Annales Geophysicae (ANGEO)
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Open Access journal
ISSN (Print) 0992-7689 - ISSN (Online) 1432-0576
Published by European Geosciences Union [8 journals]
- Seasonal MLT-region nightglow intensities, temperatures, and emission
heights at a Southern Hemisphere midlatitude site
Abstract: Seasonal MLT-region nightglow intensities, temperatures, and emission heights at a Southern Hemisphere midlatitude site
Iain M. Reid, Andrew J. Spargo, Jonathan M. Woithe, Andrew R. Klekociuk, Joel P. Younger, and Gulamabas G. Sivjee
Ann. Geophys., 35, 567-582, doi:10.5194/angeo-35-567-2017, 2017
We measured temperatures in the atmosphere at heights near 90 km using nightglow emissions and compared them with satellite measurements and with measurements made with a meteor radar. We found good agreement between the techniques, which improved when we used the meteor radar and satellite data to measure densities at two heights separated by about 10 km to estimate the nightglow emission height.
- Spatial and temporal variability in MLT turbulence inferred from in situ
Abstract: Spatial and temporal variability in MLT turbulence inferred from in situ and ground-based observations during the WADIS-1 sounding rocket campaign
Boris Strelnikov, Artur Szewczyk, Irina Strelnikova, Ralph Latteck, Gerd Baumgarten, Franz-Josef Lübken, Markus Rapp, Stefanos Fasoulas, Stefan Löhle, Martin Eberhart, Ulf-Peter Hoppe, Tim Dunker, Martin Friedrich, Jonas Hedin, Mikhail Khaplanov, Jörg Gumbel, and Aroh Barjatya
Ann. Geophys., 35, 547-565, doi:10.5194/angeo-35-547-2017, 2017
The WADIS sounding rocket mission utilized multi-point turbulence measurements in the mesosphere by different techniques, i.e., with ionization gauges carried by rockets and ground-based MAARSY and EISCAT radars. Results show that turbulence energy dissipation rates oscillate in space and time with amplitude of up to 2 orders of magnitude. Spatial oscillations show the same wavelengths as atmospheric gravity waves. Temporal variability reveals periods of atmospheric tides and gravity waves.
- Longitudinal variation of equatorial electrojet and the occurrence of its
Abstract: Longitudinal variation of equatorial electrojet and the occurrence of its counter electrojet
A. Babatunde Rabiu, Olanike Olufunmilayo Folarin, Teiji Uozumi, Nurul Shazana Abdul Hamid, and Akimasa Yoshikawa
Ann. Geophys., 35, 535-545, doi:10.5194/angeo-35-535-2017, 2017
This work examined the longitudinal variability of the equatorial electrojet (EEJ) and the occurrence of its counter electrojet (CEJ) using the available records of the horizontal component H of the geomagnetic field simultaneously recorded in the year 2009 along the magnetic equator in South American, African, and Philippine sectors. Our results indicate that the EEJ and CEJ undergo longitudinal variability. More ground observation data points are required in the African equatorial zone.
- Longitudinal, seasonal and solar cycle variation in lunar tide influence
on the equatorial electrojet
Abstract: Longitudinal, seasonal and solar cycle variation in lunar tide influence on the equatorial electrojet
Endawoke Yizengaw and Brett A. Carter
Ann. Geophys., 35, 525-533, doi:10.5194/angeo-35-525-2017, 2017
The lunar tide influence on the equatorial electrojet (EEJ) gets intensified around noon, primarily during new and full Moon periods. However, the longitudinal, seasonal and solar cycle variability in the lunar tide’s influence on ionospheric current systems is not well understood yet. In order to investigate this, 17 years (1998–2014) of extensive magnetometer observations at four longitudinal sectors (western American, western and eastern African, and Asian) have been analyzed.
- Variations in energy, flux, and brightness of pulsating aurora measured at
high time resolution
Abstract: Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution
Hanna Dahlgren, Betty S. Lanchester, Nickolay Ivchenko, and Daniel K. Whiter
Ann. Geophys., 35, 493-503, doi:10.5194/angeo-35-493-2017, 2017
Pulsating aurora are ubiquitous events that constitute a large amount of energy transfer to the ionosphere. Still there are unsolved issues regarding their formation. Using high-resolution optical and radar data, we find that it is the flux of high-energy electrons that get reduced during the OFF period of the pulsations. We also report on dips in brightness at the transition between ON and OFF, and asymmetric rise and fall times, which may have implications for understanding the pulsations.
