Longitude Zone Research Articles

Extremely Long‐Range Observations of Ionospheric Irregularities in a Large Longitude Zone From Pacific to Africa Using a Low Latitude Over‐The‐Horizon Radar in China

AbstractMonitoring the generation and movement of equatorial plasma bubbles (EPBs) in a large longitude region is crucial important for better understanding their day‐to‐day variability. Using the newly developed Low lAtitude long Range Ionospheric raDar (LARID) at Dongfang (19.2°N, 108.8°E, dip lat. 13.8°N), China, an extremely long‐range experiment for observing EPB irregularities in a range of ±9,600 km to the radar site was first carried out. The results show that EPB irregularities with ranges up to 7,000 and 9,500 km were observed by the east and west beams of LARID, respectively. By incorporating simultaneous observations from GNSS receiver and ionosonde networks, it is demonstrated that the EPBs generated from post‐sunset to sunrise over a very wide longitude of ∼140°, from Pacific to Africa could be observed by LARID. The results, for the first time, demonstrate the possibility for tracing global EPBs in real time using a few low latitude over‐the‐horizon radars.

On the Upwelling of the F Layer Base and Prediction of Equatorial Plasma Bubble

AbstractPrediction of equatorial plasma bubbles (EPBs) continues to be a challenge for the scientific community. We present a novel data analysis approach, employed on the collocated radar and ionosonde observations from Gadanki, providing new experimental results for characterizing the overhead upwelling of the bottomside F layer and linking it to EPB formation. Using this new approach we propose a new parameter based on ionosonde observations to predict overhead occurrence of fresh EPB. Employing this new parameter on a fairly large data set of a single ionosonde station we could successfully predict overhead occurrence of all the fresh EPBs about an hour in advance. We also propose how this technique can be used for EPB prediction in a broader longitude zone.

On the global model of the ionospheric equivalent slab thickness

The equivalent slab thickness τ of the ionosphere links two of its parameters: the critical frequency foF2 and the total electron content TEC and, as a consequence, allows the determination of foF2 using TEC. Interest in the parameter τ has recently increased, as evidenced by a publication in Space Science Reviews 2022, 218:37, 1-65, which provides a historical overview of τ research, presents features of τ behavior in different regions of the globe under different solar activity conditions, and indicates directions for further research. This led to the following objectives for this paper: (1) estimating the correlation coefficient between foF2 and TEC, (2) testing a unique global model τ(NSTM) - the Neustrelitz equivalent Slab Thickness Model, (3) estimating the relation between τ and the Dst index. Using data from 78 stations divided into several longitude zones, it is shown for April 2022: (1) a high correlation between foF2 and TEC on a global scale is confirmed, but there is a large dependence on data quality, (2) each longitude zone has stations for which τ(NSTM) gives good agreement with experimental values and can be used in applications, (3) the correlation coefficient ρ(τ-Dst) is found to depend on longitude, which may have a physical nature.

On the Onset Time and Background Ionospheric Conditions of Postsunset Equatorial Plasma Bubble

AbstractOnset time and conditions of the postsunset equatorial plasma bubble (EPB) observed by the Gadanki Ionospheric Radar Interferometer are presented and discussed in the light of collocated digisonde observations of background ionosphere. Observations show two important findings: (a) onset time of EPB is linked with the sunset terminator and it varies between the low latitude E region sunset and apex F region sunset with a tendency of EPB onset to be close to low latitude E region sunset, and (b) higher height of the bottomside F layer (by 50–60 km) and vertical plasma drift (by 10–30 m s−1) observed over Gadanki are found to be associated with the EPBs growing in a narrow longitude zone of ±1° centered on Gadanki than those outside this zone. The early onset of EPB coinciding with the low latitude E region sunset is attributed to the early predominance of the F region dynamo leading to prereversal enhancement (PRE) of zonal electric field, consistent with theoretical expectation. Delay in the onset of EPB is attributed to the effect of flux tube integrated Pedersen conductivity owing to low latitude sporadic E activity and the F region meridional neutral wind that could change the F region plasma density along the flux tube through field‐aligned movement of plasma. Observations also show that ionosonde observations from a single location cannot be used to predict the growth of EPB at other location, including those close to the station but away from the station by about 120 km.

