Oceanic Air Research Articles

Palmer drought severity index as soil moisture indicator: physical interpretation, statistical behaviour and relation to global climate

Palmer Drought Severity Index (PDSI) series, based on monthly homogenised temperature and precipitation data, are analysed for the 1901–1999 period at three stations in West-Hungary, i.e. in an objectively separating region of the country, concerning spatial variations of the monthly PDSI fluctuations. All displayed results represent computations by the Thorthwaite-type potential evapotranspiration. Some comparison with those index-series, computed by the Blaney–Criddle method is given in the Discussion. Series of PDSI exhibit strong correlation with series of two independent soil moisture estimations. Having the regression coefficient standardised by standard deviation of the soil-moisture, we obtain similar coefficients during the year (allowing for only 10–30% difference). This means, PDSI can be considered as a soil-moisture indicator. It is shown that the monthly standard deviation of PDSI exhibit small variation, ca. 10%, with a minimum in the summer period. Distribution of monthly PDSI can be considered as Gaussian, according to the Kolmogorov–Smirnoff test, whereas according to the χ 2-test this is true for more than 2/3 of the cases. Exceptions all fall in the second half of the year. Finally, multi-annual relation of PDSI to the global temperature trends are analysed using the method of “slices” ( Mika, 1988), dividing the local and global values into uniform time sequences, the so called time-slices and calculating regression coefficients between the local PDSI and two hemispherical temperature variables. One of the latter is the hemispherical mean, the other is the continent–ocean air temperature contrast. This correlation is always negative and frequently significant, which means that in the 20th century local soil moisture conditions became drier parallel to the hemispherical changes.

Performance Metrics for Oceanic Air Traffic Management

The Federal Aviation Administration (FAA’s) Oceanic and Offshore Integrated Product Team is developing a set of performance metrics and identifying methodologies for calculating them. These metrics will be used to benchmark and measure how well the FAA’s Oceanic Air Traffic Control Centers are meeting their goals and priorities, and delivering oceanic air traffic services and benefits.There are many challenges that must be addressed to meaningfully measure and evaluate the oceanic system performance. Some of these challenges are the same as those for measuring the performance of the National Airspace System (NAS) as a whole. However, since many oceanic flights start or end in other countries, there are additional challenges in obtaining the data necessary to calculate the oceanic performance metrics.The FAA’s Air Traffic Services (ATS) organization identified a set of system performance outcomes in the areas of safety and operation efficiency (e.g., predictability, flexibility, delay, and access). Oceanic airspace users indicated their priority areas as safety, on-time performance, fly as filed, flexibility, and fuel consumption. The oceanic performance metrics have been developed to measure the ATS outcomes and the users’ priorities. In addition, environmental factors (e.g., flight count, aircraft avionics equipage) that affect the service delivery are included to provide a proper context for the metrics.The oceanic metrics are collected in a “dashboard” to provide a general picture of the overall service quality provided to oceanic airspace users. A dashboard is generated for each of the New York and Oakland Oceanic Centers, as well as for sub-regions in each Center to account for the air traffic characteristics unique to that sub-region.This paper presents example analyses and results obtained for environmental and performance metrics for New York and Oakland Oceanic Centers, and shows how the metrics can be used to monitor the performance of air traffic management services provided to oceanic airspace users.

Convective lofting links Indian Ocean air pollution to paradoxical South Atlantic ozone maxima

We describe a broad resolution of the “Atlantic Parado” concerning the seasonal and geographic distribution of tropical tropospheric ozone. We highlight periods of significant maximum tropospheric O3 for Jan.–April, 1999, exploiting satellite estimates and SHADOZ (Southern Hemisphere Additional Ozonesondes). Trajectory analyses connecting sondes and Total Tropospheric Ozone (TTO) maps suggest a complex influence from the Indian Ocean: beginning with mixed combustion sources, then low level transport, cumulonimbus venting, possible stratospheric input, and finally high‐level transport to the west, with possible mixing over Africa. For the Jan.–March highest column‐O3 periods in the Atlantic, distinct sounding peaks trace to specific NO sources, especially lightning, while in the same episodes, recurring every 20–50 days, more diffuse buildups of Indian‐to‐Atlantic pollution make important contributions.

