Movement Of Air Masses Research Articles

Classification of aerosol radiative properties during African desert dust intrusions over southeastern Spain by sector origins and cluster analysis

The main goal of this study is to analyze the dependence of columnar aerosol optical and microphysical properties on source region and transport pathways during desert dust intrusions over Granada (Spain) from January 2005 to December 2010. Columnar aerosol properties have been derived from a non‐spherical inversion code using the solar extinction measurements and sky radiances in the principal plane. Two classification methods of the African air masses ending at the study location were used by means of the HYSPLIT back‐trajectories analysis. The first one, based on desert dust origin sources, discriminated the optical properties only for sector B (corresponding to western Sahara, northwest Mauritania and southwest Algeria). The particles present marked absorbing properties (low value of single scattering albedo at all wavelengths) during the desert dust events when the air masses were transported from sector A (north Morocco, northwest Algeria). This result may be related to the mixing of desert dust with anthropogenic pollutants from North African industrial areas in addition to the mixing with local anthropogenic aerosol and pollutants transported from European and Mediterranean areas. The second classification method was based on a statistics technique called cluster classification which allows grouping the air masses back trajectories with similar speed and direction of the trajectory. This method showed slight differences in the optical properties between the several transport pathways of air masses. High values of the aerosol optical depth and low mean values of the Angström parameter were associated with longer transport pathways over desert dust sources and slowly moving air masses. Both classification methods showed that the fine mode was mixed with coarse mode, being the fine mode fraction smaller than 55%.

Kiloyear-scale climate events and evolution during the Last Interglacial, Mu Us Desert, China

The fifth segment of the Milanggouwan stratigraphical section (MGS 5) in the Mu Us Desert provides high-resolution geological information on environmental variations during the Last Interglacial. The analysis of grain content (<50μm), organic content, SiO2, Al2O3, TOFe, and SiO2–(Al2O3+TOFe) ratios in the MGS 5 suggest that there were 17 kiloyear-scale climate fluctuations in the Last Interglacial, including 9 warm events (W1–W9) and 8 cold events (C1–C8), dominated by the East Asian summer monsoon and winter monsoon respectively. The analysis also suggests that the Eemian interglacial was unstable, with 3 warm events (W7–W9) and 2 cold events (C7–C8), indicating that climate fluctuations affected the East Asian monsoon in the Mu Us Desert during the Last Interglacial. The change cycles and the nature of the kiloyear-scale climate events have a close temporal relationship with the Greenland ice-core oxygen isotope data, suggesting that the climate forming mechanism was affected by polar weather, North Atlantic sea ice, range of the Eurasian ice front, and movement of the Arctic frontal, all of which affect the intensity of the Siberian–Mongolian high pressure region through the movement of the cold air mass.

Method for determining atmospheric motion characteristics using measurements on geostationary meteorological satellites

The method for determining the dynamic characteristics of the atmosphere using the data of sounding from geostationary meteorological satellites developed by the authors and based on using inhomogeneities of the conservative admixture concentration field as tracers and on applying the correlation extreme algorithms is described in detail. The accuracies in calculating the horizontal wind velocity vector (V) and coefficient of horizontal mesoscale turbulent diffusion (Kd) are estimated on the basis of processing the data of sounding the atmosphere with a SEVIRI (Spinning Enhanced Visible and Infrared Imager) radiometer on the Meteosat-8 and Meteosat-9 European geostationary meteorological satellites in the water vapor channels centered at 6.2 and 7.3 μm and on comparing the results with the data of independent observations and theoretical models. It is indicated that the accuracy in calculating V using the developed method almost coincides with the accuracy of the commonly used foreign methods. In contrast to the methods applied abroad, the developed method makes it possible to determine not only the wind velocity vector field but also the coefficient of mesoscale turbulent diffusion and vorticity on one scale of air mass motion.

PALEOGENE EVOLUTION OF PRECIPITATION IN NORTHEASTERN CHINA SUPPORTING THE MIDDLE EOCENE INTENSIFICATION OF THE EAST ASIAN MONSOON

The timing of the development of the East Asian monsoon in the geologic past is critically important for paleoclimatological studies, yet few quantitative data are available. Based on palynomorphs from six formations, supplemented by leaf fossils from one of these formations in Fushun, northeastern China, we present a quantitative estimate of the evolution of precipitation in this area during the middle Paleocene–late Eocene. The results demonstrate that seasonal precipitation prevailed during the interval, suggesting that the monsoonal system had already developed by this time. Comparing Paleogene climatic results from different latitudes in eastern China, we conclude that the East Asian monsoon must have been significantly enhanced after the late middle Eocene ( ,41–40 Ma), due to increased precipitation differentiation between wet and dry months as shown in the present study. The influence of both the uplift of the Da Hinggan Mountains in northeastern Asia on regional topography and the India-Asia collision globally may have contributed to early monsoon intensification by their influence on air mass movement and associated precipitation patterns in the monsoonal realm.

