Isentropic Trajectories Research Articles

Surface ozone at the Swiss Alpine site Arosa: the hemispheric background and the influence of large-scale anthropogenic emissions

An innovative and effective method using isentropic trajectory analysis based on the residence time of air masses over the polluted region of Europe was successfully applied to categorize surface ozone amounts at Arosa, Switzerland during 1996–1997. The “European representative” background ozone seasonal cycle at Arosa is associated with long-range transport of North Atlantic air masses, and displays the spring maximum–summer minimum with an annual average of 35 ppb. The photochemical ozone production due to the intense large-scale anthropogenic emission over Europe is estimated as high as 20 ppb in summer, whereas it is insignificant in winter. European sources contribute an annual net ozone production of 9–12 ppb at Arosa. Comparison with the selected regional representative site in Western Europe shows similar results indicating that the categorized ozone data at Arosa by this technique could be regarded as a representative for northern hemispheric mid-latitudes.

Saharan dust profiles measured by lidar at Lampedusa

Lidar observations of the tropospheric aerosols were carried out at the island of Lampedusa (35.5°N, 12.6°E) in the Mediterranean during May‐June 1999, within the Photochemical Activity and Ultraviolet Radiation II experiment. The measurements indicate that the troposphere is often loaded with large amounts of aerosol particles, producing relatively large values of the depolarization ratio. The aerosol content below and above 2 km shows a somewhat different behavior. In the upper region, large aerosol concentrations last for a few days; during these events aerosol is often detected up to 7 or 8 km. Large amounts were detected in mid‐May and were very often observed in June. By using meteorological analyses and isentropic backward trajectories, the aerosol behavior above Lampedusa has been related to the large‐scale transport patterns and to the source regions. Large aerosol loads are clearly due to dust transport from Africa, occurring through two main paths: from central Sahara, when a high‐pressure system was centered over northern Libya, and following the northwestern African coast, often along the Atlas Mountains, when the anticyclone is over Algeria or Libya, at latitudes lower than 30°N. Large aerosol loads are observed even when the air mass trajectories marginally overpass Africa, often up to 5–6 km. According to the isentropic trajectories, large vertical motions occur when the air masses travel over Africa. Significant differences in the aerosol profiles are found, depending on the origin of the air masses, and on the strength of the vertical motion. All the air masses that have traveled over Africa show an enhanced aerosol concentration, indicating that in this period the conditions were always favorable to dust mobilization and vertical propagation. The identified transport patterns appear to mainly affect the southern Mediterranean; in rare cases, forward trajectories reached southern Italy, Greece, Turkey, and the eastern Mediterranean.

Observations of ozone and related species in the northeast Pacific during the PHOBEA campaigns: 2. Airborne observations

During late March and April of 1999 the University of Wyoming's King Air research aircraft measured atmospheric concentrations of NO, O3, peroxyacetyl nitrate (PAN), CO, CH4, VOCs, aerosols, and J(NO2) off the west coast of the United States. During 14 flights, measurements were made between 39°–48°N latitude, 125°–129°W longitude, and at altitudes from 0–8 km. These flights were part of the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere (PHOBEA) experiment, which included both ground‐based and airborne measurements. Flights were scheduled when meteorological conditions minimized the impact of local pollution sources. The resulting measurements were segregated by air mass source region as indicated by back isentropic trajectory analysis. The chemical composition of marine air masses whose 5‐day back isentropic trajectories originated north of 40°N latitude or west of 180°W longitude (WNW) differed significantly from marine air masses whose 5‐day back isentropic trajectories originated south of 40°N latitude and east of 180°W longitude (SW). Trajectory and chemical analyses indicated that the majority of all encountered air masses, both WNW and SW, likely originated from the north‐western Pacific and have characteristics of emissions from the East Asian continental region. However, air masses with WNW back trajectories contained higher mixing ratios of NO, NOx, O3, PAN, CO, CH4, various VOC pollution tracers, and aerosol number concentration, compared to those air masses with SW back trajectories. Calculations of air mass age using two separate methods, photochemical and back trajectory, are consistent with transport from the northwestern Pacific in 8–10 days for air masses with WNW back trajectories and 16–20 days for air masses with SW back trajectories. Correlations, trajectory analysis, and comparisons with measurements made in the northwestern Pacific during NASA's Pacific Exploritory Mission‐West Phase B (PEM‐West B) experiment in 1994 are used to investigate the data. These analyses provide evidence that anthropogenically influenced air masses from the northwestern Pacific affect the overall chemical composition of the northeastern Pacific troposphere.