- Magnetic reconnection during steady magnetospheric convection and other
Abstract: Magnetic reconnection during steady magnetospheric convection and other magnetospheric modes
Benoit Hubert, Jean-Claude Gérard, Steve E. Milan, and Stanley W. H. Cowley
Ann. Geophys., 35, 505-524, doi:10.5194/angeo-35-505-2017, 2017
Remote sensing of the polar aurora and ionospheric convection is used to characterize the interaction between the solar wind and the Earth magnetosphere during steady magnetospheric convection (SMC) intervals and compare them with other previously studied geomagnetic conditions. It is found that the Earth magnetosphere may exhibit four different coupling modes ordered by increasing open magnetic flux and magnetic reconnection rate: quiet times, SMC, substorm and sawtooth events.
- Effect of water vapour absorption on hydroxyl temperatures measured from
Abstract: Effect of water vapour absorption on hydroxyl temperatures measured from Svalbard
Joshua M. Chadney, Daniel K. Whiter, and Betty S. Lanchester
Ann. Geophys., 35, 481-491, doi:10.5194/angeo-35-481-2017, 2017
A layer of excited OH molecules in the upper atmosphere produces strong airglow emission from which it is possible to obtain the temperature of the layer. To obtain accurate temperatures values, one must take into account the absorption of OH emission by water vapour in the lower atmosphere before this emission is measured by instruments on the ground. This paper provides the amount of absorption suffered by each OH line due to water vapour and presents a method to estimate water concentrations.
- Estimation of a planetary magnetic field using a reduced
Abstract: Estimation of a planetary magnetic field using a reduced magnetohydrodynamic model
Christian Nabert, Daniel Heyner, and Karl-Heinz Glassmeier
Ann. Geophys., 35, 465-474, doi:10.5194/angeo-35-465-2017, 2017
Knowledge of planetary magnetic fields provides deep insights into the structure and dynamics of planets. Due to the interaction of a planet with the solar wind plasma, electrical currents are generated which modify the planetary magnetic field outside the planet. New methods are presented to estimate the planetary magnetic field contribution from spacecraft observations. A reduced model of the interaction relates the time-varying observations to the planetary magnetic field magnitude.
- Relation of anomalous F region radar echoes in the high-latitude
ionosphere to auroral precipitation
Abstract: Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation
Hanna Dahlgren, Nicola M. Schlatter, Nickolay Ivchenko, Lorenz Roth, and Alexander Karlsson
Ann. Geophys., 35, 475-479, doi:10.5194/angeo-35-475-2017, 2017
Anomalous strong echoes with three frequency peaks are occasionally seen with incoherent scatter radars in the ionosphere near 200 km altitude at high latitudes. We investigate how they relate to electron precipitation, by finding the resulting peak electron density and the height of the peak, respectively. We find that occurrence rate increases with density and decreases with height, indicating a correlation between the echoes and precipitating electrons with high energy and energy flux.
- Diurnal variations in integrated water vapor derived from a GPS ground
network in the Volga–Ural region of Russia
Abstract: Diurnal variations in integrated water vapor derived from a GPS ground network in the Volga–Ural region of Russia
Vladislav V. Kalinnikov and Olga G. Khutorova
Ann. Geophys., 35, 453-464, doi:10.5194/angeo-35-453-2017, 2017
Here, we present estimates of diurnal and semidiurnal harmonics of variations in integrated water vapor content (IWV) according to GPS data in the Volga–Ural region during 2013–2015. Comparison of diurnal cycle from GPS data and ERA-Interim reanalysis has revealed significant differences in the phase. It is found that, as a result of evaporation from underlying surface and convective lifting of moist air, the summer diurnal variations in IWV and surface density of water vapor are in antiphase.