LOCAL AND REGIONAL SOURCES OF UFP IN URBAN STREETS

Background and Aims: Ultrafine particle (UFP) numbers show large short-term and small scale variation, making strategies to assess personal exposure to UFP in urban environment potentially very costly. Better insight in the role of local and regional processes, can give rise to methods to estimate UFP using correlated pollutants and regional indicators (Can et al 2011). Methods: UFP and NOx were measured simultaneously in Antwerp (Belgium) at three locations in a single street in Summer 2009, and in four different streets in a 1 km grid in Winter 2010. Different size fractions were compared to traffic counts and meteorological data. Regional contributions to various size fractions were assessed using night time number concentrations and air mass back-trajectory techniques. Results: In-street spatial variability of total particle number was rather low. UFP concentrations in four different streets showed a remarkably similar temporal trend on top of which the local component is added. Total particle number correlated poorly with traffic intensity. Mainly the 20 – 50 nm fractions are correlated with traffic intensity. The morning traffic peak leads to a distinct peak in total particle number, but this is not the case for the afternoon rush hour. Analysis of diurnal UFP concentrations for different size bins shows that both processes of agglomeration and condensation and meteorological conditions explain this decoupling of traffic and total particle number. Elevated total night-time UFP was mainly related to larger size fractions (50 - 100 nm). Higher concentrations of the larger size bins were associated with slow moving air masses. Conclusions: Although short-term variation in UFP number counts at urban traffic locations largely depends on local sources, similar temporal trends result both from regional processes and similar underlying traffic patterns. This study illustrates the potential to extrapolate measured UFP concentrations to similar locations using correlated pollutants and regional indicators.

Lidar observations of volcanic aerosol content in the atmosphere over Tomsk

Lidar observations carried out in Tomsk in August 2008 enabled to register the peaks of the back scattering ratio at the altitudes of 8–16 and 18–22 km. The computation of air masses movement trajectories demonstrated that the peaks at the altitudes of 8–16 km correspond to the aerosol layers formed as a result of volcanic eruptions on the Aleutian Islands in July–August 2008. The original software package along with the daily wind speed BADC data and HYSPLIT software with the six-hour GDAS data were used for computations. The periods from the time of eruptions to the time of observations amounted to one or two weeks and more. The verification of results of these computations for these long periods was made on the basis of the satellite data on the sulfur dioxide distribution in the atmosphere after the eruption of the Kasatochi volcano. The computation method applied enabled to simulate the main distribution characteristics of sulfur dioxide pollution areas in the atmosphere within one or two weeks after the eruption.

The 2010 Antarctic ozone hole: Observed reduction in ozone destruction by minor sudden stratospheric warmings

Satellite observations show that the 2010 Antarctic ozone hole is characterized by anomalously small amounts of photochemical ozone destruction (40-60% less than the 2005-2009 average). Observations from the MLS instrument show that this is mainly related to reduced photochemical ozone destruction between 20-25 km altitude. Lower down between 15-20 km the atmospheric chemical composition and photochemical ozone destruction is unaffected. The modified chemical composition and chemistry between 20-25 km altitude in 2010 is related to the occurrence of a mid-winter minor Antarctic Sudden Stratospheric Warming (SSW). The measurements indicate that the changes in chemical composition are related to downward motion of air masses rather than horizontal mixing, and affect stratospheric chemistry for several months. Since 1979, years with similar anomalously small amounts of ozone destruction are all characterized by either minor or major SSWs, illustrating that their presence has been a necessary pre-condition for reduced Antarctic stratospheric ozone destruction.

