scholarly journals Case studies on the dynamics of Pi3 geomagnetic and riometer pulsations during auroral activations

2002 ◽  
Vol 20 (2) ◽  
pp. 151-159 ◽  
Author(s):  
N. G. Kleimenova ◽  
O. V. Kozyreva ◽  
K. Kauristie ◽  
J. Manninen ◽  
A. Ranta
Keyword(s):  
Mhd Waves ◽  
Geomagnetic Pulsations ◽  
Tight Coupling ◽  
Ionospheric Currents ◽  
Particle Precipitation ◽  
Mhd Waves And Instabilities ◽  
Energetic Particle Precipitation ◽  
Particle Intensity ◽  
Auroral Phenomena ◽  
Current Signatures

Abstract. A sequence of three subsequent auroral activations (at 18:10, 19:48 and 20:00 UT) on 9 February 1997 is analysed. The brightenings of optical auroras were collocated with latitudinally localized bursts of pulsating riometer absorption and Pi3 geomagnetic pulsations. In two of the cases, the strongest westward directed electrojet currents and the footpoint of the upward directed field-aligned currents related to the auroral brightening were observed in the same region as the largest amplitude of the pulsations and their polarization changed. In the third case, field-aligned current signatures were present, but not so pronounced that their accurate location could not be defined. In all cases, the spectra of geomagnetic and absorption pulsations were similar. Based on ground-based observations alone, it is difficult to say whether the energetic particle precipitation (riometer absorption) was modulated by the geomagnetic pulsations or whether the geomagnetic pulsations were caused by varying ionospheric currents controlled by the precipitating particle intensity. However, the localized nature of both pulsations of the two different phenomena and their tight coupling with each other seem to support the latter option.Key words. Ionosphere (Particle precipitation) – Magnetospheric physics (auroral phenomena; MHD waves and instabilities)

scholarly journals A slow mode wave as a possible source of Pi 2 and associated particle precipitation: a case study

1999 ◽  
Vol 17 (5) ◽  
pp. 674-681 ◽  
Author(s):  
O. Saka ◽  
O. Watanabe ◽  
K. Okada ◽  
D. N. Baker
Keyword(s):  
Mhd Waves ◽  
Wave Form ◽  
Fluxgate Magnetometer ◽  
Syowa Station ◽  
Low Energy Electrons ◽  
Dip Equator ◽  
Substorm Activity ◽  
Mhd Waves And Instabilities ◽  
Break Up ◽  
Auroral Phenomena

Abstract. An intensification of auroral luminosity referred to as an auroral break-up often accompanies the onset of geomagnetic pulsation (Pi 2) at the dip-equator. One such auroral break-up occurred at 2239 UT on 16 June, 1986, being accompanied by weak substorm activity (AE~50 nT) which was recorded in all-sky image of Syowa Station, Antarctica (66.2°S, 71.8°E in geomagnetic coordinates). The associated Pi 2 magnetic pulsation was detected by a fluxgate magnetometer in the afternoon sector at the dip-equator (Huancayo, Peru; 1.44°N, 355.9° in geomagnetic coordinates; 12.1°S, 75.2°W in geographic coordinates; L=1.00). In spite of the large separation of the two stations in longitude and latitude, the auroral break-up and subsequent luminosity modulation were seen to be correlated with the wave form of the ground Pi 2 pulsation. This occurred in such a way that the luminosity maximum was seen to occur at the phase of maximum amplitudes of Pi 2 wave form. We argue that the observed correlation could be interpreted as indicating a Pi 2-modulation of a field-aligned acceleration of the low energy electrons that may occur near the equator of the midnight magnetosphere.Key words. Magnetospheric physics (auroral phenomena; energetic particles · precipitating; MHD waves and instabilities)

scholarly journals Impact of energetic particle precipitation on stratospheric polar constituents: an assessment using MIPAS data monitoring and assimilation

2009 ◽  
Vol 9 (5) ◽  
pp. 22459-22504
Author(s):  
A. Robichaud ◽  
R. Ménard ◽  
S. Chabrillat ◽  
J. de Grandpré ◽  
Y. J. Rochon ◽  
...  
Keyword(s):  
Gas Phase ◽  
Energetic Particle ◽  
Solar Proton ◽  
Significant Loss ◽  
Proton Event ◽  
Particle Precipitation ◽  
Gas Phase Chemistry ◽  
Energetic Particle Precipitation ◽  
Phase Chemistry ◽  
Assimilation System

