Atmospheric Circulation Research Papers - Academia.edu (original) (raw)

During the last glacial-interglacial cycle, northern hemispheric (NH) ice-sheets experienced dramatic changes in radiative forcing, due to orbitally-driven insolation changes and varying greenhouse gas concentrations. This direct forcing... more

During the last glacial-interglacial cycle, northern hemispheric (NH) ice-sheets experienced dramatic changes in radiative forcing, due to orbitally-driven insolation changes and varying greenhouse gas concentrations. This direct forcing caused temperature changes and eventually ablation anomalies. Orbital-scale variations in the atmospheric circulation caused anomalies in temperature advection and precipitation/snowfall that also strongly contributed to the mass balance and hence the time-evolution

The aim of the study is to characterize the frequency and determinants of the synoptic con- ditions of advection of arctic and tropical air masses over the Lublin region. Their occurrence in the regional scale in the years 1951–2010 was... more

The aim of the study is to characterize the frequency and determinants of the synoptic con- ditions of advection of arctic and tropical air masses over the Lublin region. Their occurrence in the regional scale in the years 1951–2010 was based on lower synoptic maps for 12 UTC, which derived from PIHM/IMGW-PIB. In turn, the calendar of circulation types for the Lublin region was used to assess the synoptic conditions of the analyzed air masses. The annual frequency of arctic air masses reached 13.4%. The highest frequency of these air masses occurred in spring, with the maximum in April (20.4%), and the lowest in summer (July and August, < 5%). Days with tropical air were recorded less frequently (4.1% of all days in the year). It is most often found in the summer (with a maximum of 9.2% in July) and the lowest in winter (< 1%). In the years 1951–2010, there were signifi cant changes in the frequency of advection of arctic and tropical air masses (average increase by 8 and 3 days per 10 years, respectively). The occurrence of arctic masses signifi cantly increased in winter, autumn and spring, and tropical in the summer. In all seasons, the arctic air was most likely to be recorded during the northern and northeastern circula- tion types, while the lowest in the southern and southwestern types. In the case of tropical air, it is most likely to occur during air fl ow from directions E-SE-S-SW. Regardless of the time of the year, arctic and tropic air masses are characterized by signifi cant anomalies in air temperature at 850 hPa and 850–1000 hPa thickness.

A numerical model was developed for the computation of the wind field, air temperature and humidity in the urban canopy layer and in the atmospheric boundary layer above urban areas. The model is of k–ε type. The ensemble-spatial averaged... more

A numerical model was developed for the computation of the wind field, air temperature and humidity in the urban canopy layer and in the atmospheric boundary layer above urban areas. The model is of k–ε type. The ensemble-spatial averaged three-dimensional Reynolds equations, equation of continuity, turbulent kinetic energy equation (k-equation), and equation for dissipation rate of turbulent energy (ε-equation) are solved together with equations of heat and moisture transfer in the air. Inside the urban canopy layer, volumes of buildings and other urban structures are accounted for by a spatial averaging procedure. With given average building height and building width for each grid mesh, effects of buildings on the momentum transfer are modelled by introducing a form drag force. Temperatures of the ground surface, building walls or roof are computed by the solution of the heat conduction equation in the ground or walls, roof. Evaporation at the ground surface is evaluated using a Bowen ratio. The exhausted heat by building air conditioning is evaluated by employing a building air conditioning model. This heat together with traffic-induced artificial heat are accounted for in the model as heat sources. A numerical model for the momentum, heat and moisture transfer in the plant canopy is also coupled to the model to investigate the effects of vegetation on the urban climate. Verification of the model against observational data in the Tokyo Metropolitan area, Japan, reveals that the model is capable of simulating the momentum, heat and mass transfer in the urban boundary layer. Especially, the model can compute air temperature, humidity and wind velocity at the street level, which cannot be computed by a general above city atmospheric circulation model.

Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1988. Observed significant changes in the atmospheric circulation throughout the troposphere... more

Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1988. Observed significant changes in the atmospheric circulation throughout the troposphere revealed a deeper and eastward shifted Aleutian low pressure system in the winter half year which advected warmer and moister air along the west coast of North America and into Alaska and colder air over the north Pacific. Consequently, there were increases in temperatures and sea surface temperatures (SSTs) along the west coast of North America and Alaska but decreases in SSTs over the central north Pacific, as well as changes in coastal rainfall and streamflow, and decreases in sea ice in the Bering Sea. Associated changes occurred in the surface wind stress, and, by inference, in the Sverdrup transport in the north Pacific Ocean. Changes in the monthly mean flow were accompanied by a southward shift in the storm tracks and associated synoptic eddy activity and in the surface ocean sensible and latent heat fluxes. In addition to the changes in the physical environment, the deeper Aleutian low increased the nutrient supply as seen through increases in total chlorophyll in the water column, phytoplankton and zooplankton. These changes, along with the altered ocean currents and temperatures, changed the migration patterns and increased the stock of many fish species. A north Pacific (NP) index is defined to measure the decadal variations, and the temporal variability of the index is explored on daily, annual, interannual and decadal time scales. The dominant atmosphere-ocean relation in the north Pacific is one where atmospheric changes lead SSTs by one to two months. However, strong ties are revealed with events in the tropical Pacific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months. Changes in the storm tracks in the north Pacific help to reinforce and maintain the anomalous circulation in the upper troposphere. A hypothesis is put forward outlining the tropical and extratropical realtionships which stresses the role of tropical forcing but with important feed-backs in the extratropics that serve to emphasize the decadal relative to interannual time scales. The Pacific decadal timescale variations are linked to recent changes in the frequency and intensity of El Niño versus La Nina events but whether climate change associated with “global warming” is a factor is an open question.

Dinoflagellate cysts and XRF core scanning data from two marine sediment cores from embayments north (Bonavista Bay) and south (Placentia Bay) of Newfoundland show significant changes in ocean and atmospheric conditions of the SW Labrador... more

Dinoflagellate cysts and XRF core scanning data from two marine sediment cores from embayments north (Bonavista Bay) and south (Placentia Bay) of Newfoundland show significant changes in ocean and atmospheric conditions of the SW Labrador Sea region during the last 5700 years. Fresh and cold conditions, probably accompanied by seasonal sea ice, prevailed both north and south of Newfoundland from c. 5.7 to 4.0 cal. kyr BP. This may be linked to intensified Labrador Current export of cold meltwater and/or sea ice from the Arctic, presumably related to warmer conditions in the northernmost latitudes and the prevalence of strong (north)westerly winds. After c. 4.0 cal. kyr BP, sea-surface conditions warmed up and sea ice decreased northeast of Newfoundland, but conditions were still cold south of Newfoundland. This suggests a decrease in Arctic meltwater export and westerly wind strength. After 2.9—2.5 cal. kyr BP, only minor changes in sea-surface conditions affected the study sites. S...

The Australian continent is characterised by an extremely variable surficial geochemistry, reflecting the varied lithology of Australian basement rocks. Samples representative of Australian aeolian dust have been collected in (1) regions... more

The Australian continent is characterised by an extremely variable surficial geochemistry, reflecting the varied lithology of Australian basement rocks. Samples representative of Australian aeolian dust have been collected in (1) regions where meteorological records, satellite observation and wind erosion modelling systems have indicated frequent dust activity today (mainly the Lake Eyre Basin), and (2) from deposits of mixed dust materials. The 87Sr/86Sr and 143Nd/144Nd isotopic composition of the fine (< 5 μm) fraction of Australian dust samples was measured for comparison with the Sr and Nd isotopic composition of fine aeolian dust that reached the interior of the East Antarctic Plateau. The isotopic field for Australian dust is characterised by 87Sr/86Sr ratios ranging from 0.709 to 0.732 and εNd(0) between − 3 and − 15. The low Sr radiogenic values and εNd(0) of − 3 obtained for Lake Eyre samples are explained by the lithology of the Lake Eyre catchment showing a dominance o...

... 11. PE Damon and JL Jirikowic, Solar forcing of global climate change?. Radiocarbon After Four Decades An Interdisciplinary Perspective, Springer-Verlag, New York (1992) p. 117–127 . 12. PE Damon and JL Jirikowic, Solar forcing of... more

... 11. PE Damon and JL Jirikowic, Solar forcing of global climate change?. Radiocarbon After Four Decades An Interdisciplinary Perspective, Springer-Verlag, New York (1992) p. 117–127 . 12. PE Damon and JL Jirikowic, Solar forcing of global climate change. ...

