Disturbed Days Research Articles

Modulation of Electromagnetic Ion Cyclotron Waves by Pc5 ULF Waves and Energetic Ring Current Ions

AbstractWe present a ground observation of modulations of strong electromagnetic ion cyclotron (EMIC) waves by short and long periodicities at Indian Antarctic station, Maitri. The signatures of these waves were evident in the magnetic field variations recorded by an induction coil magnetometer during the interval 4.7–7.2 UT on 17 September 2011, a moderately disturbed day. These waves were preceded by a gradual increase in the solar wind dynamic pressure, which started at 3.88 UT. The discrete rising tone EMIC waves were observed in the Pc1 frequency band (∼0.5–0.9 Hz). The investigation of the periodicities of the observed wave spectrogram shows the presence of short (≈2.4 min) and long (≈39–69 min) periodicities. Our analysis shows that the short periodicities are associated with the Pc5 Ultra Low Frequency (ULF) waves generated by magnetic field line oscillations, while long periodicities might be associated with the ring current drifting ions. A new method, based on the cross‐correlation technique, is adopted to determine sweep rates of the discrete rising tones. The average sweep rates estimated in the range of 0.44–1.9 mHz/s are relatively low as compared to the past reports of sweep rates derived from the satellite observations of EMIC waves. We found that the higher sweep rates are associated with the stronger EMIC waves on the ground, which is in agreement with the theoretical studies. This suggests that the theoretically proposed dependence of sweep rate on strength of EMIC wave in the generation region is retained even during the propagation of these waves to the ground.

A thermodynamic climatology of the disturbed stratospheric polar vortex

A climatology of polar vortex disturbances in the Northern Hemisphere winter stratosphere is constructed from MERRA2 Reanalysis data for the winter seasons of 1981–2017. Sixty disturbances (splits or displacements) of the polar vortex are identified during the 37 winter seasons using geometric moments of stratospheric potential vorticity. The likelihood of a disturbed day is negatively correlated with the stratospheric quasi‐biennial oscillation (positively correlated with its easterly phase). It is also, surprisingly, negatively correlated with the presence of a stratospheric Aleutian anticyclone (the Aleutian high). The position of the polar vortex during each disturbance event is averaged to generate an area‐averaging filter that is applied to thermodynamic diagnostic quantities in the air column enclosed by the polar vortex. This diagnosis reveals that the location of the disturbed polar vortex experiences, on average, cooling driven by horizontal temperature advection in the lower and middle stratosphere prior to the onset of the disturbance, along with significant residual (likely adiabatic) cooling in the troposphere in the weeks surrounding the onset. How these thermodynamic signatures associated with a disturbed polar vortex relate to the Aleutian high and the quasi‐biennial oscillation is also explored.

Characteristic of the Disturbed Days Ionospheric Current System in the 180-Degree Magnetic Meridian

The behavior of the ionospheric current during disturbed days using 10 geomagnetic observatories along 180-degree magnetic meridian was analysed. Separation of external and internal current during geomagnetic storm on 12 April until 15 April 2012 data was carried out using spherical harmonic analysis method. The contour of day to day variation of total current, external current and internal current were distinguished based on geomagnetic storm phase. These current then were correlate with the solar wind parameter, IMF Bz, and geomagnetic indices in order to identify their relationship. The results reveal that these current intensities were found higher during the initial phase. This due to the enhancement of the magnetic field during the initial phase caused by the increment of solar wind dynamic pressure and southward IMF Bz. Hence, the induced current identified in the internal current. This study demonstrated that the electric current induction can be obtained from the weak geomagnetic storm.

