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Updated: 2018-04-21T13:10:40+02:00

 



On application of asymmetric Kan-like exact equilibria to the Earth magnetotail modeling

2018-04-19T13:10:40+02:00

On application of asymmetric Kan-like exact equilibria to the Earth magnetotail modeling
Daniil B. Korovinskiy, Darya I. Kubyshkina, Vladimir S. Semenov, Marina V. Kubyshkina, Nikolai V. Erkaev, and Stefan A. Kiehas
Ann. Geophys., 36, 641-653, https://doi.org10.5194/angeo-36-641-2018, 2018
The Harris–Fadeev–Kan–Manankova family of exact two-dimensional equilibria is generalized to reproduce the slow decrease of the normal magnetic component in the tailward direction, and the magnetotail current sheet bending and shifting in the vertical plane, arising from the Earth dipole tilting and the solar wind nonradial propagation. The analytical solution is found to fit the empirical T96 model, especially, at distances beyond 10–15 Earth radii at high levels of magnetospheric activity. On application of asymmetric Kan-like exact equilibria to the Earth magnetotail modeling
Daniil B. Korovinskiy, Darya I. Kubyshkina, Vladimir S. Semenov, Marina V. Kubyshkina, Nikolai V. Erkaev, and Stefan A. Kiehas
Ann. Geophys., 36, 641-653, https://doi.org/10.5194/angeo-36-641-2018, 2018
A specific class of solutions of the Vlasov–Maxwell equations, developed by means of generalization of the well-known Harris–Fadeev–Kan–Manankova family of exact two-dimensional equilibria, is studied. The examined model reproduces the current sheet bending and shifting in the vertical plane, arising from the Earth dipole tilting and the solar wind nonradial propagation. The generalized model allows magnetic configurations with equatorial magnetic fields decreasing in a tailward direction as slow as 1∕x, contrary to the original Kan model (1∕x3); magnetic configurations with a single X point are also available. The analytical solution is compared with the empirical T96 model in terms of the magnetic flux tube volume. It is found that parameters of the analytical model may be adjusted to fit a wide range of averaged magnetotail configurations. The best agreement between analytical and empirical models is obtained for the midtail at distances beyond 10–15 RE at high levels of magnetospheric activity. The essential model parameters (current sheet scale, current density) are compared to Cluster data of magnetotail crossings. The best match of parameters is found for single-peaked current sheets with medium values of number density, proton temperature and drift velocity.



Solar rotational cycle in lightning activity in Japan during the 18–19th centuries

2018-04-18T13:10:40+02:00

Solar rotational cycle in lightning activity in Japan during the 18–19th centuries
Hiroko Miyahara, Ryuho Kataoka, Takehiko Mikami, Masumi Zaiki, Junpei Hirano, Minoru Yoshimura, Yasuyuki Aono, and Kiyomi Iwahashi
Ann. Geophys., 36, 633-640, https://doi.org10.5194/angeo-36-633-2018, 2018
Old diaries kept in Japan tell us a surprising fact. The 27-day solar rotational period in thunder and lightning activities had been persistent for the past 300 years. The intensity is found to be more prominent as solar activity increases. The physical mechanism of the Sun–Climate connection is yet uncertain, an important link surely exists between the solar activity and terrestrial climate even at a meteorological timescale. Solar rotational cycle in lightning activity in Japan during the 18–19th centuries
Hiroko Miyahara, Ryuho Kataoka, Takehiko Mikami, Masumi Zaiki, Junpei Hirano, Minoru Yoshimura, Yasuyuki Aono, and Kiyomi Iwahashi
Ann. Geophys., 36, 633-640, https://doi.org/10.5194/angeo-36-633-2018, 2018
Thunderstorm and cloud activities sometimes show a 27-day period, and this has long been studied to uncover a possible important link to solar rotation. Because the 27-day variations in the solar forcing parameters such as solar ultraviolet and galactic cosmic rays become more prominent when the solar activity is high, it is expected that the signal of the 27-day period in meteorological phenomena may wax and wane according to the changes in the solar activity level. In this study, we examine in detail the intensity variations in the signal of the 27-day solar rotational period in thunder and lightning activity from the 18th to the 19th centuries based on 150-year-long records found in old diaries kept in Japan and discuss their relation with the solar activity levels. Such long records enable us to examine the signals of solar rotation at both high and low solar activity levels. We found that the signal of the solar rotational period in the thunder and lightning activity increases as the solar activity increases. In this study, we also discuss the possibility of the impact of the long-term climatological conditions on the signals of the 27-day period in thunder/lightning activities.



A critical note on the IAGA-endorsed Polar Cap (PC) indices: excessive excursions in the real-time index values

2018-04-16T13:10:40+02:00

A critical note on the IAGA-endorsed Polar Cap (PC) indices: excessive excursions in the real-time index values
Peter Stauning
Ann. Geophys., 36, 621-631, https://doi.org10.5194/angeo-36-621-2018, 2018
The Polar Cap (PC) indices, PCN (North) based on magnetic data from Qaanaaq (Thule) and PCS (South) based on Vostok data, reflect the transpolar convection of plasma and magnetic fields. The PC indices could be used, among others, to indicate the energy transfer from the solar wind to the magnetosphere–ionosphere–thermosphere system in space weather monitoring applications. The present IAGA-endorsed methods to derive PC indices in real time are found to generate inconsistent index values. A critical note on the IAGA-endorsed Polar Cap (PC) indices: excessive excursions in the real-time index values
Peter Stauning
Ann. Geophys., 36, 621-631, https://doi.org/10.5194/angeo-36-621-2018, 2018
The Polar Cap (PC) indices were approved by the International Association for Geomagnetism and Aeronomy (IAGA) in 2013 and made available at the web portal http://pcindex.org holding prompt (real-time) as well as archival index values. The present note provides the first reported examination of the validity of the IAGA-endorsed method to generate real-time PC index values. It is demonstrated that features of the derivation procedure defined by Janzhura and Troshichev (2011) may cause considerable excursions in the real-time PC index values compared to the final index values. In examples based on occasional downloads of index values, the differences between real-time and final values of PC indices were found to exceed 3 mV m−1, which is a magnitude level that may indicate (or hide) strong magnetic storm activity.