Observations of ozone and related species in the northeast Pacific during the PHOBEA campaigns: 1. Ground‐based observations at Cheeka Peak

As part of the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere (PHOBEA) project, we made observations of CO, O3, NOx, peroxyacetyl nitrate (PAN), nonmethane hydrocarbons (NMHC), Rn, aerosol scattering, aerosol absorption, and aerosol number density during the springs of 1997 and 1998 at the Cheeka Peak Observatory (CPO) on the western tip of Washington State. The data have been segregated to quantify the mixing ratio of these species in the Pacific marine atmosphere. However, even in these marine air masses, there are occasionally substantial enhancements of NOx and aerosols, but not CO, which we attribute to diesel exhaust from ship traffic to and from major ports in the region. The marine air masses were further classified into four categories based on 10‐day back isentropic trajectories; high, mid, and low latitude and those which had crossed over the Asian industrial region. Mean marine mixing ratios in 1998 were significantly higher than the 1997 values for CO (1997 mean equal to 151, 1998 mean equal to 170 ppbv), ethane (1771, 1968 parts per trillion by volume (pptv)), and ethyne (306, 452 pptv). Also, segregation of the 1998 data by air mass origin produced smaller differences in the mixing ratios for most species when comparing different source regions. We attribute both of these results to elevated emissions associated with unusually large areas of biomass burning which took place in Indonesia and Siberia dunng late 1997 and 1998. The relative enhancements of CO, ethane, ethyne, and propane we observed at CPO are consistent with enhanced biomass burning and industrial sources in the spring of 1998, relative to the spring of 1997.

Background monitoring and long-range transport of atmospheric CFC-11 and CFC-12 at Kosan, Korea.

The background concentrations of atmospheric CFC-11 and CFC-12 were monitored to assess their impact on stratospheric ozone depletion and global warming from September 1995 to March 1999 at Kosan, Korea, located at eastern margin of the Asian Continent. The concentrations of atmospheric CFC-11 at Kosan have decreased slightly, at a rate of -2.5 pptv yr(-1), over the period in response to the Montreal Protocol. The CFC-12 mixing ratio at Kosan continues to increase in the atmosphere at a rate of 5.7 pptv yr(-1) despite international regulations, because of its extreme atmosphere persistence. Recent trends of these two chlorofluorocarbons at Kosan, Korea were concordant with those of the northern hemispheric background monitored unit at Mauna Loa, Hawaii. The maximum seasonal mean mixing ratios of CFC-11 and CFC-12 at Kosan, Korea, were 270 +/- 4 pptv in the spring and 538 +/- 9 pptv in the winter, and the corresponding seasonal minima were 267 +/- 7 and 529 +/- 12 pptv. This occurred in the summer and was due to southeasterly winds from the northwestern Pacific Ocean. By performing a three-day isentropic backward trajectory analysis, it was shown that air masses at Kosan, and with the exception of summer, mainly originated from central and northern China. In particular, the mixing ratios of these two contaminant species are closely related with their air mass trajectories.

<i>Letter to the Editor:</i> A strange cloud in the Arctic summer stratosphere 1998 above Esrange (68°N), Sweden

Abstract. When the University of Bonn lidar on the Esrange (68°N, 21°E), Sweden, was switched on in the evening of July 18, 1998, a geometrically and optically thin cloud layer was present near 14 km altitude or 400 K potential temperature, where it persisted for two hours. The tropopause altitude was 4 km below the cloud altitude. The cloud particles depolarized the lidar returns, thus must they have been aspherical and hence solid. Atmospheric temperatures near 230 K were approximately 40 K too high to support ice particles at stratospheric water vapour pressures of a few ppmv. The isentropic back trajectory on 400 K showed the air parcels to have stayed clear of active major rocket launch sites. The air parcels at 400 K had traveled from the Aleutians across Canada and the Atlantic Ocean arriving above central Europe and then turned northward to pass over above the lidar station. Parcels at levels at ±25 K from 400 K had come from the pole and joined the 400 K trajectory path above eastern Canada. Apparently the cloud existed in a filament of air with an origin different from those filaments both above and below. Possibly the 400 K level air parcels had carried soot particles from forest wild fires in northern Canada or volcanic ash from the eruption of the Korovin Volcano in the Aleutian Islands.Key words: Atmospheric composition and structure (aerosols and particles; biosphere-atmosphere interactions) · Meteorology and atmospheric dynamics (middle atmospheric dynamics)

