Long-term changes in the magnetosheath: Solar wind drivers and magnetospheric effects

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Howard Fletcher
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1 1..1 Long-term changes in the magnetosheath: Solar wind drivers and magnetospheric effects Tuija I. Pulkkinen and Andrew Dimmock Department of Radio Science and Engineering, Aalto University, Espoo, Finland Introduction Solar wind magnetosheath ionosphere coupling Coupling efficiency Key driving parameters Two solar cycles IMAGE data One solar cycle Themis data 1 Deep solar minimum Themis and IMAGE - 1 R V day averages 1

2 V MS /V SW (b)magnetic field MS / SW 1 1 (c)electric field E,MS [mv/m] Y MIPM [Re] THEMIS in the magnetosheath (a)plasma speed Quasiperp - MIPM V MS /V SW (b)magnetic field (c)electric field. (d)v MS /V SW at m pause (e) MS /. SW at m pause Electric,MS field at m pause Y= Quasiparallel -1 perp Quasi Quasiparallel (d)v MS /V SW at m pause Y= Quasiparallel.1. Quasi- perpendicular.7 Shue magnetopause model (e) MS / SW at m pause Verigin 1bow model.. Quasiparallel.1. Quasiperp MS / SW E,MS [mv/m] (f)e,ms [mv/m] at m pause (Dimmock et al., JGR 1, Pulkkinen et al., GRL 1) Solar wind driver Magnetosheath response Themis analysis: 1- month sliding averages at - month intervals Measurements close to the magentopause (% of magnetosheath thickness) IntegraMon over dayside longitudes - > magnetopause average Gray: Solar min - 1 Red: <E SW > > 1. mv/m V Vx Ex Ma OMI solar wind V. Vx... 1 Themis magnetopause Ex 1 eta

1..1 IMAGE magnetometer chain magnetometer staions Data coverage 199-1 Data processed with baseline

intensity lamtude (Deg) Electrojet total current (MA) IMAGE magnetometer chain Eastward Westward

Electrojet total current (MA) Dusk Midnidght Dawn (Amm, J Geomag. Geoelectr., 1997.

3 1..1 IMAGE magnetometer chain magnetometer staions Data coverage Data processed with baseline removal IU, IL indices (equivalent to AU, AL) Electrojet peak intensity (ma/m) Electrojet peak intensity lamtude (Deg) Electrojet total current (MA) IMAGE magnetometer chain Eastward Westward magnetometer sta,ons Data coverage Data processed with baseline removal IU, IL indices (equivalent to AU, AL) Electrojet peak intensity (ma/m) Electrojet peak intensity la,tude (Deg) Electrojet total current (MA) Dusk Midnidght Dawn (Amm, J Geomag. Geoelectr., Amm and Viljanen, Earth Planets Space, 1999)

4 1..1 Solar cycle 1 R Solar wind V day averages 1 IU [nt] 1 IMAGE EEJ [MA] IL [nt] WEJ [MA] Monthly averages Evening sector: Solar cycle + annual Morning/ midnight sector Solar cycle + semi- annual 7 Probability distribution functions Seasonal variability PDF Evening sector eastward Midnight sector westward Winter Fall Summer Spring EEJ [MA] WEJ [MA]

5 1..1 Electrojet moments Seasonal variability Eastward Strong annual variability Spring acmvity higher than fall Westward Semiannual variability, which disappears during - 1 Spring maximum higher than fall during most years Spring: Mar, Apr, May Summer: Jun, Jul, Aug Fall: Sep, Oct, ov Winter: Dec, Jan, Feb Mean EEJ Summer Spring STD EEJ Winter Fall Mean WEJ Eastward Westward.1.. STD WEJ Electrojet moments Solar cycle variability Eastward Clear solar cycle dependence with minima/maxima during sunsport minima/maxima Westward Maximum during declining phase, minima during sunspot minima Spring: Mar, Apr, May Summer: Jun, Jul, Aug Fall: Sep, Oct, ov Winter: Dec, Jan, Feb Mean EEJ Summer Spring STD EEJ Winter Fall Mean WEJ.1... STD WEJ

6 1..1 Conclusions Solar minimum period 1 semiannual variation disappears during minimum; not observed during other minima very close to linear driving by Poynting flux incident at the magnetopause Eastward and westward distribution functions qualitatively different WEJ peak does not change by season, pdf width varies with driver intensity EEJ peak and width vary with season (ionospheric conductivity & driver intensity) in both, spring activity higher than fall Energy transfer from solar wind to magnetopause depends on activity electric field and Poynting flux seem to saturate for high driving lower values of solar wind driving produce linear response at the magnetopause Energy transfer from magnetopause to ionosphere close to linear large scatter introduced by seasonal variability scatter remains for higher activity summer and spring seasons 11 Thank You!

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