Arctic Stratus Clouds Research Articles

Radiative Energy Budget in the Cloudy and Hazy Arctic

Abstract A radiation model is constructed that includes radiative interactions with atmospheric gases as well as parameterized treatments of scattering and absorption/emission by cloud droplets and haze particles. A unified treatment of solar and terrestrial radiation is obtained by using identical cloud and haze parameterization procedure for the shortwave and longwave region. The influence of the relative humidity of the haze particles is also considered. Snow conditions of the arctic region are simulated in terms of snow grain sizes and soot contamination in the surface layers. Data from the Arctic Stratus Cloud Experiment collected in 1980 are used for model comparisons and sensitivity studies under cloudy and hazy sky conditions. During the arctic summer, stratus clouds are a persistent feature and decrease the downward flux at the surface by about 130–200 W m−2. Arctic haze in the summertime is important if it is above the cloud layer or in air with low relative humidity, and it decreases the downwa...

Comments on “Interactions among Turbulence, Radiation and Microphysics in Arctic Stratus Clouds”

Comments on “Interactions among Turbulence, Radiation and Microphysics in Arctic Stratus Clouds”

Interactions among Turbulence, Radiation and Microphysics in Arctic Stratus Clouds

Abstract The Arctic Stratus Experiment, conducted during June 1980 over the Beaufort Sea, produced an extensive set of simultaneous measurements of boundary layer structure, radiation fluxes, and cloud microphysical properties. In this paper these data are used to determine the interactions between mixing, radiative transfer, and cloud microphysics for four cloud decks. The thermodynamic structure and fluxes of the thermodynamic quantities in the cloudy boundary layer are examined, including liquid water fluxes. Net radiative heating profiles are also determined. A detailed analysis of the fine-scale structure of the cloud microphysics is presented, including correlations between the cloud microphysical parameters (droplet concentration, liquid water content, mean radius, spectral dispersion, and the 95% volume liquid water drop radius), which are used to infer the nature of the mixing processes and the local effects of radiative heating/cooling. A comparison is then made with other observations and exist...

Relationships between large-scale heat and moisture budgets and the occurrence of Arctic stratus clouds [over the Beaufort Sea] : Curry, J.A. and G.F. Herman, 1985. Mon. Weath. Rev., 113(9): 1141–1457

Relationships between large-scale heat and moisture budgets and the occurrence of Arctic stratus clouds [over the Beaufort Sea] : Curry, J.A. and G.F. Herman, 1985. Mon. Weath. Rev., 113(9): 1141–1457

Relationships between Large-Scale Heat and Moisture Budgets and the Occurrence of Arctic Stratus Clouds

Abstract The occurrence of cloudiness over the Beaufort Sea region of the Arctic Basin during June 1980, is related to the ambient large-scale meteorological conditions. Cloud data are obtained from a hand analysis of the visible and infrared Defense Meteorological Satellite Program (DMSP) images and from the U.S. Air Force Three-Dimensional Nephanalysis (3DNEPH). A comparison of the two cloud cover datasets showed good agreement for mid- and high-level cloudiness, but low-level cloudiness was significantly underestimated by the 3DNEPH. The study therefore uses a composite data set consisting of the 3DNEPH data at mid- and upper-levels, and the DMSP data at lower levels. Atmospheric data are obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) objective analysis, and large-scale heat and moisture budgets are constructed. The budgets are used to investigate the processes which contribute to relative humidity changes. The budgets are related to the cloud cover for both the monthly cl...

Physical Characteristics of Arctic Stratus Clouds

Observations of the physical properties of Arctic status clouds (ASC) over the Beaufort Sea area were made by the NCAR Electra aircraft during June 1980. The cloud morphology and microstructure observed during these experiments are described here. Arctic stratus clouds were formed under various meteorological conditions, but not when the axis of the Beaufort Sea ridge was zonal and the airflow into the region was continental. The mean drop diameter in clouds observed under all conditions remained near 10 μm, while the mean liquid water content (LWC) was characteristic of the air mass forming the clouds and essentially determined by the mean drop concentration. Clouds showed considerable horizontal homogeneity but significant vertical changes occurred within them. The vertical profiles of LWC show that the values generally increased with height, as a result of an increase in droplet size rather than concentration. The drop size distribution near the base was monomodal, characteristic of condensation on a nucleus spectrum, but changed to a bimodal distribution near the top of the cloud.