Earthquake/Tsunami‐Linked Imprints in the Equatorial F Region Zonal Plasma Drifts and Spatial Structures of Plasma Bubbles

AbstractWe report preseismic and postseismic distinct features observed in equatorial ionospheric F region in Indian longitude during two major earthquakes that occurred on 28 March 2005 (Mw=8.6) and 26 December 2004 (Mw=9.1) with epicenters near Sumatra, Indonesia. We used spaced receiver scintillation observations on a 251‐MHz signal transmitted from a geostationary satellite and recorded at dip equatorial station Tirunelveli, which is ≈2,200 km away from the epicenter of these earthquakes. On 28 March 2005, we noticed significant enhancement (≈88.5 m/s) in F region zonal plasma drift as compared to their seasonal quiet time drifts, 20 min prior to the start of earthquake. This implies the presence of additional vertically downward electric field of approximately 3 mV/m, which is linked with the earthquake mechanism. It is unusual because so far we have not encountered such feature on either magnetically quiet or disturbed days. Spatial scales associated with equatorial spread F irregularities generated in the postsunset hours on this earthquake day are considerably smaller. It suggests that the earthquake‐linked electric field influenced the structuring and evolution of equatorial spread F irregularities on this earthquake day. Another earthquake that occurred on 26 December 2004 triggered a tsunami. We noticed that the earthquake‐ and tsunami‐linked effects in the F region plasma drifts are distinctly observed even 18.5 hr after the earthquake.

Correlation of solar wind velocity with different parameters during geomagnetic disturbances

We have studied the solar wind velocity and it’s relation with solar wind pressure, southward component of IMF-Bz, solar wind temperature (Tsw), solar wind density (Nsw) and geomagnetic indices during different geomagnetic disturbances. During disturbed days, there is a fluctuation of energy and plasma inside the magnetosphere, which changes the parameters like pressure, velocity, IMF-Bz, SYM-H and AE indices. The solar wind velocity shows very remarkable relationship with pressure. There is weak connection of solar wind pressure with IMF-Bz, although it is more geo-effective.BIBECHANA 16 (2019) 165-176

Comparison of observed ionospheric vertical TEC over the sea in Indian region with IRI-2016 model

The vertical ionospheric TEC values obtained from GAGAN grid based ionospheric delay correction values over the sea in the Indian equatorial region have been compared with the corresponding values derived from the International Reference Ionosphere model, IRI-2016. The objective of this work is to study the deviation of the vertical TEC derived from the IRI model from ground truths over the sea for different conditions. This will serve the basic intention of assessing the candidature of the IRI model as an alternative ionospheric correction model in navigation receivers in terms of accuracy. We have chosen different solar activity periods, seasons, geomagnetic conditions, locations etc. for our comparison and analysis. The TEC values by the IRI-2016 were compared with the actual measured values for the given conditions and errors were obtained. The measured vertical TEC values at the ionospheric grid points were derived from the GAGAN broadcast ionospheric delay data and used as reference. The IRI model with standard internal functions was used in estimating the TEC at the same ionospheric grid points. The errors in the model derived values are statistically analysed. Broadly, the results show that, for the Indian sector over the sea, the IRI model performs better on quiet days in off equatorial regions, particularly in the northern region. The overall performance degrades for other conditions with the model generally underestimating the true TEC values and most severely in the equatorial region. The performance is worst in this region for the disturbed days of the equinoctial period. The comparison study is also done with the TEC data measured directly by dual frequency GPS receivers. The results were found to be in general agreement with those obtained by comparing the model with GAGAN broadcast data as reference. This study will be useful in considering the IRI-2016 model for real time estimates of TEC as an alternative to the current parametric model in a satellite navigation receiver in absence of other options.

Heliolatitude regularities of magnetically disturbed days with daily average geomagnetic index Dst<–100 nT

This paper considers storm days for a period 1966–2015 when the daily average geomagnetic Dst index was <–100 nT. The distribution of the number of days with a high daily average Dst is shown to depend on Earth’s heliolatitude φ: the number of days increases with the absolute value of φ in both solar hemispheres. It is found, as expected, that the seasonal distribution of storm days with Dst<–100 nT has equinoctial maxima. Moreover, there is a noticeable increase in the number of such days in July and November. It is noted that at Earth’s heliolatitudes 4.1°–5.0° there is a sharp increase in the number of storm days. It is established that this increase occurs during storm events in July and November, which stand out against the seasonal distribution of highly disturbed days.