- Comparisons between high-resolution profiles of squared refractive index
gradient M2 measured by the Middle and Upper Atmosphere Radar and unmanned
aerial vehicles (UAVs) during the Shigaraki UAV-Radar Experiment 2015
Abstract: Comparisons between high-resolution profiles of squared refractive index gradient M2 measured by the Middle and Upper Atmosphere Radar and unmanned aerial vehicles (UAVs) during the Shigaraki UAV-Radar Experiment 2015 campaign
Hubert Luce, Lakshmi Kantha, Hiroyuki Hashiguchi, Dale Lawrence, Masanori Yabuki, Toshitaka Tsuda, and Tyler Mixa
Ann. Geophys., 35, 423-441, doi:10.5194/angeo-35-423-2017, 2017
Results of comparisons between data collected from a VHF Doppler radar and small unmanned aerial vehicles (UAVs) are presented. The UAVs, equipped with meteorological sensors, flew nearby the radar up to an altitude of ~ 4.0 km. Both instruments detected the same clear-air refractive index gradients at a vertical scale of ~ 20 m when the vertical stratification was strong. A VHF radar can thus provide a faithful image of the vertical stratification of the atmosphere down to decimeter scales.
- THEMIS satellite observations of hot flow anomalies at Earth's bow shock
Abstract: THEMIS satellite observations of hot flow anomalies at Earth's bow shock
Christina Chu, Hui Zhang, David Sibeck, Antonius Otto, QiuGang Zong, Nick Omidi, James P. McFadden, Dennis Fruehauff, and Vassilis Angelopoulos
Ann. Geophys., 35, 443-451, doi:10.5194/angeo-35-443-2017, 2017
Hot flow anomalies (HFAs) at Earth's bow shock were identified in Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite data from 2007 to 2009. The events were classified as young or mature and regular or spontaneous hot flow anomalies (SHFAs). HFA–SHFA occurrence decreases with distance upstream from the bow shock. HFAs are more prevalent for radial interplanetary magnetic fields and solar wind speeds from 550 to 600 kms−1.
- Rocket in situ observation of equatorial plasma irregularities in the
region between E and F layers over Brazil
Abstract: Rocket in situ observation of equatorial plasma irregularities in the region between E and F layers over Brazil
Siomel Savio Odriozola, Francisco Carlos de Meneses Jr., Polinaya Muralikrishna, Alexandre Alvares Pimenta, and Esfhan Alam Kherani
Ann. Geophys., 35, 413-422, doi:10.5194/angeo-35-413-2017, 2017
In this paper we report several ionospheric plasma irregularities detected by an instrument (Langmuir probe) installed as a rocket payload that flew over the equatorial region of Brazil. The results of our measurements were compared with measurements made on a different date and by another instrument (radar) located under the magnetic equator in Peru. Our comparison suggests that the rocket intercepted the same type of irregularity previously detected in Peru.
- High-order ionospheric effects on electron density estimation from
Fengyun-3C GPS radio occultation
Abstract: High-order ionospheric effects on electron density estimation from Fengyun-3C GPS radio occultation
Junhai Li and Shuanggen Jin
Ann. Geophys., 35, 403-411, doi:10.5194/angeo-35-403-2017, 2017
In this paper, we discuss the higher-order ionospheric effects on electron density estimation. We estimate the higher-order ionospheric effect carefully and obtain some conclusions. The results show that the second-order ionospheric effects cannot be ignored in precise ionospheric electron density estimation. The azimuth, the solar activity, and the occultation time and position are the main effect factors of the high-order ionospheric delay which we should consider.
- High-resolution coherent backscatter interferometric radar images of
equatorial spread F using Capon's method
Abstract: High-resolution coherent backscatter interferometric radar images of equatorial spread F using Capon's method
Fabiano S. Rodrigues, Eurico R. de Paula, and Gebreab K. Zewdie
Ann. Geophys., 35, 393-402, doi:10.5194/angeo-35-393-2017, 2017
We present results of Capon's method for the estimation of in-beam images of equatorial spread F (ESF) irregularities observed by the São Luís radar interferometer. Results of numerical simulations show that, despite the short baselines of the system, the method is capable of distinguishing localized features with kilometric scale sizes (zonal direction). Results from the application of Capon’s method to actual measurements show that it is able to resolve features expected to occur in ESF.
