, the oblique heating effects of the D region are becoming increasingly important. For the vertical heating, the larger the beam width of heating wave is, the more evident the oblique effects are; For the oblique heating, the D region which also exhibits evident heating effects has received less attention than the F region in previous studies; Furthermore, the oblique heating effects of the D region should be considered for the studies on multi-beam modulation heating that has arisen recently. Therefore, the numerical model for oblique heating needs to be established to develop the heating study in the D region. In this paper, the classical model for vertical heating is improved by further considering the lossy characteristic of the D region. An added factor, the real part of the refractive index, is introduced to estimate the power density of heating wave. Based on this improved model, the oblique heating model is presented by applying the oblique extension of Wentzel-Kramers-Brillouin (WKB) method and “real pseudo ray” approximation. Considered that the D region presents horizontally discrete strata, oblique absorption effects are quantitatively studied by powerful high-frequency wave heating. Notably, the electron energy absorption occurs only along the vertical direction at the different incident angles due to the special spatial characteristic of the D region. Results show that with the increase of incident angle, the absorption index increases whereas the effective power density of oblique heating wave has a considerable reduction. Therefore, the larger the incident angle is, the less the electron temperature increases. Moreover, the electron temperature in the upper region is more sensitive to variations in incident angles than that in the lower region. In the upper D region, two additional factors severely restrict the enhancement of electron temperature. The self-absorption of the heating wave, well-known as one factor, decreases with the increase of incident angle. Another factor, the real part of refractive index which is neglected in past studies also restricts the increase of electron temperature in the upper D region.

Dynamical processes in the ionosphere following the moderate earthquake in Japan on 7 July 2018

Tue, 04/02/2019 - 19:10

Publication date: May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 186

Author(s): Qiang Guo, L.F. Chernogor, K.P. Garmash, V.T. Rozumenko, Yu Zheng

Abstract

The response of the ionosphere to the earthquake of a moderate magnitude (M ≈ 5.9) that occurred in Japan at 11:23:50 UT on 7 July 2018 has been studied using a newly developed coherent multi-frequency radio diagnostic system for remotely probing the ionosphere at oblique incidence. The seismic activity in Japan on 7 July 2018 was accompanied by aperiodic processes in the ionosphere at distances of no less than (1–2) × 103 km from the epicentre, with an enhancement in multiple-mode propagation, and a significant Doppler spectrum broadening. Three ways of transporting disturbances from the earthquake to the changes in the character of Doppler spectra variations have been identified by examination. First, the disturbances are generated by a surface Raleigh wave launched at the earthquake epicentre. They have been ascertained in the infrasonic range (a 3- to 4-min period) of oscillations. The relative amplitude of these quasi-periodic oscillations in the electron density is equal to 1.7–9%. The duration of the oscillation trains is found to be in the range of 24–55 min. The wave disturbance speed of propagation is approximately 3 km/s. Second, wave disturbances have also been ascertained in a 15- to 30-min period range. They could be generated in the vicinity of the epicentre and then propagated as atmospheric gravity waves modulating the electron density in the ionosphere. The relative amplitude of the quasi-periodic disturbances in the electron density is equal to 14 – 34%. The wave train attains a temporal duration of about 100 min and a speed of approximately 0.3 km/s. Third, the broadening of the Doppler spectra toward negative Doppler shifts with the time delay estimated to be 49–124 min, depending on the orientation of the propagation path, is the most pronounced Doppler signature of the disturbances caused by the earthquake. This time delay corresponds to a speed of about 0.3 km/s, and consequently, it suggests that this effect most likely is caused by the atmospheric gravity waves launched at the earthquake epicentre. Apparently, the rearrangement of the ionosphere acts to reverse the sign of the Doppler spectrum shift when the atmospheric gravity waves arrive at the reflection level.

The semidiurnal tide for individual nights derived consistently from O<sub>2</sub> and OH intensities and temperatures

Tue, 04/02/2019 - 19:10

Publication date: May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 186

Author(s): Esteban R. Reisin, Jürgen Scheer

Abstract

The semidiurnal tide is studied with 159 special cases from the large airglow database acquired at El Leoncito (31.8ºS, 69.3ºW). These cases correspond to nights which exhibit similar periods in the temperature and intensity variations of the OH(6-2) and O2b(0–1) emissions. We find that all the periods (except one) are between 9 and 15.5 h. The phase distributions of these cases are narrow enough to ensure the identification as the semidiurnal tide, and their progression with altitude is consistent with downward phase propagation. The mean temperature amplitudes are large for both emissions. We obtain new values for Krassovsky's ratio including its phase. The vertical wavelength is determined independently for each emission using the relation suggested by the Hines and Tarasick theory. Mean vertical wavelengths derived for O2 are longer than those for OH. The longest monthly mean wavelengths are observed from May to August. The mean ratio of temperature amplitudes between the two emissions corresponds to moderate wave attenuation during the upward propagation of the tide.

