An investigation of long-distance propagation of gravity waves under CAWSES India Phase II Programme
Summary: This study investigates the long-distance propagation (~ 1200–2000km) of gravity waves in the Indian subcontinent using coordinated nightglow measurements at Allahabad and Gadanki (separated by ~ 12º latitude). On few occasions, an identical wave (period in range ~ 2.2–4.5h) was seen at both sites that shared a common source. Waves had large horizontal wavelength (~ 1194–2746km) and phase speed (77–331m/s). The m2 profile analysis suggests the ducted propagation of the common waves.
Ann. Geophys., 33, 547-560, doi:10.5194/angeo-33-547-2015, 2015
Climatology of GPS phase scintillation at northern high latitudes for the period from 2008 to 2013
Ann. Geophys., 33, 531-545, doi:10.5194/angeo-33-531-2015, 2015
Direct observations of blob deformation during a substorm
Summary: We studied the localized plasma density enhancements called blobs, which are often produced in the high-latitude ionosphere by the transportation process of plasma or particle precipitations. This subject is important because such structures affect radio wave propagation and can cause scintillation of GNSS signals in the deformation process. This paper is the first report of direct observations of blob deformation during a substorm.
Ann. Geophys., 33, 525-530, doi:10.5194/angeo-33-525-2015, 2015
Extremely intense (SML ≤–2500 nT) substorms: isolated events that are externally triggered?
Summary: Particularly intense substorms (SSS), brilliant auroral displays with strong >106A currents in the ionosphere, are studied. It is believed that these SSS events cause power outages during magnetic storms. It is shown that SSS events can occur during all intensity magnetic storms; thus power problems are not necessarily restricted to the rare most intense storms. We show four SSS events that are triggered by solar wind pressure pulses. If this is typical, ~30-minute warnings could be issued.
Ann. Geophys., 33, 519-524, doi:10.5194/angeo-33-519-2015, 2015
A quantitative study of magnetospheric magnetic field line deformation by a two-loop substorm current wedge
Summary: In this study we use two-loop model SCW (SCW2L) to quantitatively investigate distortion of the ionospheric footpoint pattern in response to changes of different SCW2L parameters. Calculation results show that SCW-related footprint shifts result in formation of auroral bulge and westward travelling surge and may contribute to rotation of auroral streamers, and that SCW2L combined with the AM03 model nicely describes the azimuthal progression and the observed magnitude of the auroral expansion.
Ann. Geophys., 33, 505-517, doi:10.5194/angeo-33-505-2015, 2015
Driving of the SAO by gravity waves as observed from satellite
Summary: The forcings of the semiannual oscillation (SAO) of the tropical zonal wind in the stratopause region are investigated based on ERA-Interim reanalysis and HIRDLS satellite observations. In particular, the SAO driving by mesoscale gravity waves is estimated directly from satellite observations of gravity waves. Our study confirms previous indirect evidence that planetary waves dominate during the westward driving of the SAO, while gravity waves mainly provide eastward forcing.
Ann. Geophys., 33, 483-504, doi:10.5194/angeo-33-483-2015, 2015
Electrostatic double layers as auroral particle accelerators – a problem
Ann. Geophys., 33, 481-482, doi:10.5194/angeo-33-481-2015, 2015
Analysis of the enhanced negative correlation between electron density and electron temperature related to earthquakes
Summary: This paper addresses the background of electron density (Ne) and temperature (Te and their relationship during local nighttime based on DEMETER satellite data. It also discusses the enhanced negative correlation of Ne and Te around strong earthquakes and the possible electric-field-coupling mechanism as well as digital calculation.
Ann. Geophys., 33, 471-479, doi:10.5194/angeo-33-471-2015, 2015
Additional acceleration of solar-wind particles in current sheets of the heliosphere
Summary: In this paper we present further observations of the solar-wind particles being accelerated to rather higher energies while passing through the HCS or a current sheet formed at the front of an interplanetary coronal mass ejection. This additional acceleration can explain the anticorrelation of ion and electron fluxes frequently observed around the ICME’s leading front. This acceleration can also provide a plausible explanation of the appearance of bidirectional strahls.
Ann. Geophys., 33, 457-470, doi:10.5194/angeo-33-457-2015, 2015
Global variation in the long-term seasonal changes observed in ionospheric F region data
Summary: We use a novel technique to infer long-term compositional changes to the thermosphere from the annual variation of the ionospheric F2 region. A global analysis of these data reveal that long-term changes differ between geographic locations in a way that is very similar to the observed variation in the ionospheric response to increased atmospheric CO2 levels. In the absence of long-term measurements of thermospheric composition, further, detailed, modelling work is required.