Modern isotope climatology of Russia: A first assessment

The spatial and temporal variation in the stable isotopic composition of precipitation collected at 13 monitoring stations across Russia between 1996 and 2000 was determined. The results show that eastward moisture transport over the continent generates a tendency toward more negative isotopic content farther inland throughout the year. This negative isotopic gradient can be explained by the gradual rain‐out of moist, oceanic air masses, which are transported inland by westerly winds. In summer, however, the isotopic gradient is less clear, because of additional moisture that is supplied from land surfaces. The isotopic pattern of summer precipitation is less sensitive to moisture content but is largely influenced by the original moisture. In Siberia, more than half of the moisture that forms summer precipitation originates from land surfaces; thus the isotopic content of precipitation in this region is controlled mainly by the contribution of recycled water; e.g., the proportion of water that is recycled (recycling ratio) and its isotopic composition. Comparisons of the observed summer isotopic content of precipitation and the calculated recycling ratio from National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data show that about 20% of the total variability of isotopic content during summer can be linked to the recycling ratio. About 45% of the summer isotopic variability cannot be explained by either temperature, which is used as an indicator of moisture content, or the recycling ratio. This remaining variability may be linked to the isotopic variability of the recycled water that falls as observed precipitation. It may be that the isotopic content of recycled water varies in space and time and the isotopic distribution in summer precipitation reveals details in this feature; thus it might be possible to deduce information about the interaction between land and atmosphere in the hydrologic cycle from the isotopic content of precipitation.

Structure and Development of Two Merged Rainbands Observed over the East China Sea during X-BAIU-99 Part II: Meso-.ALPHA.-Scale Structure and Build-up Processes of Convergence in the Baiu Frontal Region

In this paper, the synoptic- and meso-α scales structure of two oceanic rainbands, and build-up processes of the frontal convergence, are investigated with the use of a regional spectral model (RSM) and a nonhydrostatic model (NHM). Over the eastern part of the East China Sea on 27 June 1999 during the X-BAIU-99, we observed that a northern rainband (LINE2) merged into a southern rainband (LINE1), and LINE1 developed rapidly. Before their merging, LINE1 and LINE2 developed along the “water vapor front” and the Baiu front, respectively. The “water vapor front,” found by the meso-β-scale analyses of Part I of this series, is a weak convergence line with a large moisture gradient in a southerly wind field. In the RSM-simulated field, the “water vapor front” extended from the eastern coast of China with a length of about 1000 km. The NHM simulation revealed that the “water vapor front” is a convergence line with oceanic southwesterly and continental westerly flows. The convergence line formed a meso-α-scale rainband (LINE1) in the southerly wind field over the ocean without any land effects. Because an abundant moisture supply with the oceanic airflow was blocked at the “water vapor front” by the continental airflow, the rainfall intensity was quite weak along the western part of the Baiu front. The lowlevel convergence of the eastern part of the “water vapor front” was quite weak, the oceanic air had partially advected into the eastern part of the Baiu front, and LINE2 developed strongly. In a synoptic-scale cold air mass to the north of the Baiu front, a meso-α-scale cold pool formed in a stratiform precipitation region. The cold pool expanded to the south, and pushed rapidly southward the Baiu front, about 50 km in 2 hours. It was confirmed that the cold pool was created by an evaporation cooling of raindrops from a sensitivity experiment. The experiment revealed that the cold pool continuously accelerated northerly winds, and intensified the low-level convergence along the Baiu front. In the areas of the southern side of the Baiu front, and the “water vapor front,” southerly winds were greatly accelerated over 5 m s-1 in 4 hours by the pressure gradient force enhanced near the convective rainfalls of LINE1 and LINE2. The frontal convergence along both fronts were greatly enhanced by the acceleration of the southerly winds.

