Abstract
Ten-year (2004–2013) observations of cloud and surface shortwave (SW) and longwave (LW) fluxes at Ny-Ålesund were analysed to investigate monthly variations in cloudiness and their impacts on the surface LW radiation budget and near-surface temperature (Ts). The cloud fraction (CF) showed distinct monthly variations, high in summer (0.90) and lower in winter (0.79). The downward SW flux increased from March and showed a peak (~200 W m−2) in June. In contrast, the downward LW (LWD) flux increased from ~200 W m−2 in February to ~300 W m−2 in July. Both LWD and upward LW (LWU) fluxes and their difference increased during winter as lowest cloud base height (LCBH) decreased and CF increased. Ts difference and both LW fluxes difference (ΔLWD and ΔLWU), calculated as the difference in monthly mean Ts and LW between all-sky and cloud-free conditions, were highly correlated (R2 = 0.68 for LWD and R2 = 0.92 for LWU). Dramatic changes in Ts, CF and LW fluxes at Ny-Ålesund were closely associated with cold and warm air mass advection on a multi-day time scale. The average Ts under low-level clouds (LCBH ≤ 2 km) was estimated as −7.4 ± 6.1 °C due to warm air masses advected from the North Atlantic Ocean and Barents Sea, whereas the average Ts on cloud-free days was −14.5 ± 5.7 °C because of cold air mass advection from the pole. However, the duration of low-level clouds may not be long enough to drive such large Ts variations. 75-percentile of low-level cloud conditions at Ny-Ålesund persisted up to 2.3 days, whereas cloud-free and high-altitude cloud (LCBH > 2 km) conditions lasted for approximately 0.8 and 0.5 days, respectively. This implies that cloud LW effects on several warm days may be larger than the monthly average, but may not be accumulated enough to induce surface warming due to abrupt Ts drop associated with cold air mass advection.
Highlights
Arctic clouds play a key role in the surface radiation budget by modulating longwave (LW) and shortwave (SW) radiative fluxes, which affect surface temperature and the extent of sea ice and snow melting (Curry et al, 1996)
Lowest cloud base height (LCBH) and cloud fraction (CF) were estimated from cloud vertical structure measurements using a Micro-Pulse Lidar (MPL; Spinhirne, 1993; Shiobara et al, 2003), operated by National Institute of Polar Research (NIPR) as part of NASA’s Micro-Pulse Lidar Network (MPLNET)
We investigated the relationship between clouds and surface LW fluxes, and the influence of warm and cold air mass advection due to regional-scale atmospheric circulation on winter cloudiness, surface LW fluxes and T
Summary
Arctic clouds play a key role in the surface radiation budget by modulating longwave (LW) and shortwave (SW) radiative fluxes, which affect surface temperature and the extent of sea ice and snow melting (Curry et al, 1996). Investigating cloud‐radiative interactions in the Arctic is still challenging due to complex environmental conditions Reanalysis data show large discrepancies compared to groundbased and satellite observations of the radiation budget and CF over the Arctic (Zygmuntowska et al, 2012; Chaudhuri et al, 2014) These deficiencies still provide large uncertainties in estimating Arctic cloud radiative effects. We investigated the influence of warm and cold air mass advection related to regional-scale atmospheric circulations on cloudiness, surface LW fluxes and T during winter
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