Ann. Geophys., 33, 449-455, doi:10.5194/angeo-33-449-2015, 2015
The dayside magnetopause location during radial interplanetary magnetic field periods: Cluster observation and model comparison
Ann. Geophys., 33, 437-448, doi:10.5194/angeo-33-437-2015, 2015
Transitions between states of magnetotail–ionosphere coupling and the role of solar wind dynamic pressure: the 25 July 2004 interplanetary CME case
Ann. Geophys., 33, 427-436, doi:10.5194/angeo-33-427-2015, 2015
Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission
Ann. Geophys., 33, 413-426, doi:10.5194/angeo-33-413-2015, 2015
Online NARMAX model for electron fluxes at GEO
Summary: Data-based models have been derived to forecast the >0.8MeV and >2MeV electron fluxes at geostationary Earth orbit. The models employ solar wind parameters as inputs to provide an estimate of the average electron flux for the following day, i.e. the 1-day-ahead forecast. The identified models are shown to provide a reliable forecast for both >0.8MeV and >2MeV electron fluxes and are capable of providing real-time warnings of when the electron fluxes will be dangerously high.
Ann. Geophys., 33, 405-411, doi:10.5194/angeo-33-405-2015, 2015
Are dayside long-period pulsations related to the cusp?
Summary: Irregular broadband pulsations and narrow-band Pc5 waves are found to be a ubiquitous element of ULF activity in the dayside high-latitude region. To identify the ionospheric projections of the cusp, we use the width of return signal of the SuperDARN radar. The spatial structure of broadband Pc5-6 pulsation spectral power has been found to have a localized latitudinal peak, not under the cusp proper as was previously thought, but several degrees southward from the equatorward cusp boundary.
Ann. Geophys., 33, 395-404, doi:10.5194/angeo-33-395-2015, 2015
Contribution of proton and electron precipitation to the observed electron concentration in October–November 2003 and September 2005
Summary: Electron concentrations observed by EISCAT radars can be reasonable well represented using AIMOS v1.2 satellite-data-based ionization model and SIC D-region ion chemistry model. SIC-EISCAT difference varies from event to event, probably because the statistical nature of AIMOS ionization is not capturing all the spatio-temporal fine structure of electron precipitation. Below 90km, AIMOS overestimates electron ionization because of proton contamination of the satellite electron detectors.
Ann. Geophys., 33, 381-394, doi:10.5194/angeo-33-381-2015, 2015
Observation of electron biteout regions below sporadic E layers at polar latitudes
Summary: The descent of a sporadic E layer near 95km was observed with two rockets during a geomagnetically very quiet period. Four wind profiles showed that the location was surprisingly consistent with the neutral wind shear and a small electric field. Both electron probes found deep depletions just below the layers, which could be due to charged mesospheric smoke particles. Those have recently been detected in the mesosphere, but not yet in immediate connection with sporadic E.
Ann. Geophys., 33, 371-380, doi:10.5194/angeo-33-371-2015, 2015
Long-term midlatitude mesopause region temperature trend deduced from quarter century (1990–2014) Na lidar observations
Summary: The unique, quarter-century-long Na lidar observations of midlatitude mesopause region temperatures are used to yield a cooling trend starting from an insignificant value of 0.64K/decade at 85km, increasing to a maximum of 2.8K/decade between 91 and 93km, and then decreasing to a warming trend above 103km. The long warming episode observed in the 1990s is found to mirror that of the global surface cooling after the Mt Pinatubo eruption.
Ann. Geophys., 33, 363-369, doi:10.5194/angeo-33-363-2015, 2015
Comparison of aerosol extinction between lidar and SAGE II over Gadanki, a tropical station in India
Summary: This study presents an extensive comparison of aerosol extinction using lidar and Stratospheric Aerosol and Gas Experiment (SAGE) II data over Gadanki (13.5ºN, 79.2ºE), a tropical station in India. Results strongly emphasize that, for a more accurate derivation of aerosol extinction over the tropics, (i) best meteorological parameters that are close in terms of space and time to the lidar measurement site and (ii) measured values of the aerosol-backscattering--extinction ratio are crucial.
Ann. Geophys., 33, 351-362, doi:10.5194/angeo-33-351-2015, 2015
Adaptation of the de Hoffmann–Teller frame for quasi-perpendicular collisionless shocks
Ann. Geophys., 33, 345-350, doi:10.5194/angeo-33-345-2015, 2015