Trade Wind Inversion Research Articles

Diagnosing Monthly Mean Boundary Layer Properties from Reanalysis Data Using a Bulk Boundary Layer Model

Abstract The mixed-layer approach to modeling the planetary boundary layer (PBL) is particularly well suited to inversion-topped PBLs, such as the stratocumulus-topped boundary layer found off the west coast of America in the subtropical Pacific Ocean at northern and southern latitudes. However, a strong temperature inversion near 850 hPa (the trade wind inversion) is not confined to the stratocumulus regimes, but has been observed over most parts of the subtropical–tropical Pacific Ocean. In this paper, the authors test the ability of a simple bulk boundary layer model (BBLM) to diagnose entrainment velocity, cumulus mass flux, and surface latent heat flux from monthly mean reanalysis data. The PBL depth is estimated from Geoscience Laser Altimeter System data. The model is based on the conservation equations for mass, total water mixing ratio, and moist static energy. The BBLM diagnoses entrainment velocities between 1 and 8 mm s−1 in the stratocumulus and trade wind regions, with increasing rates toward the west. Large cumulus mass fluxes (1.3–2 cm s−1) mark the ITCZ and South Pacific convergence zone. Unreasonably large surface latent heat fluxes are diagnosed in regions where the vertical resolution of both model and input data are insufficient to represent the sharp gradients of moist conservable variables and winds across the PBL top. The results demonstrate that the potential exists to extract useful information about the large-scale structure of PBL physical processes by combining available observations with simple models.

Validation of the Coupled NCEP Mesoscale Spectral Model and an Advanced Land Surface Model over the Hawaiian Islands. Part II: A High Wind Event*

Abstract A high wind event (14–15 February 2001) over the Hawaiian Islands associated with a cold front is simulated using the National Centers for Environmental Prediction (NCEP) Mesoscale Spectral Model (MSM) coupled with an advanced land surface model (LSM). During this period, a strong high pressure cell moved to the northeast of the Hawaiian Islands following the passage of the cold front. The cell then merged with the semipermanent subtropical high and resulted in windy conditions across the state of Hawaii. Analyses of soundings from Lihue on Kauai and Hilo on the Big Island reveal a mean-state critical level below 400 hPa, a strong cross-barrier flow (∼13 m s−1), and the presence of a trade wind inversion. The MSM–LSM predicts downslope windstorms on the lee sides of mountains or ridges with tops beneath the trade wind inversion and within ocean channels between islands. In the case of high mountains with a peak height above the trade wind inversion, weak winds are simulated on the lee side. Around the corners of the islands and in gaps between mountains, gap winds and downslope windstorms are both important for the development of localized leeside windstorms. The localized windstorms over the Hawaiian Islands develop as a result of interactions between large-scale airflow and the complex local topography. Since the terrain is not adequately resolved by the 10-km RSM–LSM, it is no surprise that these windstorms are better simulated by the high-resolution nonhydrostatic MSM–LSM than the 10-km RSM–LSM.

Numerical Simulations of the Island-Induced Circulations over the Island of Hawaii during HaRP

