Atmospheric Circulation

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 horizontal flow of SO2 gas from day side to night side of Io is calculated. The surface is assumed to be covered by a frost whose vapor pressure at the subsolar point is orders of magnitude larger than that on the night side. Temperature of the frost is controlled by radiation. The flow is hydrostatic and turbulent, with velocity and entropy per particle independent of height. The vertically integrated conservation equations for mass, momentum, and energy are solved for atmospheric pressure, temperature, and horizontal velocity as functions of solar zenith angle. Formulas from boundary layer theory govern the interaction between atmosphere and surface. The flow becomes supersonic as it expands away from the subsolar point, as in the theory of rocket nozzles and the solar wind. Within 35 ° of the subsolar point atmospheric pressure is less than the frost vapor pressure, and the frost sublimes. Elsewhere, atmospheric pressure is greater than the frost vapor pressure, and the frost condenses. The two pressures seldom differ by more than a factor of 2. The sublimation rate at the subsolar point is proportional to the frost vapor pressure, which is a sensitive function of temperature. For a subsolar temperature of 130°K, the sublimation rate is l0 ~5 molecules/cm2/sec. Diurnally averaged sublimation rates at the equator are comparable to the 0. l cm/year resurfacing rate required for burial of impact craters. At the poles where both the vapor pressures and atmospheric pressures are low, the condensation rates are 100 times smaller. Surface pressures near the terminator are generally too low to account for the ionosphere discovered by Pioneer 10. The possibility of a noncondensable gas in addition to SO: must be seriously considered.

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.

The main purpose of this paper is to present the study of tra$c emissions impact on the Lisbon region air quality. Two approaches of emission data generation with high spatial and temporal resolution are presented and compared. Main roads were processed as line sources and hot on-road emissions were calculated based on daily mean tra$c and emission factors distinguished for several road classes and vehicle types. Also, the disaggregation of national CORINAIR inventory has been performed on the basis of statistical information of fuel consumption and population density. The comparison of emission data obtained by these two approaches demonstrates a good agreement for total values, but a signi"cant di!erence for spatial distribution of the data. To ensure completeness of the data, to improve their spatial resolution and also to analyse the impact of the tra$c emissions, a combination of the two approaches was applied to generate the emission data used by a photochemical numerical system to simulate the atmospheric circulation and the air pollution pattern in Lisbon under summer meteorological conditions, having di!erent emission scenarios. It was possible to conclude that an air pollution abatement strategy is urgently needed and it should take into account the strong contribution of road tra$c emissions to the Lisbon air pollution levels.

1] We have incorporated the cycling of water isotopes into the NCAR atmospheric general circulation model, CAM2. Isotope dynamics mostly follow those of previous isotope GCMs, with fractionation being produced by evaporation at the surface and by cloud processes. A new feature that we have added is the direct estimation of the degree of isotopic equilibration between vapor and raindrops as a function of temperature and rain rate. The model yields a reasonable global pattern of water isotopes in precipitation, but detailed comparison with observations is limited by known inaccuracies in precipitation and temperatures yielded by CAM2. We use the results to evaluate the fundamental controls on water isotopic composition in precipitation. We emphasize that, over much of the surface of the Earth, the concept of Rayleigh distillation is inadequate to understand the large-scale geographic distribution of water isotopes in precipitation, because the effects of surface fluxes are more important than those of distillation, in particular at low and midlatitudes and over the oceans. In oceanic regions the balance between precipitation and evaporation (P À E), which reflects the large-scale atmospheric circulation, is the primary determinant of the isotopic composition of precipitation and vapor. Variations of P À E at low latitudes over the oceans produce about 7% variation of precipitation d 18 O that is independent of temperature variation. Where P > E, the convergence of atmospheric vapor derived from various sources leads to low values and a particularly wide range in d ppt . In the tropical and subtropical troposphere the vertical decrease of d 18 O in vapor is different from the values expected from Rayleigh distillation because of entrainment, convective mixing, detrainment, evaporation of detrained water, and subsidence of low-d 18 O highaltitude air. The low d 18 O of atmospheric vapor over the oceans at high (ca. 55°) latitudes produces, as a result of kinetic effects associated with evaporation, a zone of heavy (high-d 18 O) evaporation from the oceans. This effect may account for the low d 18 O of some high-latitude ocean surface waters and also helps attenuate the effects of global temperature changes on the isotopic composition of polar precipitation.

