The dominant large-scale variations in the solar wind speed observed in the outer heliosphere without any averaging are very similar to the solar rotation–averaged (25.38 days) speeds propagated from 1 au. This figure shows time series plots of the solar wind speed (top) and longitudinal separation between the given 1 au spacecraft and NH (bottom). The speeds from NH (orange) are not averaged and appear at the cadence at which they were recorded ranging from 64 s to 2 hr. Here, we include the 1 au propagated solar wind solar rotation–averaged speed measurements only when they are within ±45° in longitude of NH. The 1 au propagated and solar rotation–averaged (25.38 days) solar wind speed measurements are from ACE (light purple), OMNI (dark purple), STEREO A (red), and STEREO B (blue).