Diversity of MJO Initiation Regions and Processes

Abstract The diversity of the Madden–Julian oscillation (MJO) initiation (i.e., initial onset of active convection before moving eastward) regions was explored using a clustering method. Regions favorable for MJO initiations are grouped into four longitude zones: the Atlantic and Africa (AA), the Indian Ocean (IO), the Maritime Continent (MC), and the western Pacific (WP). The region-dependent dominant initiation mechanisms are explored using a composite procedure. The AA initiation is attributed to a circumnavigating process associated with a preceding MJO. As upper-tropospheric westerly anomalies move into the AA region, the associated descending motion leads to suppressed convection over the IO, which further triggers convection onset to its west through anomalous westward moisture advection. The IO initiation arises from the downstream forcing of a preceding suppressed phase of MJO. A delayed air–sea interaction process also plays a role. The MC initiation is triggered by a westward-propagating dry equatorial Rossby wave in the Pacific. The low-level poleward flows associated with the anticyclonic Rossby wave gyres advect high mean moisture, promoting the convection onset over the MC. The WP initiation is triggered by a preceding suppressed phase of MJO that moves eastward, in a way similar to the downstream scenario in the IO. The AA initiation is usually associated with a La Niña–like background sea surface temperature pattern, which favors the decoupling of upper-tropospheric westerly anomalies from the preceding MJO. The MC and WP initiations are more frequent during El Niño, as the relevant meridional moisture gradient is sharper and the eastern Pacific is moister.

Spatial distributions of <i>X</i><sub>CO<sub>2</sub></sub> seasonal cycle amplitude and phase over northern high-latitude regions

Abstract. Satellite-based observations of atmospheric carbon dioxide (CO2) provide measurements in remote regions, such as the biologically sensitive but undersampled northern high latitudes, and are progressing toward true global data coverage. Recent improvements in satellite retrievals of total column-averaged dry air mole fractions of CO2 (XCO2) from the NASA Orbiting Carbon Observatory 2 (OCO-2) have allowed for unprecedented data coverage of northern high-latitude regions, while maintaining acceptable accuracy and consistency relative to ground-based observations, and finally providing sufficient data in spring and autumn for analysis of satellite-observed XCO2 seasonal cycles across a majority of terrestrial northern high-latitude regions. Here, we present an analysis of XCO2 seasonal cycles calculated from OCO-2 data for temperate, boreal, and tundra regions, subdivided into 5∘ latitude by 20∘ longitude zones. We quantify the seasonal cycle amplitudes (SCAs) and the annual half drawdown day (HDD). OCO-2 SCAs are in good agreement with ground-based observations at five high-latitude sites, and OCO-2 SCAs show very close agreement with SCAs calculated for model estimates of XCO2 from the Copernicus Atmosphere Monitoring Services (CAMS) global inversion-optimized greenhouse gas flux model v19r1 and the CarbonTracker2019 model (CT2019B). Model estimates of XCO2 from the GEOS-Chem CO2 simulation version 12.7.2 with underlying biospheric fluxes from CarbonTracker2019 (GC-CT2019) yield SCAs of larger magnitude and spread over a larger range than those from CAMS, CT2019B, or OCO-2; however, GC-CT2019 SCAs still exhibit a very similar spatial distribution across northern high-latitude regions to that from CAMS, CT2019B, and OCO-2. Zones in the Asian boreal forest were found to have exceptionally large SCA and early HDD, and both OCO-2 data and model estimates yield a distinct longitudinal gradient of increasing SCA from west to east across the Eurasian continent. In northern high-latitude regions, spanning latitudes from 47 to 72∘ N, longitudinal gradients in both SCA and HDD are at least as pronounced as latitudinal gradients, suggesting a role for global atmospheric transport patterns in defining spatial distributions of XCO2 seasonality across these regions. GEOS-Chem surface contact tracers show that the largest XCO2 SCAs occur in areas with the greatest contact with land surfaces, integrated over 15–30 d. The correlation of XCO2 SCA with these land surface contact tracers is stronger than the correlation of XCO2 SCA with the SCA of CO2 fluxes or the total annual CO2 flux within each 5∘ latitude by 20∘ longitude zone. This indicates that accumulation of terrestrial CO2 flux during atmospheric transport is a major driver of regional variations in XCO2 SCA.