Variation in MERRA-2 aerosol optical depth and absorption aerosol optical depth over China from 1980 to 2017

Tue, 04/02/2019 - 19:10

Publication date: May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 186

Author(s): Enwei Sun, Xiaofeng Xu, Huizheng Che, Zhiwei Tang, Ke Gui, Linchang An, Chunsong Lu, Guangyu Shi

Abstract

4258 instantaneous 550 nm Aerosol Optical Depth (AOD) values were compared between the second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) and the Aerosol Robotic Network (AERONET) in four seasons at 12 AERONET sites across China. The correlation coefficients (R) in spring, summer, autumn and winter were 0.88, 0.92, 0.91 and 0.87, respectively. The MERRA-2 AOD was compared with the Moderate resolution Imaging Spectroradiometer (MODIS/Aqua) AOD over China from 2003 to 2017, and good agreement was obtained. 4501 daily AOD values were compared between MERRA-2 and MODIS at 16 sites over China. Spatial distribution and temporal variation of MERRA-2 AOD over China were analyzed from 1980 to 2017. Mean values of MERRA-2 AOD indicated that high AOD mainly appeared in the eastern, southeastern and central China, while low AOD mostly occurred in the western and northeastern China. Mean AOD values over China during this study period in each month was also discussed, and similar spatial distribution (high AOD in developed areas, low AOD in rural and less developed areas) was found in each month. Slight AOD increase could be observed in the 1980s and 1990s, and a rapid increase happened from 2001 to 2010, followed by an AOD decrease between 2011 and 2017. Annual variation of mean AOD of the whole China (the Yangtze River Delta) showed a slight increase of 0.0010 (0.0045) per year from 1980 to 1999, a rapid increase of 0.0096 (0.0271) per year between 2000 and 2009, and a decrease of −0.0089 (−0.0206) per year from 2010 to 2017. Annual AOD Variation in Jing-jin-ji and Pearl River Delta is similar to that in the Yangtze River Delta. In four seasons, AOD change was similar to the annual AOD variation except winter with a slight decrease of −0.0012 per year between 1980 and 1999. AOD variation over China before and after the Pinatubo volcanic eruption in the Philippines in June 1991 was analyzed to get a better understanding of the transport and the impact on the environment from volcanic pollutants. AOD variation trend over China was studied in two periods. The increasing trend appeared in most part of China from 1980 to 2009, while a decreasing trend could be found in almost the entire China between 2010 and 2017. Spatial and temporal variation of MERRA-2 Absorption Aerosol Optical Depth (AAOD), Black Carbon Absorption Aerosol Optical Depth (BCAAOD) and Dust Absorption Aerosol Optical Depth (DUAAOD) were analyzed during the period between 1980 and 2017. BCAAOD (66.30%) and DUAAOD (30.56%) offered the major contribution to total AAOD in China. 38 years of variation of AAOD over China is mainly due to the variation of BCAAOD. BCAAOD experienced an increase (1980–2007) and a decrease (2008–2017) during the 38 years in China.

Seasonal variations of sea breeze and its effect on the spectral behaviour of surface layer winds in the coastal zone near Visakhapatnam, India

Tue, 04/02/2019 - 19:10

Publication date: May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 186

Author(s): N.V.P. KiranKumar, K. Jagadeesh, K. Niranjan, K. Rajeev

Abstract

Seasonal variation of sea breeze (SB) characteristics and its effect on turbulence spectra at Visakhapatnam (17.7°N, 83.3°E) located at east coast of Peninsular India are investigated by considering 244 sea breeze events during December 2012 to March 2014. The delayed onset of backdoor SB during winter occurs due to the southward component of shore-parallel background winds while the prevailing northward component of background wind enable the early onset of corkscrew SB during pre-monsoon and summer monsoon. The turbulence spectral peak of horizontal winds shifts to higher frequency side after SB onset.