This paper describes an attempt to model soil moisture over the Australian continent with an integrated system of dynamic models and a Geographic Information System (GIS) data base. A land surface scheme with improved treatment of soil hydrological processes is described. The non-linear relationships between soil hydraulic conductivity, matric potential and soil moisture are derived from the Broadbridge and White soil model. For a single location, the prediction of the scheme is in good agreement with the measurements of the Hydrological and Atmospheric Pilot Experiment (HAPEX). High resolution atmospheric and geographic data are used in soil moisture prediction over the Australian continent. The importance of reliable land surface parameters is emphasized and details are given for deriving the parameters from a GIS. Predicted soil moisture patterns over the Australian continent in summer, with a 50 km spatial resolution, are found to be closely related to the distribution of soil types, apart from isolated areas and times under the influence of precipitation. This is consistent with the notion that the Australian continent in summer is generally under water stress. In contrast, predicted soil temperatures are more closely related to radiation patterns and changes in atmospheric circulation. The simulation can provide details of soil moisture evolution both in space and time, that are very useful for studies of land use sustainability, such as plant growth modelling and soil erosion prediction.

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.

Large projectiles impacting the Earth will cause severe shock heating and chemical reprocessing of the Earth's atmosphere. This occurs during atmospheric entry and, more importantly, as a result of the supersonic plume ejected on impact. In particular, very large amounts of nitric oxide would result from the impact of the putative Cretaceous-Tertiary bolide(s). We present models of the shock chemistry, the conversion of NO to NO 2 and thence to nitrous and nitric acids, and the global dispersion of the NO 2 and acids. Two plausible projectiles are considered: an ice-rich long-period comet and a much smaller rock-metal asteroid. The comet produces semi-global atmospheric NO 2 mixing ratios of 0.1% while the asteroid produces these high mixing ratios only in the immediate region of the impact. The comet produces concentrated nitrous and nitric acid rain with a pH ~ 0-1.5 globally. The asteroid produces rain with a pH ~ 0-1 near the impact and-4-5 globally. Immediate environmental effects of these nitrogen species include inhibition of photosynthesis due to extinction of solar radiation by NO 2, foliage damage due to exposure to NO 2 and HNO 3, toxicosis resulting from massive mobilization of soil trace metals, and respiratory damage due to exposure to NO 2. The acid rain decreases the pH of the oceanic mixed layer affecting the stability of calcite with important implications for the survival of calcareous-shelled organisms and for exhalation of CO, from the mixed layer to the atmosphere. Longer-term environmental effects perhaps-1000 years in duration include a global warming due to the sudden CO 2 injection and the simultaneous extinction of the ocean microorganisms which normally help remove CO 2 from the atmosphere-mixed layer system. Havens for survival include carbonate-buffered lakes and burrows. This acid rain theory therefore serves to explain the peculiar selectivity of the extinctions seen at the Cretaceous-Tertiary boundary. The first few years of acid rain will lead to massive weathering rates of continental soils characterized by large ratios of the relatively insoluble metals (e.g. Be 2+, AI ~, Hg 2., Cu*, Fe 2+, Fe 3+, T13+, Pb 2+, Cd 2~, Mn 2., Sr 2.) to the more soluble metals (Ca 2 +, Mg 2 +) which should have left a clear signal in the fossils of neritic organisms and in unperturbed neritic sediments near river deltas if such sediments still exist for the Cretaceous-Tertiary time frame.