On the Assessment of Day‐To‐Day Occurrence of Equatorial Plasma Bubble

AbstractIn this paper, we address the day‐to‐day variation in the development of equatorial plasma bubble (EPB) using simultaneous observations made by the 30 MHz Gadanki Ionospheric Radar Interferometer (GIRI) and ionosonde (DPS‐4D) from Gadanki and C/NOFS. We show that wave‐like variations with horizontal wavelengths of 200–660 km observed prior to sunset have a close connection with EPB spacings. We also show that the locations of EPB development at their origins, which varied on a day‐to‐day basis, were as large as 2600 km from Gadanki. A detailed analysis clearly reveals the cause of such variability and provides clue as to where the background ionospheric conditions led to the growth of the Rayleigh Taylor instability (RTI) generating EPB and where they failed. Results clearly show that while ionosonde observations show great potential for understanding day‐to‐day variation and predicting EPB development overhead (within ±1° longitude), they are inadequate to assess the growth potential of EPB at longitudes away from a longitude zone of about ±1° from overhead. A detailed analysis suggests that the day‐to‐day variability in EPB development is governed by large scale wave structures (LSWS) and it is inferred that the LSWS troughs (low electron density) are the sites for the EPB development. Results further suggest that LSWS with horizontal wavelength of 200–660 km acts as seed for the growth of the RTI resulting in EPBs with same spacing. While the sources of LSWS remain to be identified, it is suggested that observations with longitudinally distributed ground‐based sensor, viz., ionosonde, preferably separated by 250–300 km, would be an immediate step forward in this effort.

Implication of Tidal Forcing Effects on the Zonal Variation of Solstice Equatorial Plasma Bubbles

AbstractEquatorial plasma bubbles (EPBs) are plasma depletions that can occur in the nighttime ionospheric F region, causing scintillation in satellite navigation and communications signals. Past research has shown that EPB occurrence rates are higher during the equinoxes in most longitude zones. An exception is over the central Pacific and African sectors, where EPB activity has been found to maximize during solstice. Tsunoda et al. (2015) hypothesized that the solstice maxima in these two sectors could be driven by a zonal wavenumber 2 atmospheric tide in the lower thermosphere. In this study, we utilize satellite observations to examine evidence of such a wave‐2 feature preconditioning the nighttime ionosphere to favor higher EPB growth rates over these two regions. We find the postsunset total electron content (TEC) observed by FORMOSAT‐3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) during boreal summer from 2007 to 2012 exhibits a wave‐2 zonal distribution, consistent with elevated vertical plasma gradients favorable for EPB formation. Numerical experiments are also carried out to determine whether such an ionospheric wave‐2 can be produced as a result of vertical coupling from atmospheric tides with zonal wavenumber 2 in the local time frame. We find that forcing from these tidal components produced increases in the Rayleigh‐Taylor growth rate over both sectors during solar maximum and minimum, as well as wave‐2 modulations on vertical ion drift, ion flux convergence, and nighttime TEC. Our results are consistent with the aforementioned hypothesis over both regions with vertical coupling effects from atmospheric tides preconditioning the nighttime ionosphere to favor higher EPB growth rates.

