Westerly Air Stream Research Articles

Paleomagnetic constraints on neotectonic deformation within the Southern Tian Shan piedmont and implications for the latest Miocene enhanced aridification in the Tarim Basin

The India-Eurasia collision reactivated the Tian Shan belt of Central Asia and led to crustal shortening which has been accommodated by fold-and-thrust belts on both flanks of the orogen. Southward propagation into the Tarim Basin has been accommodated by the Kuqa fold-and-thrust belts which record a range of well-preserved syntectonic continental sequences. Using existing magnetostratigraphic age constraints, we have conducted an in-depth paleomagnetic and rock magnetic investigation of this fold-and-thrust belt with the aim of linking the neotectonic deformation to the uplift of the Tian Shan orogen to the north. Anisotropy of magnetic susceptibility (AMS) shows “pencil structure” fabrics between levels dated 31.0 and 5.5 Ma. These are succeeded by incipient deformation fabrics at ~5.3 Ma, which dates an abrupt decrease in shortening by synsedimentary strain. This change coincides with the timing of initial syntectonic growth strata in the foreland basin of the Southern Tian Shan and contemporaneous vertical-axis rotations in the Yaha section. Collectively this evidence implies that the Southern Tian Shan piedmont underwent transpressional deformation with rotation accompanying strain partitioning during a regional sinistral shear. The extreme aridification which has occurred in the Tarim Basin since the latest Miocene is interpreted in terms of the deflection of the ambient westerly airstream away from this region due to the growth of the Tian Shan and its final collision with the Pamir.

Unraveling source-to-sink dust transport in Central and East Asia by identifying provenances of aeolian sediments

Loess deposits as a unique terrestrial archive of paleo-dust contribute to understanding the wide-scale and long-term dust transport from source to sink. This study provided diagnostic constraints on the sources of clay-sized particles in the Chinese Loess Plateau (CLP) loess by expanding the potential dust source areas with the Kyzylkum Desert and the Central Asian loess. Based on the grain sizes and the particle-size-specific trace elements, we characterized the major provenance and the sedimentary process of the Kyzylkum Desert sands. The results indicate the main derivation of Kyzylkum Desert sands from the Tian Shan-derived sediments, with limited large-scale mixing. The desert was thought to be a sink region, instead of an important dust source, which was supported by its weak genetic links to the Central Asian loess. With integration of the published data set about trace element and SrNd isotopic composition and our results, combined with the simulation results, we revealed that the Badain Jaran and Tengger deserts in northwestern CLP, rather than the Taklimakan and Kyzylkum deserts further west, played an important role in supply of the clay-sized particles for the CLP loess. The findings implied that the fine particles were primarily related to the East Asian winter monsoon, instead of the high-level westerly airstreams. In this context, we attributed the asynchronous timing of enhanced dust accumulation during the last glacial maximum (LGM) over Greenland and North Pacific (early LGM) and on the CLP (late LGM) to the differences in the major dust sources and in the atmospheric circulation systems.

Importance of decadal scale variability in shoreline response: examples from soft rock cliffs, East Anglian coast, UK

Rapidly eroding soft rock cliffs typically retreat at rates in excess of several metres per year, thus allowing the resolution of linkages between cliff dynamics and a range of climatic and marine forcing factors. New evidence from UK coastline of East Anglian coastline, southern North Sea shows that unprotected soft rock cliffs at three widely-spaced locations all show similar variability in retreat behaviour on decadal timescales, which we attribute to changing patterns of storminess in these decades. The 1990s were characterized by frequent months in which the North Atlantic Oscillation (NAO; a well-established measure of inter-annual climatic variability in North-West Europe) was extremely positive (more positive than +3) or extremely negative (more negative than −3), while the 2000s showed few occurrences of such extreme values. Depression tracks in positive NAO phases make the East Anglian coast prone to storm surges in which raised water levels result from deeply developed low pressure systems, generally associated with westerly air streams. In negative NAO phases the region is prone to easterly airflow which results in periods of strong onshore wind. Both phases are associated with high energetics in the forcing factors. Decadal-scale variability in cliffline retreat rates has implications for the practice of coastal management and policy making and suggests that cliff system responses to global environmental change are not simply driven by secular sea level rise.

