Weather systems occurring over Fort Simpson, Northwest Territories, Canada, during three seasons of 1998–1999: 1. Cloud features

Abstract

[1] An investigation of high-latitude continental cloud systems was carried out in the interior of the Northwest Territories of Canada during three multiweek periods during the fall, winter, and spring of 1998-1999 as part of the Canadian Global Energy and Water Cycle Experiment (GEWEX) Enhanced Study. Radar data supplemented by satellite, upper air, and surface observations were used to determine the seasonal behavior of cloud macroscopic properties and compare these with similar observations elsewhere. Unique features included the prevalence of multilayered systems, the cold temperatures of low clouds, and a significant diurnal trend in cloud properties in the winter. A synoptic classification was developed and shown to be an important factor in explaining the variability of cloud properties. A consistent picture emerges of the upslope component and wind shear aloft contributing to the cloud structure in five synoptic classes. Vertically resolved cloud properties highlighted the importance of the ice process in these cloud systems. The cloud system reflectivity and temperature dependencies further supported the synoptic characterizations and highlighted the significance of using seasonally based relationships in automated cloud identification algorithms. The implication of the cloud system variability for radiation measurements was also shown. The radar reflectivity data, degraded to match CloudSat resolution and sensitivity, showed that cloud detection was reliable but that there was a positive bias with cloud thickness. Negative biases in cloud top retrievals based on advanced very high resolution radiometer data were also identified. The Global Environmental Multiscale model illustrated some degree of bias in the occurrence and vertical distribution of these cloud systems. Winter situations in general and midclouds situations in particular were the most poorly handled in both the satellite applications and the model simulations.

On the simulation of regional scale sublimation over boreal and agricultural landscapes in a climate model

“…Zhang et al (1996) found that the surface net radiation balance under cloudy conditions depended strongly on cloud microphysical properties, cloud base temperature, and cloud thickness, and variability in these properties could produce variations in the onset of snow melt of more than a month. Radar studies have shown that numerical weather prediction models frequently overpredict high cloud and underpredict low cloud (Hudak et al, 2004;Hogan et al, 2001;Hinkelman et al, 1999). Hudak et al (2004) also found a significant diurnal cycle in cloud properties during winter, especially cloud thickness and cloud occurrence, both of which increased at night; consistent with radiatively induced circulations driven by cloud top infra-red cooling (Lazarus et al, 2000).…”

“…Radar studies have shown that numerical weather prediction models frequently overpredict high cloud and underpredict low cloud (Hudak et al, 2004;Hogan et al, 2001;Hinkelman et al, 1999). Hudak et al (2004) also found a significant diurnal cycle in cloud properties during winter, especially cloud thickness and cloud occurrence, both of which increased at night; consistent with radiatively induced circulations driven by cloud top infra-red cooling (Lazarus et al, 2000).…”

Northern Tales: A Synthesis of MAGS Atmospheric and Hydrometeorological Research

“…The net radiation deficit at the surface contributes to the development of deep and enduring surface-based temperature inversion layers that characterize much of the basin during the winter. Being under the influence of the broad climatological high pressure ridge and mean subsidence, winter clouds in the basin are typically shallow and have low cloud bases that are close to the top of the inversion layer (Stewart and Burford 2002;Hudak et al 2004). As such, cloud-base temperatures are often higher than surface temperatures and clouds typically exert a positive surface radiative forcing over the basin.…”

Characterization of an unexpected snowfall event in Iqaluit, Nunavut, and surrounding area during the Storm Studies in the Arctic field project

“…A number of major field programs have been conducted in the Canadian Arctic. Data sets collected during the Beaufort and Arctic Storms Experiment [ Hanesiak et al ., ; Stewart et al ., ; Hudak et al ., ] and the Mackenzie Global Energy and Water Cycle Experiment Study [ Stewart et al ., ; Asuma et al ., ] and the Storm Studies in the Arctic (STAR) [ Gascon et al ., ; Henson et al ., ; Laplante et al ., ; Fargey et al ., ], among others, have been analyzed with the purpose of characterizing Arctic clouds, precipitation, and storm systems. Unique features included the prevalence of multilayered systems, the cold temperatures of low clouds, and the significant sublimation effects in the initial stages of storm events and between cloud layers [ Stewart et al ., ; Henson et al ., ; Laplante et al ., ].…”