Estimating ocean tide model uncertainties for electromagnetic inversion studies

2018-04-13T13:10:40+02:00

Estimating ocean tide model uncertainties for electromagnetic inversion studies
Jan Saynisch, Christopher Irrgang, and Maik Thomas
Ann. Geophys. Discuss., doi:10.5194/angeo-2018-27,2018
Manuscript under review for ANGEO (discussion: open, 0 comments)
By induction, ocean tides generate electromagnetic signals. Since the launch of magnetometer satellite missions, these signals are used increasingly to infer electric properties of the Earth. In many of these inversions, ocean tide models are used to generate oceanic tidal electromagnetic signals via electromagnetic induction. The studies main goal is to provide tide model errors for the electromagnetic inversion studies. Estimating ocean tide model uncertainties for electromagnetic inversion studies
Jan Saynisch, Christopher Irrgang, and Maik Thomas
Ann. Geophys. Discuss., https://doi.org/10.5194/angeo-2018-27,2018
Manuscript under review for ANGEO (discussion: open, 0 comments)
Over a decade ago the semidiurnal lunar M2 ocean tide was identified in CHAMP satellite magnetometer data. Since then and especially since the launch of the satellite magnetometer mission Swarm, electromagnetic tidal observations from satellites are used increasingly to infer electric properties of the upper lithosphere. In most of these inversions, numerical ocean tidal models are used to generate oceanic tidal electromagnetic signals via electromagnetic induction. The modelled signals are subsequently compared to the satellite observations. During the inversion, since the tidal models are considered error free, discrepancies between forward models and observations are projected only onto the induction part of the modelling, e.g., Earth's resistivity distribution. Our study analyses uncertainties in oceanic tidal models from an electromagnetic point of view. Velocities from hydrodynamic and assimilative tidal models are converted into tidal electromagnetic signals and compared. Respective uncertainties are estimated. The studies main goal is to provide errors for electromagnetic inversion studies. At satellite height, the differences between the hydrodynamic tidal models are found to reach up to 2 nT, i.e., over 100 % of the M2 signal. Assimilative tidal models show smaller differences of up to 0.1 nT, i.e., over 30 % of the M2 signal.



Impact of disturbance electric fields in the evening on prereversal vertical drift and spread F developments in the equatorial ionosphere

2018-04-09T13:10:40+02:00

Impact of disturbance electric fields in the evening on prereversal vertical drift and spread F developments in the equatorial ionosphere
Mangalathayil A. Abdu, Paulo A. B. Nogueira, Angela M. Santos, Jonas R. de Souza, Inez S. Batista, and Jose H. A. Sobral
Ann. Geophys., 36, 609-620, https://doi.org10.5194/angeo-36-609-2018, 2018
Equatorial ionospheric irregularities have a significant detrimental impact on a variety of space application systems in navigation and communication areas that utilize satellites, especially the Global Navigation Satellite Systems (GNSS) network. The development of these irregularities in the nighttime ionosphere is controlled primarily by ionospheric electric fields and instabilities. The effect of magnetic disturbance on these electric fields and on the irregularities is investigated here. Impact of disturbance electric fields in the evening on prereversal vertical drift and spread F developments in the equatorial ionosphere
Mangalathayil A. Abdu, Paulo A. B. Nogueira, Angela M. Santos, Jonas R. de Souza, Inez S. Batista, and Jose H. A. Sobral
Ann. Geophys., 36, 609-620, https://doi.org/10.5194/angeo-36-609-2018, 2018
Equatorial plasma bubble/spread F irregularity occurrence can present large variability depending upon the intensity of the evening prereversal enhancement in the zonal electric field (PRE), that is, the F region vertical plasma drift, which basically drives the post-sunset irregularity development. Forcing from magnetospheric disturbances is an important source of modification and variability in the PRE vertical drift and of the associated bubble development. Although the roles of magnetospheric disturbance time penetration electric fields in the bubble irregularity development have been studied in the literature, many details regarding the nature of the interaction between the penetration electric fields and the PRE vertical drift still lack our understanding. In this paper we have analyzed data on F layer heights and vertical drifts obtained from digisondes operated in Brazil to investigate the connection between magnetic disturbances occurring during and preceding sunset and the consequent variabilities in the PRE vertical drift and associated equatorial spread F (ESF) development. The impact of the prompt penetration under-shielding eastward electric field and that of the over-shielding, and disturbance dynamo, westward electric field on the evolution of the evening PRE vertical drift and thereby on the ESF development are briefly examined.



An empirical model (CH-Therm-2018) of the thermospheric mass density derived from CHAMP

2018-04-06T13:10:40+02:00

An empirical model (CH-Therm-2018) of the thermospheric mass density derived from CHAMP
Chao Xiong, Hermann Lühr, Michael Schmidt, Mathis Bloßfeld, and Sergei Rudenko
Ann. Geophys. Discuss., https://doi.org/10.5194/angeo-2018-25,2018
Manuscript under review for ANGEO (discussion: open, 0 comments)
Thermospheric drag is the major non-gravitational perturbation acting on Low Earth Orbit (LEO) satellites at altitudes up to 1000 km. The drag depends on the thermospheric density, which is a key parameter in the planning of LEO missions, e.g. their lifetime, collision avoidance, precise orbit determination, as well as orbit and re-entry prediction. In this study, we present an empirical model, named CH-Therm-2018, of the thermospheric mass density derived from 9-year (from August 2000 to July 2009) accelerometer measurements at altitude from 460 to 310 km, from the CHAllenging Minisatellite Payload (CHAMP) satellite. The CHAMP dataset is divided into two 5-year periods with 1-year overlap (from August 2000 to July 2005 and from August 2004 to July 2009), to represent the high-to-moderate and moderate-to-low solar activity conditions, respectively. The CH-Therm-2018 model is a function of seven key parameters, including the height, solar flux index, season (day of year), magnetic local time, geographic latitude and longitude, as well as magnetic activity represented by the solar wind merging electric field. Predictions of the CH-Therm-2018 model agree well with the CHAMP observations (disagreements within ±20 %), and show different features of thermospheric mass density during solar activities, e.g. the March-September equinox asymmetry and the longitudinal wave pattern. We compare the CH-Therm-2018 predictions with the Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar Extended (NRLMSISE-00) model. The result shows that CH-Therm-2018 better predicts the density evolution during the last solar minimum (2008-2009) than the NRLMSISE-00 model. By comparing the Satellite Laser Ranging (SLR) observations of the ANDE-Pollux satellites during August-September 2009, we estimate 6-h scaling factors of thermospheric mass density and obtain a median value of 1.27 ± 0.60, indicating that our model, on average, slightly underestimates the thermospheric mass density at solar minimum.



