Long-Lived Convective Boundary Layer over Land

This study discusses seasonal and latitudinal variations of surface fluxes (turbulent, radiative, and soil ground heat) and other ancillary atmospheric/surface/permafrost data based on in-situ measurements made at two long-term research observatories located near the coast of the Arctic Ocean in Canada and Russia. The hourly-averaged multiyear data sets collected at Eureka (Canadian Archipelago) and Tiksi (East Siberia) are analyzed to elucidate similarities and differences in seasonal cycles at the two Arctic stations located at quite different latitudes (80.0N and 71.6N respectively). The study describes a long-lived (1.5-2 months) convective boundary layer (CBL) observed over land during Arctic summer. Long-lived CBL is associated with almost continuous unstable stratification, upward sensible heat flux, and downward carbon dioxide turbulent flux. This phenomenon is well documented at Eureka (80.0N) during 2009-2014 summer seasons. However, such long-lived CBL is not observed at Tiksi (71.6N), although Tiksi is also located within the Arctic Circle where it is 24 hours of continuous daylight in summer. This is due to the fact that a solar elevation angle (and therefore solar irradiance) at local midnight in the middle of Arctic summer is higher at Eureka, although the noon maximum of the solar irradiance is greater at Tiksi. Thus, there is a threshold of the incoming solar radiation below which the CBL cannot be maintained. Overall, the higher latitudes receive the least cumulative amount of net solar radiation over the entire year than lower latitudes; however, the diurnal mean of the solar radiation at high latitudes is greater than at lower latitudes in the midsummer. Although Eureka and Tiksi are located at the different continents and at the different latitudes, the annual course of the surface meteorology and the surface fluxes are qualitatively very similar. The air and soil temperatures display the familiar strong seasonal trend with maximum of measured temperatures in midsummer and minimum during winter. According to our data, variation in incoming short-wave solar radiation led the seasonal pattern of the air and soil temperatures, and the turbulent fluxes. During the dark Polar nights, long-lived stable boundary layers can last several months and air/ground temperatures are strongly controlled by long-wave radiation associated generally with cloud cover. A length of the warm season (Arctic summer) is shorter and midsummer amplitude of the turbulent fluxes near solar noon is generally less in Eureka than in Tiksi. The work is supported by the NOAA Climate Program Office, the U.S. National Science Foundation (NSF) with award ARC 11-07428, and by the U.S. Civilian Research & Development Foundation (CRDF) with award RUG1-2976-ST-10.