Abstract The fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5)/land surface model (LSM) is used to simulate the diurnal island-scale circulations over the island of Hawaii during the Hawaiian Rainband Project (HaRP, 11 July–24 August 1990). The model is initialized with the NCEP–NCAR reanalysis data. The diurnal variations of the land–sea thermal contrast at the land surface and the planetary boundary layer at Hilo, Hawaii, are well simulated. The main discrepancy occurs on the leeside areas of mountains or ridges below the trade wind inversion (2 km), where the simulated afternoon land–sea thermal contrast at the surface is 1°–3°C lower than observed mainly due to the misrepresentation of lava rocks by the bare ground category in the U.S. Geological Survey (USGS) data and stronger than observed simulated sea breezes bringing in relatively cool maritime air. The flow deceleration and splitting of the incoming trade wind flow and the evolution of the diurnal circulation cells on the windward side, the thermally driven diurnal winds, and the wake circulations on the lee side are well simulated. The simulated diurnal variations in rainfall are also in good agreement with observations. However, the simulated winds in areas well exposed to the trade wind flow are weaker (1–3 m s−1) than observed mainly due to the underestimation of trade wind flow in the NCEP–NCAR reanalysis. The simulated rainfall over windward lowlands at night is underestimated and the maximum rainfall axis shifts farther toward the coast as compared with observations, due to an underestimation of orographic lifting aloft and a relatively large horizontal extent of the simulated katabatic flow because of the weaker- than-observed trade wind flow in the initial conditions. In the afternoon hours on the windward side, the strongest winds (anabatic/sea breeze and trade wind flow) are simulated in low levels over land in response to the surface heating, with a westerly wind deviation beneath the mean trade wind inversion (2 km) and sinking motion over the adjacent oceans. The simulated low-level flow deceleration of the incoming trade wind flow is most significant in the early morning as a combination of island blocking and nocturnal cooling over land. At that time, the simulated upward motion representing the rising branch of the thermally direct circulation extends more than 40 km offshore. Sensitivity tests show that with better surface conditions in the model coupled with the Oregon State University (OSU) LSM, the simulated thermal forcing over land is improved. The improvements in simulated ground temperature, land–sea thermal contrast at the land surface, and mixing ratio lead to better simulation of the strength of land/sea breezes over the island.

Characterisation of TSP and PM2.5 at Izaña and Sta. Cruz de Tenerife (Canary Islands, Spain) during a Saharan Dust Episode (July 2002)

Abstract A strong African dust outbreak episode affecting the Canary Islands from 28 to 31/07/02 has been characterised at the Izana Observatory (IZO), located in the free troposphere (FT), and at Sta. Cruz de Tenerife (SCO), in the Marine Boundary Layer (MBL). The Saharan air mass intruded above the trade wind inversion layer resulting in daily mean PM levels of up to 616, 312, 98 and 26 μg m−3 of TSP, PM10, PM2.5 and PM1, respectively, at IZO. As demonstrated by the vertical sounding profiles, the MBL is compressed during the Saharan intrusion, favouring the deposition of coarse dust particles to the MBL and giving rise to daily levels of up to 85, 52 and 30 μg m−3 of PM10, PM2.5 and PM1, respectively, at SCO. A complete chemical and mineralogical characterisation has been performed for TSP and PM2.5 collected simultaneously at both sites. Levels of mineral elements increased during the Saharan episode at both sampling sites. In addition, at the MBL, the levels of the secondary inorganic aerosols registered during the Saharan episode were considerably higher than levels recorded during non-Saharan episodes. The partial formation of secondary coarse Ca and/or Na sulphates and nitrates by the reaction of gaseous pollutants (or derived oxidised phases), of a major local origin, with the natural aerosols has been deduced. These reactions may be favoured by the high concentration of coarse mineral and marine aerosols particles measured at SCO, the high relative humidity (RH) measured, as well as the strong compression of the MBL during the Saharan episode.

Thermodynamic structure of the Atmospheric Boundary Layer over the Arabian Sea and the Indian Ocean during pre-INDOEX and INDOEX-FFP campaigns

Abstract. Spatial and temporal variability of the Marine Atmospheric Boundary Layer (MABL) height for the Indian Ocean Experiment (INDOEX) study period are examined using the data collected through Cross-chained LORAN (Long-Range Aid to Navigation) Atmospheric Sounding System (CLASS) launchings during the Northern Hemispheric winter monsoon period. This paper reports the results of the analyses of the data collected during the pre-INDOEX (1997) and the INDOEX-First Field Phase (FFP; 1998) in the latitude range 14°N to 20°S over the Arabian Sea and the Indian Ocean. Mixed layer heights are derived from thermodynamic profiles and they indicated the variability of heights ranging from 400m to 1100m during daytime depending upon the location. Mixed layer heights over the Indian Ocean are slightly higher during the INDOEX-FFP than the pre-INDOEX due to anomalous conditions prevailing during the INDOEX-FFP. The trade wind inversion height varied from 2.3km to 4.5km during the pre-INDOEX and from 0.4km to 2.5km during the INDOEX-FFP. Elevated plumes of polluted air (lofted aerosol plumes) above the marine boundary layer are observed from thermodynamic profiles of the lower troposphere during the INDOEX-FFP. These elevated plumes are examined using 5-day back trajectory analysis and show that one group of air mass travelled a long way from Saudi Arabia and Iran/Iraq through India before reaching the location of measurement, while the other air mass originates from India and the Bay of Bengal.

