Zonal Trends Research Articles

Application of deep learning to estimate stratospheric gravity wave potential energy

One of the most important dynamic processes in the middle and upper atmosphere, gravity waves (GWs) play a key role in determining global atmospheric circulation. Gravity wave potential energy (GW <i>E</i>_p) is an important parameter that characterizes GW intensity, so it is critical to understand its global distribution. In this paper, a deep learning algorithm (DeepLab V3+) is used to estimate the stratospheric GW <i>E</i>_p. The deep learning model inputs are ERA5 reanalysis datasets and GMTED2010 terrain data. GW <i>E</i>_p averaged over 20−30 km from 60°S−60°N, calculated by COSMIC radio occultation (RO) data, is used as the measured value corresponding to the model output. The results show that (1) this method can effectively estimate the zonal trend of GW <i>E</i>_p. However, the errors between the estimated and measured value of <i>E</i>_p are larger in low-latitude regions than in mid-latitude regions, possibly due to the large number of convolution operations used in the deep learning model. Additionally, the measured <i>E</i>_p has errors associated with interpolation to the grid; this tends to be amplified in low-latitude regions because the GW <i>E</i>_p is larger and the RO data are relatively sparse, affecting the training accuracy. (2) The estimated <i>E</i>_p shows seasonal variations, which are stronger in the winter hemisphere and weaker in the summer hemisphere. (3) The effect of quasi-biennial oscillation (QBO) can be clearly observed in the monthly variation of estimated GW <i>E</i>_p, and its QBO amplitude may be less than that of the measured<i> E</i>_p.

Органическое вещество почв и техногенных поверхностных образований селитебных районов г. Перми

On the territory of the left-bank part of Perm, the urban pedocomplexes (UPC) were distinguished as a combination of soil and technogenic surface formations on the same soil-forming rocks within a certain functional zone. Within the UPC, formed on eluvial-deluvial loams and clays in the zone of multi-storey buildings, the surface horizons of soils and TSF (technogenic surface formations) were studied. A change in the zonal trend of humus formation in reclaimed soils was observed as an increase in the content of organic matter, as well as in a change in the type of humus to the humate side. The conservation of zonal features of humus formation in non-purposefully recultivated urban soils and TSF was noted. It manifests in a low or medium content of organic carbon, the formation of a humate-fulvate type of humus. Keywords: URBAN ECOLOGY, URBAN SOILS, URBAN PEDOCOMPLEX, HUMUS, HUMUS TYPE, SOIL PROPERTIES

ANALYSIS OF THE DISTRIBUTION AND STRUCTURE OF DIURNAL LEPIDOPTERA (LEPIDOPTERA: HESPERIOIDEA, PAPILIONOIDEA) RANGES IN UDMURTIA

The article analyzes the zonal landscape distribution and the structure of the diurnal lepidoptera ranges on the territory of the Udmurt Republic. The zonal indicators of the dynamics of the species richness of lepidoptera in the region have the following form: the southern taiga - 100 species, the subtaiga as a whole-122 species, including the northern band of the subtaiga-107 species, the southern band of the subtaiga-119 species. The zonal trend is based on the significant participation of the regional fauna of the regional representatives. The general indicators of the numerical participation of structural and arealographic groups in the fauna are as follows: 46 species are located within the generalized part of the area in the region; 22 species are located near the periphery of the area; 42 species are located on the border of the area; 13 species are located on the periphery of the area. The main share of lepidoptera located in the marginal parts of their ranges is made up of southern subboreal (steppe and non-morale) and subboreal-subtropical representatives (72 species). The proportion of such species among the northern geographical groups - the Hypo-Arctic and boreal (16 species) is significantly lower. The most important biochorological units that determine the conditions for the distribution and localization of bulavous are uplands, forest landscapes on the sands, as well as the valleys of large and medium-sized rivers in the southern part of the region.

Is our dynamical understanding of the circulation changes associated with the Antarctic ozone hole sensitive to the choice of reanalysis dataset?