The influence of several changes in atmospheric states over semi-arid areas on the incidence of mental health disorders

The incidence of suicide attempts [Deliberate Self Harm (DSH); ICD-10: X60-X84] and psychotic attacks (PsA; ICD-10, F20-F29) in association with atmospheric states, typical for areas close to big deserts, was analyzed. A retrospective study is based on the 4,325 cases of DSH and PsA registered in the Mental Health Center (MHC) of Ben-Gurion University (Be'er-Sheva, Israel) during 2001-2003. Pearson and Spearman test correlations were used; the statistical significance was tested at p < 0.1. The influence of temperature and humidity on suicide attempts (N(SU)) and psychotic attacks (N(PS)) was weakly pronounced (p > 0.1). Correlation coefficients between N(SU) and N(PS) and speed WS of westerly wind reaches 0.3 (p < 0.05), while their dependence on easterly WS was weaker (p > 0.09). Variations in easterly wind direction WD influence N(SU) and N(PS) values (p < 0.04), but no corresponding correlation with westerly winds was found (p > 0.3). Obviously ,in transition areas located between different regions ,the main role of air streams in meteorological-biological impact can scarcely be exaggerated. An unstable balance in the internal state of a weather-sensitive person is disturbed when the atmospheric state is changed by specific desert winds, which can provoke significant perturbations in meteorological parameters. Results indicate the importance of wind direction, defining mainly the atmospheric situation in semi-arid areas: changes in direction of the easterly wind influence N(SU) and N(PS), while changes in WS are important for mental health under westerly air streams. Obviously, N(SU) and N(PS) are more affected by the disturbance of weather from its normal state, for a given season, to which the local population is accustomed, than by absolute values of meteorological parameters.

A preliminary investigation of basin water response to climate forcing in a Scottish fjord: evaluating the influence of the NAO

The sea lochs (fjords) of NW Scotland bridge the land–ocean interface in a region of Europe which is particularly well situated to monitor changes in westerly air streams. Inter-annual atmospheric circulation changes at this latitude are largely governed by the North Atlantic Oscillation (NAO). Comparing two recent extreme NAO years, a two-dimensional model of Loch Sunart, NW Scotland, is used to examine the potential effects of climate oscillations on the magnitude and frequency of deep-water renewal events and the resulting water properties in the fjord basins. In the upper basin of the fjord, meteorological forcing during the high NAO index year (1988–89) resulted in less-frequent deep-water renewal, greater variability in basin salinity and a lower annual-mean salinity (by 0.52) than that predicted for the low NAO index year (1995–96). In the main basin, variations in meteorological forcing had much less effect on basin water properties. In both basins, predicted deep water inflow was significantly greater during the negative phase NAO, with annual inflow to the upper and main basins being respectively 50% and 300% greater during 1995–96 relative to 1988–99. Through a sensitivity analysis, the NAO is shown to affect upper basin water properties through the influence of low-frequency anomalies in the meteorological forcing, particularly the enhanced westerly wind stress associated with positive phases, which inhibits deep water renewal over the winter months. The salinity of the main and upper basins respond differently to the boundary forcing due to differential tidal mixing above the respectively sub- and super-critical entrance sills. Predictions of basin water isotope ratios are made by applying the salinity: δ 18O water mixing line for the region to the salinity results; the combination of the weak dependence of δ 18O water on salinity and the stable salinity predicted for the main basin suggests that some fjord basins may provide ideal sites for palaeotemperature studies.