Transport pathways of ozone to marine and free-troposphere sites in Tenerife, Canary Islands

In this study we analysed two time series of surface ozone recorded in Tenerife: one in a marine environment (Aguere, in the marine boundary layer at 580 m.a.s.l.) and other in the free troposphere (Izaña, above the trade wind inversion layer at 2367 m.a.s.l.). We performed a systematic 4-year analysis of ozone, backtrajectories and synoptic charts. The transport pathways of ozone for different O3 percentile (Pth) ranges were determined. At both sites, low ozone levels (<50 Pth, but mainly those <25 Pth) are mainly associated with transport from low altitudes over the Central North Atlantic and North Africa. Increasing ozone levels from 50 to 100 Pth are associated with a reinforcement of: (a) a northern transport pathway (off Portuguese coast) from the North Atlantic mid-latitudes and Western Europe to Aguere, and (b) a characteristic N–NW transport pathway to Izaña. At both sites, these increasing ozone levels are associated with transport pathways showing subsidence typically from 3 to 5 km.a.s.l. At Aguere, high ozone events (>90 Pth) occur from March to June, and are mainly associated with a subsiding transport pathway from the western side of lows developing over Western/Central Europe and the North Atlantic mid-latitudes. At Izaña, high ozone events (>90 Pth) occur from April to August, and are associated with subsidence at the western edge of lows over the North Atlantic (very frequently at the W or SW of the Iberian Peninsula). The results of this study highlight the importance of the downward transport of ozone. High ozone events under meteorological scenarios classically associated with stratospheric intrusions have been recorded every year at the two sites. However, with our results we cannot ultimately determine if these high ozone events are caused by downward transport from the upper troposphere/lower stratosphere, or by lifting of continental ozone pollution and subsequent subsidence. The occurrence of high ozone events (>90 Pth) at Izaña and not in Aguere during summer (when the trade wind inversion located between these sites reaches its strongest stage) is an evidence of the importance of the ozone downward supply from mid-upper troposphere in this region.

Future Climate Change of the Subtropical North Atlantic: Implications for the Cloud Forests of Tenerife

This paper is concerned with climate change in the region of the Canary Islands and the potential implications for the laurel forests of Tenerife. Frequent orographic cloud formation during the dry season is of vital importance to the altitudinal distribution of the laurel forests, because it maintains a semi-humid environment in the otherwise semi-arid climate of the Canary Islands. The distinctive environmental conditions in conjunction with the location of the Canary Islands on the Northern poleward edge of the Hadley Circulation make these ecosystems potentially highly sensitive to regional changes in climatic conditions. To explore this sensitivity, we first quantify observed trends in humidity and temperature across an altitudinal transect at the base of the Anaga peninsular, and second, analyse the results of three GCM experiments (CGCM1, ECHAM4 and CSIRO) to develop alternative climate change scenarios, and third, use these data to assess likely shifts in the elevational distribution of the laurel forest climate envelope. We report a significant increase in relative humidity and decreases in the diurnal temperature range on Tenerife at altitudes below the trade wind inversion within the last 30 years during the dry season, which suggests an increased occurrence of low-level clouds. There is also partial evidence for a drying trend across the trade wind inversion, which may be linked to an increased subsidence. Overall, the models suggest a downward shift of the area climatically suitable for laurel forests, which may be driven by changes in temperature and moisture supply in the region as well as by larger-scale changes in the atmospheric circulation. Our findings contrast with previously published findings for a tropical montane cloud region, which predict an upward shift of the cloud base. This suggests, following the assumptions inherent in the models applied, that the ecological consequences of climate change for cloud forests may be linked to their relative location in the Hadley Circulation.