A strange cloud in the Arctic summer stratosphere 1998 above Esrange (68°N), Sweden

When the University of Bonn lidar on the Esrange (68∞N, 21∞E), Sweden, was switched on in the evening of July 18, 1998, a geometrically and optically thin cloud layer was present near 14 km altitude or 400 K potential temperature, where it persisted for two hours. The tropopause altitude was 4 km below the cloud altitude. The cloud particles depolarized the lidar returns, thus must they have been aspherical and hence solid. Atmospheric temperatures near 230 K were approximately 40 K too high to support ice particles at stratospheric water vapour pressures of a few ppmv. The isentropic back trajectory on 400 K showed the air parcels to have stayed clear of active major rocket launch sites. The air parcels at 400 K had travelled from the Aleutians across Canada and the Atlantic Ocean arriving above central Europe and then turned north- ward to pass over above the lidar station. Parcels at levels at25 K from 400 K had come from the pole and joined the 400 K trajectory path above eastern Canada. Apparently the cloud existed in a filament of air with an origin diAerent from those filaments both above and below. Possibly the 400 K level air parcels had carried soot particles from forest wild fires in northern Canada or volcanic ash from the eruption of the Korovin Volcano in the Aleutian Islands.

Partitioning of reactive nitrogen in the midlatitude lower stratosphere

Balloon‐borne in situ measurements of total reactive nitrogen (NOy), nitric oxide (NO), nitric acid (HNO3), ozone (O3), and aerosols were conducted over Aire sur l'Adour, France (44°N), between October 11 and 12, 1994. NOy and NO were measured by chemiluminescence NO detectors combined with a gold catalytic converter, and HNO3 was measured by ion mass spectrometry. Two independent box models (Goddard Space Flight Center and Atmospheric and Environment Inc.) run on isentropic trajectories were used to interpret the observed partitioning of reactive nitrogen. The NOy partitioning calculated by the two models agreed within 10% of each other. The model‐calculated NO/NOy ratios increase by ∼25% when the updated reaction rates of NO2 + OH, HNO3 + OH, and NO2 + O [Portmann et al., 1999] were used instead of those given by DeMore et al. [1997], leading to a better agreement with the observations by the same amount. At 21–25 km the calculated NO/NOy ratios depended sensitively on the estimate of aerosol surface area. Within the uncertainty of the estimate of aerosol surface area the NO/NOy and HNO3/NOy ratios calculated by the models reproduced those observed within 20%. The same trajectory models also reproduced the NO/NOy ratios measured below 25 km under high aerosol loading in October and November 1992 within ±20%, which is the accuracy level of the measurements.

Persistence of stratospheric ozone layers in the troposphere

On 20th March 1994 at 12Z two dry layers with high ozone mixing ratio were encountered in the free troposphere by an ozonesonde ascent at Aberystwyth (52.4°N, 4.1°W). The layers resembled tropopause folds, but were not associated with any significant synoptic development, and did not have enhanced static stability. We use isentropic trajectory analysis, with winds taken from ECMWF analyses, to look for the origin of the layers. The analysis suggests that the two layers had different source regions. The lower layer spent 10 days over the Atlantic before reaching Northern Europe, and appears to have originated in the break-up of a stratospheric streamer between the 5th and 9th of March. The upper layer seems to have originated over the Western USA where the trajectories passed through a region of low Richardson number above the Rocky Mountains. In both cases, the low-water-vapour/high-ozone air mass had been advected with little mixing in the troposphere for at least 10 days. We argue that the air must be of stratospheric origin, since photo-chemistry cannot generate large amounts of ozone at this time of year and the trajectories do not, in any case, point to a boundary-layer origin. If, as the analysis suggests, the upper layer reached the troposphere by mixing across the jet then this may be evidence for stratosphere–troposphere exchange (STE) taking place other than by folding of the tropopause. The persistence of layers with anomalous chemical content in the troposphere for so long indicates that an accurate model of tropospheric transport and mixing is needed to assess the chemical impact of STE on tropospheric chemistry, in addition to a representation of the dynamical behaviour near to the tropopause.