Observational and Theoretical Studies of Solar Radiation in Arctic Stratus Clouds

Abstract A series of clouds-radiation experiments was carried out in June 1980 in Arctic stratus clouds occurring over the Beaufort Sea using the NCAR Electra aircraft. This paper is an analysis of the hemispheric radiation fields obtained with Eppley pyranometers and silicon flux detectors, and the cloud microphysical data obtained with the Knollenberg FSSP and 200X probes. These data were collected in a series of 12 vertical profiles in a variety of boundary layer stratus and altostratus situations. The results are interpreted with the aid of a theoretical radiative transfer model developed by Slingo and Schrecker. The Knollenberg measurements indicated a wide range of cloud liquid water contents which generally increased from cloud base to cloud top. Values of the equivalent radius of the droplet size distribution are presented. Based on the agreement between the radiation measurements and the model calculations, it is concluded that the Knollenberg FSSP probe produced realistic liquid water concentrat...

Dependence of radiative properties of Arctic stratus clouds on cloud microstructure

Observations of cloud microstructure during the Beaufort Sea Arctic Stratus Cloud Experiments of June 1980 showed that the drop size distributions typically are nonuniform changing from monomodal near the base to bimodal near the top of the cloud. The observed drop size distributions are used to compute the reflection and transmission of solar radiation by Arctic Stratus Clouds in the visible part of the spectrum. Solutions of the radiative transfer equation using three different vertically uniform drop size distributions closely resembling those observed near the bottom, middle and top of the cloud, respectively, resulted in significant changes in the radiative properties even though the column liquid water content is kept constant. This finding implies that the shortwave optical depth of Arctic Stratus Clouds cannot be related to the column liquid water content (inferred from longwave satellite radiometry) unless realistic height‐varying drop size distributions are used. It also implies that in order to make reliable predictions concerning the clouds' effect on the surface heat balance, one needs not only the column liquid water content but also height profiles of the drop size distributions.

Multiple reflection effects on irradiance in the presence of Arctic stratus clouds

For under a stratus cloud cover and for identical solar heights, irradiation values are about 70% higher in spring than in late summer at Barrow in northern Alaska. A possible explanation for these differences is by interseasonal variations in cloud thickness and water content in the atmosphere. However, we demonstrate that multiple reflection is mostly responsible for it. In spring there is a very high surface albedo (∼80%), while in summer the surface albedo is low (∼15%). Hence multiple reflection between the surface and the lower extent of the stratus cloud cover is important when snow is on the ground but fairly unimportant after the snow has melted. To verify our assumption, airborne measurements were carried out for the same cloud but over surfaces of different albedos, namely, snow covered tundra (∼80%), broken sea ice (20–40%), and open water (4–16%). These data show clearly that if the surface albedo is raised, multiple reflection is the cause of the strong increase in irradiation. The interaction by multiple reflections of the spectral characteristics of various ground surfaces with the stratus clouds also was found to be displayed in the spectral irradiance received from the cloud cover.

Thermal radiation in Arctic stratus clouds

AbstractInfrared radiative properties of Arctic stratus clouds in the 10.1 to 12.7μm wavelength region are determined from a series of aircraft measurements. The average emissivity of the clouds when scattering is neglected is unity for cloud depths greater than 350m. Under the assumption that the cloud layers are homogeneous the cloud droplet volume absorption coefficient is estimated as 17±5km−1. Several mass absorption coefficients are estimated for several assumed liquid water distributions. It is also concluded that the cloud reflectance is not larger than 2(£5%).

Formation and Persistence of Summertime Arctic Stratus Clouds

Abstract We have developed a numerical model which can explain the principle observed properties of the summertime stratus clouds occurring over the Arctic Basin. Warm, moist air from the surrounding land masses is modified as it passes over the melting pack ice. Motions are calculated on the basis of a fixed pressure field, but all other relevant fields (temperature, mixing, solar and terrestrial radiation, water in the liquid and vapor phase) are calculated on the basis of an internally consistent thermodynamic model which is considered to be complete in all essential physical processes. The ubiquitous occurrence of stratus clouds is explained in terms of the relative unimportance of cloud dissipative processes over the Arctic Ocean. The commonly observed layering results from the trapping of solar radiation inside a cloud which is opaque to thermal radiation. The absence of similar layering in mid-latitude stratus is probably due to the diurnal variation of solar radiation, which is largely absent in t...