Polycyclic aromatic hydrocarbons in mountain soils of the subtropical Atlantic.

Surface soil samples from various altitudes on Tenerife Island, ranging from sea level up to 3400 m above mean sea level, were analyzed to study the distribution of 26 polycyclic aromatic hydrocarbons (PAHs) in a remote subtropical area. The stable atmospheric conditions in this island define three vertically stratified layers: marine boundary, trade-wind inversion, and free troposphere. Total PAH concentrations, 1.9 to 6000 microg/kg dry wt., were high when compared with those in tropical areas and in a similar range to those in temperate areas. In the marine boundary layer, fluoranthene (Fla), pyrene (Pyr), benz [a]anthracene (BaA), and chrysene (C + T) were largely dominant. The predominance of Fla over Pyr may reflect photo-oxidative processes during atmospheric transport, although coal combustion inputs cannot be excluded. The PAHs found in higher concentration in the soils from the inversion layer were benzo[b + j]fluoranthene (BbjF) + benzo[k]fluoranthene (BkF) > benzo[e]pyrene (BeP) approximately indeno[1,2, 3-cd]pyrene (Ind) > benzo[a]pyrene (BaP) approximately benzo[ghi]perylene (Bghi) > coronene (Cor) approximately dibenz[a,h]anthracene (Dib), reflecting that high temperatures and insolation prevent the accumulation of PAHs more volatile than BbjF in significant amounts. These climatic conditions involve a process of standardization that prevents the identification of specific PAH sources such as traffic, forest fires, or industrial inputs. Only soils with high total organic carbon (TOC) (e.g., 10-30%) preserve the more volatile compounds such as phenanthrene (Phe), methylphenanthrenes (MPhe), dimethylphenanthrenes (DMPhe), and retene (Ret). However, no relation between PAHs and soil TOC and black carbon (BC) was found. The specific PAH distributions of the free tropospheric region suggest a direct input from pyrolytic processes related to the volcanic emission of gases in Teide.

Radiative and microphysical interactions between marine stratocumulus clouds and Saharan dust 1. Remote sensing observations

This work emphasizes the radiative impact of Saharan dust particles in the presence of clouds, over the tropical North Atlantic Ocean. A first analysis based upon recent European Centre for Medium‐Range Weather Forecasts data confirms the classical observations; that is, in summer, the dust plume lies over the trade wind inversion, that is to say, over the main cloud layer. In winter, however, dust particles generally are transported in the trade wind layer, namely, where the major part of clouds is developing. In a second part, we present a statistical analysis based upon a 6‐year series of daily VIS and IR Meteosat data. Our study reveals, at any season, a decrease in the apparent cloud reflectivity derived from satellite measurements. Minimum values of this albedo are found in geographical areas where dust particles are most often observed and where they have their highest values in optical thickness. This albedo decrease can exceed 20% during spring months, when the dust outbreaks are the most frequent. A final discussion puts forward some physical processes that may explain the observations. In summer, dust presence may result in a change of the reflectance of the system, due to an increase of the absorption of the surface‐cloud‐dust plume system. On the other hand, during the winter season, the cloud albedo decrease may be in part explained by the drying of the atmosphere due to the dry air masses associated with the dust outbreaks coming from the Saharan desert. However, an interesting and complementary explanation is put forward for the winter case: Because of its lower altitude, the dust plume is likely to mix with cloud water. Consequently, in‐cloud processes may lead to a change in droplet spectrum size, which in turn, could affect the cloud reflectivity and therefore the reflectance measured at the top of the atmosphere. Therefore, whatever the physical processes involved, the dust outbreaks seem always to lead to a decrease in the cloud cover albedo over the tropical North Atlantic Ocean. In part 2 of this study, the observations will be completed by numerical modeling dealing with radiation, microphysics, and mesoscale transport, in order to better explain and understand this radiative effect.