Nineteenth century Parisian smoke variations inferred from Eiffel Tower atmospheric electrical observations

Atmospheric electrical measurements provide proxy data from which historic smoke pollution levels can be determined. This approach is applied to infer autumnal Parisian smoke levels in the 1890s, based on atmospheric electric potential measurements made at the surface and the summit of the Eiffel Tower (48.7°N, 2.4°E). A theoretical model of the development of the autumn convective boundary layer is used to determine when local pollution effects dominated the Eiffel Tower potential measurements. The diurnal variation of the Eiffel Tower potential showed a single oscillation, but it differs from the standard oceanic air potential gradient (PG) variations during the period 09–17 UT, when the model indicates that the Eiffel Tower summit should be within the boundary layer. Outside these hours, the potential changes closely follow the clean air PG variation: this finding is used to calibrate the Eiffel Tower measurements. The surface smoke pollution concentration found during the morning maximum was 60±30 μg m−3, substantially lower than the values previously inferred for Kew in 1863. A vertical smoke profile was also derived using a combination of the atmospheric electrical data and boundary layer meteorology theory. Midday smoke concentration decreased with height from 60 μg m−3 at the surface to 15 μg m−3 at the top of the Eiffel Tower. The 19th century PG measurements in both polluted and clean Parisian air present a unique resource for European air pollution and atmospheric composition studies, and early evidence of the global atmospheric electrical circuit.

Trends and Variations in South Pacific Island and Ocean Surface Temperatures

An analysis of temperature variability and trends in the South Pacific, mainly in the twentieth century, using data from 40 island stations and optimally interpolated sea surface and night marine air temperature data is presented. The last-named dataset is new and contains improved corrections for changes in the height of thermometer screens as ships have become larger. It is shown that the South Pacific convergence zone plays a pivotal role in both variability and trends in all three datasets. Island, collocated sea surface temperature, and night marine air temperature time series for four large constituent regions are created and analyzed. These have been corrected for artificial changes in variance due to changes in the availability of constituent island stations whose intrinsic variance varies from station to station. The method is described in detail. Objective estimates of uncertainty in the sea surface temperature data are also provided. The results extend previous work, showing that annual and seasonal surface ocean and island air temperatures have increased throughout the South Pacific. Variations in trends in the island and marine data show reasonable consistency, with distinctly different patterns of multidecadal change in the four regions. However, a notable inconsistency is the recent lack of warming in night marine air temperature in one of the tropical regions relative to sea surface temperature, with signs of this effect in a second tropical region. Another tropical region near the South Pacific convergence zone shows recent strong warming in the island data but not in the marine data.

Automated Meteorological Reports from Commercial Aircraft

Commercial aircraft now provide over 130,000 meteorological observations per day, including temperature, winds, and in some cases, humidity, vertical wind gust, or eddy dissipation rate (turbulence). The temperature and wind data are used in most operational numerical weather prediction models at NCEP and at other centers worldwide. At nonsynoptic times, these data are often the primary source of upper-air information over the United States. Even at synoptic times, these data are critical in depicting the atmosphere along oceanic air routes. A Web site [http://acweb.fsl.noaa.gov/] has been developed that gives selected users access to these data. Because the data are proprietary to the airlines, real-time access is restricted to entities such as government agencies and nonprofit research institutions (although sample past data are available to all). Data can be displayed in a variety of ways and can be downloaded for local processing. These data are described here, and examples of how they have been usefu...

洋上空域の近接解決のための制御手法

Control methods were evaluated, which resolve conflict in the oceanic airspace. A simulation was carried out, in which aircraft flies on its requested altitude based on the current traffic volume of east bound traffic. Pair of adjacent aircraft were detected that fly at the same altitude at the significant point in the oceanic air route with shorter longitudinal separation than the separation standard. Cross fix time and altitude are assigned on each flight at the significant point in the oceanic air route, in order to keep separation of the pair of adjacent aircraft. The ratio of average altitude change and time change of aircraft is controlled with the time threshold of the control methods. Two control methods were compared. One method sets priority of aircraft on the sequence of departure time and another sets priority on the sequence of cross fix time at the point. The simulation result shows that the control method of the cross fix time sequence is better than that of the departure time sequence with respect to the average of altitude change, the average of time change and the variance of altitude change on the classification of departure airport. The control method of the cross fix time sequence is effective and impartial.

