Open Access

Latitudinal dependence of the solar wind density derived from remote sensing measurements using interplanetary Lyman α emission from 1999 to 2002

  • Hiromu Nakagawa17Email author,
  • Hiroshi Fukunishi27,
  • Shigeto Watanabe37,
  • Yukihiro Takahashi17,
  • Makoto Taguchi47 and
  • Rosine Lallement57
Earth, Planets and Space200961:BF03352918

Received: 31 July 2007

Accepted: 15 October 2008

Published: 3 March 2009


The interplanetary Lyman α backscattered emission is an effective tool for remote sensing of the global structure of the solar wind proton flux. This paper reports an attempt to derive the latitudinal dependence of the solar wind density by combining the interplanetary Lyman α measurements of the Nozomi spacecraft for the period 1999–2002 with the solar wind speed data derived from interplanetary scintillation measurements. This approach successfully revealed the slow and dense solar wind over the poles during the period of the solar maximum. Data on the polar solar wind density indicate a significant growth from the middle of 2000, and the polar values of solar wind density are close to those of the equatorial values as a result of the disappearance of the coronal hole. A marked density depletion occurred in the middle of 2001, which can be ascribed to the development of fast winds from the polar coronal hole. To evaluate the remote sensing method, we considered solar wind density data from in situ measurements obtained by the Ulysses spacecraft. We conclude that our method basically agrees with in situ measurements, although we found a significant (a factor of 2) difference between these in the middle of 2001.

Key words

Sun solar wind interplanetary neutral hydrogen heliosphere Nozomi