The composition of aerosol particles in the middle troposphere over the western Pacific Ocean: aircraft observations from Australia to Japan, January 1994

Abstract Individual aerosol particles were collected in the middle troposphere, at 5–6 km altitude, over the western Pacific Ocean in the Pacific Atmospheric Chemistry Experiment campaign, between 38°S and 38°N, in January 1994. Particles were collected on electron microscope grids, over approximately 1.5° latitude bands using a 1-mm diameter jet impactor and were examined with an energy-dispersive X-ray (EDX) analyzer and transmission electron microscope. Based on the EDX analysis and morphological identification, particles were classified into various types, including sea salt, mineral, sulfate, and sulfuric acid. For the radius range of 0.1–1 μm, sulfuric acid and ammonium sulfate were found across most of the observed regions and are considered important background aerosols. As well, sea salt particles were abundant over the tropical regions (present at up to 67%), in association with vertical transport by convective clouds. North of 20°N, mineral particles were dominant, suggesting transport of Asian dust–storm particles from China in the westerly air stream. Evidence for the modification of mineral particles, prior to their collection in the free troposphere, is also presented and discussed.

Bimodal grain-size distribution of Chinese loess, and its palaeoclimatic implications

Grain-size analysis indicates that Chinese loess generally shows a bimodal distribution with a coarse and a fine component. The coarse component, comprising the main part of the loess, has pronounced kurtosis and is well sorted, which is interpreted to be the product of dust storms generated by low-altitude northwesterly winds. Its grain-size reflects the strength of the low-altitude circulation in the dust seasons of the year, and its percentage provides an indicator of the source area aridity and the frequency of dust storms. Conversely, the fine component has a wide grain-size range and is poorly sorted. Sedimentary illustrations based on the grain-size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high-altitude westerly airstreams. Its grain-size provides an estimate of the westerly air stream intensity. The coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain-size data, and this procedure constitutes an approach for reconstructing the palaeowind system of Northern China.

Deep-water renewal in a Scottish fjord: temperature, salinity and oxygen isotopes

The sea lochs (fjords) of north-west Scotland are located in a region of Europe particularly well situated to monitor changes in westerly air streams. The moisture transported in these air streams has a profound effect on regional precipitation, freshwater run-off and, in turn, sea loch circulation. The gentle slope of the regional salinity:?18O mixing-line, defined as 0.18 ‰ per salinity unit, suggests that the temperature: ?18O relationship may be readily resolved in these coastal waters. Deep-water renewal events, both observed and predicted from empirical models, in the bottom-waters of Loch Etive provide an opportunity to assess the temperature, salinity and ?18O relationship. Predicted changes in ?18Ocalcite as a function of changing salinity (?S) and changing temperature (?T) during deep-water renewal events suggest that >80% fall above analytical detection limits. The theoretical likelihood of recording such renewal events in the “palaeoclimate” record appears to be promising, but temperature and salinity change during renewal events may have either sign. Scottish fjords, because of the relatively small impact which salinity has on ?18Owater, may provide useful study sites in palaeoclimate research, particularly where palaeotemperature is the primary record of interest.

Transport of SO 2 and aerosol over the Yellow sea

Aircraft measurements of air pollutants were made to investigate the characteristic features of long-range transport of sulfur compounds over the Yellow Sea for the periods of 26–27 April and 7–10 November in 1998, and 9–11 April and 19 June in 1999, together with aerosol measurements at the Taean background station in Korea. The overall mean concentrations of SO 2, O 3 and aerosol number in the boundary layer for the observation period ranged 0.1–7.4 ppb 32.1–64.1 ppb and 1.0–143.6 cm −3, respectively. It was found that the air mass over the Yellow Sea had a character of both the polluted continental air and clean background air, and the sulfur transport was mainly confined in the atmospheric boundary layer. The median of SO 2 concentration within the boundary layer was about 0.1–2.2 ppb. However, on 8 November, 1998, the mean concentrations of SO 2 and aerosol number increased up to 7.4 ppb and 109.5 cm −3, respectively, in the boundary layer, whereas O 3 concentration decreased remarkably. This enhanced SO 2 concentration occurred in low level westerly air stream from China to Korea. Aerosol analyses at the downstream site of Taean in Korea showed 2–3 times higher sulfate concentration than that of other sampling days, indicating a significant amount of SO 2 conversion to non sea-salt sulfate during the long-range transport.