Atmospheric transport pathways from the Bilibino nuclear power plant to Alaska

The Bilibino nuclear power plant (68°03′N, 166°20′E, 340 m asl) in northeastern Siberia is the closest Russian nuclear power plant to the USA. We used an isentropic trajectory model to estimate the probability that air in the Bilibino region would be transported to Alaska following a hypothetical accident. This estimate is based on the meteorological data from 1991 to 1995. Our calculations indicate that the probability that air in the Bilibino region will be transported to Alaska is approximately 6–16%, averaged over the entire year. This probability doubles in the summer and early fall with a maximum in August of 12–33%. For the entire year the mean, median, and minimum transport times from the plant to Alaska are 4, 3.5 and 1 d, respectively. Since rapid transport (1–2 d) could bring air parcels containing short-lived radionuclides, these events potentially represent the greatest risk to inhabitants of Alaska.

A Diagnostic Study of the Flateyri Avalanche Cyclone, 24–26 October 1995, Using Potential Vorticity Inversion

Abstract The evolution of a deep North Atlantic cyclone, which caused devastating avalanches in northwest (NW) Iceland in October 1995, was investigated. As the main tool for this investigation, potential vorticity analysis was used. This allows the quantification and comparison of the roles of different processes that contribute to the cyclone deepening at different stages. Interpretation of potential vorticity inversions and isentropic air trajectories yields the following picture of the cyclone development. The thermal field over the North Atlantic had acquired strong west–east gradients due to a combination of advection of cold air southeastward from a cold cyclonic gyre south of Iceland and advection of warm air northward on the westward flank of a warm anticyclonic ridge over central Europe. A low-level baroclinic wave forming just south of Ireland was rapidly reinforced due to interaction with a descending, high-value, upper-level potential vorticity anomaly and was isentropically advected from the...

Characteristics of dimethylsulfide, ozone, aerosols, and cloud condensation nuclei in air masses over the northwestern Pacific Ocean

Long‐term measurements of several trace gases and aerosols were carried out from December 1994 to October 1996 at Ogasawara Hahajima Island over the northwestern Pacific Ocean. The continental impact on the concentrations of sulfur compounds, ozone (O3), and cloud condensation nuclei (CCN) was estimated on the basis of the classification of air mass into seven types by isentropic trajectory analysis. From May to October, the air mass originating from the central North Pacific Ocean is predominant and regarded as the clean marine air for the concentrations of sulfur compounds and CCN. From the results of the molar ratio of methane sulfonic acid to non‐sea‐salt sulfate (NSS) and the positive correlation between dimethylsulfide (DMS) and CCN in this air mass it can be concluded that DMS largely contributes to the production of NSS and CCN. On the other hand, continental and anthropogenic substances are preferably transported to the northwestern Pacific Ocean by the predominant continental air mass from November to March. The enhancement of concentrations by the outflow from the Asian continent are estimated by a factor of 2.8 for O3, 3.9 for SO2, 3.5 for CCN activated at 0.5% supersaturation (0.5% CCN), 4.7 for 1.0% CCN, and 5.5 for NSS. Moreover, the CCN supersaturation spectra are also affected by the continental substances resulting in factor 2 of enhancement of cloud droplet number concentration. The diurnal variations of DMS and O3 for each air mass show a pattern of daytime minimum and nighttime maximum, which are typically found in remote ocean, even though those amplitudes are different for each air mass. Consequently, it can be concluded that the influence of nitric oxides (NOx) for the daytime O3 production and nitrate (NO3) radical for the nighttime oxidation of DMS are small even in the continental air mass.