Seasonal C-cycling variability in the open and ice-covered waters of the Barents Sea: an introduction

Models of the ocean–atmosphere system demonstrate the potentially great importance of polar oceans to the regulation of atmospheric CO2. This is due, in great part, to the action of the surface biota (Barnard et al., 1984; Sarmiento and Toggweiler, 1984; Sundquist and Broecker, 1985; Erickson et al., 1990). Phytoplankton are the major producers of organic matter in open waters and account for approximately 30% of the world’s primary production (Falkowski, 1980). These primary producers dominate the recycling of dissolved and potentially volatile carbon at the ocean–air interface. In particular they act as sink for carbon dioxide (CO2). Compared to other areas of the world’s ocean, polar seas have a large influence on the atmosphere’s CO2 content (Anderson et al., 1998, 1999), mainly due to deepwater formation and plume entrainment. Segregation of atmospheric CO2 in polar seas takes place, in great part, through the action of the surface biota (Slagstad et al., 1999; Bostrom, 2000). One way the taken-up carbon becomes inaccessible to the atmosphere is through gravitational sinking to intermediate depths in particulate form or intermediate and deepwater formation. Quantification of sources and sinks of carbon is instrumental to the basic understanding of marine ecosystems. A major loss of organic matter produced in the euphotic zone takes place through settling of phytoplankton cells, faecal pellets and phytoplankton-derived detritus (Wassmann, 1998). The sinking of POM links the surface primary production to food webs beneath the euphotic zone and finally supplies the organic matter and energy to the benthic communities (Smetacek, 1984; Grebmeier et al., 1988). Arctic shelves such as the Bering Straight, the Chuchi Sea and the Barents Sea belong to the most productive environments on earth, particularly during springtime. A distinct spring bloom at the MIZ edge and the long duration of the MIZ bloom as the ice edge recedes northwards during summer adds to the high productivity of Arctic shelves. North–south spatial ecological gradients of nutrients, phytoplankton and higher trophic levels similar to temporal succession observed at any one location are typical for the Barents Sea (Sakshaug and Skjoldal, 1989; Vernet et al., 1998; Wassmann et al., 1999). The bloom development, the secondary production and the fate of the organic matter along the west Spitsbergen and east Greenland shelf is not known in detail. However, the physical forcing and the ice dynamics in

The February 2001 Eruption of Mount Cleveland, Alaska: Case Study of an Aviation Hazard

Mount Cleveland, Alaska (528499N, 1698579W), located on Chuginadak Island, erupted on 19 February 2001. The atmosphere‐volcanic plume interactions that occurred as part of this event led to several serious encounters of commercial aircraft with the ash. A number of continental and oceanic air traffic control areas were affected. Here, a detailed case study of the eruption, subsequent movement of the airborne plume, and operational response is presented. The likelihood of such encounters in the future may be reduced as a result of lessons learned from this event. Some potential new assets for improving the detection of and response to the airborne volcanic ash hazard to aviation also are discussed.