A five-year observation of atmospheric metals on Ulleung Island in the East/Japan Sea: Temporal variability and source identification

We investigated seasonal characteristics (concentration, enrichment factors, and correlation coefficients) of chemical constituents, including sources for sea salt-corrected metals (Al, Fe, K, Ca, Mg, S, As, Cd, Co, Cu, Li, Mn, Mo, Ni, Pb, Sn, Sr, Ti, V, and Zn), in 334 aerosol samples collected during October 2003–October 2008 at Ulleung Island in the southern East/Japan Sea. High Al concentrations were found in spring (geometric means of 1.23 and 1.28 μg m−3 in March and April, respectively) due to Asian dust (yellow sand) originating from northeastern China. The dust mineral transport by strong winds resulted in a change of metal composition showing soil-dominated condition. In the rainy period (June–September), the aerosol metal concentrations and composition were influenced largely by wet deposition and the summer monsoon, together with anthropogenic aerosol transport. The correlation coefficients in the summer period (July and August) showed a positive correlation of Al with K (r = 0.74) and As (r = 0.63), probably reflecting anthropogenic-originated Al coming from coal burning. In autumn (October and November) and winter (December and January), mixed sources of soil and anthropogenic-originated aerosols were pronounced by the development of northwesterly winds from the Asian continent. Especially, the soil-originated proportion was relatively higher in autumn than in winter when the anthropogenic-originated aerosols from heating fuels predominated. Anthropogenic As, Sn, Mo, Zn, Pb, and Cd between low- and high-dust periods that had similar air–mass movements in spring were at similar concentrations, but higher in the air masses including eastern China trajectories and/or slow movement at lower height during high-dust periods.

Passive air sampling of organochlorine pesticides in a northeastern state of India, Manipur

Abstract Thirty-six polyurethane foam disk passive air samplers (PUF-PAS) were deployed over a year during January to December, 2009 at three locations, i.e., Imphal (urban site), Thoubal (rural site) and Waithou (alpine site) of Manipur, to assess the seasonal local atmospheric emission of selected organochlorine pesticides (OCPs). The average concentration of HCHs monitored at mountain site during hot season (Mar, Apr, and May) and rainy seasons (Jun, Jul, Aug, and Sep) were 403 and 349 pg/m 3, respectively. DDTs had a high concentration with 384 pg/m 3 at rural site and 379 pg/m 3 at urban site during hot seasons. Endosulfans and chlordane were found high in concentration during hot seasons (260 pg/m 3) and low during retreating monsoon seasons (44 pg/m 3) at rural site. Most of the OCPs concentrations were high during cultivation period. The OCP concentrations of rainy season were highly correlated (p < 0.01) with OCPs of hot seasons. Further, positive correlation ( p < 0.05) was also obtained between cold seasons and retreating monsoon. Principal component analysis showed a significant correlation among the four seasons and distribution pattern of OCPs in air. Back trajectory analysis by using HYPSLIT model showed a long range air transport of OCPs to the present study area. Present OCP levels at Manipur is an outcome of both local emission and also movement of air mass by long range atmospheric transport.

Determination of potential sources of Quercus airborne pollen in Córdoba city (southern Spain) using back-trajectory analysis

The northern area of Cordoba province (southern Spain) is characterised by a high spatial distribution of Quercus species. In Cordoba city, high airborne Quercus pollen counts are detected during spring despite the low presence of Quercus populations in the Guadalquivir Valley, where this city is located. This study sought to clarify and identify the potential origin of the different Quercus peaks detected in this city and chart the possible relationship between Quercus pollen curves and air-mass movements. For this purpose, an integrated study of daily and intra-diurnal Quercus pollen counts and back-trajectory analysis was performed over the March–June period of the years 2006–2008. The application of cluster techniques to back trajectory enabled the identification of six different types of air-mass movement. As a function of frequency, two different air-mass groups were identified: the main group comprised Local, Slower Northwest and Mediterranean movements, characterised by higher frequencies; a second group consisting of North, Faster Northwest and Southwest trajectories occurred less frequently over the study period. Although a significant correlation was observed between Quercus airborne pollen counts recorded in Cordoba city and the influence of the Mediterranean air-mass movements, the strongest positive correlation was found between North and Northwest air-mass movements and daily Quercus pollen counts. These results would confirm both that the major Quercus pollen sources are located at different distances north of the city and a new pollen source is also located south of the province, beyond the Guadalquivir valley, related to the arrival of Mediterranean air masses. The northern source appears to be linked to regional transport and the southern source to long-range transport.

