Solar eclipse of 20 March 2015 and impacts on irradiance, meteorological parameters, and aerosol properties over southern Italy.

The effects of the partial solar eclipse of 20 March 2015 on short-wave (SW) and long-wave (LW) irradiance measurements, meteorological variables, and near surface particle properties have been investigated. Measurements were performed at three southern Italy observatories of the Global Atmospheric Watch - World Meteorological Organization (GAW-WMO): Lecce (LE, 40.3°N, 18.1°E, 30 m a.s.l.), Lamezia Terme (LT, 38.9°N, 16.2°E, 50 m a.s.l.), and Capo Granitola (CG, 37.6°N, 12.7°E, 50 m a.s.l.), to investigate the dependence of the eclipse effects on monitoring site location and meteorology. LE, LT, and CG were affected by a similar maximum obscuration of the solar disk, but meteorological parameters and aerosol optical and microphysical properties varied from site to site on the eclipse's day. The maximum obscuration of the solar disk, which was equal to 43.6, 42.8, and 45.1% at LE, LT, and CG, respectively, was responsible for the decrease of the downward SW irradiance up to 45, 44, and 45% at LE, LT, and CG, respectively. The upward SW irradiance decreased up to 45, 48, and 44% at LE, LT, and CG, respectively. Consequently, the eclipse SW direct radiative forcing (DRF) was equal to −307, −278, and −238 W m−2 at LE, LT, and CG, respectively, at the maximum obscuration of the solar disk. The downward and upward LW irradiance decrease was quite small (up to 4%) at the three sites. The time evolution of the meteorological parameters and aerosol optical and microphysical properties and their response strength to the solar eclipse impact varied from site to site, mainly because of the local meteorology and geographical location. Nevertheless, the solar eclipse was responsible at the study sites for a temperature decrease within 0.5–0.8 K, a relative humidity increase within 3.5–4.5%, and a wind speed decrease within 0.5–1.0 m s−1, because of its cooling effect. The solar eclipse was also responsible at all the sites for the increase of near surface particle scattering coefficient (σsp) and scattering color ratio (CRσ), mainly for the increase of both ultrafine and fine mode particle concentrations. In more detail, σsp, CRσ, and number concentration increased up to 2 Mm−1, 0.2, and 9 · 103 cm−3, respectively. The atmospheric turbulence weakening, driven by the eclipse cooling effect and revealed by the decrease of turbulent kinetic energy and potential temperature flux, mainly contributed to the changes of near surface particle concentrations and size distributions.