Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

[1] Antarctic coastal polynyas are areas of reduced sea ice cover within the ice pack and their associated surface waters are noted for sustaining enhanced levels of biological production during the spring and summer. Here we present satellite-based estimates of interannual changes in the areal extent, phytoplankton abundance, and primary productivity within 37 Antarctic coastal polynya systems over five annual cycles (1997 to 2002). The largest polynya studied was located in the Ross Sea (396,500 km2) while the smallest was located in the West Lazarev Sea (1040 km2). Most polynyas attained maximum areal extents in February of less than 20,000 km2. Mean polynya chlorophyll a from 1 September to 31 March ranged from 0.16 to 2.2 mg m−3, averaging 0.69 mg m−3. Daily production averaged 0.09 to 0.76 g C m−2 d−1. Mean annual primary production ranged from 18 to 161 g C m−2 yr−1, with most coastal polynyas exhibiting annual rates of production between 20 and 80 g C m−2. Total production (the product of the open water area and the spatial mean daily primary production rate) varied by 2 orders of magnitude, from 0.03 to 48 Tg C yr−1. Taken together, the Ross Sea, Ronne Ice Shelf, Prydz Bay, and Amundsen Sea polynyas are responsible for >75% of total polynya production. In eastern Antarctica, where 91% of all Adelie penguin colonies are associated with a coastal polynya, the magnitude of annual production in polynyas explained 65% of the variance in penguin colony size.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JC001739

Phytoplankton dynamics within 37 Antarctic coastal polynya systems

MODIS detected surface urban heat islands and sinks: Global locations and controls

Hong Kong is a high-density sub-tropical city with 7 million people living in an urban area of just over 260 km2. Tall and closely packed buildings are the common urban morphology. How the urban geometry influences the microclimate in summer daytime is a primary planning concern. The sky view factor (SVF) has been commonly used to indicate the impact of urban geometry on air temperature differences in cities. However, only limited discussions in this aspect have been addressed for daytime course in high-rise and high-density urban environment such as Hong Kong. This paper firstly provides a comprehensive review of SVF analysis in urban climatology studies and then presents a simulation approach to investigate the role of SVF in determining summer daytime intra-urban air temperature differences in urban Hong Kong. An ArcGIS-embedded computer program is developed for calculating continuous SVF values for an entire urban environment and an SVF map is generated. The result is evaluated against meteorological data observed in field measurements. The regression analysis shows that the spatial average of SVF values has a close negative relationship with daytime intra-urban temperature differences. The study indicates that SVF is a significant factor for understanding the microthermal climate in Hong Kong's street canyons. The paper further raises discussions on the application of SVF analysis to urban planning. The study demonstrates that the SVF analysis is a useful and effective tool for planners and urban climatologists conducting studies on high-rise and high-density sub-tropical cities. The understanding can provide support for the development of planning standards and good practice. Copyright © 2010 Royal Meteorological Society

Sky view factor analysis of street canyons and its implications for daytime intra-urban air temperature differentials in high-rise, high-density urban areas of Hong Kong: a GIS-based simulation approach

[1] Polynyas are nonlinear-shaped openings within the ice cover, ranging in size from 10 to 105 km2. Polynyas play an important climatic role. First, winter polynyas tend to warm the atmosphere, thus affecting atmospheric mesoscale motions. Second, ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection, contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation. Since 1990, there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas. This article reviews polynya research carried out in the last 2 decades, focusing on presenting a state-of-the-art picture of the physical interactions between polynyas and the atmosphere-sea ice-ocean system. Observational and modeling studies, the surface heat budget, and water mass transformation within these features are addressed.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002RG000116

Polynya dynamics: A review of observations and modeling

A three-dimensional, non-hydrostatic, high-resolution numerical model was used toanalyse urban heat-island (UHI) intensity in an idealised but realistic configurationThe urban area was 20 km square and lay on flat land at about latitude 50° Nin a maritime climate In the model the urban area was represented by anomalies ofalbedo, anthropogenic heat flux, emissivity, roughness length, sky-view factor (SVF),surface resistance to evaporation (SRE) and thermal inertia A control simulationincluded all these factors and the resultant UHI structure, energetics and intensitywere validated against observations The results also compared favourably withearlier simulations A series of experiments was conducted in which successively one of the anomaliesthat represented the urban area was omitted from the control simulation so as toprovide the basis for an assessment of its effect In daytime the individual effectsdue to albedo, anthropogenic heat, emissivity, SVF and thermal inertia ranged from02 to 08 °C In common with albedo, anthropogenic heat, emissivity andSVF, the SRE aided the formation of a UHI; it was also the most important factorin increasing its intensity The roughness length had the opposite effect At nightemissivity, roughness length, SVF and SRE had effects ranging from 03 to075 °C, but the largest effect (2 °C) was due to the anthropogenicheat These results showed a difference in the causes of daytime and nighttime UHIsIn daytime the roughness length and SRE were the most important factors affectingUHI intensity; at night the anthropogenic heat was the most important The simulationssuggested that the size of the urban area had a minimal effect on UHI intensity