Habitat selection and assemblage structure of darkling beetles (Col. Tenebrionidae) along environmental gradients on the island of Tenerife (Canary Islands)

Relationships between biocoenotic variation trends in the darkling beetle assemblage and several environmental variables of sampling plots at different elevations were investigated at different spatial scales. Classification (UPGMA) and ordination (PCA, CCA) techniques were used to examine these data. Two large groups of species (coastal and mountane) were established, although two clear subgroups (sub-summit and summit) were found in the latter. Likewise, the sub-summit subgroup was divided into a ‘lower-montane’ and ‘middle-montane’. At large scale, several grouping trends showing significant relationships to some climatic factors were observed, principally the height of dew point temperature and the trade wind inversion zones during summer (1200 m a.s.l.) or winter (1600 m a.s.l.). The major trend was conditioned firstly by temperature and secondly by sand content on the soil (xeric habitats). The second trend was influenced by rainfall (moist habitats) and vegetation type. The third trend was opposite to the previous trends. At a fine scale (altitudinal band or stratum), vegetation parameters and edaphic variables were also significant factors (open–closed or sandy–clay microhabitats) as concerns the distribution and abundance of these detritivorous beetles. The observations at different scales reflected different conclusions in the definition of darkling beetle associations and the environmental factors.

Habitat selection and assemblage structure of darkling beetles (Col. Tenebrionidae) along environmental gradients on the island of Tenerife (Canary Islands)

Relationships between biocoenotic variation trends in the darkling beetle assemblage and several environmental variables of sampling plots at different elevations were investigated at different spatial scales. Classification (UPGMA) and ordination (PCA, CCA) techniques were used to examine these data. Two large groups of species (coastal and mountane) were established, although two clear subgroups (sub-summit and summit) were found in the latter. Likewise, the sub-summit subgroup was divided into a ‘lower-montane’ and ‘middle-montane’. At large scale, several grouping trends showing significant relationships to some climatic factors were observed, principally the height of dew point temperature and the trade wind inversion zones during summer (1200 m a.s.l.) or winter (1600 m a.s.l.). The major trend was conditioned firstly by temperature and secondly by sand content on the soil (xeric habitats). The second trend was influenced by rainfall (moist habitats) and vegetation type. The third trend was opposite to the previous trends. At a fine scale (altitudinal band or stratum), vegetation parameters and edaphic variables were also significant factors (open–closed or sandy–clay microhabitats) as concerns the distribution and abundance of these detritivorous beetles. The observations at different scales reflected different conclusions in the definition of darkling beetle associations and the environmental factors.

Chemical compositions in convective and nonconvective regions during PEM‐Tropics B

Four DC‐8 flights during Pacific Exploratory Mission (PEM)‐Tropics B are analyzed in terms of geographical location, meteorological conditions, and chemical compositions. The meteorological conditions are determined using the meteorological analysis of the Florida State University Global Spectral Model, trajectory analysis, and in situ measurements. Typical undisturbed meteorological conditions are found over the northeastern Pacific between 30° and 15°N and southeast of Hawaiian Islands during flights 5 and 6. Disturbed meteorological conditions are found over western and central equatorial Pacific especially over the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ) during flights 7 and 10. Comparison of the chemical concentrations between disturbed and undisturbed regions revealed remarkable differences. The distribution of the chemical constituents is found to be closely linked to the atmospheric state. Large amounts of pollutants are found to be capped at lower levels due to climatologically persistent trade wind inversion in the undisturbed regions. Transient convective systems are found to be the primary entity that destroys the inversion, causing the vertical transport of the chemicals. The disturbed regions displayed more homogeneous vertical distributions of chemicals resulting from low‐level convergence and associated convection. Trajectory analysis showed that in undisturbed regions centered north of Hawaiian Islands, and in disturbed regions, the interaction between lower‐level easterlies and upper‐level westerlies plays a significant role on atmospheric chemistry over these regions.

