Search Results
Abstract
Cloud characteristics at two sites on the North Slope of Alaska separated by ∼100 km have been examined for the warmer months of 2001–03 using data collected from microwave radiometers, ceilometers, rotating shadowband radiometers, and pyranometers. Clouds at the inland site, Atqasuk, were found to have approximately 26% greater optical depths than those at the coastal site, Barrow, and the ratio of measured irradiance to clear-sky irradiance was nearly 20% larger at Barrow under cloudy conditions. It is hypothesized that a significant factor contributing to these differences is the upward fluxes of heat and water vapor over the wet tundra and lakes. Support for this hypothesis is found from the behavior of the liquid water paths for low clouds, which tend to be higher at Atqasuk than at Barrow for onshore winds but not for offshore ones, from differences in sensible heat fluxes, which are small but significant over the tundra but are nearly zero over the ocean adjacent to Barrow, and from the mixing ratios, which are significantly higher at Atqasuk than at Barrow. Results from a simple model further indicate that latent heat fluxes over the tundra and lakes can account for a significant fraction of the differences in the estimated boundary layer water content between Barrow and Atqasuk.
Abstract
Cloud characteristics at two sites on the North Slope of Alaska separated by ∼100 km have been examined for the warmer months of 2001–03 using data collected from microwave radiometers, ceilometers, rotating shadowband radiometers, and pyranometers. Clouds at the inland site, Atqasuk, were found to have approximately 26% greater optical depths than those at the coastal site, Barrow, and the ratio of measured irradiance to clear-sky irradiance was nearly 20% larger at Barrow under cloudy conditions. It is hypothesized that a significant factor contributing to these differences is the upward fluxes of heat and water vapor over the wet tundra and lakes. Support for this hypothesis is found from the behavior of the liquid water paths for low clouds, which tend to be higher at Atqasuk than at Barrow for onshore winds but not for offshore ones, from differences in sensible heat fluxes, which are small but significant over the tundra but are nearly zero over the ocean adjacent to Barrow, and from the mixing ratios, which are significantly higher at Atqasuk than at Barrow. Results from a simple model further indicate that latent heat fluxes over the tundra and lakes can account for a significant fraction of the differences in the estimated boundary layer water content between Barrow and Atqasuk.
Abstract
A 6.25-km resolution dataset of meteorology, vegetation type, and soil type for a domain covering a typical global climate model grid cell is used to drive a land surface physics model for a period of 6 months. Additional simulations are performed driving the land surface physics model by spatially averaged meteorology, spatially averaged vegetation characteristics, spatially averaged soil properties, and spatially averaged meteorology, vegetation characteristics, and soil properties. By comparing the simulated water balance for the whole domain for each simulation, the relative influence of subgrid variability in meteorology, vegetation, and soil are assessed. Subgrid variability in summertime precipitation is found to have the largest effect on the surface hydrology, with a nearly twofold increase on surface runoff and a 15% increase in evapotranspiration. Subgrid variations in vegetation and soil properties also increase surface runoff and reduce evapotranspiration, so that surface runoff is 2.75 times as great with subgrid variability than without and evapotranspiration is 19% higher with subgrid variability than without.
Abstract
A 6.25-km resolution dataset of meteorology, vegetation type, and soil type for a domain covering a typical global climate model grid cell is used to drive a land surface physics model for a period of 6 months. Additional simulations are performed driving the land surface physics model by spatially averaged meteorology, spatially averaged vegetation characteristics, spatially averaged soil properties, and spatially averaged meteorology, vegetation characteristics, and soil properties. By comparing the simulated water balance for the whole domain for each simulation, the relative influence of subgrid variability in meteorology, vegetation, and soil are assessed. Subgrid variability in summertime precipitation is found to have the largest effect on the surface hydrology, with a nearly twofold increase on surface runoff and a 15% increase in evapotranspiration. Subgrid variations in vegetation and soil properties also increase surface runoff and reduce evapotranspiration, so that surface runoff is 2.75 times as great with subgrid variability than without and evapotranspiration is 19% higher with subgrid variability than without.
Abstract
Continuous estimates of the oceanic meridional heat transport in the Atlantic are derived from the Rapid Climate Change–Meridional Overturning Circulation (MOC) and Heatflux Array (RAPID–MOCHA) observing system deployed along 26.5°N, for the period from April 2004 to October 2007. The basinwide meridional heat transport (MHT) is derived by combining temperature transports (relative to a common reference) from 1) the Gulf Stream in the Straits of Florida; 2) the western boundary region offshore of Abaco, Bahamas; 3) the Ekman layer [derived from Quick Scatterometer (QuikSCAT) wind stresses]; and 4) the interior ocean monitored by “endpoint” dynamic height moorings. The interior eddy heat transport arising from spatial covariance of the velocity and temperature fields is estimated independently from repeat hydrographic and expendable bathythermograph (XBT) sections and can also be approximated by the array.
The results for the 3.5 yr of data thus far available show a mean MHT of 1.33 ± 0.40 PW for 10-day-averaged estimates, on which time scale a basinwide mass balance can be reasonably assumed. The associated MOC strength and variability is 18.5 ± 4.9 Sv (1 Sv ≡ 106 m3 s−1). The continuous heat transport estimates range from a minimum of 0.2 to a maximum of 2.5 PW, with approximately half of the variance caused by Ekman transport changes and half caused by changes in the geostrophic circulation. The data suggest a seasonal cycle of the MHT with a maximum in summer (July–September) and minimum in late winter (March–April), with an annual range of 0.6 PW. A breakdown of the MHT into “overturning” and “gyre” components shows that the overturning component carries 88% of the total heat transport. The overall uncertainty of the annual mean MHT for the 3.5-yr record is 0.14 PW or about 10% of the mean value.
Abstract
Continuous estimates of the oceanic meridional heat transport in the Atlantic are derived from the Rapid Climate Change–Meridional Overturning Circulation (MOC) and Heatflux Array (RAPID–MOCHA) observing system deployed along 26.5°N, for the period from April 2004 to October 2007. The basinwide meridional heat transport (MHT) is derived by combining temperature transports (relative to a common reference) from 1) the Gulf Stream in the Straits of Florida; 2) the western boundary region offshore of Abaco, Bahamas; 3) the Ekman layer [derived from Quick Scatterometer (QuikSCAT) wind stresses]; and 4) the interior ocean monitored by “endpoint” dynamic height moorings. The interior eddy heat transport arising from spatial covariance of the velocity and temperature fields is estimated independently from repeat hydrographic and expendable bathythermograph (XBT) sections and can also be approximated by the array.
The results for the 3.5 yr of data thus far available show a mean MHT of 1.33 ± 0.40 PW for 10-day-averaged estimates, on which time scale a basinwide mass balance can be reasonably assumed. The associated MOC strength and variability is 18.5 ± 4.9 Sv (1 Sv ≡ 106 m3 s−1). The continuous heat transport estimates range from a minimum of 0.2 to a maximum of 2.5 PW, with approximately half of the variance caused by Ekman transport changes and half caused by changes in the geostrophic circulation. The data suggest a seasonal cycle of the MHT with a maximum in summer (July–September) and minimum in late winter (March–April), with an annual range of 0.6 PW. A breakdown of the MHT into “overturning” and “gyre” components shows that the overturning component carries 88% of the total heat transport. The overall uncertainty of the annual mean MHT for the 3.5-yr record is 0.14 PW or about 10% of the mean value.
