Hemispheric asymmetries in ionospheric electrodynamics during the solar wind void of 11 May 1999

Abstract

Abstract. We use the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure to produce composite maps of high-latitude ionospheric parameters for 11 May 1999. On that day there was a near void in the solar wind momentum flux. Yet, focused high-latitude interactions occurred at Earth. Our maps of convection, Joule heating, particle precipitating power and field-aligned current show a striking asymmetry between hemispheres. In the latter three parameters there is at least a five-fold difference in values between the hemispheres. The northern hemisphere polar cap particle precipitation is the strongest we have ever mapped. Strong electrodynamic interactions were focused above 70 ø north magnetic latitude. In the southern hemisphere only weak, irregular patterns are mapped. We attribute these differences to the strong interplanetary magnetic field spiral configuration, the sunward tilt of the northern hemisphere and the direct beam or "strahl" of solar electrons impinging on the northern polar cap during the momentum void. BackgroundOn 11 May 1999 both ACE and WIND satellites observed the solar wind density and velocity to be unusually low with an average number density less than 1/cm '3 and an average We have investigated the validity of such a long-interval mapping. The IMF components were relatively steady during the 11-hr period (Fig 1). AMIE maps from individual 30-min intervals (not shown) suggest minimal large-scale ionospheric variations and confirm the presence of the large-scale features we illustrate in this study. However, higher resolution maps, which will be discussed in a future paper, show some of the small-scale variations reported by Papitashvili et al. [2000]. DataThe multi-hour window allows us to accumulate data from several hundred points along polar orbiting satellite tracks and from thousands of radar observations. We also incorporate data from sensors on the polar orbiting Defense Meteorological Satellite Program (DMSP) and NOAA satellites that measure downward flux and mean energy of precipitating electrons in the range of 30 eV to 300 keV. DMSP ion drifts 450 I I

Climatological patterns of high‐latitude convection in the Northern and Southern hemispheres: Dipole tilt dependencies and interhemispheric comparisons

“…It should also be noted that all of our interhemispherical comparisons have been performed after changing the sign of both IMF B y and the dipole tilt in the Southern Hemisphere. If the hemispheres are compared simultaneously, significant differences can be observed if there is a strong IMF B y component or a non‐zero dipole tilt, such as in the case studies by Knipp et al [1993, 2000] and Lu et al [1994].…”

“…Case studies by Knipp et al [1993, 2000] and Lu et al [1994] used ground‐based magnetometer measurements combined with satellite and sometimes ground‐based radar measurements using the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique [ Richmond and Kamide , 1988] to derive patterns for both hemispheres, showing significant interhemispheric asymmetries in the strengths and configurations of the convection.…”

Seasonal effect for polar cap sunward plasma flows at strongly northward IMF Bz

“…Numerous observations [e.g., Huang et al ., ; Ambrosino et al ., ; Cousins and Shepherd , ] are consistent with this expectation. Although the occurrence of four cells seems to be undisputed, SuperDARN observations often show more complicated patterns [e.g., Greenwald et al ., ; Knipp et al ., ] warranting further studies. This is of particular importance in view of a recent discovery that the lobe reconnection in one hemisphere can be affected by the lobe reconnection in the other hemisphere leading to the so‐called interchange cycle [e.g., Watanabe et al ., ; Watanabe and Sofko , ; Watanabe et al ., ].…”

Interhemispheric asymmetry of the high‐latitude ionospheric convection on 11–12 May 1999

“… Knipp et al [2000] calculated the overall potential pattern during the present period of interest by using the AMIE algorithm, but the pattern in the Southern Hemisphere did not show any localized intense flows in the dusk to midnight sector. One possibility is that in their algorithm the small‐scale structures might have been smeared out in the global convection pattern.…”