On the short-term variability of turbulence and temperature in the winter mesosphere

2018-04-05T13:10:40+02:00

On the short-term variability of turbulence and temperature in the winter mesosphere
Gerald A. Lehmacher, Miguel F. Larsen, Richard L. Collins, Aroh Barjatya, and Boris Strelnikov
Ann. Geophys. Discuss., doi:10.5194/angeo-2018-30,2018
Manuscript under review for ANGEO (discussion: open, 0 comments)
We used sounding rockets to obtain 4 high-resolution profiles in the mesosphere over a limited area. We found consistent deep isothermal and adiabatic layers, but variable and finely structured turbulence preferentially in the lower stable mesosphere. Accompanying tracer releases showed horizontal winds in the lower thermosphere with extreme shears and 200 m/s winds under moderately disturbed geomagnetic conditions, and convective structures just below the mesopause. On the short-term variability of turbulence and temperature in the winter mesosphere
Gerald A. Lehmacher, Miguel F. Larsen, Richard L. Collins, Aroh Barjatya, and Boris Strelnikov
Ann. Geophys. Discuss., https://doi.org/10.5194/angeo-2018-30,2018
Manuscript under review for ANGEO (discussion: open, 0 comments)
Four mesosphere-lower thermosphere temperature and turbulence profiles were obtained in situ within ~ 30 minutes and over an area of about 100 by 100 kilometers during a sounding rocket experiment conducted on January 26, 2015 at Poker Flat Research Range in Alaska. Using active payload attitude control, neutral density fluctuations, a tracer for turbulence, were observed with very little interference from the payload spin motion, and with high precision (< 0.01 %) at sub-meter resolution. The large-scale vertical temperature structure was very consistent between the four soundings. The mesosphere was almost isothermal, which means more stratified, between 60 and 80 km, and again, between 88 and 95 km. The stratified regions adjoined quasi-adiabatic regions assumed to be well mixed. Additional evidence for vertical transport and convective activity comes from sodium densities and trimethyl aluminum trail development, respectively, which were both observed simultaneously with the in situ measurements. We found considerable kilometer scale temperature variability with amplitudes of 20 K in the stratified region below 80 km. Several thin turbulent layers were embedded in this region, differing in width and altitude for each profile. Energy dissipation rates varied between 0.1 and 10 mW/kg, which is typical for the winter mesosphere. Very little turbulence was observed above 82 km, consistent with very weak small-scale gravity wave activity in the upper mesosphere during the launch night. On the other hand, above the cold and prominent mesopause at 102 km, large temperature excursions of +40 K to +70 K were observed. Simultaneous wind measurements revealed extreme wind shears near 108 km, and combined with the observed temperature gradient, isolated regions of unstable Richardson numbers (0 < Ri < 0.25) were detected in the lower thermosphere. The experiment was launched into a bright auroral arc under moderately disturbed conditions (Kp ~ 5).



Quantifying the relationship between the plasmapause and the inner boundary of small-scale field-aligned currents, as deduced from Swarm observations

2018-04-05T13:10:40+02:00

Quantifying the relationship between the plasmapause and the inner boundary of small-scale field-aligned currents, as deduced from Swarm observations
Balázs Heilig and Hermann Lühr
Ann. Geophys., 36, 595-607, https://doi.org10.5194/angeo-36-595-2018, 2018
This paper presents a statistical study of the equatorward boundary of small-scale field-aligned currents (SSFACs) as observed by ESA's Swarm satellites and investigates the relation between this boundary and NASA’s Van Allen probe observed plasmapause (PP). It is found that the two boundaries are closely coincident in the midnight LT sector, where the new PP is formed. Our results point to the role of SSFACs in the creation of the PP and offer a unique tool to monitor PP dynamics. Quantifying the relationship between the plasmapause and the inner boundary of small-scale field-aligned currents, as deduced from Swarm observations
Balázs Heilig and Hermann Lühr
Ann. Geophys., 36, 595-607, https://doi.org/10.5194/angeo-36-595-2018, 2018
This paper presents a statistical study of the equatorward boundary of small-scale field-aligned currents (SSFACs) and investigates the relation between this boundary and the plasmapause (PP). The PP data used for validation were derived from in situ electron density observations of NASA's Van Allen Probes. We confirmed the findings of a previous study by the same authors obtained from the observations of the CHAMP satellite SSFAC and the NASA IMAGE satellite PP detections, namely that the two boundaries respond similarly to changes in geomagnetic activity, and they are closely located in the near midnight MLT sector, suggesting a dynamic linkage. Dayside PP correlates with the delayed time history of the SSFAC boundary. We interpreted this behaviour as a direct consequence of co-rotation: the new PP, formed on the night side, propagates to the dayside by rotating with Earth. This finding paves the way toward an efficient PP monitoring tool based on an SSFAC index derived from vector magnetic field observations at low-Earth orbit.