Late Quaternary history of spruce in southern Europe

The late Quaternary history of fossil spruces in southern Europe ( Picea abies (L.) Karsten and Picea omorika (Pancic) Purkyne) is based on 163 selected pollen, charcoal and macrofossil records. The timing of immigration of P. abies is estimated from data where the Picea curve passed the threshold value of 4%. P. abies occupied the southern European mountain ranges – excluding the Pyrenees – during the middle part of the last interglacial. Spruce reached its late Quaternary maximum expansion during the early Weichselian, after which it retired from central Europe and expanded in southern Europe during the middle Weichselian interstadials. A general decline in geographical distribution occurred during the last glacial maximum, and populations were most restricted during the Alpine deglaciation. The concept of ‘glacial refugia’ does not apply to residual populations because current climatic reconstructions relate periods of maximum spruce decline to maximum continental dryness during the growth season, rather than to full glacial conditions. Spruce took part in late glacial and early Holocene tree expansions in the eastern Alps and Carpathian, but failed to spread from residual populations in the Apennines and the Pirin–Rila–Rhodopes Mountains. These differences are explained by the influence of oceanic air masses on upper forest belts with relation to geographic location and maximum elevation of mountain ranges. Late glacial spruce expansion in the Alps coincides with the abrupt warming at 14 700–14 500 yr cal BP. High migration rates were reached in the upper forest belts (e.g. 1500–2300 masl) during the early Holocene, and decreased since about 6 kyr cal BP, as a result of climatic cooling during the Neoglaciation (treeline depression), ecological competition with other tree species ( Abies alba), climatic and physical setting of the highest ranges in western Alps, and human impact. The long late Quaternary fossil history of presently isolated spruce stands from the Apennines accounts for their state of genetic differentiation, which could not be fully understood from the shorter time interval of postglacial events.

Role of oceanic air bubbles in atmospheric correction of ocean color imagery.

Ocean color is the radiance that emanates from the ocean because of scattering by chlorophyll pigments and particles of organic and inorganic origin. Air bubbles in the ocean also scatter light and thus contribute to the water-leaving radiance. This additional water-leaving radiance that is due to oceanic air bubbles could violate the black pixel assumption at near-infrared wavelengths and be attributed to chlorophyll in the visible. Hence, the accuracy of the atmospheric correction required for the retrieval of ocean color from satellite measurements is impaired. A comprehensive radiative transfer code for the coupled atmosphere--ocean system is employed to assess the effect of oceanic air bubbles on atmospheric correction of ocean color imagery. This effect is found to depend on the wavelength-dependent optical properties of oceanic air bubbles as well as atmospheric aerosols.

Comparison of Measured Ozone Production Efficiencies in the Marine Boundary Layer at Two European Coastal Sites under Different Pollution Regimes

Ozone production efficiencies (EN), which can be defined as the netnumber of ozone molecules produced per molecule of NOxoxidised, have been calculated from measurements taken during three intensive field campaigns (one in the spring, EASE 96, and two in the summer, EASE 97 and TIGER 95), at two European coastal sites (Mace Head, Ireland (EASE) and Weybourne, Norfolk (TIGER)) impacted by polluted air masses originating from both the U.K. and continental Europe, as well as relatively clean oceanic air masses from the Arctic and Atlantic. From a detailed wind sector analysis of the EASE 96 and 97 data it is clear that two general types of pollution regime were encountered at Mace Head. The calculated ozone production efficiency in clean oceanic air masses was approximately 65, which contrasted to more polluted air, from the U.K. and the continental European plume, where the efficiency decreased to between 4 and 6. The latter values of ENagree well with literature measurements conducted downwind of various urban centres in the U.S. and Europe, which are summarised in a wide-ranging review table. The EN value calculated for clean oceanic air is effectivelyan upper limit, owing to the relatively rapid deposition of HNO3 tothe ocean. Consideration of the variation of EN with NOx forthe three campaigns suggests that ozone production efficiency is relatively insensitive to both geographical location and season. The measuredEN values are also compared with values derived from steady-state expressions. An observed anti-correlation between EN and measured ozone tendencyis briefly discussed.