EVALUATING THE SUN’S POSITION AND TRACKING THE SUN PATH FOR DUTSIN-MA, KATSINA STATE, NIGERIA

Solar energy is the most promising renewable energy source because of its free availability and an environmentally friendly source. The crucial applications of solar energy depend upon determining the precise position of the sun. In this research, we had made an attempt to determine the precise location of the sun for any topographical position of the earth using solar azimuth/altitude reckoner to track the path of the sun and related sun data. For the purpose of this work, we measured the position of Dutsin-Ma in Katsina State, Northwestern part of Nigeria. Solar online calculator (Keisan online calculator) was used to obtain primary data of sun’s (solar) angle parameters in order to calculate a series of variations in the azimuth and altitude angles using some inputs such as latitude, longitude, date, year, time and time zone. The results revealed that the maximum azimuth angles obtained from the sun are 294.38° for the winter solstice and 248.32° for the summer solstice with elevation angles of 79.01° and 53.46° respectively. Furthermore, the highest values of the hour angles were found to be 97.05° and 97.86° for the summer solstice and the winter solstice respectively. The findings of this work will help individual, government, and non-governmental organizations towards the utilization of solar energy and harnessing it especially during the installations of solar panels and other solar devices.

Effects of CME and CIR induced geomagnetic storms on low-latitude ionization over Indian longitudes in terms of neutral dynamics

This paper presents the response of the ionosphere during the intense geomagnetic storms of October 12–20, 2016 and May 26–31, 2017 which occurred during the declining phase of the solar cycle 24. Total Electron Content (TEC) from GPS measured at Indore, Calcutta and Siliguri having geomagnetic dips varying from 32.23°N, 32°N and 39.49°N respectively and at the International GNSS Service (IGS) stations at Lucknow (beyond anomaly crest), Hyderabad (between geomagnetic equator and northern crest of EIA) and Bangalore (near magnetic equator) in the Indian longitude zone have been used for the storms. Prominent peaks in diurnal maximum in excess of 20–45 TECU over the quiet time values were observed during the October 2016 storm at Lucknow, Indore, Hyderabad, Bangalore and 10–20 TECU for the May 2017 storm at Siliguri, Indore, Calcutta and Hyderabad. The GUVI images onboard TIMED spacecraft that measures the thermospheric O/N2 ratio, showed high values (O/N2 ratio of about 0.7) on October 16 when positive storm effects were observed compared to the other days during the storm period. The observed features have been explained in terms of the O/N2 ratio increase in the equatorial thermosphere, CIR-induced High Speed Solar Wind (HSSW) event for the October 2016 storm. The TEC enhancement has also been explained in terms of the Auroral Electrojet (AE), neutral wind values obtained from the Horizontal Wind Model (HWM14) and equatorial electrojet strength from magnetometer data for both October 2016 and May 2017 storms. These results are one of the first to be reported from the Indian longitude sector on influence of CME- and CIR-driven geomagnetic storms on TEC during the declining phase of solar cycle 24.

Community structure and distribution pattern of small mammals in agricultural area of Yunnan Province, China.

To understand the characteristics of community structure and spatial distribution of small mammals in agricultural area of Yunnan Province, a systematic investigation was carried out in 104 quadrats of 25 regions in Yunnan Province from August 2010 to April 2018 by rat trap night method. The spatial variation of community characteristics along environmental gradients was analyzed by community ecological indicators. The results showed that a total of 3240 small mammals were captured and cold be classified into 42 species in 21 genera, 9 families, and 4 orders. The largest number of small mammal was rodents, dominated by Apodemus chevrieri and Rattus tanezumi. The 25 regions were clustered into three classes. The altitudinal distribution of small mammals was similar to the latitudinal distribution in agricultural areas. The number of species was relatively less in the low latitude and altitude range, with Rattus spp. and Mus spp. as the dominant species. In the high latitude and altitude region, the dominant species changed into Apodemus, Niviventer and Eothenomys. With the increases of altitude, the diversity index showed unimodal distribution, with the highe-st species diversity occurred in the mid-altitude area. The diversity index of small mammal showed the "V" type pattern in longitude, being the highest in the 98°-99° E gra-dient zone. At the latitude level, it showed an overall upward trend from south to north. Results from the GAM analysis showed that the degree of influence on the small animals in the agricultural area was in order of longitude, altitude and latitude. The similarity analysis in the composition of small mammals showed that the moderate similarity occurred in the adjacent gradient zone, and the highest similarity occurred in middle altitude zone, middle latitude zone, and low longitude zone. The farther the distance between different gradient zones, the lower the similarity of community structure. There was high spatial heterogeneity in different dimensions of small mammals' community structure in Yunnan Province. The geographical distribution trend of species diversity showed different distribution patterns across environmental gradients.

