Relationships between the solar wind magnetic field and ground-level longwave irradiance at high northern latitudes

• Published in: Journal of atmospheric and solar-terrestrial physics 2019-10, Vol.193, p.105063, Article 105063
• Main Authors: Frederick, John E., Tinsley, Brian A., Zhou, Limin
• Format: Article
• Language: English
• ISSN: 1364-6826; 1879-1824
• DOI: 10.1016/j.jastp.2019.105063

Longwave irradiances measured from two sites at different geomagnetic latitudes show different responses to changes in the east-west component of the interplanetary magnetic field (IMF By). At Barrow, Alaska, geomagnetic latitude 69-70oN, neither downward longwave irradiance from the atmosphere nor upward longwave irradiance from the ground show a significant correlation with By. However, at Alert, Canada, geomagnetic latitude near 87oN, a negative correlation that is marginally significant at the 95% level of confidence exists between By and downward longwave irradiance measured 3 days later. On average, a +3.5 nT increase in By is followed by a daily-mean downward longwave irradiance that is smaller by −0.60 ± 0.60% than would exist for a constant By. Similarly, daily-mean upward irradiance at a lag of 4 days is −0.51 ± 0.30% smaller than would exist otherwise, where error bars denote the 95% confidence range. The difference in upward irradiance corresponds to a surface cooling at Alert of approximately 0.33 ± 0.19 K. These results are qualitatively consistent with a previously proposed mechanism in which the interplanetary magnetic field perturbs the ionosphere-to-ground potential difference and the downward atmospheric current density over limited regions near the geomagnetic poles, altering local cloud properties. We find that the atmospheric longwave emission is altered on a time scale of 3 days, with a change in surface temperature appearing one day later, attributable to the thermal inertia of the surface. When one moves from the geomagnetic latitude of Alert (3° from the north geomagnetic pole) to the latitude of Barrow (∼20° from that pole), any connection between By and longwave irradiance becomes too small to isolate from the natural background variability. •Downward longwave radiation measured at Alert, Canada, shows responses to the interplanetary magnetic field.•Upward longwave radiation responds similarly a day later.•The phenomenon is consistent with solar wind inputs to atmospheric electricity affecting cloud microphysics.