- MONITOR Ionospheric Network: two case studies on scintillation and
electron content variability
Abstract: MONITOR Ionospheric Network: two case studies on scintillation and electron content variability
Yannick Béniguel, Iurii Cherniak, Alberto Garcia-Rigo, Pierrick Hamel, Manuel Hernández-Pajares, Roland Kameni, Anton Kashcheyev, Andrzej Krankowski, Michel Monnerat, Bruno Nava, Herbert Ngaya, Raül Orus-Perez, Hughes Secrétan, Damien Sérant, Stefan Schlüter, and Volker Wilken
Ann. Geophys., 35, 377-391, doi:10.5194/angeo-35-377-2017, 2017
The work presented in this paper was done in the frame of an ESA activity. The aim of this project was to study ionosphere disturbances liable to impact navigation systems. This project has been running over several years, allowing enough data acquisition to gain sufficient knowledge of ionosphere variability. It was launched to support the European Satellite-Based Augmented System (EGNOS), also considering a possible extension of the system over Africa.
- Non-triggered auroral substorms and long-period (1–4 mHz) geomagnetic
and auroral luminosity pulsations in the polar cap
Abstract: Non-triggered auroral substorms and long-period (1–4 mHz) geomagnetic and auroral luminosity pulsations in the polar cap
Nadezda Yagova, Natalia Nosikova, Lisa Baddeley, Olga Kozyreva, Dag A. Lorentzen, Vyacheslav Pilipenko, and Magnar G. Johnsen
Ann. Geophys., 35, 365-376, doi:10.5194/angeo-35-365-2017, 2017
A substorm is a dramatic phenomenon in the near-Earth space that is visualized as an aurora. Mostly substorms are caused by changes in the solar wind, but some of them can develop without any evident trigger. Such substorms together with undisturbed days were investigated using magnetometer and photometer data from Svalbard. Substorm precursors, i.e., specific features in 1–4 mHz geomagnetic and auroral luminosity pulsations, have been found at high geomagnetic latitudes.
- Ionospheric response to magnetar flare: signature of SGR J1550–5418 on
coherent ionospheric Doppler radar
Abstract: Ionospheric response to magnetar flare: signature of SGR J1550–5418 on coherent ionospheric Doppler radar
Ann. Geophys., 35, 345-351, doi:10.5194/angeo-35-345-2017, 2017
This is the first time a traveling ionospheric disturbance caused by an extraterrestrial source like a magnetar has been detected. The source entered an active phase on 22 January 2009, during which a large number of bursts were observed by several satellites. We detected its ionospheric signature using the coherent ionospheric Doppler radar system. In general, the Earth's ionosphere is a gigantic detector that responds to the ionizing radiation emitted through high-energy astrophysical objects.
- A comparison of ground-based hydroxyl airglow temperatures with
SABER/TIMED measurements over 23° N, India
Abstract: A comparison of ground-based hydroxyl airglow temperatures with SABER/TIMED measurements over 23° N, India
Navin Parihar, Dupinder Singh, and Subramanian Gurubaran
Ann. Geophys., 35, 353-363, doi:10.5194/angeo-35-353-2017, 2017
Using an all-sky imager, near-mesopause OH temperatures were derived from OH(6, 2) Meinel band intensity measurements. A limited comparison of OH temperatures with SABER/TIMED measurements performed by defining almost-coincident criteria of ±1.5° latitude–longitude and ±3 min indicated fair agreement between ground-based and SABER measurements in general. The difference of two measurements increased when the peak of the OH emission layer lay in the vicinity of large temperature inversions.
- New results on equatorial thermospheric winds and temperatures from
Abstract: New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa
Fasil Tesema, Rafael Mesquita, John Meriwether, Baylie Damtie, Melessew Nigussie, Jonathan Makela, Daniel Fisher, Brian Harding, Endawoke Yizengaw, and Samuel Sanders
Ann. Geophys., 35, 333-344, doi:10.5194/angeo-35-333-2017, 2017
Measurements of equatorial thermospheric winds obtained from an optical instrument called a Fabry–Perot interferometer in Ethiopia show a significance difference as compared with other longitudinal sectors. The zonal wind in this sector is small and shows a gradual decrease through out the night. Application of climatological wind and temperature models shows good agreement with the observations over Ethiopia.