# Presentation: 054638

## Polar UVI Support of THEMIS Science:

**Pre- and Post-Launch**
- _M. O. Fillingim_, G. K. Parks, E. Lee,
- and S. B. Mende
- Space Sciences Laboratory,
- University of California, Berkeley
- Polar Telecon UVI Science Report		September 28, 2007

## Part 1: Pre-THEMIS Launch

**Our goal**: Combine plasma sheet measurements with global auroral images to address the question: “Do substorm effects travel in  out (current disruption) or out  in (NENL)?”
- Rather than use several spacecraft in a radial alignment, analyze several single-spacecraft events at different radial distances
- Quasi-statistical – not instantaneous – picture (few events)
- 	(Not a new idea:  e.g., *Angelopoulos et al.* [1997]; *Fairfield et al. *[1999];* Fillingim et al.* [2000; 2001; 2003]; *Baker et al.* [2002]; *Nakamura et al.* [2002]; and ***many, many*** others)
**Our results**: Activity in the near-Earth plasma sheet (X < -20 RE) is magnetically connected to intense auroral emission
**Our conclusion**: Plasma sheet disturbances propagate tailward as intense auroral emission moves poleward **** **source ~ 10 R****E**

## Example 1: 1997-07-26

_**Example 1: 1997-07-26**_
**Polar UVI** observed a series of small scale, short lived auroral brightenings –  pseudo-breakups and/or small substorms – also see *Fillingim et al.* [2000; 2001; 2003]
**Wind** located in the near-Earth plasma sheet at X ~ −10 RE

## Top two panels:

_*Top two panels*_*:*
- Magnetic latitude and
- local time keograms;
- black line is Wind footprint
_*Bottom two panels*_*:*
- Plasma sheet **<v>** and **B**
- Excellent correlation between large **<v>**, ∆B,  and the onset of auroral brightenings near Wind footprint
- Plasma sheet activity and auroral brightenings ***simultaneous*** within resolution of instruments  (~ 1 minute)

## Example 2: 1996-03-27

_**Example 2: 1996-03-27**_
**Polar UVI** observed two major multi-intensification substorms – also see *Angelopoulos et al.* [1997]; *Fillingim et al.* [2001; 2003]
**Wind** at X ~ −15 RE
- Large **<v>** only seen when region of intense aurora expands to encompass footprint ***or*** intensification occurs near footprint
- Large amplitude, high frequency fluctuations of **B** well correlated with **<v>** (∆**B** also associated with current sheet and PSBL)

## Example 3: 2001-08-27

_**Example 3: 2001-08-27**_
**IMAGE FUV** observed precursor activity followed by onset at 4:08 UT – also see *Baker et al.* [2002]
**Cluster** at X ~ −18 RE
- Large **<v>** seen by C1 and C3 when aurora brightens near footprint (3:25, 3:45, 4:01, 4:09, 4:14, 4:22 UT)
- Different interpretation than *Baker et al.* [2002]: Reconnection occurs at 4:01 UT, 7 minutes ***before*** substorm expansion
_***However***__**, at 4:01 UT, Cluster maps to aurora!**_

## Example 4: 2001-08-12

_**Example 4: 2001-08-12**_
**Polar UVI **observed onset at 18:38:30 UT ± 18 sec (red line) – also see *Nakamura et al.* [2002]
**Cluster** at X ~ −18 RE
- From onset to 18:44 UT, aurora expands poleward at ~ 1°/min or ~ 2 km/s
- Emission reaches Cluster ~ 2 min after onset;    onset maps to ~ 6 RE;  from 6 to 18 RE in 2 min   ~ 600 km/s tailward
- As auroral emission moves poleward, plasma sheet activity propagates tailward

## Coupling through Field Aligned Currents

- Field aligned currents can provide connectivity between plasma sheet and ionosphere
- Determine currents using curlometer (**J** = ** **X **B**)
-  Significant FAC during large **<v>** event (circled)
- Plasma sheet-ionosphere travel time for thermal electrons (1⁄2 – 1 keV) is  ~ 10 seconds
-  “Simultaneous” within resolution of detectors

_**Coupling through Field Aligned Currents**_

## Summary and Conclusions

- In the near-Earth plasma sheet (X < ~ -20 RE), **plasma sheet activity** (large **<v>** and ∆B) is **magnetically** **connected**  to  **intense auroral emission ** FACs provide M-I connection
- Plasma sheet activity propagates **tailward** as auroral emission moves **poleward ** this suggests a **near-Earth **(~ 10 RE) source
_***Caveat***_***:*** Our interpretation relies on accuracy of magnetospheric model [*Tsyganenko*, 1996]  static model, dynamic conditions
- Our results appear **inconsistent** with the NENL (out  in) model of substorm onset: mid-tail source (~ 25 RE), Earthward propagation
- However, we cannot completely *exclude* a NENL interpretation ***if...***
-  There is no auroral signature of reconnection
-  Fast flows launched by reconnection are confined to a “thin” layer
-  There is no auroral signature of Earthward fast flows
-  Extensive literature discussing auroral signatures of fast flows!
-        [*Henderson et al.*, 1998; *Fairfield et al.*, 1999; *Sergeev et al.*, 1999; *Fillingim et al.*, 2000;
*        **Zesta et al.*, 2000; *Nakamura et al.*, 2001; *Ohtani*, 2004; just to name a few]

## Part 2: Post-THEMIS Launch

- Polar currently supports THEMIS science by providing space-based observations of global aurora during THEMIS events
- These data are especially useful during times when THEMIS Ground Based Observatory (GBO) observations are limited; i.e.,
- During northern hemisphere summer
- During dayside events (see Example 3)
- During inclement weather/full Moon
- Polar observations are conjugate to THEMIS GBO observations  further investigate conjugacy of substorm processes

## Example 1: 2007-03-23

- Ground based magnetometers recorded substorm onset at ~11:18 UT
**Polar UVI** observed onset at 11:10 UT and intensification    at 11:18 UT
- Propagation of intensification
- ~ 1 hour MLT/min (or ~ 15°/min) westward  consistent with **THEMIS** timing

_**Example 1: 2007-03-23**_

## Example 2: 2007-06-21

_**Example 2: 2007-06-21**_
**THEMIS** observed solar wind pressure pulse-induced magnetopause compression at ~ 12:46 UT
**Polar** **UVI** observed localized activity starting at 12:36 UT (pre-midnight) and 12:41 UT (post-midnight); pressure pulse-induced onset near midnight at 12:46 UT –
- at the same time or a few seconds *before* THEMIS observed magnetopause compression (it’s OK –
- THEMIS was post-noon, pressure pulse hit pre-noon)

## Example 3: 2007-07-04

_**Example 3: 2007-07-04**_

**THEMIS** observed a hot flow anomaly (HFA) outside the magnetopause
- Ground based magnetometers observed disturbance traveling dawnward from noon
**Polar UVI** observed emission in the pre-noon sector – auroral signature of HFA interacting with magnetosphere?

## Summary & Future Opportunities

- Propagation speeds of auroral emission determined from Polar UVI images are consistent with propagation speeds of magnetospheric disturbance determined from timing between THEMIS spacecraft
- Pressure pulse-induced onset nearly coincident with magnetopause compression (PP-induced vs. “normal” onsets)
- Possible dayside auroral signature of HFA interacting with magnetosphere
-  all warrant further study!
- Polar should remain operational through THEMIS tail phase (confirm or disprove interpretation presented in Part 1?)
- Conjugate observations with GBOs
- Unpredicted new opportunities...