Гелиоширотные закономерности магнитно-возмущенных дней со среднесуточным значением геомагнитного индекса Dst<–100 нТл

This paper considers storm days for a period 1966–2015 when the daily average geomagnetic Dst index was <–100 nT. The distribution of the number of days with a high daily average Dst is shown to depend on Earth’s heliolatitude φ: the number of days increases with the absolute value of φ in both solar hemispheres. It is found, as expected, that the seasonal distribution of storm days with Dst<–100 nT has equinoctial maxima. Moreover, there is a noticeable increase in the number of such days in July and November. It is noted that at Earth’s heliolatitudes of 4.1°÷5.0° there is a sharp increase in the number of storm days. It is established that this increase occurs during storm events in July and November, which stand out against the seasonal distribution of highly disturbed days.

Evaluation of the NeQuick model performance under different geomagnetic conditions over South Africa during the ascending phase of the solar cycle (2009–2012)

Abstract. In order to provide a scientific base to the NeQuick characterisation under disturbed conditions, the comparison of its performance for quiet and storm days is investigated in the southern mid-latitude. This investigation was realised using the two versions of the NeQuick model which were adapted to local and storm-specific response by using the critical frequency of the F2 layer (foF2) and the propagation factor (M(3000)F2) derived from three South African ionosonde measurements, Hermanus (34.40∘ S, 19.20∘ E), Grahamstown (33.30∘ S, 26.50∘ E) and Louisvale (28.50∘ S, 21.20∘ E). The number of free electrons contained within a 1 m squared column section known as total electron content (TEC) is a widely used ionospheric parameter to estimate its impact on the radio signal passing through. In this study, the TEC derived from the adapted NeQuick version is compared with observed TEC derived from Global Navigation Satellite System (GNSS) data from co-located or nearby GNSS dual-frequency receivers. The Hermanus K-index is used to select all the disturbed days (K-index ≥ 5) upon moving from low to high solar activity (from 2009 to 2012). For each disturbed day, a quiet reference day of the same month was chosen for the investigation. The study reveals that the NeQuick model shows similar reliability for both magnetic quiet and disturbed conditions, but its accuracy is affected by the solar activity. The model is much better for moderate solar activity epochs (2009 and 2010), while it exhibits a discrepancy with observations during high solar activity epochs. For instance in Hermanus, the difference between GPS TEC and NeQuick TEC (ΔTEC) is generally lower than 10 TECu in 2009, and it sometimes reaches 20 TECu in 2011 and 2012. It is also noticed that NeQuick 2 is more accurate than NeQuick 1, with an improvement in TEC estimation more significant for the high solar activity epochs. The improvement realised in the latest version of NeQuick is more than 15 % and sometimes reaches 50 %. Keywords. Ionosphere (mid-latitude ionosphere; modelling and forecasting)

Comparison of Variations of TEC at Disturbed and Quiet Time Using Nonlinear Dynamics Tools

AbstractWe analyze the underlying dynamics at three different latitudes of ionosphere through total electron content‐series for 4 months. The global dynamics reconstructed from the data is shown to be deterministic with low dimensional chaotic attractors at all the locations, and the dynamics is seen to be less complex at the midlatitude station with smaller dimension of correlation (CD) and maximum Lyapunov exponent (MLE). The influence of geomagnetic storms on the ionospheric dynamics is studied, by analyzing the local dynamics during disturbed and quiet periods, reconstructed from segments of total electron content‐series of shorter duration. With positive MLEs and smaller CDs, the local dynamics is seen to be deterministic and chaotic at the low latitude, midlatitude, and high latitude during both the disturbed and quiet days. However, it is interesting to observe that the dynamics is less chaotic and complex during the disturbed days of the entire period of observation compared to the adjacent quiet days at the three locations. This is further evidenced by sample predictions made using nonlinear tools, yielding better predictions during storms. The smaller CD value during disturbed periods indicates that the geomagnetic activities tend to make a few of the variables dominant enough to control the essential dynamics of the system. Further, the MLEs of the disturbed days are found to increase nearly in a linear fashion from beginning to end of the observation period at all the locations considered. This is an indication of the strong influence of geomagnetic activities on the ionosphere and might have caused the restructuring of the ionospheric dynamics.

