Accueil > Actualités > Séminaires > Séminaire de Sang-Woo Kim au LATMOS-Jussieu


Titre : 10-Year Observations of Cloud and Surface Longwave Radiation at Ny-Ålesund, Svalbard
Nom du conférencier : Sang-Woo Kim
Son affiliation : School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea
Laboratoire organisateur : LATMOS
Date et heure : 06-07-2016 10h30
Lieu : Campus de Jussieu, Salle de réunion du LATMOS, 4e étage, Tour 45-46
Résumé :

Arctic clouds play a key role in surface radiation budget and may influence the extent of sea ice and snow melting. In this study, 10-year (2004-2013) observations of cloud from ground-based Micro-Pulse Lidar (MPL) and surface shortwave (SW) and longwave (LW) radiation at Ny-Ålesund, Svalbard are analyzed to investigate the variations of cloudiness and their impacts on the surface LW radiation. The cloud fractions (CFs) derived from MPL show distinct monthly variations, having higher CF (0.90) in summer and lower CF (0.79) in winter. These CFs are comparable to those collected at the Atmospheric Radiation Measurement (ARM) North Slope of Alaska site and the nearby NOAA/ESRL/GMD Barrow observatory (0.86 by Dong and Mace, J. Climate, 2003; 0.76 by Dong et al., JGR, 2010). The monthly means of all-sky downward SW flux increase monotonically from March and show a maximum (~ 200 W m-2) in June, then decrease gradually.  The all-sky downward LW (DLW) fluxes gradually increase from about 200 W m-2 (February) to about 300 Wm-2 (July), and decrease gradually into winter. Values of DLW flux measured at the surface during wintertime (November, December, January, and February) decrease as cloud base heights (CBH) increase.  The values of DLW flux for CBH < 1km (264.7 ± 35.4 W m-2) are approximately 1.46 times larger than those for cloud-free (181.8 ± 25.8 W m-2) conditions. The temperature difference (DT) and DLW flux difference (DDLW), which are calculated as the difference of monthly mean temperature and DLW between all-sky and cloud-free conditions, are highly correlated (R2 = 0.83). As is reported in many modeling studies, this implies that an increase of DLW flux may influence the increase of near surface temperature. On the other hand, we found dramatic changes of near surface temperature, cloud and DLW flux at Ny-Ålesund associated with the advection of cold and warm air masses. The averaged near surface temperature with the presence of low-level clouds (CBH < 2km) is estimated to be -6.9 ± 6.1°C due to the influence of relatively warm air masses from Barents and Kara Sea, whereas the averaged near surface temperature on cloud-free days is -14.5 ± 5.7°C because of the inflow of cold air from the pole. The duration of low-level clouds, showing both relatively high DLW flux and surface temperature, is estimated to be about 2.5 days. This suggests that the effect of DLW induced by low-level clouds on the near surface temperature may not be as great as those reported from modeling results, which estimates based on monthly mean data.

Contact :