Sondrestrom Joule Heating Estimates

Transcription

1 Sondrestrom Joule Heating Estimates Barbara Emery (HAO/NCAR), Arthur Richmond (HAO/NCAR), Anja Stromme (SRI International), J Michael Ruohoniemi (VT) CEDAR POLA-04 Tuesday 24 June 2014

2 Abstract The Sondrestrom Fjord incoherent scatter radar calculates the Joule heat per unit volume as a function of height in the lower thermosphere using the MSIS model to estimate the neutral composition and temperature. The Joule heat per unit volume peaks in the E region near the peak of the Pedersen conductivity. We repeat the calculation of the Joule heat per unit volume, and expand our calculations to estimate the Joule heat per unit mass using only the observed electric fields. The Joule heat per unit mass peaks in the F-region near the peak of the electron density. We present our Sondrestrom Joule heat estimates for a moderate storm in February 2008 and compare them to estimates from the Thermosphere- Ionosphere-Electrodynamics General Circulation (TIEGCM) model and to observations and estimates from DMSP-F13 overflights.

3 Sondrestrom Incoherent Scatter Radar (ISR) operated during a high-speed solar wind stream moderate storm February 28-29, 2008 during solar minimum when Bz was ~-5nT and Dst went to ~-45nT. The Thermosphere- Ionosphere-Electrodynamics General Circulation Model (TIEGCM) was run with 2 different high-latitude inputs from February 26 though March 5. One used the Weimer [2005] convection model based on solar wind parameters (W05), while the second used SuperDARN estimates from Virginia Tech (SDVT). Both used a parameterized aurora with a radius 2 degrees larger than the convection reversal radius. The height integrated Joule heat from SDVT (pastels) was smaller than that from W05 because the convection radius of SDVT was smaller, so the high latitude inputs were located over a smaller area.

4 The electric field is assumed to map throughout the entire thermospheric region, but is averaged above 181km from the long pulse observations. The perpendicular east electric field Epe observed at Sondrestrom (67N, 310E) is relatively well matched by both Weimer [2005] (W05) and SuperDARN (SD), but the northward electric field Epn is not as well matched. The dashed magenta lines are for overpasses of DMSP F13.

5 The TIEGCM height-integrated Joule heat over Sondrestrom Feb 28-29, 2008 misses the observed auroral precipitation 0-11UT (~21-8LT) for both W05 and SD convection. The SD QJ estimates are relatively low during the day also. The TIEGCM calculation of the height integrated Joule heat QJ using only the Pedersen conductance and E field squared, is similar to the QJ found in the neutral wind frame.

6 The Sondrestrom Pedersen conductance (the height integrated Pedersen conductivity) is similar in shape to the conductance from the TIEGCM run using SuperDARN convection.

7 F13 passes at dashed magenta times QJ/mass peaks similar to ht-integ QJ/vol The aurora is at night. The peak QJ/mass (sea-green) is usually just above hmax (brown).

8 F13 overflight of Sondrestrom near cusp F13 passed close to Sondrestrom ~930MLT in a region of sunward convection and poleward precipitation in the region marked by 2 brown boxes.

9 F13 overflight of Sondrestrom near cusp Sondrestrom was located in a region of low electron energy near the poleward edge of the aurora after 2 areas of ~4mW/m 2 fluxes of ~800eV that ionize ~185km. The Pedersen conductance mostly from EUV is ~7mhos, and the estimated height-integrated Joule heating is ~3mW/m 2, both similar to observations.

10 Observations show Ti (green) >Te (red) by almost 1000K ~185km and ~195km, with increases in Ne also, which are especially apparent at ~185km. Since the electric field E maps to all altitudes, the SigP*E2 calculation of Joule heat will only show variations from the Pedersen conductivity. Other Joule heat calculations in the neutral wind frame that examine (Un-Vi), will show more structure from Un and Vi.

11 The Sondrestrom analysis code CWINDS calculates various portions of the Joule heat using the observations of the neutral winds (good to 120 or 135km), ion drifts, and the Pedersen conductivity calculated using the MSIS model. The best Joule heat estimate J.Eprime is in the neutral wind frame, but is only good to 135km. The simpler SigP*E 2 can be extended beyond 135km and into the F region.

12 Joule Heat per Volume and per Mass The simple Joule heat (QJ) calculation of SigP*E 2 is shown per volume in mw/m 3 and divided by the neutral density as W/kg. The QJ per volume peaks near 120km while the QJ per mass peaks around 250km just above the peak in the electron density profiles (hmax). The TIEGCM calculation of J.Eprime can be considerably different than SigP*E 2.

13 Ti>Te indicates Joule Heating The large Ti increase at ~188km (red circle) at the F13 crossing ~1150UT possibly demonstrates the ionization from the ~800keV electrons observed on F13.

14 Future Work 1) Get MSIS00 working for observations without CWINDS to calculate SigP for the Sigp*E 2 Joule heat calculation 2) Examine more cases near the cusp for evidence of low energy electron precipitation with Ti>Te and elevated Ne