Atmospheric temperature responses to solar irradiance and geomagnetic activity

The relative effects of solar irradiance and geomagnetic activity on the atmospheric temperature anomalies (Ta) are examined from the monthly to interdecadal timescales. Geomagnetic Ap (Ap) signals are found primarily in the stratosphere, while the solar F10.7-cm radio flux (Fs) signals are found in both the stratosphere and troposphere. In the troposphere, 0.1–0.4 K increases in Ta are associated with Fs. Enhanced Fs signals are found when the stratospheric quasi-biennial oscillation (QBO) is westerly. In the extrapolar region of the stratosphere, 0.1–0.6 and 0.1–0.7 K increases in Ta are associated with solar irradiance and with geomagnetic activity, respectively. In this region, Fs signals are strengthened when either the QBO is easterly, or geomagnetic activity is high, while Ap signals are strengthened when either the QBO is westerly, or solar irradiance is high. High solar irradiance and geomagnetic activity tend to enhance each other's signatures either making the signals stronger and symmetric about the equator or extending the signals to broader areas, or both. Positive Ap signals dominate the middle Arctic stratosphere and are two to five times larger than those of Fs. When solar irradiance is low, the signature of Ap in Ta is asymmetric about the equator, with positive signals in the Arctic stratosphere and negative signals at midlatitudes of the NH stratosphere. Weaker stratospheric QBO signals are associated with high Ap and Fs, suggesting possible disturbances on the QBO. The signals of Ap and Fs are distinct from the positive temperature anomalies resulting from volcanic eruptions.