A systematic 22-year pattern in solar wind

It has been shown recently [1] that the average solar wind speed at 1 AU is faster (slower) in Spring than in Fall around positive (negative, respectively) helicity minima. This implies a related 22-year variation in the solar hemisphere from which a faster solar wind stream is received at 1 AU during each season. We have earlier studied [2] the effective latitudinal gradients of the solar wind speed in the two magnetic hemispheres around the heliographic equator by comparing observations at the Earth's orbit in Spring and Fall. We found that there is a large effective gradient of about 10 km/s/deg in the southern magnetic hemisphere around each solar minimum. However, no statistically significant effective gradient was found in the northern magnetic hemisphere. Here we discuss the related properties of the solar wind proton temperature and show that the temperature and speed behave very similarly in the two hemispheres. In particular, there is a large effective gradient of about 2700-5400 K/deg in the southern magnetic hemisphere while no significant gradient exists in the northern hemisphere. This supports the earlier result [2] that the streamer belt is systematically displaced toward the northern magnetic hemisphere. The displacement of the streamer belt implies a new, persistent north-south asymmetry related to the solar magnetic cycle which needs to be explained by realistic solar dynamo models.