Abstract. This study quantifies differences among four widely used atmospheric reanalysis datasets (ERA5, JRA-55, MERRA-2, and CFSR) in their representation of the dynamical changes induced by springtime polar stratospheric ozone depletion in the Southern Hemisphere from 1980 to 2001. The intercomparison is undertaken as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The reanalyses are generally in good agreement in their representation of the strengthening of the lower stratospheric polar vortex during the austral spring–summer season, associated with reduced radiative heating due to ozone loss, as well as the descent of anomalously strong westerly winds into the troposphere during summer and the subsequent poleward displacement and intensification of the polar front jet. Differences in the trends in zonal wind between the reanalyses are generally small compared to the mean trends. The exception is CFSR, which exhibits greater disagreement compared to the other three reanalysis datasets, with stronger westerly winds in the lower stratosphere in spring and a larger poleward displacement of the tropospheric westerly jet in summer. The dynamical changes associated with the ozone hole are examined by investigating the momentum budget and then the eddy heat and momentum fluxes in terms of planetary- and synoptic-scale Rossby wave contributions. The dynamical changes are consistently represented across the reanalyses and support our dynamical understanding of the response of the coupled stratosphere–troposphere system to the ozone hole. Although our results suggest a high degree of consistency across the four reanalysis datasets in the representation of these dynamical changes, there are larger differences in the wave forcing, residual circulation, and eddy propagation changes compared to the zonal wind trends. In particular, there is a noticeable disparity in these trends in CFSR compared to the other three reanalyses, while the best agreement is found between ERA5 and JRA-55. Greater uncertainty in the components of the momentum budget, as opposed to mean circulation, suggests that the zonal wind is better constrained by the assimilation of observations compared to the wave forcing, residual circulation, and eddy momentum and heat fluxes, which are more dependent on the model-based forecasts that can differ between reanalyses. Looking forward, however, these findings give us confidence that reanalysis datasets can be used to assess changes associated with the ongoing recovery of stratospheric ozone.

Spatially patterned microribbon-based hydrogels induce zonally-organized cartilage regeneration by stem cells in 3D

Regenerating cartilage with biomimetic zonal organization, which is critical for tissue function, remains a great challenge. The objective of this study was to evaluate the potential of spatially-patterned, multi-compositional, macroporous, extracellular matrix-based microribbon (µRB) µRB scaffolds to regenerate cartilage with biochemical, mechanical, and morphological zonal organization by mesenchymal stem cells (MSCs) compared to conventional multi-layer nanoporous hydrogels. MSCs were seeded in either trilayer microribbon (µRB) or hydrogel (HG) scaffolds that were composed of layered biomaterial compositions that had been chosen for their ability to differentiate MSCs into chondrocytes with zonal properties. To mimic the aligned collagen morphology in the superficial layer of native cartilage, an additional experimental group added MSC-laden aligned µRBs to the surface of the superficial layer of a µRB trilayer. Tuning µRB alignment and compositions in different zones led to zonal-specific responses of MSCs to create neocartilage with zonal biochemical, morphological, and mechanical properties, while trilayer HGs led to minimal cartilaginous deposition overall. Trilayer µRBs created neocartilage exhibiting significant increases in compressive modulus (up to 456 kPa) and > 4-fold increase in sGAG production from superficial to deep zones. Aligned gelatin µRBs in the superficial zone further enhanced biomimetic mimicry of the produced neocartilage by leading to robust collagen deposition and superficial zone protein production. Statement of significanceRegenerating cartilage with zonal organization using mesenchymal stem cells (MSCs) remains a great challenge. We developed a spatially-patterned, gradient, macroporous, trilayer microribbon (µRB) scaffold that we used to engineer MSC-based neocartilage with zonal trends that match native cartilage in many aspects, including collagen, sGAG, superficial zone protein, and compressive moduli. This is in direct contrast to conventional trilayer nanoporous hydrogels which led to minimal cartilage deposition and weak mechanical properties. It took only 21 days for MSC-seeded trilayer µRB scaffolds to reach cartilage-mimicking compressive moduli without requiring high cell seeding density, which has never been reported before. While this paper focuses on cartilage zonal organization, gradient µRB scaffolds can be used to repair other tissue interfaces such as osteochondral defects.

