New formula representations of high- New formula representations of - PowerPoint PPT Presentation

New formula representations of high- New formula representations of high- latitude O + + ionospheric ionospheric outflows for outflows for latitude O use in global magnetospheric magnetospheric use in global modeling modeling J. L. Horwitz and W. Zeng J. L. Horwitz and W. Zeng Department of Physics Department of Physics The University of Texas at Arlington The University of Texas at Arlington Presented to IAGA Symposium Presented to IAGA Symposium Peruggia, Italy , Italy Peruggia July 2007 July 2007

High-latitude Ionosphere High-latitude Ionosphere

Flux tube extends from 8 R E 120 km to several R E altitude. Semi-Kinetic Treatment Fluid-region upper boundary conditions for 1100 km successive steps from 800 km advancing GSK treatment. Fluid Lower boundary of Treatment 120 km GSK treatment set at 800 km altitude. Simulation The dynamic boundary coupling H + and O + ions injected in an overlap region between the at lower boundary of fluid and generalized semi- GSK based on fluid- kinetic treatments in the DyFK treatment results there. model [after Estep et al., 1999]

Strangeway et al.[2005] analysis of FAST particle Strangeway et al.[2005] analysis of FAST particle and field observations at 4000 km altitude : and field observations at 4000 km altitude : Ion flux correlated with electron precipitation: Ion flux correlated with electron precipitation: 9±0.341 n 2.200±0.489 f i = 1.022 × 10 9±0.341 n ep 2.200±0.489 f i = 1.022 × 10 ep − 2 − 1 is the ion flux in cm − s − where f f i 2 s 1 and and n n ep is precipitating where i is the ion flux in cm ep is precipitating electron density. electron density. Correlation with Poynting Poynting flux: flux: Correlation with 7±0.242 S 1.265±0.445 f i = 2.142 × 10 7±0.242 S 1.265±0.445 f i = 2.142 × 10 where S is the Poynting Poynting flux at 4000 km altitude in mW- flux at 4000 km altitude in mW- where S is the − 2 m − 2 . . m Somewhat similar analysis by Zheng et al.[2005] with Somewhat similar analysis by Zheng et al.[2005] with POLAR observations near 6000 km altitude. POLAR observations near 6000 km altitude.

Winglee et al. [JGR, 2002]: Global impact of Winglee et al. [JGR, 2002]: Global impact of ionospheric outflows on the dynamics of the outflows on the dynamics of the ionospheric magnetosphere and cross-polar cap potential magnetosphere and cross-polar cap potential

Moore et al.[2007]: Use of Strangeway et Moore et al.[2007]: Use of Strangeway et al. formula for ionospheric ionospheric ion trajectory ion trajectory al. formula for based global modeling— —input input based global modeling parameters provided by MHD model parameters provided by MHD model

From Lotko et al.: How do ionospheric outflows impact magnetosphere-ionosphere system dynamics? 12 Alfvénic 12 dc EM power flows electrodynamic–inertial linkage coupling and feedback superthermal 12 flux outflow global modeling 12 thermal 12 outflow TEC mass V || transport

To obtain an appropriate formula representation based on To obtain an appropriate formula representation based on DyFK simulations, 924 simulations, 924 DyFK DyFK runs were used to obtain the runs were used to obtain the DyFK O + + outflux outflux at 3 R at 3 R E altitude in a flux tube (as then mapped O E altitude in a flux tube (as then mapped to 1000 km altitude) subjected to the two indicated to 1000 km altitude) subjected to the two indicated auroral processes for two hours. The evolution of the O processes for two hours. The evolution of the O + + auroral density for a typical run is displayed here. density for a typical run is displayed here.

