О возможности моделирования изменения размеров и формы ионопаузы Венеры в цикле солнечной активности презентация

и формы ионопаузы Венеры
в цикле солнечной активности

GDRE ‘Cosmophysique workshop, Toulouse, France, April 2-4, 2008

М.И. Веригин, Г.А. Котова

Доклад на конференции
“Физика плазмы в солнечной системе”
17-20 февраля 2009 г., ИКИ РАН

radiooccultations at different SZA

Savich et al., Proc 13th Int.Symp.Space Tech.Sci. Tokyo, 1982, p.1533.

A distinct upper boundary of the Venusian ionosphere, called ionopause, was first observed by lone radio occultation of Mariner 5 (Mariner Stanford Group,1967).

Subsequent radio occultation of Mariner 10 found the ionopause at lower heght and not as sharp as in Mariner 5 case (Howard et al., 1974), thus originating some uncertainty in this boundary.

The permanent existence of the Venusian ionopause became evident after multiple Venera 9 and 10 radio occultations (Aleksandrov et al., 1976)

(proxy) for three subsets of SZA

Elphic et al., GRL, 7,No.8, 561,1980

Pioneer Venus Orbiter (PVO) data provide large array of this boundary observations by different instruments at different solar zenith angles (SZA) and under various upstream solar wind and EUV flux (Feuv) conditions (see, e.g., Elphic et al., 1980, Brace et al., 1983, Phillips et al., 1988).

(JGR, A5, 3927, 1988) included its ~ 800 PVO ionopause crossings with SZA < 90o and with upstream solar wind measurements

Venusian ionopause observations

Average ionopause height dependence on SZA as determined by different methods over PVO observations

Philips et al., JGR, 89, 10676-10684, 1984

of observations under maximal solar activity conditions (SAmax) only

Among all PVO ionopause observations, only 86 of its crossings took place under controlled solar ρV2 and EUV flux conditions.

Hopeless situation ???

Venusian ionopause observations

Latest Venus Express (VEX) orbiter enabled possibility of near solar minimum (SAmin) in situ studies of magnetic barrier region but not the ionopause, since it was seldom observed with VEX periapsis at 250 – 350 km (Zhang et al., 2008)

variations in initial PVO period was ~50% of its global value…

Variation of Solar EUV flux during period of PVO measurements. Red points corresponds to period used in present analysis.

balance at ionopause :

Ionopause shape parameterization

with

Theoretical description:

with upper ionosphere pressure profile:

Ionopause shape parameterization

Analytic approximation of D:

with

distance between observed ionopause positions and model ionopause surface



req = Rv + 291 + 52(Feuv – 1.65) km, peq = 8.3 + 6.2(Feuv – 1.65) nP

H1 = 11.9 + 9.9(Feuv – 1.65) km, H2 = 286 + 20(Feuv – 1.65) km

Ionopause shape parameterization

Ionopause shape analytic equation:

pressure variations used in fitting





Resulted scatter plot of external and internal pressures across the ionopause

Variation of subsolar ionopause position or internal plasma pressure during the solar cycle

ionopause positions

within solar cycle that influence neutral exosphere ionization rate

Solar cycle variation of the Venusian terminator BS is the strongest and most reliably established

Venusian bow shock: Search for Solar cycle variations

Russell et al., Adv. Space Res., 10, 55, 1990
Zhang et al., JGR, 95, 14961, 1990

Relative role of other factors, e.g.
- solar wind Alfvenic Mach number systematic variation,
- magnetic barrier shape variation …,

yet to be defined by advance modeling

моделирования околовенерианской ударной волны, что может обеспечить:

Построена аналитическая модель ионопаузы Венеры, описывающая изменения ее положения и формы в зависимости от динамического давления солнечного ветра и потока УФ излучения Солнца.

Такая модель позволяет проследить вариации размеров и формы ионопаузы на протяжении солнечного цикла и, следовательно, может быть использована для начального периода измерений на спутнике Венера Экспресс, орбита которого не позволяла проводить прямые измерения в окрестности ионопаузы.

расширенные возможности для правильного переноса в подсолнечную точку и на терминатор ее наблюдавшихся положений, а также для их нормализации и мультифакторного анализа;

выяснение относительной роли различных факторов влияющих на необычно большую вариацию в солнечном цикле положения околовенерианской ударной волны на терминаторе.

for the Venusian bow shock thus providing:

Venusian analytical ionopause model is developed including variations of its position and shape separately from solar wind ram pressure and solar EUV flux.

This model provides possibility to trace ionopause its position and shape variations within solar cycle and, thus, can be applied for the SAmin period of Venus Express observations, which orbit do not provides possibility for direct ionopause studies.

enhanced possibilities for reasonably correct mapping, normalization, and multifactor analysis of its crossings;

clearification of relative role of different factors of unusually large variation of the bow shock terminator position within solar cycle.