Tropospheric water vapor imaging by combination of ground‐based and spaceborne GNSS sounding data

The Global Navigation Satellite System (GNSS) comprises the U.S. system GPS (Global Positioning System), its Russian pendant GLONASS, and presumably, in the future, the European system Galileo. The potential of GNSS‐based phase delay measurements for accurately estimating vertically and slant‐path‐integrated water vapor has been demonstrated recently for radio links between GPS satellites and ground‐based GPS receivers. GNSS‐based radio occultation, on the other hand, has been demonstrated via the GPS/Meteorology experiment to deliver accurate near‐vertical profiles of atmospheric variables such as temperature and humidity with high vertical resolution. Height‐resolving imaging of atmospheric water vapor becomes feasible when occultation profiles from spaceborne receivers in Low Earth Orbits (LEO) are combined with ground‐based GNSS data from a colocated receiver network. We developed a two‐dimensional, height‐resolving tomographic imaging technique following the Bayesian approach for optimal combination of information from different sources. Using simulated GNSS‐based water vapor measurements from LEO and ground, we show representative results derived from simple synthetic refractivity fields as well as from a realistic refractivity field based on a European Centre for Medium‐Range Weather Forecasts (ECMWF) analysis. For cases located poleward of ∼40° we found a new simple mapping function to perform best within our forward model scheme, where the only free parameter is the climatological scale height in the troposphere, the exact value of which is not critical. The mapping function exploits the ratio between the straight‐line ray path length within the first two scale heights above surface and the “effective height” defined by these first two scale heights. We found our technique capable of reconstructing atmospheric features like water vapor maxima near the top of the trade wind inversion. Adjustment of the integral over the water vapor profile measurements to the horizontally averaged ground‐based vertical integrated water vapor data efficiently mitigates potential biases in the former data. Accuracies are best in areas with high absolute humidities but also over drier areas such as Finland, useful two‐dimensional information can still be obtained. Thus it is attractive to apply the developed technique in a next step to real data.

Numerical Simulations of Airflow and Cloud Distributions over the Windward Side of the Island of Hawaii. Part I: The Effects of Trade Wind Inversion*

Abstract Initialized by the composite upstream sounding during the Hawaiian Rainband Project, high-resolution numerical experiments are conducted using the Pennsylvania State University–National Center for Atmospheric Research fifth generation Mesoscale Model to study the island-scale airflow and cloud distributions over the island of Hawaii without considering the diurnal heating cycle. The observed mean patterns of island airflow and weather under the summer trade wind conditions are well simulated. These features include orographic clouds on the windward slopes, flow deceleration and splitting on the windward side, leeside vortices, and cool and moist (warm and dry) conditions on the windward (lee) side. In addition to Fr (Froude number), the simulated island airflow and cloud distributions are sensitive to net diabatic heating associated with clouds and precipitation and rain evaporative cooling. The trade wind inversion height determines the depth of the moist trade wind layer, which also affects the...

A comparison of water vapor derived from GPS occultations and global weather analyses

Despite its fundamental importance in radiative transfer, atmospheric dynamics, and the hydrological cycle, atmospheric water is inadequately characterized particularly at a global scale. Occultation measurements from the Global Positioning System (GPS) should improve upon this situation. Individual occultations yield profiles of specific humidity accurate to 0.2 to 0.5 g/kg providing sensitive measurements of lower and middle tropospheric water vapor with global coverage in a unique, all‐weather, limb‐viewing geometry with several hundred meters to a kilometer vertical resolution. We have derived water vapor profiles from June 21 to July 4, 1995, using GPS occultation data combined with global temperature analyses from the European Center for Medium‐Range Weather Forecasts (ECMWF) and reanalyses from the National Centers for Environmental Prediction (NCEP). The zonal mean structure of the profiles exhibits basic climatological features of tropospheric moisture. Specific humidity biases between the GPS results and the ECMWF global humidity analyses in the middle to upper troposphere are ∼0.1 g/kg or less. Occultation results below 6 km altitude are generally drier than those of ECMWF with the bias generally increasing toward warmer temperatures. Near the height of the trade wind inversion, the ECMWF analyses are significantly moister than the occultation results due to vertical smoothing and overextension of the boundary layer top in the analyses. Overall, the occultation results are drier than the NCEP reanalyses with a marked exception near the Intertropical Convergence Zone (ITCZ) where occultation results are wetter by more than 10%. The occultation results are significantly wetter near the ITCZ and drier in the subtropics than the classical moisture climatology of Peixoto and Oort. Similarities between the NCEP and the Peixoto and Oort near‐ITCZ differences suggest that a common analysis/model problem may be responsible. The generally wetter Peixoto and Oort results in the subtropics are due in part to moist radiosonde biases. Discrepancies between these data sets are significant and limit our ability to resolve uncertainties in moisture control and feedbacks in a changing climate.