Solar activities and climate change during the last millennium recorded in Korean chronicles

Tue, 04/02/2019 - 19:10

Publication date: May 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 186

Author(s): Hong-Jin Yang, Chan-Gyung Park, Rok-Soon Kim, Kyung-Suk Cho, Junhyeok Jeon

Abstract

Korean chronicles have a large amount of observational records of natural phenomena, including astronomical and meteorological events over two thousand years. Here we examine the correlation of solar activity and climate change from historical sunspot and frost records in the Korean chronicles. There are 42 sunspot records in Goryeo Dynasty (918–1392 CE) and 13 records in Joseon Dynasty (1392–1910 CE). The sunspot records in Goryeo Dynasty show a periodicity in good agreement with the well-known solar activity of 11 years. Korean sunspot records suggest that the solar activity in Joseon Dynasty decreased compared with that in the previous ∼500 years. In order to examine the long-period variation of solar activity, we include Chinese historical sunspot records in our analysis to supplement the lack of Korean records, and find a new ∼240-yr long-period solar activity from the power spectral analysis. Korean chronicles also have about 700 frost records during the last millennium. We investigate these frost records and find a sign of cooling down that can be interpreted as climate change during the last millennium. We also find ∼240-yr cooling period from the historical frost records, which is well in accord with that of solar activity. Therefore, we conclude that the solar activity has decreased during the last one thousand years and also has a long-term variation of ∼240 years.

Editorial Board

Sun, 03/10/2019 - 19:10

Publication date: April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 185

Author(s):

Optical and physical properties, time-period, and severity of dust activities as a function of source for the main dust sources of the Middle East

Sun, 03/10/2019 - 19:10

Publication date: April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 185

Author(s): A. Masoumi, E. Laleh, A. Bayat

Abstract

To achieve long-time and comparable aerosol properties with the maximum geographical coverage possible in the Middle East, four AERONET sites (Kuwait university, Solar village, IASBS, and Mezaira) are selected. Aerosol optical depth (AOD) at 870 nm, Ångström exponent (α) for two wavelengths, 440 and 870 nm, real and imaginary parts of aerosol refractive index at 870 nm (mr, mi), and aerosol effective radius are studied for these sites during 2010–2017. Daily-mean values of aerosol properties (mr ≥ 1.51, mi ≤ 0.013, and α ≤ 0.88), show that dust particles are the dominant aerosol type in the atmosphere of the Middle East area. It has been seen that dusty days (daily-mean AOD(870) ≥ 0.50, and α ≤ 0.50), assign a notable percentage (14%–19%) of all days of data for all sites with the exception of the IASBS site. Based on the monthly-averaged MODIS-Terra Deep Blue AOD at 550 nm, it is seen four main dust sources in the Middle East: Mesopotamian area in Iraq and East Syria, northern part of the Arabian Peninsula, Elrob Elkhali desert at southern part of the Arabian Peninsula, and sources of East Arabian Peninsula located in Oman country. All sources of dust are active during dry months in spring and summer seasons. The monthly-averaged wind field data of ERA-interim ECMWF model reveals that dust events in northern part of the Arabian Peninsula are mainly originated from North Arabian Peninsula (Tigris-Euphrates basin) sources in spring (summer). In East Arabian Peninsula (Mezaira site), dusty conditions have continued until late summer and it is related to dust activities of sources, located at southern (Elrob Elkhali desert) and eastern part (Oman country) of the Arabian Peninsula. Dust recorded in Iran plateau (IASBS site), can be originated from sources of Tigris-Euphrates basin via westerly wind at higher altitudes. Also, it seems that dust particles originated from Tigris-Euphrates basin, have smaller sizes and higher values of complex refractive index and therefore it is essential to consider source functionality of dust particles optical and physical properties for each sub-region of the Middle East.

On the linear theory of oblique magnetospheric chorus excitation

Sun, 03/10/2019 - 19:10

Publication date: April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 185

Author(s): P.A. Bespalov, O.N. Savina

Abstract

Some aspects of the theory of generation of magnetospheric chorus are discussed. An original approach to solving the problem of oblique chorus generation near the Gendrin angle is outlined and partially realized within the framework of a beam pulsed amplifier mechanism. Parameters of the resonance electron beam in the chorus excitation region are determined theoretically. A short electromagnetic pulse amplification is calculated by means of a linear approach. Some important properties of the oblique chorus emissions, such as the location of the excitation region, frequency band, wave vector direction, group velocity direction, temporary dynamics, and energy of particles and waves are explained.