+ field-aligned flux profile Evolution of the O + field-aligned flux profile Evolution of the O for the same DyFK DyFK simulation run. simulation run. for the same

O + + Outflows versus Wave Spectral Level and Electron Outflows versus Wave Spectral Level and Electron O Precipitation Parameters based on DyFK DyFK Runs Runs Precipitation Parameters based on From DyFK simulations for various parameters of wave spectral density, soft electron precipitation energy flux, and characteristic electron precipitation energy we obtained O + outflow dependences (next slides) which may be approximately represented by the formula representing the O + outflows: Flux ( 3 . 1 10 10 f ) 6 8 0 . 2 = � + e + O 500 En � 2 . 6 ( ) (tanh( 10 D ) 0 . 2 D ) e 5 . 0 10 0 . 6 6 500 Z + + � � wave wave 1 . 4 where Z 160 f ( 1 e ) f 0 . 2 � = � e e where Flux O+ is the O + number flux in cm -2 s -1 at 3 R E mapped to 1000 km altitude; f e is the electron precipitation energy flux in ergs cm -2 s -1 , and D wave is the wave spectral density at 6.5 Hz in (mV) 2 m -2 Hz -1 , E n is the characteristic energy of the electron precipitation.

Comparison of DyFK DyFK simulation results simulation results Comparison of with empirical formula representation with empirical formula representation The top panel displays a spectrogram of the O + outflows versus the wave spectral density-electron precipitation energy flux from the DyFK simulations, while the bottom panel is the O + outflow spectrogram represented by the formula presented on the previous slide. These spectrogram “cuts” are for a fixed characteristic electron precipitation energy of 100 eV.

Comparison of DyFK DyFK simulation results with simulation results with Comparison of empirical formula representation (continued) empirical formula representation (continued) Here the top panel displays a Here the top panel displays a spectrogram of the O + + spectrogram of the O outflows versus the wave outflows versus the wave spectral density and electron spectral density and electron precipitation characteristic precipitation characteristic energy from the DyFK DyFK energy from the simulations, while the bottom simulations, while the bottom panel is the O + + outflow outflow panel is the O spectrogram represented by spectrogram represented by the formula presented on the the formula presented on the earlier slide. These spectro spectro- - earlier slide. These gram “ “cuts cuts” ” are for a fixed are for a fixed gram electron precipitation energy electron precipitation energy flux of 0.7 ergs cm -2 -2 s s -1 -1 . . flux of 0.7 ergs cm

Summary of Results for Formula Summary of Results for Formula Representation Representation ▶ The wave heating process functions as a kind of The wave heating process functions as a kind of “valve valve” ” on the net O on the net O + + outflux outflux. If heating is . If heating is “ insufficient, the produced outflux outflux is limited. If wave is limited. If wave insufficient, the produced spectral density exceeds a certain threshold which spectral density exceeds a certain threshold which causes energization energization of majority of the entering O of majority of the entering O + + causes ions to escape energies, further increases of wave ions to escape energies, further increases of wave spectral density cause no significant further spectral density cause no significant further increase in O + + (number) (number) outflux outflux. . increase in O ▶ However, increases in electron precipitation However, increases in electron precipitation cause ~ monotonic increases of O + + outflux outflux. . cause ~ monotonic increases of O

Observational evidence for wave-heating Observational evidence for wave-heating “valve valve” ” effect? effect? “ Knudsen et al[1998] examined Knudsen et al[1998] examined Freja Freja measurements, at ~1700 km altitude, measurements, at ~1700 km altitude, for correlations between ion for correlations between ion energization and electron bursts and and electron bursts and energization BBELF waves. The plot at the right BBELF waves. The plot at the right displays integrated 0-20 eV eV ion counts ion counts displays integrated 0-20 versus wave spectral density which versus wave spectral density which suggest that significant local heating suggest that significant local heating occurs only above a critical wave occurs only above a critical wave spectral density level. This is, however, spectral density level. This is, however, somewhat different than the “ “valve valve” ” somewhat different than the question of attainment of significant question of attainment of significant escape fluxes of O + requiring such a escape fluxes of O + requiring such a threshold in wave power. threshold in wave power.