A Climatology of Rossby Wave Breaking along the Subtropical Tropopause

Ten years (1986–95) of global analyses from the European Centre for Medium-Range Weather Forecasts are used to investigate the temporal and spatial distributions of Rossby wave breaking (RWB) at 350 K along the tropopause, herein defined by the ±1.5 potential vorticity (PV) unit (10−6 K m2 s−1 kg−1) contours. Though many studies acknowledge RWB as an important contributor to the complex of mixing processes in the atmosphere, there exists no prior climatological study of its distribution near the tropopause. As in previous studies, RWB is identified in the global analyses by southward directed PV gradients. At 350 K, RWB along the tropopause occurs preferentially during summer over the midoceans, in relative proximity to the planetary-scale high pressure systems in the subtropics. Isentropic trajectories at 350 K show that outflow from the tops of these subtropical highs directly participates in RWB over the adjacent, downstream oceanic regions. Two regions are highlighted in this study: the North Pacific during boreal summer and the South Atlantic during austral summer. Synoptic maps of breaking Rossby waves in these regions are provided to reveal the acute tropopause folding in the meridional plane, which characteristically accompanies RWB. The rich interaction between the tropical flow and the extratropical westerly current exhibited by these cases suggests that the subtropical highs serve as important agents in the coupling between the tropical troposphere and the extratropical stratosphere. As expected from theoretical considerations, the locations where RWB occurs most frequently, known as “surf zones,” are shown to coexist with regionally weak time-mean wind speeds and horizontal gradients of PV at 350 K.

Influence of regional‐scale anthropogenic activity in northeast Asia on seasonal variations of surface ozone and carbon monoxide observed at Oki, Japan

Surface O3 and CO measurements were carried out at Oki, Japan during March 1994 to February 1996 in order to elucidate the processes determining temporal variations of O3 and CO in the northeast Asian Pacific rim region. The isentropic trajectory analysis was applied to sort out the influences of the air mass exchange under the Asian monsoon system and the regional‐scale photochemical buildup of O3. The trajectories were categorized into five groups which cover background and regionally polluted air masses. The seasonal cycles of O3 and CO in the background continental air mass revealed spring maximum‐summer minimum with averaged concentrations ranging from 32 and 120 ppb to 45 and 208 ppb, respectively. In contrast, O3 concentrations in the regionally polluted continental air mass ranged from 44 to 57 ppb and showed a winter minimum and a spring‐summer‐autumn broad maximum, which was characterized by photochemical O3 production due to anthropogenic activities in northeast Asia. CO concentrations in the same air mass showed a spring maximum of 271 ppb and a summer‐autumn minimum of 180 ppb. The photochemical buildup of O3 resulting from anthropogenic activities in this region was estimated to be 21 ppb in summer, while its production was insignificant, an average 3 ppb, in winter. A comparison between data in northeast Asia and in Europe shows many similarities, supporting the contention that photochemical buildup of O3 from large‐scale precursor emissions in both regions is very significant.

Transport of polluted boundary layer air from the Po Valley to high-alpine sites

Within the EUROTRAC subproject ALPTRAC the occurrence of reactive trace species at high-alpine sites was investigated. As a part of these studies, the transport of boundary layer air from the Po Valley, which is one potential major source region for air pollution in the Alps, to the high-mountain sites Sonnblick (3106 m) in Austria and Jungfraujoch (3579 m) in Switzerland was studied. A case study based on isentropic trajectories derived from a fine-mesh analysis showed the potential of such transports to cause substantial peaks in the aerosol concentration at Sonnblick. However, on a climatological basis the Po Valley does not seem to cause higher-than-average concentrations of species such as SO 2, SO 2- 4, NH + 4 and NO - 3. Its contribution was estimated to be about 15% in summer and much less in winter. Indications of orographically induced, subgrid vertical transports were found which are important for the interpretation of data from pollution monitoring programmes at high-alpine sites.

On the Antarctic origin of low ozone events at the South American continent during the springs of 1993 and 1994

This paper reports the detection of several low total ozone events at mid-latitudes in the South American continent during the springs of 1993 and 1994. During these ozone depletions the total ozone column reached values as low as 150 Dobson Units at high latitudes (56S). It was found that the temperature of the lower stratosphere for the 450 K isentropic surface decreased with each low ozone event observed, suggesting that masses of ozone poor air were transported from the cold polar vortex to the South American continent. Isentropic back trajectory analyses corroborate the Antarctic origin of the observed low ozone events.