Spatio -temporal variations in urban heat island and its interaction with heat wave

Sun, 03/10/2019 - 19:10

Publication date: April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 185

Author(s): Shahnilla Haider Rizvi, Khan Alam, Muhammad Jawed Iqbal

Abstract

Most of the urban localities are facing the effects of Urban Heat Island (UHI) and extreme heat wave (HW) events. It is expected that these HW events are likely to be intensified by the effect of UHI in the future. As these events project to increase in both severity and frequency therefore, it is crucial to assess the intensity of UHI and examine the relationship between HW and UHI. In this study, observations for different coastal areas are used to quantify the impacts of UHI during the HW events. The spatial and temporal variability patterns of UHI in the metropolitan city of Karachi were also investigated using hourly temperature observations for a period of 10 years in two phases (a) from 1998 to 2002 (b) from 2012 to 2016. During the first phase (1998–2001), the maximum Urban Heat Island Intensity (UHII) for night time in summer was 1.9 °C, while during the second phase (2012–2016), it increased by 0.6 °C. Despite the fact that both phases have shown similar pattern for seasonal UHII, urban-rural temperature difference was found to be significant in summer especially in the night time. Temporal distribution of UHII for winter shows that average intensity of UHI during daytime varies between 0.1 °C and 3.2 °C, considering the overall time duration. The results indicate that UHII increased significantly during the HW period which caused more than 800 deaths in Karachi between 17th June and 24th June 2015.

Correlations between the CME acceleration, other CME parameters and flare energy

Sun, 03/10/2019 - 19:10

Publication date: April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 185

Author(s): G.S. Suryanarayana

Abstract

While the Coronal Mass Ejections (CMEs) without associated flares are known to accelerate and decelerate being moderated by the Lorentz force, gravity and the drag force due to solar wind, the flare association is known to prolong the acceleration. However, with or without the flare association, a significant proportion of slow CMEs decelerate and a similar proportion of fast CMEs accelerate. In the case of accelerating CMEs, various parameters of CMEs such as the mass, angular width etc. show good correlation and this improves with flare association. When the flares and CMEs are associated, there is apparently a division of energy between the flares and the CMEs. It is also known that the magnetic flux spanned by the flare arcade and ribbons after flare maximum, roughly equals the magnetic flux content of the CME and their ratio could be between one and two. The magnetic flux content of the CME can be estimated from the final angular width of the CME. Hence, we suggest that the CMEs experience net acceleration when the different parameters of CMEs such as angular width, mass etc. are correlated and when the CME parameters are correlated with flare duration and peak flux. The absence of the same may lead to CMEs experience net deceleration.

Application of the T2-Hotelling test for investigating ionospheric anomalies before large earthquakes

Sun, 03/10/2019 - 19:10

Publication date: April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 185

Author(s): Zahra Sadeghi, Masoud Mashhadi-Hossainali

Abstract

In view of the frequent occurrence of large earthquakes, researchers have been always looking for ways to study and analyze these risky phenomena. Today, abnormal changes in ionosphere are taken as a means for this purpose. This article concentrates on the application of the T2-Hotelling test for detecting significant changes in the Total Electron Content (TEC) as an ionospheric parameter. The Global Ionosphere Maps (GIMs) are used for this purpose. The basic assumption is that TECs are normally distributed. This has been analyzed by using ten normality tests. Proposed method statistically analyzes the mean TEC changes using two samples of TECs. The first or the reference sample is 30 days long. The second or the target sample which is a moving one in time is 4 days long. The method is applied to the entire globe and therefore is a global method in nature. TECs associated with high solar and/or geomagnetic activity are not used when the reference sample is made. A sample of 12 earthquakes, occurred in 2010, with the moment magnitudes greater than 6 is used to analyze the efficiency of the proposed method. For 75% of the earthquakes in this study, proposed method confirms the seismo-ionospheric anomalies some of which have been already reported in the other researches. The rest of the studied quakes conform to the assertion that seismo-ionospheric anomalies might not be clearly visible even for some large earthquakes.