Complex study of characteristics of a Cb cloud developing over the Arabian Peninsula under high dew point deficit in the atmosphere. Part 1. Field observations and numerical modeling

Basing on airmass motion trajectory calculations over the Arabian Peninsula on April 10, 2008, it can be assumed that in the lower and middle troposphere, zones with increased air moisture exist due to air inflow from the Red Sea. As a result, mesoscale volumes of dry and moist air are neighboring, though large-scale field is comparatively homogeneous with low humidity. In the mesoscale zones, intense thunderstorm and hailstorm Cb clouds developed, whose characteristics and evolution are studied in the paper. Continuous radar observations of the clouds are carried out during 5 hours. Numerical simulation of the cloud evolution is performed with nonstationary 1.5-dimensional model. It is noted that under the mentioned atmospheric conditions, in the area under consideration, heavy rain and hail from the Cb clouds are observed. The main factors of their origination are high thermal instability of the atmosphere and moist air inflow from outside.

Observation of the Movement of the Precipitation by Using Tritium Tracer

Tracer techniques have proven to be one of the most powerful tools to characterize the movement of air mass and pollutant transport in hydrological systems. In order to clarify the behavior of low-level tritium in the rain water, we have employed the measuring method of tritium applying a distillation process and an electrolytic enrichment process. The activity of tritium (T specific activity) in the obtained water was measured by liquid scintillation counter. This procedure was applied to bulk precipitation, imitative ground infiltrated precipitation and short term precipitation collected in Niigata City. Moreover, we investigated the concentrations of cations (Na+, K+, Ca2+, and Mg2+) in the precipitation to associate with air mass transport patterns arriving at the place. From the above mentioned, next matters have been clarified:(1) T specific activity in precipitation was found to have a strong dependence on location and season. (2) The chemical components in precipitation during typhoon have notable character of marine air mass. (3) Associated ions in monthly precipitation showed seasonal variation, in fact, the seasonal variation of Ca2+ and tritium were very similar. (4) Backward trajectory analysis method is useful for the analysis of the behavior of T specific activity and several ions in short-term precipitation.

Study of radon exhalation rate from soil, Bangalore, South India

The 222 Rn exhalation rate measurements are useful in identifying the locations of high radon exposure. On the other hand, atmospheric 222 Rn concentrations have been observed as an effective tracer for terrestrial air mass movements and atmospheric mixing mass movements. In view of this, year-long measurements of 222 Rn and its exhalation rates were carried out at J B Campus of Bangalore city, and the diurnal and seasonal variations have also been studied. Diurnally, exhalation rate was found to be high during night and early morning hours and low during afternoon hours. The diurnal variability of temperature difference between the lower and upper layers of the soil was found to be responsible for the observed diurnal variations. The monthly average of 222 Rn exhalation rate ranges from 10.63 ± 1.75 to 4.95 ± 0.65 mBq m -2 s -1 . The annual mean value of radon exhalation rate was found to be 8.27 ± 1.83 mBq m -2 s -1 .

Po-210 and Pb-210 as atmospheric tracers and global atmospheric Pb-210 fallout: a Review

Over the past ∼5 decades, the distribution of 222Rn and its progenies (mainly 210Pb, 210Bi and 210Po) have provided a wealth of information as tracers to quantify several atmospheric processes that include: i) source tracking and transport time scales of air masses; ii) the stability and vertical movement of air masses iii) removal rate constants and residence times of aerosols; iv) chemical behavior of analog species; and v) washout ratios and deposition velocities of aerosols. Most of these applications require that the sources and sink terms of these nuclides are well characterized. Utility of 210Pb, 210Bi and 210Po as atmospheric tracers requires that data on the 222Rn emanation rates is well documented. Due to low concentrations of 226Ra in surface waters, the 222Rn emanation rates from the continent is about two orders of magnitude higher than that of the ocean. This has led to distinctly higher 210Pb concentrations in continental air masses compared to oceanic air masses. The highly varying concentrations of 210Pb in air as well the depositional fluxes have yielded insight on the sources and transit times of aerosols. In an ideal enclosed air mass (closed system with respect to these nuclides), the residence times of aerosols obtained from the activity ratios of 210Pb/ 222Rn, 210Bi/ 210Pb, and 210Po/ 210Pb are expected to agree with each other, but a large number of studies have indicated discordance between the residence times obtained from these three pairs. Recent results from the distribution of these nuclides in size-fractionated aerosols appear to yield consistent residence time in smaller-size aerosols, possibly suggesting that larger size aerosols are derived from resuspended dust. The residence times calculated from the 210Pb/ 222Rn, 210Bi/ 210Pb, and 210Po/ 210Pb activity ratios published from 1970’s are compared to those data obtained in size-fractionated aerosols in this decade and possible reasons for the discordance is discussed with some key recommendations for future studies. The existing global atmospheric inventory data of 210Pb is re-evaluated and a ‘ global curve’ for the depositional fluxes of 210Pb is established. A current global budget for atmospheric 210Po and 210Pb is also established. The relative importance of dry fallout of 210Po and 210Pb at different latitudes is evaluated. The global values for the deposition velocities of aerosols using 210Po and 210Pb are synthesized.