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 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...

Spatial and temporal variability of the stable isotope composition of precipitation in the southeast Asia and western Pacific region is discussed, with emphasis on the China territory, based on the database of the International Atomic Energy Agency/World Meteorological Organization Global Network "Isotopes in Precipitation" and the available information on the regional climatology and atmospheric circulation patterns. The meteorological and pluviometric regime of southeast Asia is conn'olled by five different air masses: (1) polar air mass originating in the Arctic, (2) continental air mass originating over central Asia, (3) tropical-maritime air mass originating in the northern Pacific, (4) equatorial-maritime air mass originating in the western equatorial Pacific, and (5) equatorial-maritime air mass originating in the Indian Ocean. The relative importance of different air masses in the course of a given year is modulated by the monsoon activity and the seasonal displacement of the Intertropical Convergence Zone (ITCZ). Gradual rain-out of moist, oceanic air masses moving inland, associated with monsoon circulation, constitutes a powerful mechanism capable of producing large isotopic depletions in rainfall, often completely overshadowing the dependence of 6180 and 62H on temperature. For instance, precipitation at Lhasa station (Tibetan Plateau) during rainy period (June-September) is depleted in •80 by more than 6 ø/oo with respect to winter rainfall, despite of 10øC higher surface air temperature in summer. This characteristic isotopic imprint of monsoon activity is seen over large areas of the region. The oceanic air masses forming the two monsoon systems, Pacific and Indian monsoon, differ in their isotope signatures, as demonstrated by the average 6180 of rainfall, which in the south of China (Haikou, Hong Kong) is about 2.5%0 more negative than in the Bay of Bengal (Yangoon). Strong seasonal variations of the deuterium excess values in precipitation observed in some areas of the studied region result from a complete reversal of atmospheric circulation over these areas and changing source of atmospheric moisture. High d-excess values observed at Tokyo and Pohang during winter (15-25%0) result from interaction of dry air masses from the northern Asian continent passing the Sea of Japan and the China Sea and picking up moisture under reduced relative humidity. The isotopic composition of precipitation also provides information about the maximum extent of the ITCZ on the continent during summer. deposits, tree cellulose, and others [e.g., Johnsen et al. 1989;

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 (&lt; 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 global climate change. ...

En los últimos años, han sido numerosos los estudios en torno a la interacción entre los rayos cósmicos galácticos (RCGs) y el clima de la tierra con una gran variedad de resultados, algunos de ellos controversiales. Parece haberse dado un gran avance en el aspecto teórico de la posible interacción, siendo dos los principales mecanismos físicos candidatos: la nucleación mediada-por-el-ión (ion-mediated nucleation, IMN) y la electrocolección. En una y otra teoría, el papel fundamental de los RCGs es la ionización en la atmósfera. La teoría del IMN prescribe cambios en las propiedades de la microfísica de la nube (vida de la nube, albedo, espesor óptico, concentración de núcleos de condensación, entre otros) y consecuentes cambios en la cobertura nubosa global. La electrocolección añade a la anterior, modificaciones en la dinámica de la nube que, en mayor escala, produce modificaciones en la circulación atmosférica. Hay algunas evidencias observacionales de relación consistente con las teorías propuestas a lo largo del ciclo solar de 11 años entre RCGs y variables climáticas (cobertura nubosa global, circulación atmosférica, precipitación). No obstante, la complejidad del sistema deja entrever otros posibles mecanismos; por ejemplo, la interacción estratosfera-troposfera por la relación UV-ozono. A su vez, la existencia de tendencias seculares en el flujo de RCGs, que se asociarían al calentamiento global, sugiere incorporar otra variable a evaluar en la problemática del cambio global.

