Association of the pre-monsoon thermal field over north India and the western Tibetan Plateau with summer monsoon rainfall over India
Summary: In this paper inter-annual variability of tropospheric air temperature over the Asian summer monsoon region during the pre-monsoon months is examined in relation to Indian summer monsoon rainfall (ISMR; June to September total rainfall). The results indicate a strong and significant northwest–southeast dipole structure in the spatial correlations over the Indian region with highly significant positive (negative) correlations over the regions of north India and the western Tibetan Plateau region.
Ann. Geophys., 33, 1051-1058, doi:10.5194/angeo-33-1051-2015, 2015
Magnetohydrodynamic modeling of three Van Allen Probes storms in 2012 and 2013
Ann. Geophys., 33, 1037-1050, doi:10.5194/angeo-33-1037-2015, 2015
Observation of a new type of low-frequency waves at comet 67P/Churyumov-Gerasimenko
Summary: We present a first report on magnetic field measurements made in the coma of comet 67P/C-G in its low-activity state. The plasma environment is dominated by quasi-coherent, large-amplitude, compressional magnetic field oscillations around 40mHz, differing from the observations at strongly active comets where waves at the cometary ion gyro-frequencies are the main feature. We propose a cross-field current instability associated with the newborn cometary ions as a possible source mechanism.
Ann. Geophys., 33, 1031-1036, doi:10.5194/angeo-33-1031-2015, 2015
Numerical study of upper hybrid to Z-mode leakage during electromagnetic pumping of groups of striations in the ionosphere
Summary: Large-amplitude radio waves lead to the structuring of the ionospheric plasma into groups magnetic field-aligned density cavities, or striations. A large part of the electromagnetic wave with ordinary mode polarization is then mode converted into upper hybrid waves trapped in the striations, further enforcing the striations. This simulation study investigates numerically this mode conversion and leakage of the the upper hybrid waves to back to electromagnetic waves in the Z-mode branch.
Ann. Geophys., 33, 1019-1030, doi:10.5194/angeo-33-1019-2015, 2015
Profile of a low-Mach-number shock in two-fluid plasma theory
Summary: The magnetic profile of a laminar collisionless shock is described within two-fluid plasma theory. This description is valid only for the upstream part of the shock, before the ions begin to gyrate strongly. The emerging structure is fairly universal in a wide range of shock angles and mainly depends on the ratio of the dissipative to the dispersive length.
Ann. Geophys., 33, 1011-1017, doi:10.5194/angeo-33-1011-2015, 2015
Nonlinear wave interactions of kinetic sound waves
Summary: We reconsider the interaction of waves in a magnetized plasma, with a focus on the solar wind. The importance of a kinetic description, taking the detailed velocity distribution of electrons and ions into account, is emphasized. Our result for the coupling strength between different wave modes agrees with previous results in the limiting case when kinetic effects are negligible, however.
Ann. Geophys., 33, 1007-1010, doi:10.5194/angeo-33-1007-2015, 2015
Ionospheric variations over Indian low latitudes close to the equator and comparison with IRI-2012
Ann. Geophys., 33, 997-1006, doi:10.5194/angeo-33-997-2015, 2015
Strange VLF bursts in northern Scandinavia: case study of the afternoon "mushroom-like" hiss on 8 December 2013
Summary: A non-typical 1-4 kHz hiss was studied. It shows a sequence of separated noise bursts with strange “mushroom-like” shapes in the frequency-time domain, each lasting several minutes. This sequence could be a result of the modulation of the VLF hiss electron-cyclotron instability by Pc5 geomagnetic pulsations. This strange “mushroom-like” shape of the considered VLF hiss could be a combined mutual effect of the magnetospheric ULF-VLF wave interaction and the ionosphere waveguide propagation.
Ann. Geophys., 33, 991-995, doi:10.5194/angeo-33-991-2015, 2015
Stimulated Brillouin scattering during electron gyro-harmonic heating at EISCAT
Summary: This paper reports the first experimental observation of stimulated Brillouin scattering near the third electron gyro-harmonic induced by high-frequency, high-power radio waves at EISCAT. The stimulated Brillouin scattering has also been correlated with simultaneous observations of the field-aligned irregularities and electron temperature. The observed stimulated Brillouin scattering becomes enhanced for pumping near electron gyro-harmonics.
Ann. Geophys., 33, 983-990, doi:10.5194/angeo-33-983-2015, 2015
Statistical analysis of storm-time near-Earth current systems
Summary: The different electric current systems flowing in the near-Earth nightside magnetosphere each have a unique contribution to the magnetic and electric field distortion of geospace. This study quantifies the intensity and timing of five current systems as calculated from 90 storm events using an inner magnetospheric drift physics model. There is a systematic progression through the various current systems, leading to implications for nonlinear feedback on the geospace system.