Clouding the Issue

Biophysics As anyone who has played table tennis knows, it's hard to throw a table tennis ball very far. Fungal spores, being even smaller and lighter, suffer much more from drag when they are ejected into air; individual Sclerotinia sclerotiorum spores are roughly 10 µm in size and would be predicted to travel only 3 mm after having been launched at a speed of almost 10 m s−1. Streamlining the shape of the spore and sticking to one's brethren do confer some aerodynamic advantages and lead to wider dispersal. Roper et al. show that emerging in a cloud helps, too, and can boost the distance traveled to as much as 10 cm. This enhancement arises from the earliest spores having set the proximal layer of air into motion so that later spores can go with the flow. The authors numerically simulate the spatiotemporal behavior of the spore jet and find a good match with particle-imaging velocimetry measurements. They also find that spores that wait to emerge, so as to board the already moving air mass, can delay their departure only by around 50 ms lest the train leave the station without them. Proc. Natl. Acad. Sci. U.S.A. 107 , 10.1073/pnas.1003577107 (2010).

Pedogenic carbonate carbon isotopic constraints on paleoprecipitation: Evolution of desert in the Pacific Northwest, USA, in response to topographic development of the Cascade Range

The Cascade Range in the northwestern U.S. acts as an orographic barrier to the easterly movement of humid air masses from the Pacific Ocean, producing a massive rain shadow with arid to semi-arid climate conditions on the leeward side of the range. Pedogenic carbonates formed in the C 3-dominated landscapes east of the range have δ 13C carbonate that is enriched by approximately 4‰ relative to carbonates formed in sub-tropical C 3-dominated ecosystems. We measured stable isotopic compositions of pedogenic carbonates preserved in the Quaternary and Neogene sedimentary rock units in the inland Pacific Northwest, and examined the impact of long-term aridification and paleohydrology on their isotopic compositions. The determined δ 13C carbonate record shows a gradual increase of 5‰ from approximately − 10‰ in older pedogenic carbonates to − 5‰ in younger ones whereas δ 18O carbonate record indicates a decrease of approximately 4‰ in the late Neogene. In addition, the Quaternary δ 13C carbonate and δ 18O carbonate records indicate the highest δ 13C and δ 18O among the samples during the Pleistocene and significant fluctuation over the time period. The gradual increase in the δ 13C carbonate and the decrease in the δ 18O carbonate in the late Neogene are interpreted by the development of the rain shadow as a result of topographic development of the Cascade Range. Changes in the Quaternary isotope records suggest a decrease in regional precipitation and isotopically depleted winter precipitation, resulting from changes in large-scale atmospheric circulation patterns due to advance and retreat of northern hemisphere continental ice sheet. The isotope record from pedogenic carbonates provides a direct record of climatic change, suggesting that long-term carbon isotope data can provide useful constraints on timing and intensity of regional desertification, and its associated climate and topographic interaction.

NMOC, ozone, and organic aerosol in the southeastern United States, 1999–2007: 2. Ozone trends and sensitivity to NMOC emissions in Atlanta, Georgia

Non-methane organic carbon (NMOC) measurements made in Atlanta, Georgia from 1999–2007 are used with nitrogen oxide (NO x or NO y) and ozone (O 3) data to investigate relationships between O 3 precursors and peak 8-hour O 3 concentrations in the city. Data from a WNW-to-ENE transect of sites illustrate that the mean urban peak 8-hour O 3 excess constitutes about 20% of the peak 8-hour O 3 measured at the area-wide maximum O 3 site when air-mass movement is from the northwest quadrant; local influence is potentially greater on days with more stagnation or recirculation. The peak 8-hour O 3 concentrations in Atlanta increase as (1) surface temperature (T), ambient NMOC and NO y concentrations, and previous-day peak O 3 concentrations increase, and as (2) relative humidity, surface wind speeds, and ratios of NMOC-to-NO y decrease. An observation-based statistical model is introduced to relate area-wide peak 8-hour O 3 concentrations to ambient NMOC and NO y concentrations, while accounting for the non-linear dependences of peak 8-hour O 3 concentrations on meteorological factors. On the majority of days when the area-wide peak 8-hour O 3 exceeds 75 ppbv, meteorologically-adjusted peak 8-hour O 3 concentrations increase as ambient NMOC concentrations increase (NMOC sensitive) and ambient NO y concentrations decrease. This result contrasts with regional conditions in which O 3 formation appears to be NO x-sensitive in character. The results offer observationally-based information of relevance to O 3 management strategies in the Atlanta area, potentially contributing to “weight-of-evidence” assessments.