Carbon dioxide flux techniques performed during GasEx-98

A comprehensive study of air–sea interactions focused on improving the quantification of CO2 fluxes and gas transfer velocities was performed within a large open ocean CO2 sink region in the North Atlantic. This study, GasEx-98, included shipboard measurements of direct covariance CO2 fluxes, atmospheric CO2 profiles, atmospheric DMS profiles, water column mass balances of CO2, and measurements of deliberate SF6–3He tracers, along with air–sea momentum, heat, and water vapor fluxes. The large air–sea differences in partial pressure of CO2 caused by a springtime algal bloom provided high signals for accurate CO2 flux measurements. Measurements were performed over a wind speed range of 1–16 m s−1 during the three-week process study. This first comparison between the novel air-side and more conventional water column measurements of air–sea gas transfer show a general agreement between independent air–sea gas flux techniques. These new advances in open ocean air–sea gas flux measurements demonstrate the progress in the ability to quantify air–sea CO2 fluxes on short time scales. This capability will help improve the understanding of processes controlling the air–sea fluxes, which in turn will improve our ability to make regional and global CO2 flux estimates.

Satellite detection of dust using the IR imagery of Meteosat: 1. Infrared difference dust index

The Infrared Difference Dust Index (IDDI) is a satellite dust product designed for climatological applications, designed specifically for dust remote sensing in arid regions such as the Sahel and Sahara. It is based on the atmospheric response to dust, extracted from midday Meteosat‐IR imagery, and takes advantage of the impact of dust aerosols on the thermal infra‐red radiance outgoing to space. Simulations show a quasi‐linear relationship between satellite response to dust and shortwave optical depth, with a sensitivity depending on particle size distribution and radiative surface properties. Comparison of measured satellite response with photometric optical depth agrees with the simulations. Water vapor significantly affects the satellite signal for cases of large columnar amounts and oceanic air masses advected inland. Hence apart from possible coastal effects, the water vapor effect can be neglected in the Sahelian‐Saharan zone north of the Intertropical Convergence Zone, coinciding with the major regions of African dust emission and transport. The construction of the IDDI involves the processing of reference images, theoretically representing the outgoing radiance obtaining under clear‐sky conditions. Errors may arise from (1) dust remaining in the reference images and (2) seasonal shifts of the reference level; however, the latter error will be offset by averaging used in climatological processing. An error budget is presented for the station of Gao. A statistical comparison of IDDI data with visibility measured at synoptic stations results in (1) a validation of the product, and (2) a climatologically relevant visibility‐IDDI relation, valid for the arid regions of northern Africa. The latter relation is consistent with both simulations and photometric measurements. IDDI maps over Africa compare successfully with optical depth over adjacent ocean regions derived from Meteosat‐VIS imagery. The observed continuity of dust plumes across the African coast demonstrates the consistency between both products.

Observations Of The Turbulence Structure Within Two Stratocumulus-Topped, Marine Boundary Layers

Two situations observed during the second Aerosol Characterization Experiment (ACE-2) are analysed from aircraft measurements in the broken stratocumulus (Sc)-topped marine boundary layer. The first one (26 June 1997), characterized by a non-polluted, oceanic air mass, presents a decoupling between the Sc layer (1400–1520 m) and the turbulent mixed layer, this latter extending from the surface up to 580 m. In contrast, the second case (9 July 1997), during which continental air had been advected over the experimental area, presents a well-coupled layer extending from the surface up to the top of the Sc layer(910 m). This coupling, uncommon in this area in the middle of the day, isrelated to the relative shallowness of the boundary layer. For both situations,it is shown that the turbulent fluxes can be computed with reasonably goodaccuracy (better than 10 %), taking into account both the random and thesystematic errors involved in the eddy-correlation technique. Estimationof random error is based on the computation of the integral scale of thecovariance, and systematic error is estimated from the parameterizationof Mann and Lenschow. The fluxes show that the buoyancy, as a sourceof turbulence, is due to latent heat flux rather than sensible heat flux,with values comparable to previous experiments in the Azores-Canariesbasin. In addition, we propose a method to analyse, for coupled situations,the relationship between the fractional cloudiness and the organization ofthe turbulent field below the clouds. This method is based on a conditionalsampling technique. It is shown that this organization cannot be deducedfrom the analysis of the velocity signal, which is dominated by turbulence.However, when the signals are conditionally sampled according to thepresence or absence of clouds, a weak cloud-related organization can beshown, and the cloud-related transports quantified; the values found areof the order of 10 % of the total transfers, i.e. the same order of magnitude asthe errors on the total flux computation. The method developed is thereforepromising, provided that the uncertainties can be reduced by analyzing a highamount of data.