We review recent advances in classifications of circulation patterns as a specific research area within synoptic climatology. The review starts with a general description of goals of classification and the historical development in the... more

We review recent advances in classifications of circulation patterns as a specific research area within synoptic climatology. The review starts with a general description of goals of classification and the historical development in the field. We put circulation classifications into a broader context within climatology and systematize the varied methodologies and approaches. We characterize three basic groups of classifications: subjective (also called manual), mixed (hybrid), and objective (computer-assisted, automated). The roles of cluster analysis and principal component analysis in the classification process are clarified. Several recent methodological developments in circulation classifications are identified and briefly described: the introduction of nonlinear methods, objectivization of subjective catalogs, efforts to optimize classifications, the need for intercomparisons of classifications, and the progress toward an optimum, if possible unified, classification method. Among the recent tendencies in the applications of circulation classifications, we mention a more extensive use in climate studies, both of past, present, and future climates, innovative applications in the ensemble forecasting, increasing variety of synoptic–climatological investigations, and steps above from the troposphere. After introducing the international activity within the field of circulation classifications, the COST733 Action, we briefly describe outputs of the inventory of classifications in Europe, which was carried out within the Action. Approaches to the evaluation of classifications and their mutual comparisons are also reviewed. A considerable part of the review is devoted to three examples of applications of circulation classifications: in historical climatology, in analyses of recent climate variations, and in analyses of outputs from global climate models.

The Outer Banks barrier islands of North Carolina, USA, contain a geologic record of inlet activity that extends from ca. 2200 cal yr BP to the present, and can be used as a proxy for storm activity. Optically stimulated luminescence... more

The Outer Banks barrier islands of North Carolina, USA, contain a geologic record of inlet activity that extends from ca. 2200 cal yr BP to the present, and can be used as a proxy for storm activity. Optically stimulated luminescence (OSL) dating (26 samples) of inlet-fill and flood tide delta deposits, recognized in cores and geophysical data, provides the basis for understanding the chronology of storm impacts and comparison to other paleoclimate proxy data. OSL ages of historical inlet fill compare favorably to historical documentation of inlet activity, providing confidence in the technique. Comparison suggests that the Medieval Warm Period (MWP) and Little Ice Age (LIA) were both characterized by elevated storm conditions as indicated by much greater inlet activity relative to today. Given present understanding of atmospheric circulation patterns and sea-surface temperatures during the MWP and LIA, we suggest that increased inlet activity during the MWP responded to intensified hurricane impacts, while elevated inlet activity during the LIA was in response to increased nor'easter activity. A general decrease in storminess at mid-latitudes in the North Atlantic over the last 300 yr has allowed the system to evolve into a more continuous barrier with few inlets.

SUMMARY: The first part of the paper gives a review of recent and projected climatic variations in the Norwegian Arctic. The annual temperature has increased in the Svalbard region and at Jan Mayen during the latest decades, but the... more

SUMMARY: The first part of the paper gives a review of recent and projected climatic variations in the Norwegian Arctic. The annual temperature has increased in the Svalbard region and at Jan Mayen during the latest decades, but the present level is still lower than in the 1930s. Measured annual precipitation has increased by more than 2.5% per decade during

The constructal law states that every flow system evolves in time so that it develops the flow architecture that maximizes flow access under the constraints posed to the flow. Earlier applications of the constructal law recommended it as... more

The constructal law states that every flow system evolves in time so that it develops the flow architecture that maximizes flow access under the constraints posed to the flow. Earlier applications of the constructal law recommended it as a self-standing law that is distinct from the second law of thermodynamics. In this paper, we develop a model of heat transport on the earth surface that accounts for the solar and terrestrial radiation as the heat source and heat sink and with natural convection loops as the transport mechanism. In the first part of the paper, the constructal law is invoked to optimize the latitude of the boundary between the Hadley and the Ferrel cells, and the boundary between the Ferrel and the Polar cells. The average temperature of the earth surface, the convective conductance in the horizontal direction as well as other parameters defining the latitudinal circulation also match the observed values. In the second part of the paper, the constructal law is invoked in the analysis of atmospheric circulation at the diurnal scale. Here the heat transport is optimized against the Ekman number. Even though this second optimization is based on very different variables than in the first part of the paper, it produces practically the same results for the earth surface temperature and the other variables. The earth averaged temperature difference between day and night was found to be approximately 7 K, which matches the observed value. The accumulation of coincidences between theoretical predictions and natural flow configuration adds weight to the claim that the constructal law is a law of nature.