Akstract--Emission, transport, chemistry and rainout of the sulfur species DMS, SO 2 and sulfate are calculated on-line with the meteorology in a global atmospheric circulation model. The model simulates the main components of the hydrological cycle, including the liquid water content of clouds, and hence it allows an explicit treatment of cloud transformation processes and precipitation scavenging. The importance of the different oxidation pathways of DMS and SO2 is estimated. About 2/3 of the sulfate is produced within clouds, with H202 being the most efficient pathway (59%) and with a minor contribution due to oxidation with O3 (7%). Predicted atmospheric surface concentrations of SO2 and sulfate and the deposition fluxes are compared with the observations. Over most parts of the globe the agreement between simulated and observed annual averages is within a factor of 2. A significant underestimate of the simulated sulfate concentrations was found in high latitudes in winter. This bias may be attributed to a too slow oxidation in clouds. The calculated global mean turn-over times for DMS (2.2 d), SO2 (1.6 d) and sulfate (4.4 d) are within the range of previous estimates.

Late Quaternary paleoclimatic changes in the Levant are difficult to extract from carbonate oxygen isotope records partly because the factors controlling the terrestrial d 18 O signals are not fully understood in this region characterized by sharp climatic gradients. Here, we address this purpose by presenting the first 14 C-dated isotope record from the northern Levant. The record is based on oxygen isotopes from ostracod shells from lacustrine-palustrine deposits accumulated in a small karstic, hydrologically open basin (Yammoû neh), located on the eastern flank of Mount Lebanon. We have first constructed a composite isotopic record obtained from three different ostracod taxa. This yields an oxygen isotope record of ostracods (d ost) related to the most widespread species (Ilyocypris inermis), and converted to d 18 O values coeval with calcite precipitated in equilibrium (d C) with the lake water (d L). As with other records from the Mediterranean region, the Yammoû neh profile shows maximum and minimum d C values during the LGM and the early Holocene, respectively, and a slight late Holocene increase. In order to discuss the potential causes of the observed d 18 O values fluctuations (e.g., changes in the isotopic composition of the moisture source, temperature, precipitation minus evaporation (P-E) balance, or atmospheric circulation), we tentatively reconstruct the lake water isotope composition by correcting the d C values for lake water temperature using regional paleotemperature estimates. Inferred d L values were then corrected for the isotopic composition of the Eastern Mediterranean sea surface water (the moisture source) derived from planktonic foraminifera d 18 O values corrected for alkenone-based sea surface temperature. Our study suggests that Holocene d L fluctuations are primarily linked to changes in the sea surface water composition (source effect) amplified by enhanced inland rainfall during the early Holocene. During the LGM, low d L values at Yammoû neh are likely due to the ground-temperature effect on the rainfall isotope composition, possibly associated with a steeper altitudinal thermal gradient inland, and with changes in air mass trajectories over the Mediterranean Sea.

The Katowice Region is the most urbanised and industrialised region in Poland. Local meteorological and circulation conditions significantly influence the pollution level. The study has integrated measurement results of temperature and selected air pollution indices (PM10, SO 2 , NO, NO 2 , O 3 , CO) with the calendar of synoptic circulation types by Niedźwiedź. Because the highest values of temperature inversion in the near-ground air layer occur in the south-western (SWa) and southern (Sa) anticyclone circulation as well as in the anticyclone centre (Ca) and anticyclonic ridge (Ka), the allowable limits of atmospheric pollution concentrations are often exceeded in the Katowice Region.