Semidiurnal solar tide differences between fall and spring transition times in the Northern Hemisphere

2018-04-03T13:10:40+02:00

Semidiurnal solar tide differences between fall and spring transition times in the Northern Hemisphere
J. Federico Conte, Jorge L. Chau, Fazlul I. Laskar, Gunter Stober, Hauke Schmidt, and Peter Brown
Ann. Geophys. Discuss., doi:10.5194/angeo-2018-29,2018
Manuscript under review for ANGEO (discussion: open, 0 comments)
Based on comparisons of meteor radar measurements with HAMMONIA model simulations, we show that the differences exhibited by the semidiurnal solar tide (S2) observed at middle and high latitudes of the Northern Hemisphere between equinox times are mainly due to distinct behaviors of the migrating semidiurnal (SW2) and the non-migrating westward propagating wave number 1 semidiurnal (SW1) tidal components. Semidiurnal solar tide differences between fall and spring transition times in the Northern Hemisphere
J. Federico Conte, Jorge L. Chau, Fazlul I. Laskar, Gunter Stober, Hauke Schmidt, and Peter Brown
Ann. Geophys. Discuss., https://doi.org/10.5194/angeo-2018-29,2018
Manuscript under review for ANGEO (discussion: open, 0 comments)
We present a study of the semidiurnal solar tide (S2) during the fall and spring transition times in the Northern Hemisphere. The tides have been obtained from wind measurements provided by three meteor radars located at: Andenes (69° N, 16° E), Juliusruh (54° N, 13° E) and Tavistock (42° N, 81° W). During the autumn, S2 is characterized by a sudden and pronounced decrease occurring every year and at all height levels. The spring transition also shows a decrease of S2, but not sudden and that ascends from lower to higher altitudes during an interval of ~ 15 to 40 days. To assess contributions of different semidiurnal tidal components, we have examined a 20-year free run simulation by the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA). We found that the differences exhibited by the S2 tide between equinox times are mainly due to distinct behaviors of the migrating semidiurnal and the non-migrating westward propagating wave number 1 tidal components (SW2 and SW1, respectively). Specifically, during the fall both, SW2 and SW1 decrease, while during the spring time SW2 decreases but SW1 remains approximately constant or decreases only slightly. The decrease shown by SW1 during the fall occurs later than that of SW2 and S2, which indicates that the behavior of S2 is mainly driven by the migrating component. Nonetheless, the influence of SW1 is necessary to explain the behavior of S2 during the spring. In addition, a strong shift in the phase of S2 (of SW2 in the simulations) is also observed during the fall. Our meteor radar wind measurements show more gravity wave activity in the autumn than during the spring, which might be indicating that the fall decrease is partly due to interactions between SW2 and gravity waves.



New results on the mid-latitude midnight temperature maximum

2018-04-03T13:10:40+02:00

New results on the mid-latitude midnight temperature maximum
Rafael L. A. Mesquita, John W. Meriwether, Jonathan J. Makela, Daniel J. Fisher, Brian J. Harding, Samuel C. Sanders, Fasil Tesema, and Aaron J. Ridley
Ann. Geophys., 36, 541-553, https://doi.org10.5194/angeo-36-541-2018, 2018
The midnight temperature maximum (MTM) is a phenomenon resulting from the constructive interference of the atmospheric tides. This paper brings the analysis of a long data set (846 nights) from the NATION network along with new analysis techniques (harmonic background removal and 2-D temperature interpolation) to detect the MTM in the mid-latitude range. New results on the mid-latitude midnight temperature maximum
Rafael L. A. Mesquita, John W. Meriwether, Jonathan J. Makela, Daniel J. Fisher, Brian J. Harding, Samuel C. Sanders, Fasil Tesema, and Aaron J. Ridley
Ann. Geophys., 36, 541-553, https://doi.org/10.5194/angeo-36-541-2018, 2018
Fabry–Perot interferometer (FPI) measurements of thermospheric temperatures and winds show the detection and successful determination of the latitudinal distribution of the midnight temperature maximum (MTM) in the continental mid-eastern United States. These results were obtained through the operation of the five FPI observatories in the North American Thermosphere Ionosphere Observing Network (NATION) located at the Pisgah Astronomic Research Institute (PAR) (35.2° N, 82.8° W), Virginia Tech (VTI) (37.2° N, 80.4° W), Eastern Kentucky University (EKU) (37.8° N, 84.3° W), Urbana-Champaign (UAO) (40.2° N, 88.2° W), and Ann Arbor (ANN) (42.3° N, 83.8° W). A new approach for analyzing the MTM phenomenon is developed, which features the combination of a method of harmonic thermal background removal followed by a 2-D inversion algorithm to generate sequential 2-D temperature residual maps at 30 min intervals. The simultaneous study of the temperature data from these FPI stations represents a novel analysis of the MTM and its large-scale latitudinal and longitudinal structure. The major finding in examining these maps is the frequent detection of a secondary MTM peak occurring during the early evening hours, nearly 4.5 h prior to the timing of the primary MTM peak that generally appears after midnight. The analysis of these observations shows a strong night-to-night variability for this double-peaked MTM structure. A statistical study of the behavior of the MTM events was carried out to determine the extent of this variability with regard to the seasonal and latitudinal dependence. The results show the presence of the MTM peak(s) in 106 out of the 472 determinable nights (when the MTM presence, or lack thereof, can be determined with certainty in the data set) selected for analysis (22 %) out of the total of 846 nights available. The MTM feature is seen to appear slightly more often during the summer (27 %), followed by fall (22 %), winter (20 %), and spring (18 %). Also seen is a northwestward propagation of the MTM signature with a latitude-dependent amplitude. This behavior suggests either a latitudinal dependence of thermosphere tidal dissipation or a night-to-night variation of the composition of the higher-order tidal modes that contribute to the production of the MTM peak at mid-latitudes. Also presented in this paper is the perturbation on the divergence of the wind fields, which is associated with the passage of each MTM peak analyzed with the 2-D interpolation.