Estimation of PMx Concentrations from Landsat 8 OLI Images Based on a Multilayer Perceptron Neural Network

The estimation of PMx (incl. PM10 and PM2.5) concentrations using satellite observations is of great significance for detecting environmental issues in many urban areas of north China. Recently, aerosol optical depth (AOD) data have been being used to estimate the PMx concentrations by implementing linear and/or nonlinear regression analysis methods. However, a lot of relevant research based on AOD published so far have demonstrated some limitations in estimating the spatial distribution of PMx concentrations with respect to estimation accuracy and spatial resolution. In this research, the Google Earth Engine (GEE) platform is employed to obtain the band reflectance (BR) data of a large number of Landsat 8 Operational Land Imager (OLI) remote sensing images. Combined with the meteorological, time parameter and the latitude and longitude zone (LLZ) method proposed in this article, a new BR (band reflectance)-PMx (incl. PM10 and PM2.5) model based on a multilayer perceptron neural network is constructed for the estimation of PMx concentrations directly from Landsat 8 OLI remote sensing images. This research used Beijing, China as the test area and the conducted experiments demonstrated that the BR-PMx model achieved satisfactory performances for the PMx-concentration estimations. The coefficient of determination (R2) of the BR-PM2.5 and BR-PM10 models reached 0.795 and 0.773, respectively, and the root mean square error (RMSE) reached 20.09 μg/m3 and 31.27 μg/m3. Meanwhile, the estimation results have been compared with the results calculated by Kriging interpolation at the same time point, and the spatial distribution is consistent. Therefore, it can be concluded that the proposed BR-PMx model provides a new promising method for acquiring accurate PMx concentrations for various cities of China.

The first all-season sample set for mapping global land cover with Landsat-8 data

We report the world’s first all-season training and validation sample sets for global land cover classification with Landsat-8 data. Prior to this, such samples were only available at a single date primarily from the growing season. It is unknown how much limitation such a single-date sample has to mapping global land cover in other seasons of the year. To answer this question, we selected available Landsat-8 images from four seasons and collected training and validation samples from them. We compared the performances of training samples in different seasons using Random Forest algorithm. We found that the use of training samples from any individual season would result in the best overall classification accuracy when validated by samples in the same season. The global overall accuracy from combined best seasonal results was 67.2% when classifying the 11 Level-1 classes in the Finer Resolution Observation and Monitoring of Global Land Cover (FROM-GLC) classification system. The use of training samples from all seasons (named all-season training sample set hereafter) produced an overall accuracy of 67.0%. We also tested classification within 10° latitude 60° longitude zones using all-season training subsample within each zone and obtained an overall accuracy of 70.2%. This indicates that properly grouped subsamples in space can help improve classification accuracies. All the results in this study seem to suggest that it is possible to use an all-season training sample set to reach global optimality with universal applicability in classifying images acquired at any time of a year for global land cover mapping.

A study on multifrequency scintillations near the EIA crest of the Indian zone

Occurrence features of ionospheric scintillations at S band (2492.028MHz) are reported for the first time. The same have been explored in the context of scintillations at VHF (250.650MHz) and L5 (1176.45MHz) bands. Observations were carried out during the period April–December, 2015 at Raja Peary Mohan College Centre (RPMC: 22.66° N, 88.4° E), located near the equatorial ionization anomaly (EIA) crest of the Indian longitude zone. Mostly weak (<10dB), short duration, slow fading rate with shallower slope power spectra characterize the S band scintillations compared to VHF and L5 band. In the severe scintillation conditions of VHF frequent loss of lock in L5 channel is reflected. Fade depth of 4.2±1.3dB and fade rate ∼9 fades/minute at S band mostly precede the loss of lock at L5 channel. A good correspondence between fade rates at multi frequency band is reflected irrespective of phases of scintillation. Spectral analysis reveals weak scattering is the dominating mechanism for scintillation at S band while VHF and L5 band scintillations are mostly attributed to multiple scattering. The estimated threshold coherence length of <23m at VHF may be suggested to be a good indicator for occurrence of L5 and S band scintillations. Occurrence of simultaneous multi-satellite multi-frequency scintillations leads to speculation over the failsafe navigation using available IRNSS constellation. The results are discussed in terms of existing theory of evolution, structure and dynamics of electron density irregularities in the low latitude region.

