Fig. 1.
Variations in monthly averages of (a) cloud fractions with the six-categorized lowest cloud base heights; upward and downward (b) shortwave and (c) longwave fluxes; and (d) near-surface air temperature at Ny-Ålesund, Svalbard from 2004 to 2013.
Fig. 2.
Relationship between longwave radiation and lowest cloud base height during winter, November–February. The longwave fluxes for wintertime cloud-free conditions are also provided. In the box-whisker plot, the 25th and 75th percentiles bound the centre box with the horizontal line representing the 50th percentile, or median, and the dot depicts the mean.
Fig. 3.
Scatter plot of monthly mean upward (blue empty circle) and downward (red full circle) longwave fluxes and cloud fraction during the winter periods, November–February, of 2004–2013.
Fig. 4.
Relationship between near-surface temperature difference and downward (left panel) and upward (right panel) longwave radiation difference for monthly (black open circle) and 30-min (data points expressed in colour) averaged data during the winter periods, November–February, of 2004–2013. Temperature and downward and upward longwave differences are calculated between all-sky and cloud-free conditions. The solid and dashed lines represent the least-square linear regression for monthly and 30-min averaged data, respectively.
Fig. 5.
Cloud, longwave radiation and near-surface temperature measurements at Ny-Ålesund, Svalbard, from 1 to 10 February 2010: (upper panel) Lidar-derived backscattering intensity at 523-nm wavelength, (lower panel) near-surface temperature (T s ; green), upward (blue) and downward (red) longwave radiation (LWU, LWD) and cloud base height (LCBH; black dot) estimated from lidar measurements.
Fig. 6.
Frequency distribution (%) of near-surface temperature for cloud-free (blue), LCBH < 2 km (black) and LCBH > 2 km (red) conditions.
Fig. 7.
Cumulative frequency distribution (%) of cloud duration (in hours) for cloud-free (blue), LCBH < 2 km (black) and LCBH > 2 km (red).
Fig. 8.
Geopotential height and wind field at 850 hPa pressure level over North Atlantic sector of Arctic during winter averaged from 2004 to 2013: (a) overall period, (b) low-level cloud conditions and (c) clear conditions at Ny-Ålesund. The red dot indicates the location of Ny-Ålesund station.