RCM Modeling of Penetration Electric Fields During Magnetic Storms

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1 RCM Modeling of Penetration Electric Fields During Magnetic Storms S. Sazykin, R. A. Wolf, R. W. Spiro, Haystack Workshop on Penetration Electric Fields November 8, 2005

2 Low Latitude E-field: Massive Undershielding Plasma sheet/ring current Alfvén Layer P p Convection electric field Figure Courtesy of Y. Ebihara High-latitude convection E-field drives region-2 FAC Region-2 FAC, generated via pressure-gradients at the inner edge of the plasma sheet, tend to partially shield low-latitude ionosphere from convection E-field, but not during large storms November 8, 2005 Haystack Workshop 2

3 Northward IMF Turning Can Cause Overshielding Southward IMF Turning Can Cause Undershielding Under steady magnetospheric conditions, region-2 FAC currents shield the inner magnetosphere from the convection E-field Changes in IMF Bz orientation are not the only solar wind cause of promptpenetration electric fields, but may be among the most efficient one. A sudden northward IMF Bz turning renders region-2 currents too strong, which generates a short-lived (~1 hour) E-field at low-latitude ionosphere that is duskdawn and backwards convection in inner magnetosphere. A southward turning causes the opposite effect (undershielding) due to initially region-2 currents being too weak, which then adjust. Response is attenuation + time decay Understanding is relevant for isolated cases of penetration electric fields associated with convection enhancements. There is massive undershielding during large geomagnetic storms. An entirely different regime? Equatorial equipotentials. Corotation not displayed. Fejer, in Solar-Wind Magnetosphere Coupling, 1986 November 8, 2005 Haystack Workshop 3

4 Effect of Strong Penetration on Equatorial Ionosphere Basu et al. (GRL, 28, 3577, 2001) showed dropout of the equatorial ionosphere at 840 km altitude in main phase of the Bastille Day storm. They interpreted that as the result of upward drift of the F-layer above that altitude. This uplift was accompanied by strong scintillations.eastward electric field causes a downward drag that acts like increased gravity and encourages the Rayleigh-Taylor instability that causes spread F. November 8, 2005 Haystack Workshop 4

5 Is it possible that during large magnetic storms, there is no shielding in the traditional sense? How long can penetration E-fields last during large storms? How large can penetration E-fields get in the equatorial ionosphere? Numerical Model (RCM): solves adiabatic drift equations in the inner magnetosphere FAC via pressure gradients (Vasyliunas equation) Ionospheric current conservation equation Case study: April 17-18, 2002 magnetic storm November 9-10, 2004 magnetic storm November 8, 2005 Haystack Workshop 5

6 April 17, 2002 Magnetic Storm Solar Wind and IMF RCM inputs November 8, 2005 Haystack Workshop 6

7 How Southward Turning Affects RCM Inputs Electromagnetic: It increases polar-cap potential Magnetic flux in the tail lobes increases, tail field stretches Plasma Southward IMF changes PV 5/3 in the middle and distant plasma sheet, but the change is highly uncertain due to lack of knowldege and understanding of how solar wind controls plasma sheet. Specifying ionospheric conductance model is another uncertainty affecting penetration E-fields. Polar cap potential: Boyle et al.+ Siscoe- Hill saturation. Magnetic field model: Hilmer-Voigt model had input parameters: Estimate standoff distance from solar-wind ρv 2. Use observed ABI Use measured Dst (SYM-H). The principal parameters we need to specify are PV 5/3 and TV 2/3. Estimate PV 5/3 and TV 2/3 at 13 R E in the plasma sheet from plasma sheet statistics hold plasma boundary condition constant in time. or produce equatorial maps of PV 5/3, and TV 2/3, combine statistical models: Tsyganenko-Mukai From Toffoletto (JGR, et al.(space 108 (A3), 2003) Weather plasma-sheet AGU Monog., model. 2001) T01 magnetic field models. November 8, 2005 Haystack Workshop 7

8 Low-Latitude E-field Penetration Potential Main Phase time-dep. B.C. time-const B.C. solar-min PV 5/3 =3*PV 5/3 November 8, 2005 Haystack Workshop 8 N ps =3*N ps T ps =T ps /3

9 Upward E B drift (zonal E) at Jicamarca (289ºlong., 2º N dip lat.) RCM E-field + CTIP firstprinciples ionospheric model Total ionospheric E-field (penetration + wind dynamo) at fixed point on Earth Naomi Maruyama s work. Orange curve is IS radar data November 8, 2005 Haystack Workshop 9

10 Primary RCM Input Parameters for Event of November PCP estimated using ACE data and Boyle formula, modified for saturation by T. Hill. ABI was smoothed by 5- point averaging. Standoff distance estimated from ACE data, assuming proportional to (ρv 2 ) 1/6. November 8, 2005 Haystack Workshop 10

11 Jicamarca IS Vertical Drift Measurements Data and Figure courtesy of Bela Fejer and Chaosong Huang Figure courtesy of Bela Fejer Almost continuous data Circles connected by dashed lines are times of strong spread-f over broad range of altitudes. Otherwise data of excellent quality Daytime eastward penetration E-fields are the largest ever measured at Jicamarca (up to 3 mv/m) Total E-field (includes neutral wind dynamo component) Penetration is relative to the quiet-time baseline (continuous line). November 8, 2005 Haystack Workshop 11

12 RCM Simulation: November 9-10, 2004 Top curve is ratio of PCP to Penetration Potential (max. value of 0.23). Bottom curve is the Eastward E-field component at 300 km altitude at the equator. [Slight error in timing...] November 8, 2005 Haystack Workshop 12

13 Top curve gives overall strength of penetration of the driving potential Bottom (E-field at JRO) shifts in LT as the Earth rotates. November 8, 2005 Haystack Workshop 13

14 Summary of Results Magnetosphere-ionosphere coupling electrodynamic processes Increase in the polar-cap potential Increase in the magnetic flux in the tail lobes, magnetotail stretching will drive time-depedence of low-latitude penetration E-field Plasma sheet properties (PV 5/3, and TV 2/3 from combined statistical models) and ionospheric conductivity levels will control the magnitudes of low-lat. E-field May be no shielding for many hours in the usual sense during large (super) storms. Equatorial E(east-west) reaches up to 3 mv/m November 8, 2005 Haystack Workshop 14