A field study of orographic precipitation anomalies during high velocity winds using an aerofoil rain gauge

This study was prompted by a need to explain an anomaly in the apparent precipitation distribution over a prominent mountain subject to a high velocity westerly airstream. Historical data reveal that the lee receives 58% more precipitation than the summit. A novel rain gauge with a vertically orientated collecting orifice, 3 standard rain gauges and complementary wind data were procured from 3 sites on the mountain to assess the effect of the airstream on the precipitation distribution. The catch efficiency of standard rain gauges decrease after the wind velocity exceeds 2.5 ms−1 Results indicate that the summit actually receives 59% more precipitation than the lee, where a vortex directly affects the precipitation distribution over, and east, of the mountain.

The geological setting of ventifacts and wind‐sculpted rocks at Mason Bay, Stewart Island, and their implications for late Quaternary paleoclimates

Abstract A complex sequence of late Quaternary beach and dune sands overlies a locally emergent basement of granite at Mason Bay, Stewart Island. Granite outcrops are commonly decorated with striations and grooves formed by abrasion of wind‐blown sand. Ventifacts are widespread and appear to be derived from breccia layers interbedded with and capping the beach sand complex. Palynology and radiocarbon dating of a peat horizon overlying the upper ventifact‐bearing breccia indicate that conditions before 10 000 yr B.P. saw the slow drying out of swamps and encroachment of the forests in response to improving climate until, at Mason Bay, they were overwhelmed by dunefield migration in response to the onset of a strong westerly airstream. This, the most recent aeolian event, also caused sandblasting and resulted in striated outcrops of basement granite. These decorated outcrops also record some local easterly windflow, possibly due to eddying or turbulence. The buried ventifacts suggest that two earlier periods of strong windflow also occurred: one following deposition of the upper beach sand before the deposition of the peat, and the other during the ?periglacial interval between the deposition of the upper and lower sands. The ventifact‐forming episodes on Stewart Island probably correspond to periods of sand and loess deposition in southern South Island, the sand being derived from the exposed coastal plain during periods of lowered sea level.

Trough-Merger Characteristics over North America

Split flow, defined by the presence or two separate westerly airstreams in the mid- and upper troposphere, is common in middle latitudes. Occasionally, individual troughs in the separate branches of the westerlies will merge into one trough with a single vorticity maximum. Illustrative examples are used to demonstrate the significance of the trough merger process to the cyclogenesis process. The results of a subjective climatological study revealed the existence of 21 merger events across North America based upon the amalgamation of separate 500-mb vorticity centers. Eighteen of these occurred during the 1978–85 sampling period and three were added from other years. The trough merger cases were found to occur only in central and eastern North America east of 100°W and north of 35°N. Trough merger locations varied seasonally with the position of the principal tropospheric baroclinic zone. A composite of 17 trough-merger events demonstrated that the orientation of the 500-mb trough axis changed from northern-southwest to northwest-southeast (negative tilt) while the trough amplitude nearly doubled in the 24 hours preceding trough merger. Explosive cyclogenesis occurred in 14 out of 21 events in response to the development of the negatively tilted 500-mb trough associated with the merger process. The trough merger process was not well simulated by the then operational limited fine mesh (LFM) prediction model with 12 (2) of the 21 events correctly predicted 24 h (48 h) in advance. Finally, the physical implications of the climatological findings are discussed.

The Loch Lomond Readvance on the Isle of Skye, Scotland: Glacier reconstruction and palaeoclimatic implications

AbstractGeomorphological mapping of southern Skye indicates evidence for a single readvance of locally‐nourished glaciers. These comprised a major icefield that occupied c. 155 km2of the main mountain area, a small icefield c. 10 km2in extent in the Kyleakin hills and ten corrie glaciers with a total area of c. 16 km2. The absence of Lateglacial pollen sites, shorelines and periglacial features within the limits of local glaciation implies a Loch Lomond Readvance age for this glacial event. The area‐weighted mean equilibrium line altitude (ELA) of the reconstructed Loch Lomond Readvance glaciers (319 m) conforms with a regional eastwards rise in ELAs that indicates dominant westerly airstreams during the Loch Lomond Stadial. An easterly decline in ELAs across the former icefields is interpreted in terms of easterly transfer of snow across ice‐sheds by westerly winds, though the altitudes of corrie glacier ELAs suggest that the dominant snow‐bearing winds were southerlies. Calculations based on the area‐weighted mean ELA for the major icefield (308 m) indicate a stadial mean July sea‐level temperature of c. 6 °C. The anomalously low gradients of certain former icefield outlet glaciers are attributed to deformation of subglacial sediment, an effect that may vitiate the assumption of linear ablation/accumulation gradients in the calculation of former ELAs for reconstructed glaciers.

