Origin of Ionospheric Hot Spots During Quiet Times

J. Raeder, W. Li

Space Science Center, UNH

D. Knipp

NCAR/HAO MURI/NADIR Workshop, Boulder, CO, October 27, 2010

Bx By Bz

Introduction

• • High Poynting flux into the polar ionosphere is expected during storms = strong southward IMF.

However, there are times when the IMF is not southward (= quiet magnetosphere, Kp<2), but strong, localized Poynting flux is observed.

IMF and Solar Wind Poynting Flux-DMSP AMIE Joule Heat |V| 2

• CHAMP Data: Neutral Density Enhancement The localized energy input has a profound effect on neutral density.

DMSP Poynting Flux Northward Turning, Shock Arrival SW Density Increase 3

OpenGGCM: Global Magnetosphere Modeling

The Open Geospace General Circulation Model : Aurora • Coupled global magnetosphere - ionosphere - thermosphere model.

• 3d Magnetohydrodynamic magnetosphere model.

• Coupled with NOAA/SEC 3d dynamic/chemistry ionosphere thermosphere model (CTIM).

• Coupled with inner magnetosphere / ring current models: Rice U. RCM, NASA/GSFC CRCM.

• Model runs on demand (>300 so far) provided at the Community Coordinated Modeling Center (CCMC at NASA/GSFC).

http://ccmc.gsfc.nasa.gov/ • Fully parallelized code, real-time capable. Runs on IBM/datastar, IA32/I64 based clusters, PS3 clusters, and other hardware.

• Used for basic research, numerical experiments, hypothesis testing, data analysis support, NASA/THEMIS mission support, mission planning, space weather studies, and Numerical Space Weather Forecasting in the future.

• Funding from NASA/LWS, NASA/TR&T, NSF/GEM, NSF/ITR, NSF/PetaApps, AF/MURI programs. Ionosphere Potential

Personnel:

J. Raeder, D. Larson, W. Li, A. Vapirev, K. Germaschewski, L. Kepko, H.-J. Kim, M. Gilson, B. Larsen (UNH), T. Fuller Rowell, N. Muriyama (NOAA/SEC), F. Toffoletto, A. Chan, B. Hu (Rice U.), M.-C. Fok (GSFC), A. Richmond, A. Maute (NCAR)

OpenGGCM Simulations of Three Events

• • • These events happen frequently (see afternoon session).

OpenGGCM can reproduce them.

Which allows us to study their causes.

2004 November 7 2005 January 21 2005 August 24 5

North Polar Cap Distribution of Joule Heating and FAC Small clock angle & large B yz -> large hot spot of JH & FAC -> large Poynting flux Positive FAC is downward +Zgse 23nT +Ygse DMSP f15 NH JH: 651 GW; Global: 1161GW SM Northern Hemisphere 6

North Polar Cap Distribution of Joule Heating and FAC small clock angle & small B yz -> small area of enhanced JH & FAC -> small Poynting flux Positive FAC is downward +Zgse 9.4nT

+Ygse DMSP f15 NH JH: 182 GW; Global: 336GW AMPERE: Positive FAC is upward AMPERE/Iridium statistical FAC for northeast IMF [Anderson et. Al. 2008]  7

North Polar Distributions of Joule Heating and FAC small clock angle & large B yz -> small hot spot; missed by DMSP Positive FAC is downward 22nT +Zgse +Ygse DMSP f15 NH JH: 352GW; Global: 717GW Positive FAC is upward Iridium statistical FAC for northeast IMF [Anderson et. Al. 2008] 8

North Polar Distributions of Joule Heating and FAC Hot spot moves in response to IMF clock angle: DMSP missed hot spot Positive FAC is downward Fast Rotating +Zgse +Ygse DMSP f15 NH JH: 260GW; Global: 510GW Positive FAC is upward Iridium statistical FAC for northwest IMF [Anderson et. Al. 2008] 9

South Polar Distributions of Joule Heating and FAC IMF clock angle controls total energy input, |B| is less important.

