Summertime Clouds Are All Wet in Alaska

 
Published: 31 July 2005

Two ARM sites—Barrow and Atqasuk—at the North Slope of Alaska (NSA) provide key data about cloud and radiative processes at high latitudes. Barrow is located at the northern most point of Alaska, on the shore of the Arctic Ocean, while Atqasuk is located on the Arctic tundra about 100 km south (inland) of Barrow. Analyses of data from years of research on cloud and meteorological properties measured at the NSA have shown systematic differences between summertime cloud liquid water paths at Barrow and Atqasuk as a function of wind direction. Surprisingly, inland low clouds appear to be “wetter” than the coastal clouds during the Alaskan summer months. However, these differences are not captured in current climate models. On July 11, 2005, ARM researchers began the Boundary Layer Cloud Intensive Operational Period (IOP) to improve scientific understanding of the cloud-tundra interactions for summertime (warm) arctic clouds. Data obtained during the IOP will allow for a detailed comparison of boundary layer phenomena in terms of surface turbulence fluxes and of the coupling between the surface and boundary layer clouds.

ARM Operations staff check out the radiosonde sensor package prior to launch during pre-experiment testing in Barrow, Alaska.

In addition to using routine data from the NSA sites, the research team is collecting supplemental measurements of surface fluxes through the use of several eddy correlation flux systems. The researchers are also measuring low-level winds and profiles of temperature and humidity, requiring the use of radiosondes, rawinsondes, and a sodar. These measurements will be obtained from instruments on the tundra at Barrow, Atqasuk, and—for upwind marine surface fluxes—Point Barrow, which juts out into the Arctic Ocean. Soundings at Barrow and Atqasuk, in particular, will provide a unique dataset for examining the role of surface interactions by identifying when clouds are coupled to or decoupled from the surface. They will also help them define whether the diurnal cycle is a significant modulator of cloud-surface coupling and, if so, whether this appreciably modulates cloud properties.

To prepare for the IOP, the research team conducted a sodar demonstration and public meeting in Atqasuk in May, and received approvals on all the necessary permits. In addition, university students were recruited to help with radiosonde launches at Atqasuk, and lodging for them was arranged in part through a local church. Off-duty technicians from the National Weather Service are handling the radiosonde launches in Barrow. Each site will launch six sondes per day during the four-week field campaign.