Persistence of Solar Wind Velocity along Radial, Longitudinal, and Latitudinal Spacecraft Separation

Abstract Recent missions, including the Parker Solar Probe, Solar Orbiter, and the Mars Atmosphere and Volatile EvolutioN (MAVEN), have probed a wide range of heliocentric distances, enabling new investigations of solar wind evolution. By comparing solar wind measurements from spacecraft located at different positions in the heliosphere (0.1–1.5 au), we study the persistence of solar wind velocity in longitude, latitude, and over radial distance. To this end, we introduce a new persistence model based on in situ observations being propagated across longitudes and radial distance, conserving latitude. The resulting time-dependent two-dimensional maps of projected solar wind parameters are then compared with in situ measurements from the OMNI database at 1 au and from MAVEN orbiting Mars. We find that the mean absolute error (MAE) of the solar wind velocity increases by 2.4 km s −1 for each degree of latitudinal spacecraft separation over a range of up to 14 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 3. In addition, we identify a logarithmic relationship between persistence time and MAE, revealing spatial and temporal solar wind variability in the heliosphere. Over radial separation, we find no clear relationship based on current data coverage.