A case study of a severe winter storm in the Middle East

A detailed synoptic and mesoscale analysis is conducted of an intense convective outbreak which struck much of Israel, Jordan, Lebanon and Syria in early March 1980. Severe winter weather caused considerable personal hardship and economic disruption over a wide area. The planetary-scale circulation featured a confluent flow pattern across North Africa and southern Europe downstream of a block just west of the Greenwich meridian. A strong subtropical jet stream was maintained across North Africa in the confluent flow regime. Synoptic-scale disturbances from the Atlantic were diverted northward across Scandinavia from where they plunged south-eastward toward the Mediterranean to the west of the Black Sea. A series of three disturbances, the last being the most powerful, swept through the eastern Mediterranean as the vortex settled south-eastward toward the Middle East. Our analysis of the available evidence has established that three physical mechanisms contributed primarily to the extreme nature of the event. First, the steady south-eastward movement of mobile short wave troughs resulted in the progressive cooling of the lower and middle troposphere over the eastern Mediterranean Sea and the Middle East. Second, sea surface heat and moisture fluxes contributed to destabilization and the generation of extreme instability where the cold air from higher latitudes had a long overwater fetch. Third, exceptionally heavy precipitation fell where a strong low-level moist, unstable westerly air stream impinged on the coastal mountains. The strong westerly flow was generated to the south of an intense subsynoptic-scale vortex that formed in the lower and mid troposphere as the updraught region of a powerful short-wave-trough/ jet-streak system aloft ingested air that had been destabilized below.

A case study of a severe winter storm in the Middle East

AbstractA detailed synoptic and mesoscale analysis is conducted of an intense convective outbreak which struck much of Israel, Jordan, Lebanon and Syria in early March 1980. Severe winter weather caused considerable personal hardship and economic disruption over a wide area.The planetary‐scale circulation featured a confluent flow pattern across North Africa and southern Europe downstream of a block just west of the Greenwich meridian. A strong subtropical jet stream was maintained across North Africa in the confluent flow regime. Synoptic‐scale disturbances from the Atlantic were diverted northward across Scandinavia from where they plunged south‐eastward toward the Mediterranean to the west of the Black Sea. A series of three disturbances, the last being the most powerful, swept through the eastern Mediterranean as the vortex settled south‐eastward toward the Middle East.Our analysis of the available evidence has established that three physical mechanisms contributed primarily to the extreme nature of the event. First, the steady south‐eastward movement of mobile short wave troughs resulted in the progressive cooling of the lower and middle troposphere over the eastern Mediterranean Sea and the Middle East. Second, sea surface heat and moisture fluxes contributed to destabilization and the generation of extreme instability where the cold air from higher latitudes had a long overwater fetch. Third, exceptionally heavy precipitation fell where a strong low‐level moist, unstable westerly air stream impinged on the coastal mountains. The strong westerly flow was generated to the south of an intense subsynoptic‐scale vortex that formed in the lower and mid troposphere as the updraught region of a powerful short‐wave‐trough/ jet‐streak system aloft ingested air that had been destabilized below.

Enrichment of sulphate in maritime aerosols

Radioactive tracers were used to show that the ratio of sulphate to sodium in spray exceeds that in sea water by 10 to 30%. A much greater enrichment occurred for iron. The enrichment of sulphate is sufficient to account for some observations of excess sulphate in rain in clean air in mid ocean, but does not explain the larger excess observed in westerly air streams over Scandinavia.