Highly localized unique electrodynamics and plasma irregularities linked with the 17 March 2015 severe magnetic storm observed using multitechnique common‐volume observations from Gadanki, India

AbstractIn this paper we study equatorial electrodynamics and plasma irregularities linked with the 17 March 2015 severe magnetic storm in the Indian sector by using common volume observations made by the Gadanki Ionospheric Radar Interferometer, airglow imager, Digisonde, and GPS receiver established at Gadanki (13.5°N, 79.2°E). Observations show that with the initiation of the storm at ~06:00 UT on 17 March, which happened to be midday in the Indian sector, the low‐latitude ionosphere responded in tune with the storm‐induced electric field and by the sunset time the base of the F layer ascended to an altitude of 470 km with a peak upward velocity of 50 m s−1 eventually manifesting equatorial plasma bubble and irregularities causing strong GPS scintillation. The most important finding found in this study is the confinement of plasma bubble and irregularities in a narrow longitude zone of 69°E–98°E. Results also show reversal of zonal drift of the irregularities from ~120 m s−1 eastward drift to ~120 m s−1 westward drift in a time span of ~30 min. Both observations are shown to be linked with very special electrodynamical conditions induced by the magnetic storm‐related electric field in the dusk sector. Intriguing details of the longitudinally localized electrodynamics and plasma irregularities are discussed in terms of prompt penetration and disturbed dynamo electric field effects.

GEO space debris flux determination based on earth-fixed coordinate system

An analysis is performed on the space debris flux determination of geosynchronous (GEO) orbit based on earth-fixed coordinate system. As part of the examination, flux contribution from different components of space debris is presented here in order to clarify the linkage between orbital characteristic and resulting flux distribution. The analysis of GEO flux determination based on earth-fixed coordinate system reveals several new insights: 1) Near the GEO equatorial plane, average flux mainly centralizes in two azimuth ranges: the higher priority one, local azimuth close to±90°, mainly contributed from objects with relatively larger inclination; the lower priority one, local azimuth close to 0°, mainly contributed from objects with relatively smaller inclination. 2) Impact flux against geostationary satellites is not unified by longitude. Longitude-dependent flux determination based on earth-fixed frame reveals that impact flux against geostationary satellite near the geopotential wells (105°W and 75°E longitude zones) is about two to three times larger than average. 3) The comparison of flux determination against certain targets based on earth-fixed coordinate system and inertially-fixed coordinate system shows significant difference.

Principal components of quiet time temporal variability of equatorial and low‐latitude geomagnetic fields

AbstractDiurnal variations of the horizontal component of the geomagnetic field ΔH on International Quiet days of 1999–2012, measured hourly at two stations in the same longitude zone in the Northern Hemisphere, near and away from the dip equator, have been subjected to principal component analysis. This technique is also applied to the difference ΔHEEJ of ΔH at these two stations, which is attributed to the equatorial electrojet (EEJ). The first three principal components, PC1–PC3, account for 91–96% of the variances in the data. Maximum contribution to the quiet day variations in ΔH around its peak in the morning hours at both the stations, and in the EEJ, comes from the day‐to‐day variation of the amplitude of PC1. Patterns of day‐to‐day variations of PC1 amplitudes for the equatorial station and the EEJ are essentially semiannual modulated by solar EUV flux, superimposed on a longer timescale solar EUV flux‐dependent trend. Contributions from PC2 and to a lesser extent from PC3 are seen to be responsible for the absence of semiannual variations in ΔH in the afternoon hours at the equatorial station. Distribution of amplitudes of PC2 and PC3 for ΔHEEJ for weak electrojet days shows seasonal features in accordance with greater occurrence of afternoon (morning) counter electrojet during June (December) solstice. During the extended solar minimum, PC3 amplitudes for ΔH at the equatorial station and for the EEJ display annual variation. Possible sources for these seasonal features in the variations of equatorial ΔH are discussed.