Statistical Analysis of Separation Distance Between Equatorial Plasma Bubbles Near Suvarnabhumi International Airport, Thailand

AbstractIonospheric disturbances can lead to the major detrimental effects on the availability of ground‐based augmentation system. In low‐latitude regions, equatorial plasma bubbles (EPBs) frequently arise. They originated from the bottom side of the ionosphere with the electron density inside the plasma bubbles lower than the outside area. It is well known that the EPB causes the strong fluctuation on Global Positioning System signals when passing through the ionospheric disturbed regions. Sometimes the EPBs may have more than one front. To better understand the ionospheric anomaly effect on ground‐based augmentation system efficiency, the separation distance between EPBs needs to be studied. In this work, we analyze the slant total electron content from dual‐frequency Global Positioning System receivers near Suvarnabhumi International Airport, Thailand, to ascertain the EPB occurrence. The distance between observed EPBs is computed based on the Haversine formula technique. The results found that the estimated separation distances between depletions on disturbed days in 2015 are in the range of 100 to 1,200 km.

İyonkürede jeomanyetik aktivite günlerine göre ‘O+ + N2 → NO+ + N’ reaksiyonunun çarpışma parametrelerinin değişimi


 
 A plasma is a
 medium containing a large number of charged particle interactions. For this reason, it is common and appropriate to
 examine the plasma in terms of kinetic theory. In this context, the collision
 dynamics of the ‘O+ + N2
 → NO+ + N’ reaction for geomagnetically quiet day (04/09/2017)
 and disturbed day (08/09/2017) were calculated for ionospheric altitudes with
 the help of kinetic theory. As a result of the calculation, it was seen that
 the mean free path values were less on the disturbed day, as expected. The
 total collisions number was seen to reach maximum at the height of hmF2 on both
 quiet and disturbed days, and the disturbed day values were greater. It was
 seen that the collision frequency decreased exponentially with altitude. 
 

Regular Variations of Intensity of the Westward Auroral Electrojet according to the Geomagnetic AL Index

Diurnal and seasonal variations of the geomagnetic AL index are studied. It is found in disturbed days that the mode of AL diurnal variation depends on the angle between the Sun–Earth line prolongation in the direction towards the magnetotail and the plane of geomagnetic equator; on quiet days, AL depends on the angle of attack between the geomagnetic axis and the Earth–Sun line. Seasonal AL variations are characterized by annual variations with summer maximum and semiannual variations with equinoctial maxima. It is shown that the semiannual AL variations can be described by a simplified model of plasma convection in the magnetotail based on a plasma electron cooling mechanism.

Modeling ionospheric [formula omitted] response during geomagnetic storms using neural network and linear regression techniques

In this paper, the modeling of the ionospheric foF2 changes during geomagnetic storms by means of neural network (NN) and linear regression (LR) techniques is presented. The results will lead to a valuable tool to model the complex ionospheric changes during disturbed days in an operational space weather monitoring and forecasting environment. The storm-time foF2 data during 1996–2014 from Grahamstown (33.3°S, 26.5°E), South Africa ionosonde station was used in modeling. In this paper, six storms were reserved to validate the models and hence not used in the modeling process. We found that the performance of both NN and LR models is comparable during selected storms which fell within the data period (1996–2014) used in modeling. However, when validated on storm periods beyond 1996–2014, the NN model gives a better performance (R = 0.62) compared to LR model (R = 0.56) for a storm that reached a minimum Dst index of −155 nT during 19–23 December 2015. We also found that both NN and LR models are capable of capturing the ionospheric foF2 responses during two great geomagnetic storms (28 October–1 November 2003 and 6–12 November 2004) which have been demonstrated to be difficult storms to model in previous studies.