Effects of solar activity and galactic cosmic ray cycles on the modulation of the annual average temperature at two sites in southern Brazil

2018-04-03T13:10:40+02:00

Effects of solar activity and galactic cosmic ray cycles on the modulation of the annual average temperature at two sites in southern Brazil
Everton Frigo, Francesco Antonelli, Djeniffer S. S. da Silva, Pedro C. M. Lima, Igor I. G. Pacca, and José V. Bageston
Ann. Geophys., 36, 555-564, https://doi.org/10.5194/angeo-36-555-2018, 2018
Quasi-periodic variations in solar activity and galactic cosmic rays (GCRs) on decadal and bidecadal timescales have been suggested as a climate forcing mechanism for many regions on Earth. One of these regions is southern Brazil, where the lowest values during the last century were observed for the total geomagnetic field intensity at the Earth's surface. These low values are due to the passage of the center of the South Atlantic Magnetic Anomaly (SAMA), which crosses the Brazilian territory from east to west following a latitude of ∼ 26°. In areas with low geomagnetic intensity, such as the SAMA, the incidence of GCRs is increased. Consequently, possible climatic effects related to the GCRs tend to be maximized in this region. In this work, we investigate the relationship between the ∼ 11-year and  ∼ 22-year cycles that are related to solar activity and GCRs and the annual average temperature recorded between 1936 and 2014 at two weather stations, both located near a latitude of 26° S but at different longitudes. The first of these stations (Torres – TOR) is located in the coastal region, and the other (Iraí – IRA) is located in the interior, around 450 km from the Atlantic Ocean. Sunspot data and the solar modulation potential for cosmic rays were used as proxies for the solar activity and the GCRs, respectively. Our investigation of the influence of decadal and bidecadal cycles in temperature data was carried out using the wavelet transform coherence (WTC) spectrum. The results indicate that periodicities of 11 years may have continuously modulated the climate at TOR via a nonlinear mechanism, while at IRA, the effects of this 11-year modulation period were intermittent. Four temperature maxima, separated by around 20 years, were detected in the same years at both weather stations. These temperature maxima are almost coincident with the maxima of the odd solar cycles. Furthermore, these maxima occur after transitions from even to odd solar cycles, that is, after some years of intense GCR flux. The obtained results offer indirect mathematical evidence that solar activity and GCR variations contributed to climatic changes in southern Brazil during the last century. A comparison of the results obtained for the two weather stations indicates that the SAMA also contributes indirectly to these temperature variations. The contribution of other mechanisms also related to solar activity cannot be excluded.



Climatology of the scintillation onset over southern Brazil

2018-04-03T13:10:40+02:00

Climatology of the scintillation onset over southern Brazil
Jonas Sousasantos, Alison de Oliveira Moraes, José H. A. Sobral, Marcio T. A. H. Muella, Eurico R. de Paula, and Rafael S. Paolini
Ann. Geophys., 36, 565-576, https://doi.org10.5194/angeo-36-565-2018, 2018
This work presents an analysis of the scintillation onset over the southern Brazil based on data from two solar maximum periods and simulation of the ionospheric conditions before the scintillation onset. The results shows some patterns which may help to prevent several satellite-based technological applications suffering disruptions due to scintillation issues. Climatology of the scintillation onset over southern Brazil
Jonas Sousasantos, Alison de Oliveira Moraes, José H. A. Sobral, Marcio T. A. H. Muella, Eurico R. de Paula, and Rafael S. Paolini
Ann. Geophys., 36, 565-576, https://doi.org/10.5194/angeo-36-565-2018, 2018
This work presents an analysis of the climatology of the onset time of ionospheric scintillations at low latitude over the southern Brazilian territory near the peak of the equatorial ionization anomaly (EIA). Data from L1 frequency GPS receiver located in Cachoeira Paulista (22.4° S, 45.0° W; dip latitude 16.9° S), from September 1998 to November 2014, covering a period between solar cycles 23 and 24, were used in the present analysis of the scintillation onset time. The results show that the start time of the ionospheric scintillation follows a pattern, starting about 40 min earlier, in the months of November and December, when compared to January and February. The analyses presented here show that such temporal behavior seems to be associated with the ionospheric prereversal vertical drift (PRVD) magnitude and time. The influence of solar activity in the percentage of GPS links affected is also addressed together with the respective ionospheric prereversal vertical drift behavior. Based on this climatological study a set of empirical equations is proposed to be used for a GNSS alert about the scintillation prediction. The identification of this kind of pattern may support GNSS applications for aviation and oil extraction maritime stations positioning.



High-resolution vertical velocities and their power spectrum observed with the MAARSY radar – Part 1: frequency spectrum

2018-04-03T13:10:40+02:00

High-resolution vertical velocities and their power spectrum observed with the MAARSY radar – Part 1: frequency spectrum
Qiang Li, Markus Rapp, Gunter Stober, and Ralph Latteck
Ann. Geophys., 36, 577-586, https://doi.org10.5194/angeo-36-577-2018, 2018
With the powerful MAARSY radar, we detected 3D wind fields and the vertical winds show a non-Gaussian distribution. We further obtained the frequency spectrum of vertical wind. The distribution of the spectral slopes under different wind conditions is derived and their comparisons with the background horizontal winds show that the spectra become steeper with increasing wind velocities under quiet conditions, approach a slope of −5/3 at 10 m/s and then maintain this slope for even stronger winds. High-resolution vertical velocities and their power spectrum observed with the MAARSY radar – Part 1: frequency spectrum
Qiang Li, Markus Rapp, Gunter Stober, and Ralph Latteck
Ann. Geophys., 36, 577-586, https://doi.org/10.5194/angeo-36-577-2018, 2018
The Middle Atmosphere Alomar Radar System (MAARSY) installed at the island of Andøya has been run for continuous probing of atmospheric winds in the upper troposphere and lower stratosphere (UTLS) region. In the current study, we present high-resolution wind measurements during the period between 2010 and 2013 with MAARSY. The spectral analysis applying the Lomb–Scargle periodogram method has been carried out to determine the frequency spectra of vertical wind velocity. From a total of 522 days of observations, the statistics of the spectral slope have been derived and show a dependence on the background wind conditions. It is a general feature that the observed spectra of vertical velocity during active periods (with wind velocity  >  10 m s−1) are much steeper than during quiet periods (with wind velocity  <  10 m s−1). The distribution of spectral slopes is roughly symmetric with a maximum at −5/3 during active periods, whereas a very asymmetric distribution with a maximum at around −1 is observed during quiet periods. The slope profiles along altitudes reveal a significant height dependence for both conditions, i.e., the spectra become shallower with increasing altitudes in the upper troposphere and maintain roughly a constant slope in the lower stratosphere. With both wind conditions considered together the general spectra are obtained and their slopes are compared with the background horizontal winds. The comparisons show that the observed spectra become steeper with increasing wind velocities under quiet conditions, approach a spectral slope of −5/3 at a wind velocity of 10 m s−1 and then roughly maintain this slope (−5/3) for even stronger winds. Our findings show an overall agreement with previous studies; furthermore, they provide a more complete climatology of frequency spectra of vertical wind velocities under different wind conditions.