The past decade has seen substantial advances in understanding Arctic amplificationthat trends and variability in surface air temperature tend to be larger in the Arctic region than for the Northern Hemisphere or globe as a whole. We provide a synthesis of research on Arctic amplification, starting with a historical context and then addressing recent insights into processes and key impacts, based on analysis of the instrumental record, modeling studies, and paleoclimate reconstructions. Arctic amplification is now recognized as an inherent characteristic of the global climate system, with multiple intertwined causes operating on a spectrum of spatial and temporal scales. These include, but are not limited to, changes in sea ice extent that impact heat fluxes between the ocean and the atmosphere, atmospheric and oceanic heat transports, cloud cover and water vapor that alter the longwave radiation flux to the surface, soot on snow and heightened black carbon aerosol concentrations. Strong warming over the Arctic Ocean during the past decade in autumn and winter, clearly associated with reduced sea ice extent, is but the most recent manifestation of the phenomenon. Indeed, periods of Arctic amplification are evident from analysis of both warm and cool periods over at least the past three million years. Arctic amplification being observed today is expected to become stronger in coming decades, invoking changes in atmospheric circulation, vegetation and the carbon cycle, with impacts both within and beyond the Arctic.

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.

We present a continuous record of the Asian monsoon over the last 16 ka from y 18 O measurements of stalagmite calcite. Over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230 Th dates. y 18 O and therefore Asian monsoon intensity generally follows changes in insolation, although changes in y 18 O are generally accommodated in abrupt shifts in contrast to smoothly varying insolation, indicating that threshold effects may be important. y 18 O decreased dramatically (~3x) at the start of the Holocene (~11.5 ka) and remained low for~6 ka. Four positive y 18 O events centered at 11225F97 yr BP (1.05x), 10880F117 yr BP (1.15x), 9165F75 yr BP (1.4x), and a double event centered at 8260F64 yr BP (1.1x) and 8080F74 yr BP (1.0x) punctuated this period of high monsoon intensity. All four events correlate within error with climate changes in Greenland ice cores. Thus, the relationship between the Asian monsoon and the North Atlantic observed during the glacial period appears to continue into the early Holocene. In addition, three of the four events correlate within error with outburst events from Lake Agassiz. The decline of monsoon intensity in the mid-late Holocene is characterized by an abrupt positive shift in y 18 O which occurs at 3550F59 yr BP (1.1x in~100 yr). In addition, the Holocene is punctuated by numerous centennial-and multi-decadal-scale events (amplitudes 0.5 to 1x) up to half the amplitude of the glacial interstadial events seen in the last glacial period. Thus, Holocene centennialand multi-decadal-scale monsoon variability is significant, although not as large as glacial millennial-scale variability. The monsoon shows a strong connection with northern South American hydrological changes related by changes in ITCZ position. Spectral analysis of the y 18 O record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing. However, there are numerous other significant peaks including peaks at El Niño frequencies (observed for high-resolution portions of the record between 8110 and 8250 yr) which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling Holocene monsoon Earth and Planetary Science Letters 233 www.elsevier.com/locate/epsl climate. In addition, for this high-resolution portion, we observe a distinctive biennial oscillation of the Asian monsoon, which has been associated with the Tropospheric Biennial Oscillation (TBO).

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 statistics of extremes have played an important role in engineering practice for water resources design and management. How recent developments in the statistical theory of extreme values can be applied to improve the rigor of hydrologic applications and to make such analyses more physically meaningful is the central theme of this paper. Such methodological developments primarily relate to maximum likelihood estimation in the presence of covariates, in combination with either the block maxima or peaks over threshold approaches. Topics that are treated include trends in hydrologic extremes, with the anticipated intensification of the hydrologic cycle as part of global climate change. In an attempt to link downscaling (i.e., relating large-scale atmosphereocean circulation to smaller-scale hydrologic variables) with the statistics of extremes, statistical downscaling of hydrologic extremes is considered. Future challenges are reviewed, such as the development of more rigorous statistical methodology for regional analysis of extremes, as well as the extension of Bayesian methods to more fully quantify uncertainty in extremal estimation. Examples include precipitation and streamflow extremes, as well as economic damage associated with such extreme events, with consideration of trends and dependence on patterns in atmosphere-ocean circulation (e.g., El Niñ no phenomenon).