Climate Cycles, Geomorphological Change, and the Interpretation of Soil and Ecosystem Development

We evaluated changes in temperature and precipitation associated with climate change, subsidence, and erosion on a chronosequence of sites across Hawaii. The sites range in age from 0.3 to 4100 ky, and the current temperature and precipitation are similar at all sites. Interpretations of fossil pollen records suggest that cooler, dryer conditions prevailed in windward Hawaii during the last glacial period. If the previous glacial periods were similar, the 20-, 150-, and 1400-ky-old sites would have spent 60% or more of their development under relatively cool and dry conditions, whereas the 0.3- and 2.1-ky-old sites have experienced only the warmer, wetter climate of the present interglacial. Subsidence and erosion have also affected the temperature and precipitation of these sites over time; in the past, some of them have been in the dry air above the trade wind inversion or in the lee of larger mountains. Combining these components of change, we estimate that the average temperature over the history of Pleistocene-aged sites (20, 150, and 1400 ky) was up to 2.2°C cooler and that the average precipitation was only about 50% of current values. Under current conditions, it would take only 230 ky for as much water to leach through the 1400-ky-old site as we calculate has leached over 1400 ky. Incorporating more reasonable assumptions about environmental history has the potential to allow more powerful interpretations of chronosequence data and thereby improve the predictive potential of models of soil and ecosystem development.

Tropospheric reactive odd nitrogen over the South Pacific in austral springtime

The distribution of reactive nitrogen species over the South Pacific during austral springtime appears to be dominated by biomass burning emissions and possibly lightning and stratospheric inputs. The absence of robust correlations of reactive nitrogen species with source‐specific tracers (e.g., C2H2 [combustion], CH3Cl [biomass burning], C2Cl4 [industrial], 210Pb [continental], and 7Be [stratospheric]) suggests significant aging and processing of the sampled air parcels due to losses by surface deposition, OH attack, and dilution processes. Classification of the air parcels based on CO enhancements indicates that the greatest influence was found in plumes at 3–8 km altitude in the distributions of HNO3 and peroxyacetyl nitrate (PAN). Here mixing ratios of these species reached 600 parts per trillion by volume (pptv), values surprisingly large for a location several thousand kilometers removed from the nearest continental areas. The mixing ratio of total reactive nitrogen (the NOy sum), operationally defined in this paper as measured (NO + HNO3 + PAN + CH3ONO2 + C2H5ONO2) + modeled (NO2), had a median value of 285 pptv within these plumes compared with 120 pptv in nonplume air parcels. Particle NO−3 was not included in this analysis of the NOy sum due to its 10‐ to 15‐min sampling time resolution, but, in general, it was &lt;10% of the NOy sum. Comparison of the two air parcel classifications for NOy and alkyl nitrate distributions showed no perceivable plume influence, but recycling of reactive nitrogen may have masked this direct effect. In the marine boundary layer, the NOy sum averaged 50 pptv in both air parcel classifications, being somewhat isolated from the polluted conditions above it by the trade wind inversion. In this region, however, alkyl nitrates appear to have an important marine source where they comprise 20–80% of the NOy sum in equatorial and high‐latitude regions over the South Pacific.

