importance of the height distribution of joule heating for thermospheric density arthur d. richmond...

Importance of the Height Distribution of Joule Heating for Thermospheric Density

Arthur D. Richmond and Astrid MauteNCAR High Altitude Observatory

Field-Aligned Poynting Flux, IMF Bz = -5 nT, By = 0

Summer

Winter

.b .b Sp||.b

104 GW

56 GW

177 GW

120 GW64 GW

73 GW

10

mW

/m2

mW

/m2

mW

/m2

mW

/m2

mW

/m2

mW

/m2

10 10

10

-10 -10

-10 -10

-10

-10

20

20

TIE-GCM Experiments

Base case: - Steady-state, Day number = 80- F10.7 = 150 - Polar-cap Potential = 45 kV- Hemispheric Power of auroral particles = 16 GW

Test cases:- 9 GW additional neutral heating in each hemisphere - proportional to vi

2 in latitude and longitude- turned on during UT hours 1-6 on Day 1, then off

(a) High Heat at 270 km ± 1 scale height(b) Low Heat at 120 km ± 1 scale height

High Heat is centered 5 scale heights above Low Heat (e5 = 148)

Height-Integrated Additional Heating

mW

/m2

X

700 W

0.56

0.28

0.06

6 UT 12 UT 18 UTTemperature Difference at -700 Longitude

High Heat, 3 K contour interval

Low Heat, 1K contour interval

6 UT 12 UT 18 UTDensity Difference (%) at -700 Longitude

High Heat, 3% contour interval

Low Heat, 1% contour interval

High Heat

Low Heat

Global Mean

Global Mean

KK

KKTemperature Difference at 400 km

700 W

700 W

Conclusions- F-region Joule heating, though only a small fraction of total Joule heating, produces a strong, fast (hours) temperature and density response at 400 km that decays rapidly.

- F-region Joule heating depends on highly variable conductivity. It may be much more important with intense soft particle precipitation and at solar maximum.

- E-region heating produces a slow (~1 day) response at 400 km that decays slowly. It is important for long-term variations of temperature and density.

- Poynting flux and geomagnetic indices are inadequate for determining high-altitude Joule heating. Observations and modeling of polar F-region electron densities, in relation to electric fields, are needed.