Influence of solar activity changes on European rainfall

Sun, 03/10/2019 - 19:10

Publication date: April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 185

Author(s): Ludger Laurenz, Horst-Joachim Lüdecke, Sebastian Lüning

Abstract

European hydroclimate shows a high degree of variability on every time scale. The variability is controlled by natural processes such as Atlantic ocean cycles, changes in solar activity, volcanic eruptions and anthropogenic factors. This contribution concentrates on the solar influence on European precipitation, a relationship which has been documented by a large body of published case studies. Here we are concentrating on the period 1901–2015 for which we compare sunspot data with monthly precipitation series of 39 European countries by calculating Pearson correlation coefficients for a multi-year cross-correlation window. The coefficients have been mapped out across Europe with the aim to identify areas in which solar activity may have influenced precipitation. Results show that February precipitation in Central and Western Europe yields the strongest solar response with coefficients reaching up to +0.61. Rainfall in June–July is equally co-driven by solar activity changes, whereby the solar-influenced zone of rainfall shifts from the British Isles towards Eastern Europe during the course of summer. Other months with noteworthy solar responses are April, May and December. On a decadal scale, the correlation between precipitation and solar activity in central Europe appears to be mostly positive, both statistically and by visual curve comparison. Yet, best positive correlations coefficients of February, June, July and December are typically reached when the solar signal lags rainfall by 1.5–2 years. Taking into account cause and effect, it is suspected that increases in Central European rainfall are actually triggered by the solar minimum some 3–4 years before the rainfall month, rather than the lagging solar maximum. Similar lags of a few years occur between solar activity and the solar-synchronized North Atlantic Oscillation (NAO) due to memory effects in the Atlantic. The literature review demonstrates that most multidecadal studies from Central Europe encountered a negative correlation between solar activity and rainfall, probably because short time lags of a few years are negligible on timescales beyond the 11 year solar Schwabe cycle. Flood frequency typically increases during times of low solar activity associated with NAO- conditions and more frequent blocking.

Causes of non-stationary relationships between geomagnetic activity and the North Atlantic Oscillation

Sun, 03/10/2019 - 19:10

Publication date: April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 185

Author(s): Václav Bucha

Abstract

The North Atlantic Oscillation (NAO) is known to be influenced by internal variability of the atmosphere and the ocean and respond to natural or anthropogenic external forcing. However, there is no consensus on the exact mechanisms. The NAO correlates with geomagnetic activity (considered as the parameter for the solar wind intensity) positively during one period (i.e. 1951–1996) but negatively in another period (i.e.1870–1950), making the Sun-climate connection a controversial subject. We try to explain this non-stationary relationship and to find the causes why the correlation had changed the sign during the past 148 years. At the times of low geomagnetic activity before 1950 and after 1997 the correlation between geomagnetic activity and the NAO was relatively weak. The variability of the NAO during those periods was mainly due to other processes. In order to answer the question why a more positive NAO phase has prevailed over the last 30 years of the past century, we study the geomagnetic signal near the surface conditioning upon the strength, shape and location of the stratospheric polar vortex and examine the immediate effect of geomagnetic storms in the troposphere. At times of prevailing high geomagnetic activity (1951–1996) the polar vortex strengthened. The effect of the solar wind was mainly over northern Europe in association with the positive phase of the NAO; a strengthened mid-latitude westerly jet kept the cold air in the Arctic and northern mid-latitudes became milder than average. When geomagnetic activity decreased, the stratospheric polar vortex also weakened. The solar wind signal prevailed over Canada in association with the negative NAO index and more of Arctic air was able to penetrate North America and Eurasia. We finally show that the geomagnetic storms may play a role in the acceleration of the downward penetration of pressure anomalies from the upper stratosphere into the troposphere.

Multi- decadal variations and periodicities of the precipitable water vapour (PWV) and their possible association with solar activity: Arabian Peninsula

Sun, 03/10/2019 - 19:10

Publication date: April 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 185

Author(s): A.H. Maghrabi

Abstract

In this study, radiosonde observations from seven sites in Saudi Arabia for the period 1985 to 2016 were utilized to investigate the interannual, monthly, and seasonal variations and trends of precipitable water vapour (PWV). The magnitudes of these trends have been characterized and tested using the Mann-Kendall (MK) rank statistics at different significance levels. A significant decrease in the annual mean PWV by about 7% is found for the entire period. A seasonal cycle of PWV with a maximum during summer time and a minimum during winter has been found and can be mostly attributed to the variations of air temperature. On a monthly basis, the PWV values revealed a decreasing trend with the rate of decrease ranging between 0.47 and 2.6 mm per 32 years. There was a decrease in PWV in all the seasons, but it was only significant for the spring season, when it was the highest (1.79 mm per 32 years).

Power spectra analyses using the Fourier Transform (FT) technique were carried out for the period 1985–2016 to investigate the periodicities in the PWV time series. Several long, mid, and short-term periodicities were recognized. Short-term periodicities such as one year, six months, three months, and four months were found. On the other hand, long and mid term periodicities such as 10.8–11 years, 1.7 years, and 1.3 years were detected. The obtained periodicities are similar to those reported by several investigators and found in solar, interplanetary, and cosmic ray parameters. The spectral results suggest that the obtained PWV periodicities in Arabian Peninsula are, possibly, related to the solar activities, as well as, the effect of terrestrial meteorological phenomena.