Accuracy of trajectories as determined from the conservation of meteorological tracers

AbstractDynamical structures as well as transport processes are often investigated using trajectories. Several alternative techniques are currently in use to calculate trajectories, which may produce significantly different results. In this study, three‐dimensional, isentropic, isobaric and isoeta (terrain‐following coordinate surfaces) trajectories are calculated. In the case of the isentropic trajectories, both the kinematic and the dynamic calculation method are applied.Using a tracer that is conserved along the real three‐dimensional trajectories, it is possible to determine which of these trajectories are the most accurate. Here, conservative meteorological quantities, namely potential vorticity, specific humidity and potential temperature, are used. As these tracers are conserved only in the absence of diabatic processes, regions of the atmosphere where these processes are important, i.e. the boundary layer and moist regions, are excluded. Tracer conservation along the different trajectories is studied to find the most accurate trajectory type.It is found that three‐dimensional trajectories are the most accurate ones, and kinematic isentropic trajectories, affected more by dynamical inconsistencies between meteorological fields, are the second best in the troposphere. In the stratosphere, three‐dimensional and isentropic trajectories may be of similar accuracy. Isobaric and isoeta trajectories are much less accurate, both in the troposphere and in the stratosphere. Dynamic trajectories tend to perform unrealistic inertial oscillations and thus give clearly worse results than any of the kinematic trajectories.Since there exists no direct relationship between the average errors in tracer conservation and average spatial position errors of the trajectories, a transformation of the tracer conservation errors into spatial position errors is difficult.

Mesoscale Evolution of a Continental Occluded Cyclone

Abstract A diagnostic study of a continental occluding extratropical cyclone (ETC) during 1–2 November 1992 is presented using initializations from the Mesoscale Atmospheric Prediction System (MAPS), a hybrid sigma–isentropic coordinate model. Whereas recent studies have concentrated on maritime ETCs and have used numerical model simulations, this study employs diagnostic, observational data and model initializations to develop an occlusion model. In addition, isentropic parcel trajectories from a diabatic trajectory model are examined to trace the origin and termination of air parcels associated with the development of the occluded front. The chosen storm was a moderately deepening (i.e., typical) ETC over a data-rich continental region. This storm developed over the central United States, where commercial aircraft and a network of wind profilers provided copious asynoptic data aloft, which was ingested by the MAPS. Analyses of this well-defined occluded cyclone tend to verify that the advancing cold fro...

An investigation into the source of the springtime tropospheric ozone maximum at Mauna Loa Observatory

Measurements of CH4, CO, O3, and H2O vapor from Mauna Loa Observatory (MLO) are examined in conjunction with isentropic trajectories to investigate the cause of a maximum in tropospheric O3 consistently observed during spring. CO and O3 have been found to be positively correlated in pollution plumes containing O3 precursors downwind of industrialized regions. However, we report that during continental transport from Asia, O3 is not correlated with either CO or CH4, although CO and CH4 are strongly correlated. The relationship between CO and CH4 suggests common source regions. The lack of correlation between these species and O3 probably indicates an O3 source distinct from that of CO and CH4. While Asian pollution does not appear to be a strong candidate for causing the spring increase in O3, transport characteristics and H2O vapor measurements are consistent with both an upper‐tropospheric/stratospheric contribution and an enhancement from transport across O3 gradients.

Multifragmentation of the remnant produced in the reaction of1AGeV gold with carbon

A high-statistics exclusive study of the multifragmentation of 1A GeV gold on carbon has been performed. Particles with Z{le}2 show evidence of emission in a first prompt stage as well as in a second equilibrium stage whereas fragments with Z{ge}3 appear to be emitted essentially only in the second stage. Two methods for the separation of the Z{le}2 particles into the two stages are given and they are in agreement. The yields for each stage are determined as a function of the event charged particle multiplicity m. The mass, nuclear charge, excitation energy per nucleon, and temperature of the remnant left after the first stage and their fluctuations have been determined as a function of m. The expansion of the remnant to fragment freeze-out is examined. The freeze-out temperature is determined from double isotope ratios as a function of m and isentropic trajectories are obtained in the temperature-density plane. The caloric curve shows a monotonic increase with excitation energy. Some of the energy is in the form of radial flow. Overall, the results are consistent with a previous statistical analysis of the data which suggests that, over a certain range of excitation energies, multifragmentation involves a continuous phase transition. {copyright}more » {ital 1998} {ital The American Physical Society}« less