Positive is downward 16nT +Zgse +Ygse DMSP f15 SH JH: 992GW; Global: 1611GW 10

South Polar Distributions of Joule Heating and FAC

For ~90 o clock angle power input becomes large, but also more spread out; DMSP missed hot spot Positive FAC is downward +Zgse 19nT +Ygse GSE 90 o ≠ GSM 90 o IMF may be slightly southward DMSP f15 SH JH: 708GW; Global: 1604GW Iridium statistical FAC for dawnward and duskward IMF in north polar [Anderson et. Al. 2008]

North Polar Distributions of Joule Heating and FAC - Brief Southward IMF Positive FAC is downward +Zgse +Ygse 9.7nT

DMSP f15 NH JH: 543GW; Global: 1226GW Positive FAC is upward Iridium statistical FAC for southeast IMF [Anderson et. Al. 2008] 12

South Polar Distributions of Joule Heating and FAC

Brief Southward IMF: total power input less than during E-W IMF period!

Positive FAC is downward +Zgse +Ygse 24nT DMSP f15 SH JH: 661GW; Global: 1065GW Iridium statistical FAC for southward IMF [Anderson et. Al. 2008] 13

Relation to Cusp Reconnection

Field lines traced from SM latitude 80 o traced from DMSP and nearby points near SM lat. 70 o Traced from SM latitude 60 o +Zgse 23nT 14 +Ygse

Relation with Cusp Reconnection Origin, evolution, and motion of open field lines, fluid element tracing Newly created open line moving westward Blue field lines traced from SM latitude 80 o IMF Cyan field lines Traced to R=5RE Path of a fluid element +Zgse 23nT +Ygse 15

Relation to Cusp Reconnection

Freshly reconnected field lines are dragged east-west: Blue field lines traced from SM latitude 60 o Southern Hemisphere Newly created open line moving eastward Field lines traced from DMSP and nearby points +Zgse +Ygse 16

Field Line Dragging, FACs, and Flow Channels

• • • Mechanical view (V/B, are primary variables): field lines are dragged through the ionosphere, along with ionospheric plasma. Friction between plasma and neutrals causes heating.

Electrical view (J/E are primary variables): reconnection causes B shear   FAC  Joule heating.

resistive closure in the ionosphere These views are equivalent. E/J easier to observe/compute; V/B more fundamental.

From Tanaka 2007 17

E

×

B flow channels and FAC

Maximum Cross-track

E

× B (Vy) at dot Clock angle SYM-H [Anderson et. Al. 2008] Eriksson et.al. 2008 found sunward E × B flow between two adjacent & opposite FACs 18

OpenGGCM/CTIM Neutral Density

2005 January 21 16:00 – 21:00 UT Northern Hemisphere 19

CTIM Neutral Density: latitude versus time

00:00 LT 03:00 LT 06:00 LT 09:00 LT 12:00 LT 15:00 LT 18:00 LT 21:00 LT 2005 January 21 16:00 – 21:00 UT 20

• • • • • • • • •

Summary

Strong Joule heating is unexpectedly observed in the dayside high o (-60 o ) and 80 o (-80 o ) SM latitude in the Northern (Southern) Hemisphere for northward IMF conditions. These “hot spots” extend from noon to dawn (dusk) for positive (negative) IMF By in the Northern Hemisphere, and extends to an opposite direction in the Southern Hemisphere. Total energy input correlates with IMF clock angle and often exceeds energy deposition during southward IMF (storm main phase).

A stronger IMF or a higher solar wind speed may also lead to increased Joule heating.

The “hot spots” are sandwiched by two adjacent and opposite high latitude FACs. For northern and southern hemispheres, downward FAC locates equatorward (poleward) of upward FAC with respect to the “hot spot” in the afternoon (morning) sector. Open field lines created by cusp reconnection drive drive the FAC that dissipates in the ionosphere and creates the hot spots.

OpenGGCM has reproduced observed PF and Joule heating in several cases.

A new NSF/GEM challenge is planned to test the fidelity of these predictions. 21

South Polar Distributions of Joule Heating and FAC

Big clock angle & big B yz -> large hot area of JH & FAC -> large Poynting flux Positive is downward FAC 45nT +Zgse +Ygse DMSP f15 SH JH: 488GW; Global: 964GW 22