Study of sporadic E layers based on GPS radio occultation measurements and digisonde data over the Brazilian region

2018-04-03T13:10:40+02:00

Study of sporadic E layers based on GPS radio occultation measurements and digisonde data over the Brazilian region
Laysa C. A. Resende, Christina Arras, Inez S. Batista, Clezio M. Denardini, Thainá O. Bertollotto, and Juliano Moro
Ann. Geophys., 36, 587-593, https://doi.org10.5194/angeo-36-587-2018, 2018
We present new results on the behavior of sporadic E layers (Es layers) using GPS (global positioning system) radio occultation (RO) measurements obtained from the FORMOSAT-3/COSMIC satellites and digisonde data over Cachoeira Paulista, a low-latitude station in Brazil. Study of sporadic E layers based on GPS radio occultation measurements and digisonde data over the Brazilian region
Laysa C. A. Resende, Christina Arras, Inez S. Batista, Clezio M. Denardini, Thainá O. Bertollotto, and Juliano Moro
Ann. Geophys., 36, 587-593, https://doi.org/10.5194/angeo-36-587-2018, 2018
This work presents new results about sporadic E-layers (Es layers) using GPS (global positioning system) radio occultation (RO) measurements obtained from the FORMOSAT-3/COSMIC satellites and digisonde data. The RO profiles are used to study the Es layer occurrence as well as its intensity of the signal-to-noise ratio (SNR) of the 50 Hz GPS L1 signal. The methodology was applied to identify the Es layer on RO measurements over Cachoeira Paulista, a low-latitude station in the Brazilian region, in which the Es layer development is not driven tidal winds only as it is at middle latitudes. The coincident events were analyzed using the RO technique and ionosonde observations during the year 2014 to 2016. We used the electron density obtained using the blanketing frequency parameter (fbEs) and the Es layer height (h'Es) acquired from the ionograms to validate the satellite measurements. The comparative results show that the Es layer characteristics extracted from the RO measurements are in good agreement with the Es layer parameters from the digisonde.



The effect of subauroral polarization streams on the mid-latitude thermospheric disturbance neutral winds: a universal time effect

2018-03-29T13:10:40+02:00

The effect of subauroral polarization streams on the mid-latitude thermospheric disturbance neutral winds: a universal time effect
Hui Wang, Kedeng Zhang, Zhichao Zheng, and Aaron James Ridley
Ann. Geophys., 36, 509-525, https://doi.org10.5194/angeo-36-509-2018, 2018
For subauroral polarization streams (SAPS) commencing at different universal times (UT), the strongest westward neutral winds exhibit large variations in amplitudes. The effect of a sine-wave oscillation of SAPS on the neutral wind also exhibits UT variations in association with the solar illumination. The reduction in the electron density and enhancement in the air mass density are strongest when the maximum solar illumination collocates with the SAPS. The effect of subauroral polarization streams on the mid-latitude thermospheric disturbance neutral winds: a universal time effect
Hui Wang, Kedeng Zhang, Zhichao Zheng, and Aaron James Ridley
Ann. Geophys., 36, 509-525, https://doi.org/10.5194/angeo-36-509-2018, 2018
The temporal and spatial variations in thermospheric neutral winds at an altitude of 400 km in response to subauroral polarization streams (SAPS) are investigated using global ionosphere and thermosphere model simulations under the southward interplanetary magnetic field (IMF) condition. During SAPS periods the westward neutral winds in the subauroral latitudes are greatly strengthened at dusk. This is due to the ion drag effect, through which SAPS can accelerate neutral winds in the westward direction. The new findings are that for SAPS commencing at different universal times, the strongest westward neutral winds exhibit large variations in amplitudes. The ion drag and Joule heating effects are dependent on the solar illumination, which exhibit UT variations due to the displacement of the geomagnetic and geographic poles. With more sunlight, stronger westward neutral winds can be generated, and the center of these neutral winds shifts to a later magnetic local time than neutral winds with less solar illumination. In the Northern Hemisphere and Southern Hemisphere, the disturbance neutral wind reaches a maximum at 18:00 and 04:00 UT, and a minimum at 04:00 and 16:00 UT, respectively. There is a good correlation between the neutral wind velocity and cos0.5(SZA) (solar zenith angle). The reduction in the electron density and enhancement in the air mass density at an altitude of 400 km are strongest when the maximum solar illumination collocates with the SAPS. The correlation between the neutral wind velocity and cos0.5(SZA) is also good during the northward IMF period. The effect of a sine-wave oscillation of SAPS on the neutral wind also exhibits UT variations in association with the solar illumination.