How lichens and mosses reflect atmospheric deposition of natural and artificial radionuclides

In a national survey in Slovenia, two biomonitors, the epiphytic lichen Hypogymnia physodes and the terrestrial moss Hypnum cupressiforme, were analysed for 210 Pb and 137 Cs. Further, the results for 210 Pb were compared with outdoor 222 Rn and with precipitation data. 210 Pb activity concentrations in moss carpets and lichen thalli ranged between 180-2450 and 200-1990 Bq kg -1 , respectively. 210 Pb showed similar spatial distributions in the two biomonitors with the highest levels in north-western and southern parts of the country, with a strong gradient to the eastern part, reflecting the movement of global air masses and the amount of precipitation. Increased 222 Rn concentrations over carbonate rocks were not reflected in lichen and moss 210 Pb levels. 137 Cs activity concentrations in lichens and mosses in the ranges 73-1400 and 49-600 Bq kg -1 , respectively, were obtained. There was a relatively good agreement between the two biomonitors, with the highest values in the northern part of the country.

Sources and Pathways of Polycyclic Aromatic Hydrocarbons Transported to Alert, the Canadian High Arctic

A probabilistic function (integrated source contribution function, ISCF) based on backward air mass trajectory calculation was developed to track sources and atmospheric pathways of polycyclic aromatic hydrocarbons (PAHs) to the Canadian High Arctic station of Alert. In addition to the movement of air masses, the emission intensities at the sources and the major processes of partition, indirect photolysis, and deposition occurring on the way to the Arctic were incorporated into the ISCF. The predicted temporal trend of PAHs at Alert was validated by measured PAH concentrations throughout 2004. The PAH levels in the summer are orders of magnitude lower than those in the winter and spring when long-range atmospheric transport events occur more frequently. PAHs observed at Alert are mostly from East Asia (including Russia Far East), North Europe (including European Russia), and North America. These sources account for 25, 45, and 27% of PAHs atmospheric level at Alert, respectively. Source regions and transport pathways contributing to the PAHs contamination in the Canadian High Arctic vary seasonally. In the winter, Russia and Europe are the major sources. PAHs from these sources travel eastward and turn to the north at approximately 120 degrees E before reaching Alert, in conjunction with the well-known Arctic haze events. In the spring, PAHs from Russia and Europe first migrate to the west and then turn to the north at 60 degrees W toward Alert. The majority of PAHs in the summer are from northern Canada where they are carried to Alert via low-level transport pathways. In the fall, 70% of PAHs arriving at Alert are delivered from North American sources.

Integrated climate model-oxygen isotope evidence for a North American monsoon during the Late Cretaceous

During the Late Cretaceous, western North America was characterized by a close geographic association between the Sevier highlands and the Western Interior Seaway. In this paper, an atmospheric general circulation model (AGCM) is used to simulate the impact of this geographic association on surface pressure, wind direction, and precipitation, and it is predicted that seasonal changes in these variables resulted in a strong monsoon along the eastern flank of the Sevier Highlands. Confirmation that these model simulations are accurate is provided by isotopic data from foreland basin sediments. In particular oxygen isotope records from different environments (large rivers, small streams and ponds) and proxies (unionid bivalve shells and paleosol carbonates) indicate that foreland basin streams were recharged by local precipitation with high oxygen isotope ratios while large trunk rivers were recharged by high-elevation precipitation. This hydrologic pattern is observed from Alberta to Utah and is consistent with east to west monsoonal air mass movements and associated seasonal rainfall. Recognition of a highland-driven monsoon has implication in regard to studies of fossil taphonomy, of water vapor transport, and of links between climate and mountain uplift and exhumation in this region.