Numerical Modelling of Urban Heat-Island Intensity

A combination of observations and a numerical model revealed the meso-scale structure of the near-surface atmospheric conditions over the Persian Gulf. Low-level winds were dominated by a single, coherent, perennial land–sea breeze circulation (LSBC) that varied seasonally and diurnally. In summer the sea breeze was deeper and wider than in winter. At night the core of the LSBC over the Gulf was confluent with uplift, whereas in daytime it was difluent with subsidence. Sensitivity tests with the model revealed the influence on the LSBC of the land–sea distribution, orography and the ambient wind. The latter resulted in different conditions over the north, east, south and west coasts. Over the north coast, where the opposing ambient wind created a sea breeze front, landward penetration was very limited; over the south coast it was over 250 km. The thermal effect of the Iranian mountains accentuated the depth and penetration, landward and seaward, of the LSBC, thus influencing the duration of the land and sea breezes over the east coast. From spring to autumn the marine boundary layer over the Gulf was shallow, cool, moist and stable, with strong vertical gradients of temperature and humidity at its top. Its depth increased in the ambient flow from northwest to southeast and also, in daytime, from west to east, because of different magnitudes of the subsidence in the sea breeze circulation over the west and east coasts. Copyright © 2004 Royal Meteorological Society

Observed and modelled climatology of the land–sea breeze circulation over the Persian Gulf

Two models were used to assess the effects of coastal characteristics on radar propagation in ducting conditions in the Persian Gulf. The NCAR/Penn State MM5 model simulated atmospheric conditions at a 5-km horizontal spatial and hourly temporal resolution on a day on which observations of ducts existed. The output from this model was input to the AREPS propagation model to produce radar coverage over coastal areas. Four factors influenced radar propagation: the sea breeze; coastal configuration; orography; and ambient wind. The sea breeze alone allowed propagation to extend about 100 km inland in a layer 200 m deep. When the breeze was aided by a following ambient wind the propagation layer extended for 150 km and was 400 m deep. A coastal indentation caused differences in depth and intensity of propagation over a distance of about 30 km parallel to the coast in which the indentation occurred. Steep near-coastal orography blocked radar propagation. Copyright © 2006 Royal Meteorological Society.

https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1017/S1350482705001970

Coastal effects on radar propagation in atmospheric ducting conditions

Although it is well known that sea-ice regions are important components of the Earth's climate system, the exchanges of energy between ocean, ice and atmosphere are not well understood. The majority of past observational and modelling studies of atmosphere-surface interactions over sea-ice regions were primarily concerned with airflow over a single, isolated area of open water. The more realistic situations of multiple polynyas within a sea-ice field and different areal concentrations of sea ice were studied here. Spatial structure of the atmospheric boundary layer in response to this surface was simulated using a high-resolution numerical model. A sea-ice concentration of 80%, typical of the Southern Ocean sea-ice zone, was maintained within a 100-km wide domain. The effects of three polynya characteristics were assessed: their horizontal extent; local concentration of sea ice (LCI); and their arrangement with ice floes. Over polynyas of all sizes distinct plumes of upward heat flux, their width and height closely linked to polynya width, resulted in mixed layers 600 to 1000 m deep over and downwind of the polynyas, their depth increasing with polynya width. Mean surface heat flux (MSHF) increased with size in polynyas less than 30 km wide. The air-to-ice MSHF over the first 10 km of sea-ice downwind of each polynya and the domain-average surface heat flux increased linearly with polynya width. Turbulent kinetic energy plumes occurred over all polynyas, their heights and widths increasing with polynya widths. Downward flux of high momentum air in the plumes caused increased wind speeds over polynyas in the layer from about 300–1000 m above the surface, the depth varying directly with polynya width. MSHFs decreased as LCIs increased. The arrangement of polynyas had relatively little effect on the overall depth of the modified layer but did influence the magnitude and spatial structure of vertical heat transfer. In the two-polynya case the MSHF over the polynyas was larger when they were closer together. Although the MSHF over the sea ice between the polynyas decreased in magnitude as their separation increased, the percentage of the polynya-to-air heat recaptured by this ice floe increased fivefold.

Atmospheric Response To Spatial Variations In Concentration And Size Of Polynyas In The Southern Ocean Sea-Ice Zone

A simulated climatology of ducts in the Persian Gulf area was produced with the MM3 atmospheric model. From November to January ducts were sporadic, land and surface based, shallow and weak. From February to October ducts of all types occurred. In the duct season, spatial and temporal variations were related to the land/sea distribution and to day and night. Over land at night, widespread, shallow, weak surface ducts occurred well away from the sea; within about 100 km of the south-western coast in the late evening, ducts were S-shaped. Over land in daytime, the dry, convective boundary layer prevented duct formation. Over the Gulf in the season, duct coverage was complete throughout night and day. A spatial sequence of shallow, weak surface ducts, deeper, stronger S-shaped ducts and deep, strong elevated ducts lay from north-west to south-east over the Gulf. This sequence was related to the growth of a marine internal boundary layer (MIBL) and the effects of land- and sea-breeze circulations. Subsidence in the sea-breeze circulation reduced magnitudes of depth and strength and created gradients in a direction normal to the main growth axis of the MIBL. Ducts growing in the MIBL were tilted upward from west to east. The combined effect gave relatively weak surface ducts in the north-west and strong elevated ducts in the south-east. Duct depth and strength increased as the season progressed, owing to increased wind speed within, and increased depth of, the MIBL.

B. W. Atkinson

Papers

Numerical Modelling of Urban Heat-Island Intensity

Observed and modelled climatology of the land–sea breeze circulation over the Persian Gulf

Coastal effects on radar propagation in atmospheric ducting conditions

Atmospheric Response To Spatial Variations In Concentration And Size Of Polynyas In The Southern Ocean Sea-Ice Zone

Simulated Climatology of Atmospheric Ducts Over the Persian Gulf