ISSI International Team

EUV Solar Irradiance at High Heliographic Latitutdes

June 1-3 2004 : first team meeting at ISSI

Second meeting schedulded for March 2005 (exact date TBD)

Team members

Scientific objectives

The goal of our team is to improve our understanding of the neutral He density measurements from Ulysses at higher heliospheric latitudes, by using a line-of-sight dependent solar EUV flux and He photoionization rates. Changes in the GAS experiment measurements as Ulysses passes over the solar poles are largely controlled by the changing photoionization of neutral He, itself dependent on the varying EUV flux with time and spacecraft position. Using our more accurate solar inputs, we will relate the absolute values of the polar GAS neutral He measurements o the pristine original He density of the LISM originally entering the heliosphere.

Schematic of the heliosphere. The distribution of dark (coronal holes) and bright (active regions) features at the surface of the Sun produce an anisotropic illumination of the heliosphere. Along its polar orbit, Ulysses successively crosses regions of low (dark blue) and high (light blue) irradiances. As a result, the local in-flowing neutral He photoionization rate is variable with heliocentric latitude and over the solar cycle. This effect must be taken into account when deducing the He density in the LISM "at infinity" from GAS measurements. (Distances not to scale.)

First meeting (June 1-3 2004)

Attendees

Participating institutes