Editorial Board

Thu, 02/14/2019 - 19:10

Publication date: March 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 184

Author(s):

MLP based predictive model for surface ozone concentration over an urban area in the Gangetic West Bengal during pre-monsoon season

Thu, 02/14/2019 - 19:10

Publication date: March 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 184

Author(s): Goutami Chattopadhyay, Subrata Kumar Midya, Surajit Chattopadhyay

Abstract

The present paper reports a comparative study among two neurocomputing models in the form of Multilayer Perceptron (MLP) models and non-linear regression for the prediction of surface ozone (O3) during pre-monsoon season over Gangetic West Bengal (GWB), India considering NOx, SO2, PM10 and temperature as predictors. Learning the MLPs through gradient descent (GD) with tanhyperbolic and sigmoid nonlinearities, we found that all the models under consideration have almost the same degrees of prediction efficiency for O3 over GWB during pre-monsoon season with the said predictors. However, the MLP model with tanhyperbolic activation function is found to produce a significantly higher correlation and Willmott's index of agreement between actual and predicted O3 than the other models. Finally, MLP with GD learning characterized by tanhyperbolic nonlinearity is identified to have significant efficiency in surface ozone prediction over the region as mentioned above.

Morphology of the equatorial ionization anomaly in Africa and Middle East due to a sudden stratospheric warming event

Thu, 02/14/2019 - 19:10

Publication date: March 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 184

Author(s): O.S. Bolaji, E.O. Oyeyemi, O.E. Jimoh, A. Fujimoto, P.H. Doherty, O.P. Owolabi, J.O. Adeniyi, E.O. Falayi, E. Abe, R.O. Kaka, A. Kotoye

Abstract

Using total electron content (TEC) data deduced from 18 Global Positioning System (GPS) receivers in Africa and Middle East, we investigated the morphology of the equatorial ionization anomaly (EIA) and its underlying variations before, during and after the 2009 sudden stratospheric warming (SSW) event. A southern EIA crest stronger than the northern EIA crest was observed for most of the days before the SSW event, while the EIA troughs were significantly obliterated after these SSW induced phases. In addition to the observed marked depletion of the hemispheric EIA crests during the SSW peak phase, we observed a terdiurnal variation straddling the northern EIA crests. This background terdiurnal signature is suggested to be partly responsible for the transport of more plasma to the northern hemisphere at the expense of southern hemisphere during the SSW peak phase. The consequences are higher pre-noon and post noon crests in the northern hemisphere compared to a single crest in the southern hemisphere. Contrary to previous modeling and experimental reports that the reductions in ionospheric TEC are due to semidiurnal variations resulting from the SSW peak phase, our results show that a terdiurnal variation was responsible for reducing the EEJ strength and TEC at the E-region and F2-region's topside, respectively. At the southern middle latitudes, an underlying diurnal variation was seen to initiate an increment in TEC during the SSW descending phase.

Distinct thermospheric mass density variations following the September 2017 geomagnetic storm from GRACE and Swarm

Thu, 02/14/2019 - 19:10

Publication date: March 2019

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 184

Author(s): Liangliang Yuan, Shuanggen Jin, Andres Calabia

Abstract

Geomorphologies and mechanisms of thermospheric mass density variations caused by geomagnetic storms are still challenging due to limited observations and imprecise models. Recently, precise orbit determination (POD) of Gravity Recovery and Climate Experiment (GRACE) and Swarm satellites is able to estimate thermospheric mass density variations, which may provide data to study thermospheric mass density variations following the storm. In this paper, the thermospheric mass density is estimated from GRACE-A and Swarm-A POD and the distinct thermospheric mass density variations are investigated as function of latitude during the September 2017 geomagnetic storm. Different enhancements in mass density response to the geomagnetic storm are presented for the Northern (GRACE) and the Southern (Swarm) Hemispheres. Swarm observations show symmetric mass density variations between two hemispheres and a slightly stronger enhancement in Southern Hemisphere. GRACE POD and accelerometer observations both show a very strong enhancement in Northern Hemisphere while no corresponding enhancement in Southern Hemisphere. This anomaly may attribute to the effects of vertical winds in high latitude region and plasma drift considering the similar solar zenith angles in both hemispheres.

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