We report progresses made by our group in the elaboration of a weather engineering technology for generating clouds and rainfalls in specific arid and semi-arid sub-tropical regions. In these regions, large amount of humidity can be... more

We report progresses made by our group in the elaboration of a weather engineering technology for generating clouds and rainfalls in specific arid and semi-arid sub-tropical regions. In these regions, large amount of humidity can be present in the low atmosphere in Spring and Summer seasons without leading to cloud formation. This results from a too large stability of the atmosphere that inhibits thermal convection. The Geshem technology we are developing is based on a large solar absorbing artificial black surface of area of about 10-12 km2 set at the ground. The upward heat flux produced by this artificial heat island dilates the lower humid air layers flowing over the artificial surface. Rainfalls could be triggered by this system on sunny days during which the thermal convection induced by the artificial solar captor can overcome the atmospheric stability. The dominant wind would carry the resulting clouds over an area behind the solar absorber that can extend up to 20-40 km far...

... The 1.0 and 0.8%o reduc-tion in summer and winter Ô180 values, respectively, between AD 975 and AD 1720 signals the climate change from the highs of Medieval warming (Medieval Warm Period or MWP) to the lows of Little Ice Age (LIA)... more

... The 1.0 and 0.8%o reduc-tion in summer and winter Ô180 values, respectively, between AD 975 and AD 1720 signals the climate change from the highs of Medieval warming (Medieval Warm Period or MWP) to the lows of Little Ice Age (LIA) cooling. ...

The Lower Toarcian Posidonia Shale is famous for its excellently preserved fossils and its high amount of organic matter (up to 16%). Both quality of preservation and accumulation of organic matter have been explained by permanent anoxic... more

The Lower Toarcian Posidonia Shale is famous for its excellently preserved fossils and its high amount of organic matter (up to 16%). Both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions. High-resolution geochemical, sedimentological and palaeoecological investigations of various sections of the Posidonia Shale in SW-Germany, however, indicate that oxygen availability was variable and ranged from short oxygenated periods to longer-term anoxia. The benthic macrofauna consists of nine fossil communities and was used, in combination with geochemical data, to reconstruct a time-averaged oxygen curve. Anoxic conditions prevailed during the deposition of the Toarcian black shales; they were, however, punctuated by various short periods (weeks to years) with oxygenated bottom water conditions. Sedimentological (e.g. distinctiveness of microlamination, siliciclastic content) and geochemical parameters (e.g. organic matter content, isotopic signatures: δ18O and δ13C, molecular redox parameters: pristane/phytane ratio, arylisoprenoids) exhibit a remarkable covariation and seem to be controlled by sea level fluctuations. Maximum oxygen depletion and an extreme negative shift of δ13Corg values (−34‰) occurred during the early falciferum-zone. This is explained by the recycling of 12C-enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia. The subsequent transgression permitted enhanced water exchange with the Tethyan Ocean and caused improvement of living conditions at the end of the falciferum-zone.Other important factors controlling the depositional environment are the overall palaeogeographic situation and climate. The early Jurassic is the latest period before break-up of Pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade- and monsoon-wind systems. An estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti-estuarine circulation and a negative water balance in the winter. During the summer months a stratified water column with anoxic conditions below the halocline developed. δ18O data indicate low salinity in the surface water during the monsoon-influenced summer. High productivity was then located in the photic zone and the corresponding isotopically light δ18O-signal was fixed in the calcareous nannoplankton. During the winter months a saline circulation system brought oxygen to the benthic environment, favouring temporary benthic colonization, especially during times of relative sea level high stand.

Changes in global climate will have significant impact on local and regional hydrological regimes, which will in turn affect ecological, social and economical systems. However, climate-change impact studies on hydrologic regime have been... more

Changes in global climate will have significant impact on local and regional hydrological regimes, which will in turn affect ecological, social and economical systems. However, climate-change impact studies on hydrologic regime have been relatively rare until recently, mainly because Global Circulation Models, which are widely used to simulate future climate scenarios, do not provide hourly or daily rainfall reliable enough