In studies of the potential effects of global climate change on freshwater ecosystems, water temperature is a primary factor. Linear regressions of stream temperature versus air temperature are attractive for this purpose, because they require only one input variable (air temperature) which can be simulated by General Circulation Models (GCMs) better than other climate variables. Under a warmer climate scenario, high stream temperatures must be projected by extrapolation. The question arises whether linear extrapolation is valid.

From late 1995 through early 2001, three major interannual climate events occurred in the tropical Pacific; the 1995-97 La Nina (LN), 1997-98 El Nino (EN), and 1998-2001 LN. We analyze atmospheric and upper oceanic anomalies in the northeast Pacific (NEP) during these events, and compare them to anomalies elsewhere in the north Pacific and tropical Pacific, and to typical EN and LN anomaly patterns. Atmospheric and oceanic anomalies varied strongly on intraseasonal and interannual scales. During the 1995-97 LN and 1997-98 EN, the NEP was dominated by negative SLP and cyclonic wind anomalies, and by upper ocean temperature and sea surface height (SSH) anomalies that were positive along the North American west coast and in the NEP thermal anomaly pool (between Hawaii, Vancouver Island, and Baja California), and negative in the central north Pacific. This atmospheric/oceanic anomaly pattern is typical of EN. An eastward shift in the atmospheric teleconnection from east Asia created EN-like anomalies in the NEP during the 1995-97 LN, well before the 1997-98 EN had begun. The persistence of negative SLP and cyclonic wind anomalies in the NEP during the 1997-98 EN intensified pre-existing upper oceanic anomalies. Atmospheric anomalies shifted eastward during late 1996-early 1998, leading to a similar onshore shift of oceanic anomalies. This produced exceptionally strong positive upper ocean temperature and SSH anomalies along the west coast during the 1997-98 EN, and explains the unusual coastal occurrence of several large pelagic warm-water fish. The growth and eastward shift of these pre-existing anomalies does not appear to have been linked to tropical Pacific EN anomalies until late 1997, when a clear atmospheric teleconnection between the two regions developed. Prior to this, remote atmospheric impacts on the NEP were primarily from east Asia. As the 1998-2001 LN developed, NEP anomalies began reversing toward the typical LN pattern. This led to predominantly negative SLP and cyclonic wind anomalies in the NEP, and upper ocean temperature and SSH anomalies that were mainly negative along the west coast and positive in the central north Pacific. The persistence of these anomalies into mid-2001, and a number of concurrent biological changes in the NEP, suggest that a decadal climate shift may have occurred in late 1998.

... 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. ...

There is a strong chance that 20th century warming will cause differences in precipitation distribution, hydrological cycle and effective moisture changes over the globe. Arid central Asia (ACA), a unique dryland area whose atmospheric circulation is dominated today by the westerlies, is one of the specific regions that are likely to be strongly impacted by global warming. An understanding of past variations in effective moisture in such regions is an important prerequisite for the prediction of future hydrological change. Here we evaluate spatial and temporal patterns of effective moisture variations documented by different proxies from 17 records in ACA, and synthesize a decadal-resolution moisture curve for ACA over the past millennium, using 5 of the 17 records selected on the basis of reliable chronologies and robust proxies. The high-and low-resolution data all show that, over the past millennium, ACA has been characterized by a relatively dry Medieval Warm Period (MWP; the period from w1000 to 1350 AD), a wet Little Ice Age (LIA; from w1500 to 1850 AD) and increasing moisture during recent decades. As a whole, the LIA in the ACA was not only relatively humid but also had high precipitation. Over the past millennium, the multi-centennial moisture changes in ACA show a generally inverse relationship with the temperature changes in the Northern Hemisphere, China, and western central Asia. The effective moisture history in ACA also shows an out-of-phase relationship with that in monsoon Asia (especially during the LIA). We propose that the humid LIA in ACA, possibly extending to Mediterranean Sea and Western Europe, may have resulted from increased precipitation due to more frequent mid-latitude cyclone activities as a result of the strengthening and equator-ward shift of the westerly jet stream, and the predominantly negative North Atlantic Oscillation conditions, coupled with a decrease in evapotranspiration caused by the cooling at that time.

