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
Outflow of low-energy O+ ion beams observed during periods without substorms
Summary: Ions from Earth's ionosphere continually escape into space. This article examines ions escaping the auroral oval, a region in the polar region of Earth where auroras occur. Previous works have shown that ionospheric ions escape during active auroras, and more as the intensity of the aurora increases. In contrast, we have examined times of no auroras and find that ions are still escaping the auroral ionosphere. These escaping ions are an important source of auroral ions in the magnetosphere.
Ann. Geophys., 33, 333-344, doi:10.5194/angeo-33-333-2015, 2015
Modeling of rain attenuation and site diversity predictions for tropical regions
Summary: Presented in this paper is an empirical model for long-term rain attenuation prediction and statistical prediction of site diversity gain on slant path. The novelty of the model is the inclusion of low elevation angles and high link frequency up to 70GHz in the model derivation. The comparison results with Hodge, Panagopoulos and Nagaraja empirical predictions show that the proposed model provides better performance for site separation distance and elevation angle. The model performance is good.
Ann. Geophys., 33, 321-331, doi:10.5194/angeo-33-321-2015, 2015
Coupling in the middle atmosphere related to the 2013 major sudden stratospheric warming
Summary: Sudden stratospheric warmings (SSWs) are a natural laboratory to study vertical and horizontal coupling throughout the whole atmosphere. This study presents MLS derived pole-to-pole temperature anomalies associated with the 2013 major SSW. The results provide observational evidence for interhemispheric coupling, and the wave-mean flow interactions thought to be responsible for the formation of temperature anomalies in the summer hemisphere.
Ann. Geophys., 33, 309-319, doi:10.5194/angeo-33-309-2015, 2015
O+ transport in the dayside magnetosheath and its dependence on the IMF direction
Ann. Geophys., 33, 301-307, doi:10.5194/angeo-33-301-2015, 2015
Stimulated electromagnetic emission polarization under different polarizations of pump waves
Summary: The results of stimulated electromagnetic emission (SEE) polarization investigations under different modes of the pumping wave polarization are presented. The results were obtained in November 2012 during a heating campaign utilizing the SPEAR heating facility and a PGI radio interferometer. The polarization ellipse parameters of the SEE DM components were determined. It was found that the polarization direction of DM components was preserved under different polarizations of the pump waves.
Ann. Geophys., 33, 295-300, doi:10.5194/angeo-33-295-2015, 2015
Vlasov simulations of trapping and loss of auroral electrons
Summary: In this paper, we simulate the plasma on a magnetic field line above the aurora. Initially, about half of the acceleration voltage is concentrated in a thin double layer at a few thousand km altitude. When the voltage is lowered, electrons trapped between the double layer and the magnetic mirror are released. In the process we see formation of electron beams and phase space holes. A temporary reversal of the polarity of the double layer is also seen as well as hysteresis effects in its position.
Ann. Geophys., 33, 279-293, doi:10.5194/angeo-33-279-2015, 2015
Long-term response of stratospheric ozone and temperature to solar variability
Summary: The paper investigates the long-term variability in stratospheric ozone (O3) and temperature (T) from 1979 to 2013, and its relationship with the 11-year solar cycle. It is found that O3 and T anomalies are characterized by long-term trends; (ii) correlations are consistent with photochemical reactions and large-scale transports; and (iii) wavelet cross-spectra between O3 and Mg II index show common power during the 11-year period, proving the impact of the solar variability on the atmosphere.
Ann. Geophys., 33, 267-277, doi:10.5194/angeo-33-267-2015, 2015
Magnetic field-aligned plasma currents in gravitational fields
Summary: Currents due to slow bulk electron motion along vertical magnetic fields are studied for plasmas subject to a gravitational force. A general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models thus do not allow general steady-state solutions for field-aligned currents. The alternative is that only time-varying solutions exist.
Ann. Geophys., 33, 257-266, doi:10.5194/angeo-33-257-2015, 2015
Azimuthal velocity shear within an Earthward fast flow – further evidence for magnetotail untwisting?
Summary: An azimuthal velocity shear with a reversal within an earthward magnetotail fast flow is studied using Cluster observations. In addition, ionospheric SuperDARN data and different magnetospheric models (T96 and TF04) are utilized when interpreting the Cluster observations. Untwisting of twisted tail B field lines is a good candidate to explain the observations.
Ann. Geophys., 33, 245-255, doi:10.5194/angeo-33-245-2015, 2015
Relation between stratospheric sudden warming and the lunar effect on the equatorial electrojet based on Huancayo recordings
Summary: This paper presents the long-term observations of lunar tidal signatures in the equatorial electrojet (EEJ) and their relation to stratospheric sudden warming (SSW) events. We propose an approach to estimate the occurrence of SSW events before their direct observations (before 1952) from the magnetic field observations at Huancayo.
Ann. Geophys., 33, 235-243, doi:10.5194/angeo-33-235-2015, 2015
A solar-wind-driven empirical model of Pc3 wave activity at a mid-latitude location
Summary: This paper describes the development of empirical models that are capable of predicting Pc3 pulsation intensity from solar wind parameters (e.g. plasma flow speed, proton density, and interplanetary magnetic field (IMF) orientation). We also calculate the typical timescales at which different solar wind parameters influence the excitation of these waves: solar wind speed influences pulsation intensity at much longer timescales (about 2 days) than IMF orientation (about 1 hour).
Ann. Geophys., 33, 225-234, doi:10.5194/angeo-33-225-2015, 2015
Auroral vortex street formed by the magnetosphere–ionosphere coupling instability
Summary: By performing 3-D MHD simulations including Alfven eigenmode perturbations most unstable to the ionospheric feedback effects, we examined the auroral vortex street that often appears just before substorm onset. We found that an initially placed arc splits, intensifies, and rapidly deforms into a vortex street. We also found that there is a critical convection electric field. The vortex street is shown to be a consequence of M-I coupling between field-aligned currents and Pedersen/Hall currents.
Ann. Geophys., 33, 217-224, doi:10.5194/angeo-33-217-2015, 2015
The influence of solar activity on action centres of atmospheric circulation in North Atlantic
Summary: A possible link between solar activity and the atmospheric pressure fields is investigated using NCEP/NCAR data at ground level and at 500hPa, in the Northern Hemisphere for the cold season, with a focus on the North Atlantic centres of action. The Icelandic low seems to be most sensitive to the solar signal by moving towards north and by confining its activity area during months with high solar activity.
Ann. Geophys., 33, 207-215, doi:10.5194/angeo-33-207-2015, 2015
The Hiccup: a dynamical coupling process during the autumn transition in the Northern Hemisphere – similarities and differences to sudden stratospheric warmings
Summary: A vertical coupling process in the northern high-latitude middle atmosphere has been identified during the equinox transitions, which we call the “hiccup” and which acts like a “mini sudden stratospheric warming (SSW)”. We study the average characteristics of the hiccup based on a composite analysis using a nudged model. A comparison of the average characteristics of hiccups and SSWs shows both similarities and differences between the two vertical coupling processes.
Ann. Geophys., 33, 199-206, doi:10.5194/angeo-33-199-2015, 2015