Effect of geomagnetic storms on the daytime low-latitude thermospheric wave dynamics

The equatorial- and low-latitude thermospheric dynamics is affected by both equatorial electrodynamics and neutral wave dynamics, the relative variation of which is dependent on the prevalent background conditions, which in turn has a seasonal dependence. Depending on the ambient thermospheric conditions, varying effects of the geomagnetic disturbances on the equatorial- and low-latitude thermosphere are observed. To investigate the effect of these disturbances on the equatorial- and low-latitude neutral wave dynamics, daytime airglow emission intensities at OI 557.7 nm, OI 630.0 nm, and OI 777.4 nm are used. These emissions from over a large field-of-view (FOV∼1000) have been obtained using a high resolution slit spectrograph, MISE (Multiwavelength Imaging Spectrograph using Echelle grating), from a low-latitude location, Hyderabad (17.50N, 78.40E; 8.90N MLAT), in India. Variations of the dayglow emission intensities are investigated during three geomagnetic disturbance events that occurred in different seasons. It is seen that the neutral dayglow emission intensities at all the three wavelengths showed different type of variations with the disturbance storm time (Dst) index in different seasons. Even though the dayglow emission intensities over low-latitude regions are sensitive to the variation in the equatorial electric fields, during periods of geomagnetic disturbances, especially in solstices, these are dependent on thermospheric O/N2 values. This shows the dominance of neutral dynamics over electrodynamics in the low-latitude upper atmosphere during geomagnetic disturbances. Further, spectral analyses have been carried out to obtain the zonal scale sizes in the gravity wave regime and their diurnal distributions are compared for geomagnetic quiet and disturbed days. Broadly, the zonal scales seem to be breaking into various scale sizes on days of geomagnetic disturbances when compared to those on quiet days. This contrast in the diurnal distribution of the zonal scale sizes brings to light, for the first time, the varying nature of the neutral wave coupling in the daytime thermosphere during periods of geomagnetic disturbances.

Assessing the effects of helicopter disturbance in a mountain ungulate on different time scales

Noisy human activities such as helicopter traffic may affect physiology and behaviour of wild animals. Since chronic behavioural modifications can ultimately alter reproductive success and population dynamics, studying the response of different taxa and species to human-induced disturbance in different habitats is paramount. The present study analysed data collected from 10 male Alpine ibex (Capra ibex) monitored with GPS collars to assess their response to disturbance caused by helicopter overflights. We compared ibex activity levels in the hours before and after 34 helicopter overflights during the summer of 2013 in Gran Paradiso National Park (Italy), a protected area that is essential for the conservation of Alpine ibex. The behaviour of Alpine ibex was affected both during and after helicopter overflights: compared to the average activity levels in the hours before the disturbance event, activity increased during the disturbance and decreased during the hour following the overflights. The reduction in activity persisted over the whole day of the helicopter disturbance and finally went back to normal levels during the following day. There was no evidence of habituation to the disturbance throughout the study period. The prolonged behavioural response to the disturbance suggests that frequent helicopter overflights may ultimately affect the ibex’s body conditions, as well as the life-history traits of a population. These findings highlight the importance of considering medium and long-term behavioural responses in assessing disturbance-related effects on wildlife populations.

Observational Study on Formation of a Localized Rainfall on a Basin with Heat and Aridity on Days of Weak Synoptic Disturbance in Summer

Observational Study on Formation of a Localized Rainfall on a Basin with Heat and Aridity on Days of Weak Synoptic Disturbance in Summer

Cellular mechanisms of cyclophosphamide-induced taste loss in mice.