Monitoring of ozone in a marine environment in Tenerife (Canary Islands)

In the Aguere Valley (in the oceanic boundary layer at Tenerife, 28°N, 16°W, 580 m a.s.l.) the ozone levels were monitored for ambient air quality assessment. Although precursors are emitted in this area, the strong correlation between ozone levels and wind velocity indicates that ozone is transported into the valley from the ocean. The inland ozone supply along the valley is induced by an orographic channelling effect of the northern oceanic air masses. The highest ozone concentrations are mostly recorded during the nocturnal stage under the influence of fresh oceanic air masses, and during high wind speed events. The seasonal cycle is characterised by elevated ozone mixing ratios in the spring (nighttime levels >45 ppbv) and low mixing ratios in the summer (nighttime levels in the range 20–35 ppbv). Back-trajectory analysis shows that the ozone monitored in the Aguere Valley is associated with long-range transport processes. High ozone events in the spring are associated with transport from upper tropospheric levels, both over the North Atlantic-high latitudes (>45°N) and Europe. This downward transport was observed in the western edge of upper tropospheric cyclones, which suggests that the upper tropospheric/low stratospheric ozone sources play a significant role. In summer, ozone is mainly transported from the North Atlantic-high latitudes (>45°N) and from mid- to low-tropospheric levels. In autumn and winter, the high ozone concentrations are transported from sources located a few km above the North Atlantic-high latitudes (>45°N) and over Europe. The Central-North Atlantic (<45°N) and North Africa are not significant sources of ozone. The high spring and lower summer ozone events in the Aguere Valley agree with other North Atlantic ozone observation in the oceanic boundary layer. However, this behaviour contrasts with the high ozone events frequently recorded at Izaña BAPMoN station (located in the free troposphere in Tenerife) during the summer, which have been attributed in the literature to downward transport from upper levels. An intensification of the inversion layer that separates the oceanic boundary layer of the free troposphere during the summer in Canary Islands is interpreted as the cause of this different behaviour between ozone in the Aguere Valley and Izaña BAPMoN station.

The Diabatic Deacon Cell*

Abstract Southern Ocean air–sea fluxes from the COADS dataset are examined for compatibility between buoyancy gain and northward Ekman transport. An analysis in density classes points to an upwelling of Upper Circumpolar Deep Water and subsequent buoyancy gain from air–sea exchange as water flows northward in the Ekman layer. The Upper Circumpolar Deep Water layer is too shallow to admit southward geostrophic flow along topography, and an eddy mass flux mechanism for southward transport in this layer to replenish the upwelling is advanced, based on observed large-scale potential vorticity gradients. Estimates of the strength and vertical structure of the meridional flow are given using repeated hydrographic sections and a new climatology.

Agreement between Observed Rainfall Trends and Climate Change Simulations in the Southwest of Europe

The lowest spatial scale at which current climate models are considered to be skillful is on the order of 1000 km because of resolution and computer capabilities. The estimation of the regional changes caused by anthropogenic emissions of greenhouse gases and aerosols therefore is problematic. Here a statistical downscaling scheme is used to study the relationship between large-scale sea level pressure and regional precipitation in southwestern Europe, both in observed data and in outputs from a general circulation model (GCM) forced with increasing levels of greenhouse gases and sulfate aerosols. The results indicate that the GCM does reproduce the main aspects of the large- to local-scale coupled variability. Furthermore, these large- to local-scale relationships remain stable in the scenario simulations. The GCM runs predict increases of advection of oceanic air masses to the Iberian Peninsula that will produce a slight decrease of precipitation amounts in the north coast and the opposite effect in the rest of the territory, with values that could reach 10 mm decade−1 in the south. In the homogenized historical records, the obtained pattern of change is very similar. These results support estimations of future regional trends simulated by the GCM under future emission scenarios.