The Ten-Rotation Quasi-periodicity in Sunspot Areas

Sunspot-area fluctuations over an epoch of 12 solar cycles (12 – 23) are investigated in detail using wavelets. Getko (Universal Heliophysical Processes, IAU Symp. 257, 169, 2009) found three significant quasi-periodicities at 10, 17, and 23 solar rotations, but two longer periods could be treated as subharmonics of the ten-rotation quasi-periodicity. Therefore we focused the analysis on the occurrence of this quasi-periodicity during the low- and high-activity periods of each solar cycle. Because of the N – S asymmetry, each solar hemisphere was considered separately. The skewness of each fluctuation-probability distribution suggests that the positive and negative fluctuations could be examined separately. To avoid the problem that occurs when a few strong fluctuations create a wavelet peak, we applied fluctuation transformations for which the amplitudes at the high- and the low-activity periods are almost the same. The wavelet analyses show that the ten-rotation quasi-periodicity is mainly detected during the high-activity periods, but it also exists during a few low-activity periods. The division of each solar hemisphere into 30∘-wide longitude bins and the wavelet calculations for the areas of sunspot clusters belonging to these 30∘ bins enable one to detect longitude zones in which the ten-rotation quasi-periodicity exists. These zones are present during the whole high-activity periods and dominate the integrated spectra.

Evolution of equatorial irregularities under varying electrodynamical conditions: A multitechnique case study from Indian longitude zone

A comprehensive multitechnique study on the postsunset evolutions of equatorial ionization anomaly (EIA) and equatorial plasma density irregularities in the context of the varying electrodynamical conditions under normal equatorial electrojet (EEJ), complete and partial counter electrojet (CEJ) events is presented from the Indian longitude zone. The study involves analysis of scintillation data at VHF (250 MHz) and GPS L1 (1575.42 MHz) frequency, ionosonde data, magnetometer data along with global ionospheric maps (GIMs) of total electron content (TEC) for the vernal equinoctial months (March–April) of 2011. The investigation reveals inefficiency of the noontime peak EEJ to dictate the day‐to‐day variability of postsunset irregularity phenomena. Intensification of EEJ after ∼1530 IST (Indian standard time) on normal EEJ days and significantly enhanced residual fields presumably due to CEJ event after ∼1700 IST on complete and partial CEJ days are found to be associated with the resurgence of EIA and evolution of postsunset irregularities. The results are discussed in terms of superposition effects of electric fields arising from E‐ and F‐ region dynamos.

Spot activity on HD 89546 (FG UMa) from long‐term photometry

AbstractWe present the analysis of 20 years of time‐series BV photometry of the SB1 RS CVn binary HD 89546. The system's yearly mean V brightness, the B – V color index, the photometric period, and the light curve amplitude all show clear cyclic variability with an ≈9‐year time scale. We also find some evidence for brightness variability on a time scale longer than the 20‐year time span of our observations, perhaps indicating a longer cycle analogous to the solar Gleissberg cycle. We estimate the unspotted V magnitude of HD 89546 to be 7.m154, which is ≈0.m2 brighter than the observed maximum brightness. Spot modelling of the system shows that spot temperature variations affect the observed B – V color as well as the V brightness. Two active longitudes are observed, centered around 180° and 360° longitude on the G9 III primary, each covering a longitude range of 120°. Furthermore, two inactive longitude zones are seen spanning only 60° between the two active longitudes. The longitudinal distribution of the spots exhibits no strong cyclic variability but does show rapid jumps of 120° that look like the flip‐flop phenomenon. We estimate the differential rotation coefficient of the star as k = 0.086 by considering the range of observed photometric period variations and assumed latitudinal spot variations over 45° (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)