GREEN: A new Global Radiation Earth ENvironment model

2018-03-29T13:10:40+02:00

GREEN: A new Global Radiation Earth ENvironment model
Angélica Sicard, Daniel Boscher, Sébastien Bourdarie, Didier Lazaro, Denis Standarovski, and Robert Ecoffet
Ann. Geophys. Discuss., doi:10.5194/angeo-2018-26,2018
Manuscript under review for ANGEO (discussion: open, 0 comments)
GREEN (Global Radiation Earth ENvironment) is a new model providing particles fluxes at any location in the radiaiton belts, for energy between 1 keV to 10 MeV for electrons and between 1 keV and 800 MeV for protons. This model is composed of global models: AE8/AP8 and SPM and local models: SLOT model, OZONE, IGE-2006 for electrons and OPAL and geostationary model for protons. GREEN: A new Global Radiation Earth ENvironment model
Angélica Sicard, Daniel Boscher, Sébastien Bourdarie, Didier Lazaro, Denis Standarovski, and Robert Ecoffet
Ann. Geophys. Discuss., https://doi.org/10.5194/angeo-2018-26,2018
Manuscript under review for ANGEO (discussion: open, 0 comments)
GREEN (Global Radiation Earth ENvironment) is a new model providing fluxes at any location between L* = 1 and L* = 8 all along the magnetic field lines and for any energy between 1 keV to 10 MeV for electrons and between 1 keV and 800 MeV for protons. This model is composed of global models: AE8/AP8 and SPM for low energies and local models: SLOT model, OZONE, IGE-2006 for electrons and OPAL and geostationary model for protons. GREEN is not just a collection of various models, it calculates the electron and proton fluxes from the more relevant existing model for a given energy and location. Moreover, some existing models can be updated or corrected in GREEN. For examples, a new version of the SLOT model is presented here and has been integrated in GREEN. Moreover, a new model of proton flux at geostationary orbit (IGP), developed few years ago is also detailed here and integrated in GREEN. Finally a correction of AE8 model at high energy for L* < 2.5 has also been implemented.



Three-dimensional density and compressible magnetic structure in solar wind turbulence

2018-03-29T13:10:40+02:00

Three-dimensional density and compressible magnetic structure in solar wind turbulence
Owen W. Roberts, Yasuhito Narita, and C.-Philippe Escoubet
Ann. Geophys., 36, 527-539, https://doi.org10.5194/angeo-36-527-2018, 2018
In this study we use multi-point spacecraft measurements of magnetic field and electron density derived from spacecraft potential to investigate the three-dimensional structure of solar wind plasma turbulence. We see that there is a dependence on the plasma beta (ratio of thermal to magnetic pressure) as well as a dependence on the type of wind i.e. fast or slow. Three-dimensional density and compressible magnetic structure in solar wind turbulence
Owen W. Roberts, Yasuhito Narita, and C.-Philippe Escoubet
Ann. Geophys., 36, 527-539, https://doi.org/10.5194/angeo-36-527-2018, 2018
The three-dimensional structure of both compressible and incompressible components of turbulence is investigated at proton characteristic scales in the solar wind. Measurements of the three-dimensional structure are typically difficult, since the majority of measurements are performed by a single spacecraft. However, the Cluster mission consisting of four spacecraft in a tetrahedral formation allows for a fully three-dimensional investigation of turbulence. Incompressible turbulence is investigated by using the three vector components of the magnetic field. Meanwhile compressible turbulence is investigated by considering the magnitude of the magnetic field as a proxy for the compressible fluctuations and electron density data deduced from spacecraft potential. Application of the multi-point signal resonator technique to intervals of fast and slow wind shows that both compressible and incompressible turbulence are anisotropic with respect to the mean magnetic field direction P ≫ P and are sensitive to the value of the plasma beta (β; ratio of thermal to magnetic pressure) and the wind type. Moreover, the incompressible fluctuations of the fast and slow solar wind are revealed to be different with enhancements along the background magnetic field direction present in the fast wind intervals. The differences in the fast and slow wind and the implications for the presence of different wave modes in the plasma are discussed.



Ionospheric and thermospheric response to the 27–28 February 2014 geomagnetic storm

2018-03-28T13:10:40+02:00

Ionospheric and thermospheric response to the 27–28 February 2014 geomagnetic storm Khalifa Malki, Aziza Bounhir, Zouhair Benkhaldoun, Jonathan J. Makela, Nicole Vilmer, Daniel J. Fisher, Mohamed Kaab, Khaoula Elbouyahyaoui, Brian J. Harding, Amine Laghriyeb, Ahmed Daassou, and Mohamed Lazrek Ann. Geophys. Discuss., doi:10.5194/angeo-2018-24,2018 Manuscript under review for ANGEO (discussion: open, 1 comment) The novelty of this paper resides in the fact that it addresses the termosphere/ionosphere coupling in a mid-latitude site in north Africa. We have used Fabry-Perot measurements of the thermospheric winds and wide-angle camera detection of ionospheric structurers, at an altitude of about 250 km. We have also used GPS data to extract the TEC over the studied area. We have focused our study on the 27 Feb geomagnetic storm. Ionospheric and thermospheric response to the 27–28 February 2014 geomagnetic storm Khalifa Malki, Aziza Bounhir, Zouhair Benkhaldoun, Jonathan J. Makela, Nicole Vilmer, Daniel J. Fisher, Mohamed Kaab, Khaoula Elbouyahyaoui, Brian J. Harding, Amine Laghriyeb, Ahmed Daassou, and Mohamed Lazrek Ann. Geophys. Discuss., https://doi.org/10.5194/angeo-2018-24,2018 Manuscript under review for ANGEO (discussion: open, 1 comment) The present work explores the ionospheric and thermospheric responses to the 27–28 February 2014 geomagnetic storm. For the first time, a geomagnetic storm is explored in north Africa using interferometer, all-sky imager and GPS data. This storm was caused by coronal mass ejection (CME) associated flares that occurred on 25 February 2014. A Fabry-Perot interferometer located at the Oukaimeden Observatory (31.206° N, 7.866° W, 22.84° N magnetic) in Morocco provides measurements of the thermospheric neutral winds based on the observations of the 630 nm redline emission. A wide angle imaging system records images of the 630-nm emission. The effects of this geomagnetic storm on the thermosphere are evident from the clear departure of the neutral winds from their seasonal behavior. During the storm, the winds experience an intense and steep equatorward flow from 21 to 01 LT and a westward flow from 22 to 03 LT. The equatorial wind speed reaches a maximum of 120 m/s for the meridional component at 22 LT, when the zonal wind reverses to the westward direction. Shortly after 00 LT a maximum westward speed of 80 m/s was achieved for the zonal component of the wind. The features of the winds are typical of TAD (Traveling Atmospheric Disturbances) induced circulation; the first TAD coming from the northern hemisphere reaches the site at 21 LT and a second one coming from the southern hemisphere reaches the site at about 00 LT. We estimate the propagation speed of the northern TAD to be 550 m/s. We compared the winds to DWM07 (Disturbance Wind Model) prediction model and find that this model gives a good indication of the new circulation pattern caused by storm activity, but deviates largely inside the TADs. The effects on the ionosphere were also evident through the change observed in the background electrodynamics from the reversal in drift direction in an observed equatorial plasma bubble. TEC measurements of a GPS station installed in Morocco, at Rabat (33.998° N; 6.853° W, geographic) revealed a positive storm. [...]