Many commonly prescribed chemotherapy drugs such as cyclophosphamide (CYP) have adverse side effects including disruptions in taste which can result in loss of appetite, malnutrition, poorer recovery and reduced quality of life. Previous studies in mice found evidence that CYP has a two-phase disturbance in taste behavior: a disturbance immediately following drug administration and a second which emerges several days later. In this study, we examined the processes by which CYP disturbs the taste system by examining the effects of the drug on taste buds and cells responsible for taste cell renewal using immunohistochemical assays. Data reported here suggest CYP has direct cytotoxic effects on lingual epithelium immediately following administration, causing an early loss of taste sensory cells. Types II and III cells in fungiform taste buds appear to be more susceptible to this effect than circumvallate cells. In addition, CYP disrupts the population of rapidly dividing cells in the basal layer of taste epithelium responsible for taste cell renewal, manifesting a disturbance days later. The loss of these cells temporarily retards the system’s capacity to replace Type II and Type III taste sensory cells that survived the cytotoxic effects of CYP and died at the end of their natural lifespan. The timing of an immediate, direct loss of taste cells and a delayed, indirect loss without replacement of taste sensory cells are broadly congruent with previously published behavioral data reporting two periods of elevated detection thresholds for umami and sucrose stimuli. These findings suggest that chemotherapeutic disturbances in the peripheral mechanisms of the taste system may cause dietary challenges at a time when the cancer patient has significant need for well balanced, high energy nutritional intake.

Study of Ionospheric Amplitude Scintillation during Geomagnetic Activities of 2012 at Low Latitude Region

The impact of scintillation on radio communications, geodesy, radar system and navigation cannot be underemphasized. The first evident effect of space weather in the phase of radio signals and amplitude that passes over ionosphere is fluctuations. If there are intense fluctuations in the quality of the signals received, such signals might degrade or attenuate in quality. This phenomenon is referred to as scintillations. To study the effects of magnetic activity on scintillations, the percentage occurrence of scintillations has been separated for the five international quiet (Q) days and five international disturbed (D) days over Ilorin for the year 2012 which was obtained from world data centre Kyoto. The occurrences of S4 were recorded during quiet days than the disturbed days in the study area. Generally, occurrence of \(S_4\) was enhanced during pre-midnight hours but was suppressed during post-midnight hour both at quiet and disturbed days in Ilorin, Kwara State, Nigeria.

Statistical characteristics of the polar ionospheric scale height around the peak height of F2 layer with observations of the ESR radar: Disturbed days

In this paper, based on observations of the European Incoherent Scatter Svalbard Radar (ESR) between 1997 and 2008, we analyzed variations of HmF2, the ionospheric scale height around the peak height of F2 layer (hmF2) at high latitude with geomagnetic activities, as well as variations of the HmF2 with the local time (LT), season and solar activity under disturbed conditions (2<Kp≤5). We found that the HmF2 shows a significant increment with enhancements of geomagnetic activities. In addition, based on a linear regression, the correlation and fitting coefficients are shown, which quantitatively describe the correlations between polar HmF2 and geomagnetic activity index Kp. The HmF2 shows a diurnal variation with a maximum early in the morning and a minimum around noon in disturbed days (2<Kp≤5), which is more complex in comparison with that in quiet days. However, in summer and autumn, the HmF2 in disturbed days shows a bulge during 06:00–11:00 LT instead of the continuous decline under quiet condition. We consider that the ESR was under the cusp region during the period so that the bulge might be related to the high-energy particles precipitating into the ionosphere resulting in changes of the electron density profile. The HmF2 has the highest seasonal magnitude in summer and the lowest seasonal magnitude in winter generally. The seasonal magnitude of the HmF2 in autumn is lower than that in spring and larger than that in winter under low solar activity, while the HmF2 shows the same seasonal variations in spring and autumn under moderate and high solar activities.