How GLOWS will reveal the latitudinal structure of the solar wind

Solar wind features a latitudinal structure that evolves during the solar activity cycle. The only in-situ measurements of the solar wind speed and density available so far were performed by Ulysses at the turn of the 20th and 21st centuries. They showed that when the solar activity is low, the wind is fast and rare, with an equatorial band filled with a slower but denser outflow. During epochs of high activity, the band of slow wind expands to all latitudes. However, details of possible north/south asymmetries and regular structure evolution at shorter time scales could not be established because the measurements were performed in-situ along a highly elliptical orbit with a period of the order of half of the solar cycle.

Complementary methods of monitoring the solar wind latitudinal profiles include remote-sensing observations such as interplanetary scintillations (IPS) and hydrogen Lyman-α backscatter glow observations. Existing analyses of IPS and helioglow observations returned somewhat conflicting conclusions. Helioglow maps observed by SOHO/SWAN suggested that the solar wind flux temporarily features flux maxima at mid-latitudes. Analysis of IPS observations for equivalent times did not reveal such maxima in the solar wind speed.

Insight from Ulysses resulted in a hypothesis that the energy flux of solar wind is latitudinally invariant, which cannot be verified without additional observations. A confirmation of this invariance would be an important milestone in the understanding of the solar wind emission mechanism and provide a handy tool supporting retrieval of the solar wind structure from observations of either IPS or the helioglow.

GLObal solar Wind Structure (GLOWS) is a Lyman-α photometer onboard Interstellar Mapping and Acceleration Probe (IMAP), dedicated to helioglow observations aimed at retrieval of the solar wind structure. We present how GLOWS observations can be interpreted to resolve the helioglow/IPS solar wind structure dilemma and to verify the hypothesis of latitudinal invariance of the solar wind energy flux.