Non-Gaussianity and cross-scale coupling in interplanetary magnetic field turbulence during a rope–rope magnetic reconnection event

2018-03-23T13:10:40+01:00

Non-Gaussianity and cross-scale coupling in interplanetary magnetic field turbulence during a rope–rope magnetic reconnection event
Rodrigo A. Miranda, Adriane B. Schelin, Abraham C.-L. Chian, and José L. Ferreira
Ann. Geophys., 36, 497-507, https://doi.org10.5194/angeo-36-497-2018, 2018
The solar wind is a tenuous turbulent plasma permeating the interplanetary space and is not well understood. A complex process called magnetic reconnection can act as a source of solar wind turbulence. Here we study this process using statistics. We demonstrate that high-order statistics of the magnetic field display a parabolic relation that is enhanced when magnetic reconnection occurs. Our results can help us understand the nature of solar wind turbulence. Non-Gaussianity and cross-scale coupling in interplanetary magnetic field turbulence during a rope–rope magnetic reconnection event
Rodrigo A. Miranda, Adriane B. Schelin, Abraham C.-L. Chian, and José L. Ferreira
Ann. Geophys., 36, 497-507, https://doi.org/10.5194/angeo-36-497-2018, 2018
In a recent paper (Chian et al., 2016) it was shown that magnetic reconnection at the interface region between two magnetic flux ropes is responsible for the genesis of interplanetary intermittent turbulence. The normalized third-order moment (skewness) and the normalized fourth-order moment (kurtosis) display a quadratic relation with a parabolic shape that is commonly observed in observational data from turbulence in fluids and plasmas, and is linked to non-Gaussian fluctuations due to coherent structures. In this paper we perform a detailed study of the relation between the skewness and the kurtosis of the modulus of the magnetic field |B| during a triple interplanetary magnetic flux rope event. In addition, we investigate the skewness–kurtosis relation of two-point differences of |B| for the same event. The parabolic relation displays scale dependence and is found to be enhanced during magnetic reconnection, rendering support for the generation of non-Gaussian coherent structures via rope–rope magnetic reconnection. Our results also indicate that a direct coupling between the scales of magnetic flux ropes and the scales within the inertial subrange occurs in the solar wind.



Simultaneous 6300 Å airglow and radar observations of ionospheric irregularities and dynamics at the geomagnetic equator

2018-03-22T13:10:40+01:00

Simultaneous 6300 Å airglow and radar observations of ionospheric irregularities and dynamics at the geomagnetic equator
Dustin A. Hickey, Carlos R. Martinis, Michael Mendillo, Jeffrey Baumgardner, Joei Wroten, and Marco Milla
Ann. Geophys., 36, 473-487, https://doi.org10.5194/angeo-36-473-2018, 2018
We present observations of the Earth's upper atmosphere (ionosphere and thermosphere) near the Equator. Instruments such as cameras and radar systems are used to measure the characteristics of the this region and compare the different observations. One focus of the paper is on structured regions of low density and we find patterns in its development along with other new observations. We also show results of a local increase in temperature near midnight and investigate its extent and evolution. Simultaneous 6300 Å airglow and radar observations of ionospheric irregularities and dynamics at the geomagnetic equator
Dustin A. Hickey, Carlos R. Martinis, Michael Mendillo, Jeffrey Baumgardner, Joei Wroten, and Marco Milla
Ann. Geophys., 36, 473-487, https://doi.org/10.5194/angeo-36-473-2018, 2018
In March 2014 an all-sky imager (ASI) was installed at the Jicamarca Radio Observatory (11.95° S, 76.87° W; 0.3° S MLAT). We present results of equatorial spread F (ESF) characteristics observed at Jicamarca and at low latitudes. Optical 6300 and 7774 Å airglow observations from the Jicamarca ASI are compared with other collocated instruments and with ASIs at El Leoncito, Argentina (31.8° S, 69.3° W; 19.8° S MLAT), and Villa de Leyva, Colombia (5.6° N, 73.52° W; 16.4° N MLAT). We use Jicamarca radar data, in incoherent and coherent modes, to obtain plasma parameters and detect echoes from irregularities. We find that ESF depletions tend to appear in groups with a group-to-group separation around 400–500 km and within-group separation around 50–100 km. We combine data from the three ASIs to investigate the conditions at Jicamarca that could lead to the development of high-altitude, or topside, plumes. We compare zonal winds, obtained from a Fabry–Pérot interferometer, with plasma drifts inferred from the zonal motion of plasma depletions. In addition to the ESF studies we also investigate the midnight temperature maximum and its effects at higher latitudes, visible as a brightness wave at El Leoncito. The ASI at Jicamarca along with collocated and low-latitude instruments provide a clear two-dimensional view of spatial and temporal evolution of ionospheric phenomena at equatorial and low latitudes that helps to explain the dynamics and evolution of equatorial ionospheric/thermospheric processes.