Physical, chemical, and optical properties of regional hazes dominated by smoke in Brazil

Gas and particle measurements are described for optically thick regional hazes, dominated by aged smoke from biomass burning, in the cerrado and rain forested regions of Brazil. The hazes tended to be evenly mixed from the surface to the trade wind inversion at 3–4 km in altitude. The properties of aged gases and particles in the regional hazes were significantly different from those of young smoke (&lt;4 min old). As the smoke aged, the total amount of carbon in non‐methane hydrocarbon species (C&lt;11) was depleted by about one third due to transformations into CO2, CO, and reactive molecules, and removed by dry deposition and/or by conversion to particulate matter. As the smoke particles aged, their sizes increased significantly due to coagulation and mass growth by secondary species (e.g., ammonium, organic acids and sulfate). During aging, condensation and gas‐to‐particle conversion of inorganic and organic vapors increased the aerosol mass by ∼20–40%. One third to one half of this mass growth likely occurred in the first few hours of aging due to the condensation of large organic molecules. The remaining mass growth was probably associated with photochemical and cloud‐processing mechanisms operating over several days. Changes in particle sizes and compositions during aging had a large impact on the optical properties of the aerosol. Over a 2 to 4 day period, the fine particle mass‐scattering efficiency and single‐scattering albedo increased by 1 m2g−1, and ∼0.06, respectively. Conversely, the Angstrom coefficient, backscatter ratio, and mass absorption efficiency decreased significantly with age.

Global simulation of tropospheric O3‐NOx‐hydrocarbon chemistry: 2. Model evaluation and global ozone budget

Results from a global three‐dimensional model for tropospheric O3‐NOx‐hydrocarbon chemistry are presented and evaluated with surface, ozonesonde, and aircraft measurements. Seasonal variations and regional distributions of ozone, NO, peroxyacetylnitrate (PAN), CO, ethane, acetone, and H2O2 are examined. The model reproduces observed NO and PAN concentrations to within a factor of 2 for a wide range of tropospheric regions including the upper troposphere but tends to overestimate HNO3 concentrations in the remote troposphere (sometimes several fold). This discrepancy implies a missing sink for HNO3 that does not lead to rapid recycling of NOx; only in the upper troposphere over the tropical South Atlantic would a fast conversion of HNO3 to NOx improve the model simulation for NOx. Observed concentrations of acetone are reproduced in the model by including a large biogenic source (15 Tg C yr−1), which accounts for 40% of the estimated global source of acetone (37 Tg C yr−1). Concentrations of H2O2 in various regions of the troposphere are simulated usually to within a factor of 2, providing a test for HOx chemistry in the model. The model reproduces well the observed concentrations and seasonal variations of ozone in the troposphere, with some exceptions including an underestimate of the vertical gradient across the tropical trade wind inversion. A global budget analysis in the model indicates that the supply and loss of tropospheric ozone are dominated by photochemistry within the troposphere and that NOx. emitted in the southern hemisphere is twice as efficient at producing ozone as NOx emitted in the northern hemisphere.

Geomorphic Traces of Quaternary Climates in the Cordillera Central, Dominican Republic

The Cordillera Central in the Dominican Republic, island of Hispaniola, exceeds 3,000 m in height. Schubert and Medina (1982) identified possible relict glacial geomorphic features on air photographs. Modern mid-elevation lapse rates of -8.50C km-1 yield plausible paleo-snowlines below peak elevations with sea-surface temperature depressions between 2' and 8 'C, although paleo-dynamics of the tradewind inversion may be more important. This paper reports results of initial field reconnais- sance during 1996. In addition to surfaces interpreted as modern and as Tertiary relicts, there are also features that post-date sur- faces of postulated Tertiary age yet are unexplained by modern processes. These include diamictons, cirque-like depressions, in- cised alluvial fans, block fields, and debris lobes (interpreted by Schubert and Medina, 1982, as solifluction remnants). It is concluded that the climate of Hispaniola has not been complacent during the Quaternary because the present climatic state can- not explain the observed landscape.