Ann. Geophys., 33, 965-982, doi:10.5194/angeo-33-965-2015, 2015
Van Allen Probe observations of drift-bounce resonances with Pc 4 pulsations and wave–particle interactions in the pre-midnight inner magnetosphere
Summary: We studied localized Pc 4 pulsations in the pre-midnight inner magnetosphere observed by Van Allen Probe B on May 1 2013. Although we attribute the pulsations to a drift-bounce resonance, we demonstrate that the energy-dependent response of the ion fluxes result from pulsation-associated velocities sweeping energy-dependent radial ion flux gradients back and forth past the spacecraft.
Ann. Geophys., 33, 955-964, doi:10.5194/angeo-33-955-2015, 2015
A case study on generation mechanisms of a sporadic sodium layer above Tromsø (69.6° N) during a night of high auroral activity
Ann. Geophys., 33, 941-953, doi:10.5194/angeo-33-941-2015, 2015
How much does weather control fire size and intensity in the Mediterranean region?
Ann. Geophys., 33, 931-939, doi:10.5194/angeo-33-931-2015, 2015
Several notes on the OH* layer
Summary: The expressions that determine the altitude and number density at peak of the OH* layer were derived. OH* number density in the vicinity of the OH* layer is directly proportional to the atomic oxygen concentration and inversely proportional to the power of temperature. The peak of the layer number density is anti-correlated with the height of the peak. Atomic oxygen is responsible for the vertical separation of sub-layers with different vibrational numbers, and for the distance between them.
Ann. Geophys., 33, 923-930, doi:10.5194/angeo-33-923-2015, 2015
Observations of thermosphere and ionosphere changes due to the dissipative 6.5-day wave in the lower thermosphere
Summary: The 6.5-day traveling planetary wave is able to impact the ionosphere/thermosphere via a dissipation mechanism. Ionospheric TEC and thermosphere O/N2 exhibit an apparent decrease as the result of extra meridional circulation induced by 6.5-day wave dissipation. Our work suggests that the modulation of E-dynamo is not the unique pathway through which planetary waves substantially influence the IT system.
Ann. Geophys., 33, 913-922, doi:10.5194/angeo-33-913-2015, 2015
Planetary period oscillations in Saturn's magnetosphere: comments on the relation between post-equinox periods determined from magnetic field and SKR emission data
Summary: We compare the reported properties of oscillations in Saturn's outer plasma environment near the ~10.6 hour planetary rotation period, as observed in magnetic field and radio emission data obtained by the Cassini spacecraft. We highlight similarities and differences, and suggest possible reasons for the latter.
Ann. Geophys., 33, 901-912, doi:10.5194/angeo-33-901-2015, 2015
Spectral properties of electrostatic drift wave turbulence in the laboratory and the ionosphere
Summary: The present review describes a number of laboratory studies of low-frequency electrostatic drift wave turbulence together with related results obtained by instrumented spacecraft in the Earth's near and distant ionospheres. The summary emphasizes readily measurable quantities, such as the turbulent power spectra for the fluctuations in plasma density, potential and electric fields. A number of future studies are suggested in order to resolve some outstanding issues.
Ann. Geophys., 33, 875-900, doi:10.5194/angeo-33-875-2015, 2015
WHU VHF radar observations of the diurnal tide and its variability in the lower atmosphere over Chongyang (114.14° E, 29.53° N), China
Summary: The diurnal tide and its variability in the lower atmosphere over Chongyang (114.14ºE，29.53ºN) were studied based on the newly established Wuhan University VHF radar observations in the whole year of 2012. We find that the diurnal tide was the dominant tidal component and showed remarkable height and season variations, as well as dramatic short-term variability.
Ann. Geophys., 33, 865-874, doi:10.5194/angeo-33-865-2015, 2015
Eddy diffusion coefficients and their upper limits based on application of the similarity theory
Summary: For the first time, the authors show that, by using the similarity theory, the same formula can be obtained for the eddy diffusion coefficient as the commonly used formula derived by J. Weinstock. Our results also explain the discrepancy between the large cooling rates calculated by the authors and the temperatures given by the MSIS-E-90 model.
Ann. Geophys., 33, 857-864, doi:10.5194/angeo-33-857-2015, 2015
Solar-wind control of plasma sheet dynamics
Ann. Geophys., 33, 845-855, doi:10.5194/angeo-33-845-2015, 2015