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.

The modern pole-to-equator sea-level temperature difference is about 50°C; that of the mid-Cretaceous ranged from 30°C to as little as 24°C, implying a much more equable climate. This may have been caused by 1) reduction of the ice-forced albedo of the polar regions, 2) more efficient meridional energy transport by the atmosphere and ocean, and 3) increased atmospheric greenhouse gas concentrations. Earth's icy polar regions stabilize its present 'inequable' climate through the ice-albedo feedback effect. The polar ice results in permanent atmospheric highs that stabilize Earth's wind systems. In turn the stable winds drive the ocean currents and determine the location of the frontal systems that separate the low-and high-latitude oceanic gyre systems and bound the region where water sinks into the ocean interior as thermocline and intermediate water masses. Increased ocean heat transport can assist in making a more equable climate, but unrealistic volume transports would be required to warm the polar regions to Cretaceous levels. The major factor forcing the equable climate of the Cretaceous is now thought to be increased greenhouse gas concentrations, dominated by CO 2 . The modern rate of change in atmospheric concentration is greater than 200 ppmv per century and increasing. This compares with 1 ppmv per century during the last deglaciation. At current rates of fossil fuel burning, atmospheric CO 2 levels will reach Cretaceous levels of 2 times the pre-industrial level about 2070 and 8 times the pre-industrial level shortly after 2300. It is likely that Cretaceous atmospheric CO 2 concentrations will last for many thousands to tens of thousands of years. In addition to increased atmospheric greenhouse gas concentrations, a return to climatic conditions resembling those of the Cretaceous would require ice-free poles and large changes in atmospheric and oceanic circulation. Arctic sea-ice is melting much more rapidly than had been expected, and the Arctic Ocean will soon be free of sea-ice in summer. The Greenland ice sheet is melting more rapidly than expected because of greenhouse warming. Surface meltwater forms lakes, and then flows down through crevasses and holes in the ice to lubricate the base, allowing ice steams to flow much more rapidly. The lifetime of the Greenland ice sheet may be only a few hundred years. The West Antarctic ice sheet is inherently unstable, being grounded on rock well below sea level. The ice shelves blocking ice streams off West Antarctica have begun to melt from beneath and break up as the southern ocean warms. The East Antarctic ice sheet has been regarded as highly stable but discovery of lakes beneath the ice and fast-flowing ice streams raises questions about whether the ice sheet will ultimately succumb to global warming and disintegrate. I conclude that a return to climatic conditions resembling those of the mid-Cretaceous is not only possible but also likely unless humanity can organize an effective campaign to stop CO 2 emissions to the atmosphere and remove some of the excess CO 2 already introduced.

The kinematics and dynamics of tropical cyclone (TC) tracks are studied by using a mathematical model of track curvature. The results indicate that the curvature of storm track is determined by a set of 'controlling parameters' related to the storm characteristics and the ambient atmospheric circulation. These controlling parameters include the speed of storm motion, storm intensity and size, the Coriolis parameter, ambient atmospheric pressure field, and surface friction. In northern hemisphere, a northward moving TC tends to gain anti-cyclonic curvature and deflect to the right. A westward or northwestward moving TC will also deflect to the right when it slows down. A westwardmoving TC along the southern edge of the sub-tropical high tends to deflect to the right as it moves toward the "turning point" of the large scale flow field (i.e. the southwest corner of the subtropical high). An eastward-moving TC along the northern edge of the sub-tropical high tends to deflect leftward toward the low-pressure side of the steering flow. A TC located in front of a westerly trough will gain cyclonic curvature. Thus, a re-curving TC after passing its western most location will tend to deflect to the low-pressure side. Finally, TC intensity and size change can also affect the TC movement. For example, a westward moving, deepening or enlarging TC tends to move anti-cyclonically. ᭧