Long-term Solar Activity Studies using Microwave Imaging Observations and Prediction for Cycle 25

TL;DR

This study uses microwave imaging from Nobeyama to analyze long-term solar activity, revealing correlations between microwave brightness and magnetic fields, and predicting that Solar Cycle 25 will be similar in strength to Cycle 24.

Contribution

It introduces a novel method of predicting solar cycle strength using microwave brightness correlations and extends historical analysis of polar magnetic field asymmetries.

Findings

Polar microwave brightness correlates with magnetic field strength and solar wind speed.

Cycle 25 is predicted to have similar strength to Cycle 24.

North-south asymmetry in magnetic reversal shows 3-5 cycle quasi-periodicity.

Abstract

We use microwave imaging observations from the Nobeyama Radioheliograph at 17 GHz for long-term studies of solar activity. In particular, we use the polar and low-latitude brightness temperatures as proxies to the polar magnetic field and the active-regions, respectively. We also use the location of prominence eruptions as a proxy to the filament locations as a function of time. We show that the polar microwave brightness temperature is highly correlated with the polar magnetic field strength and the fast solar wind speed. We also show that the polar microwave brightness at one cycle is correlated with the low latitude brightness with a lag of about half a solar cycle. We use this correlation to predict the strength of the solar cycle: the smoothed sunspot numbers in the southern and northern hemispheres can be predicted as 89 and 59, respectively. These values indicate that cycle 25 will not be too different from cycle 24 in its strength. We also combined the rush to the pole data from Nobeyama prominences with historical data going back to 1860 to study the north-south asymmetry of sign reversal at solar poles. We find that the reversal asymmetry has a quasi-periodicity of 3-5 cycles.