Thursday, June 21, 2007

GEM workshop, Thursday plenary session

Today's plenary session speakers were Vassilis Angelopoulos of UC Berkeley (soon to join the UCLA faculty) on "Maximizing substorm science on THEMIS: Probe alignments and ground conjunctions" and Eric Donovan of Calgary on "Diffuse Aurora".

Angelopoulos is PI of the THEMIS mission. He reviewed the status of the THEMIS mission and some of the scientific topics to which THEMIS can contribute. At present THEMIS is in a string-of-pearls configuration with a separation of ~10000 km between the leading and trailing satellites and ~200 km between the middle three. Electric field antennas have been successfully deployed on three of the five spacecraft, and all other instruments are working on all five spacecraft. When the spacecraft are boosted to their final orbits sometime this fall, the orbits will be phased so that there will be a five-spacecraft conjunction every four days and four-spacecraft conjunctions every two days. Apogee will be in the tail from January through March with the conjunctions over the North America sector, where ground magnetometers and all sky cameras are deployed from Alaska to Labrador. Nominal science operations will begin 1 July, and science software will be rolled out to the community 31 July. There is an open data policy (consult with PI or co-Is, and credit NASA grant NAS5-02099). Already THEMIS is obtaining useful science data, including an observation of substorm onset with westward traveling surge, a measurement of a flux transfer event, and an observation of magnetopause reconnection. THEMIS will be able to track radial motion of electrons inward from the tail and measure electric and magnetic fields and waves locally. There are also potential contributions to dayside magnetospheric physics (this summer) and tracking of solar wind interaction with the magnetopause (summer 2008). Nominal mission lasts until about March 2009, with extensions possible given consumables budget and radiation margin. There are at least two web sites of interest: data from and orbit visualization from SSCWeb at There is a removable attenuator (x50) which ensures that the particle instruments do not saturate in the radiation belt.

Donovan's talk was an overview of the breakout sessions on diffuse aurora which started yesterday and continue this afternoon. Although diffuse aurora is operationally defined as structureless precipitation, the precipitation actually reflects significant turbulence in the central plasma sheet. There are separate electron and ion aurora. On the duskside, the proton aurora is equatorward of the ion aurora, while postmidnight the proton aurora can be poleward of the electron diffuse aurora. The poleward boundary of the 630 nm oxygen line is a proxy for the open-closed field line boundary.

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