Abstract. In 2003, strong geomagnetic events occurred which produced massive amounts of energetic particles penetrating the top of the atmospheric polar region, significantly perturbing its chemical state down to the middle stratosphere. These events and their effects are generally left unaccounted for in current models of stratospheric chemistry and large differences between observations and models are then noted. In this study, we use a coupled 3-D stratospheric dynamical-chemical model and assimilation system to ingest MIPAS temperature and chemical observations. The goal is to gain further understanding and to evaluate the impacts of EPP (energetic particle precipitation) on stratospheric polar chemistry. Moreover, we investigate the feasibility of assimilating valid "outlier" observations associated with such events. We focus our analysis on OmF (Observation minus Forecast) residuals as they filter out phenomena well reproduced by the model (such as gas phase chemistry, transport, diurnal and seasonal cycles) thus revealing a clear trace of the EPP. Inspection of OmF statistics in both the passive (without chemical assimilation) and active (with chemical assimilation) cases altogether provides a powerful diagnostic tool to assess the model and assimilation system. We also show that passive OmF can permit a satisfactory evaluation of the ozone partial column loss due to EPP effects. Results suggest a small but significant loss of 5–6 DU (Dobson Units) during an EPP-IE (EPP indirect effects) event in the Antarctic winter of 2003, and about only 1 DU for the SPE (solar proton event) of October/November 2003. Despite large differences between the model and MIPAS chemical observations (NO2, HNO3, CH4 and O3), we demonstrate that a careful assimilation of these constituents with only gas phase chemistry included in the model (i.e. no provision for EPP impacts) and with relaxed quality control nearly eliminated the short-term bias and significantly reduced the standard deviation error below 1 hPa.

scholarly journals Magnetospheric lion roars

2000 ◽  
Vol 18 (4) ◽  
pp. 406-410 ◽  
Author(s):  
W. Baumjohann ◽  
E. Georgescu ◽  
K.-H. Fornacon ◽  
H. U. Auster ◽  
R. A. Treumann ◽  
...  
Keyword(s):  
Sampling Rate ◽  
Cone Angle ◽  
Mhd Waves ◽  
Lower Hybrid ◽  
High Sampling Rate ◽  
Polarized Waves ◽  
Magnetospheric Configuration And Dynamics ◽  
Mhd Waves And Instabilities ◽  
Electron Gyrofrequency ◽  
First Time

Abstract. The Equator-S magnetometer is very sensitive and has a sampling rate normally of 128 Hz. The high sampling rate for the first time allows detection of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dawnside magnetosphere. The characteristics of these waves are virtually identical to the lion roars typically seen at the bottom of the magnetic troughs of magnetosheath mirror waves. The magnetospheric lion roars are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.2 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient field is nearly always smaller than 1°.Key words: Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma waves and instabilities)

scholarly journals Energetic particle precipitation in the Brazilian geomagnetic anomaly during the “Bastille Day storm” of July 2000

2006 ◽  
Vol 58 (5) ◽  
pp. 607-616 ◽  
Author(s):  
Masanori Nishino ◽  
Kazuo Makita ◽  
Kiyofumi Yumoto ◽  
Yoshizumi Miyoshi ◽  
Nelson J. Schuch ◽  
...  
Keyword(s):  
Energetic Particle ◽  
Particle Precipitation ◽  
Energetic Particle Precipitation ◽  
Geomagnetic Anomaly

scholarly journals Post-noon two-minute period pulsating aurora and their relationship to the dayside convection pattern

1999 ◽  
Vol 17 (7) ◽  
pp. 877-891 ◽  
Author(s):  
S. E. Milan ◽  
T. K. Yeoman ◽  
M. Lester ◽  
J. Moen ◽  
P. E. Sandholt
Keyword(s):  
Current System ◽  
Wave Activity ◽  
Mhd Waves ◽  
Magnetohydrodynamic Wave ◽  
Auroral Emission ◽  
Minute Period ◽  
Optical Signature ◽  
Short Period ◽  
Auroral Emissions ◽  
Auroral Phenomena

Abstract. Poleward-moving auroral forms, as observed by meridian-scanning photometers, in the vicinity of the cusp region are generally assumed to be the optical signature of flux transfer events. Another class of quasi-continuous, short period (1-2 min) wave-like auroral emission has been identified, closely co-located with the convection reversal boundary in the post-noon sector, which is similar in appearance to such cusp aurora. It is suggested that these short period wave-like auroral emissions, the optical signature of boundary plasma sheet precipitation in the region 1 field-aligned current system, are associated with ULF magnetohydrodynamic wave activity, which is observed simultaneously by ground magnetometer stations. This association with ULF wave activity is strengthened by the observation of several harmonic frequencies in the pulsation spectrum, each an overtone of the fundamental standing wave resonance frequency.Key words. Magnetospheric physics (auroral phenomena; magnetopause · cusp · and boundary layers; MHD waves and instabilities)

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