Mapping water ice clouds on Mars with MRO/MARCI

Observations by the Mars Color Imager (MARCI) onboard the Mars Reconnaissance Orbiter (MRO) in the ultraviolet (UV, Band 7; 320 nm) are used to characterize the spatial and temporal behavior of atmospheric water ice over a period of 6 Mars Years. Exploiting the contrast of the bright ice clouds to the low albedo surface, a radiative transfer-based retrieval algorithm is developed to derive the column-integrated optical depth of the ice (τice). Several relatively unique input products are created as part of the retrieval development process, including a zonal dust climatology based on emission phase function (EPFs) sequences from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), a spatially variable UV-reflectance model for Band 7 (as well as for Band 6, 260 nm), and a water ice scattering phase function based on a droxtal ice habit. Taking into account a radiometric precision of 7%, an error analysis estimates the uncertainty in τice to be ∼0.03 (excluding particle size effects, which are discussed separately). Zonal trends are analyzed over the full temporal extent of the observations, looking at both diurnal and interannual variability. The main (zonal) features are the aphelion cloud belt (ACB) and the polar hoods. For the ACB, there can be an appreciable diurnal change in τice between the periods of 14h30–15h00 and 15h00–15h30 Local True Solar Time (LTST). The amplitude of this effect shows relatively large interannual variability, associated mainly with changes in the earlier time block. When averaged over the interval 14h00–16h00 LTST, the interannual differences in the ACB structure are appreciably smaller. When the MARCI τice are compared to those from the Thermal Emission Spectrometer (TES), there is a good correlation of features, with the most significant difference being the seasonal (LS) evolution of the ACB. For TES, the ACB zonal profile is relative symmetric about LS = 90°. In the MARCI data, this profile is noticeably asymmetric, with the centroid shifted to later in the northern summer season (LS = 120°). The MARCI behavior is consistent with that observed by several other instruments. The correspondence of MARCI τice zonal and meridional behaviors with that predicted by two Global Circulation Models (GCM) is good. Each model captures the general behavior seen by MARCI in the ACB, the polar hoods, and the major orographic/topographic cloud features (including Valles Mariners). However, the mismatches between GCM results and MARCI reinforce the challenging nature of water ice clouds for dynamical models. The released τice are being archived at Malin Space Science Systems at https://www.msss.com/mro_marci_iceclouds/.

Geographical variation and the response to hydrothermal factor of stable carbon isotope (δ13C) in Pinus massoniana.

We used 10 representative provenances at different latitudes in two 33-year-old Pinus massoniana provenance test stands (Chun'an Laoshan in Zhejiang and Taizi Mountain Shilong in Hubei) to measure the differences among provenances, study the geographical variation, and identify its responses to hydrothermal factors. The results showed that the δ13C of the average annual rings was significantly different among the provenances of P. massoniana, being higher in trees from high latitude than from low latitude. The δ13C of average annual rings showed a zonal variation trend, indicating an adaptation to the original environment. The δ13C of annual rings was negatively correlated with mean annual temperature (MAT), mean temperature in January (T1), annual precipitation (MAP), precipitation from May to September (P5-9) and cumulative temperature above 10 ℃ (CT). It was positively correlated with the aridity index (AI). The response function of AI toδδ13C annual rings in Chun'an and Taizi Mountain explained 37.5% and 42.5% of the variation, respectively, indicating that AI was the most important limiting factor. The Taizi Mountain test site in Hubei Province located in the central and western region with relatively dry soil and high aridity. Therefore, the δ13C of the average annual ring was 1.8% higher than that in the Chun'an test site. The δ13C rings of P. massoniana at the Taizi Mountain and Chun'an were sensitive to the temperature in July and August, respectively. Summer precipitation was the main factor for carbon isotope fractionation with stable rings. The sensitivity of different provenances to future climate changes was different.

Chlorophyll-a vertical distribution patterns during summer in the Bay of La Paz, Gulf of California, Mexico

An understanding of chlorophyll-a vertical distribution patterns is essential for evaluating the productive potential of the oceans and implications for food webs. Based on high-resolution in-situ observations for conductivity, temperature and fluorescence of chlorophyll-a made at 30 stations during a multidisciplinary research cruise, this paper aims to assess the vertical distribution of chlorophyll-a in the Bay of La Paz, Gulf of California, Mexico, during the summer of 2009. The maximum chlorophyll-a concentration was 3.03 mg m−3 with a vertical distribution consistent with two patterns: 1) a peak closely related with the seafloor at the stations in the shelf area, close to the coast, and 2) a peak related with the thermocline and pycnocline, either above or below, in the central region of the bay. These patterns might have several implications for food webs, particularly for grazers, recently reported in high abundances in the bay. On the basis of these observations, a zonal trend would be expected for summer, whereby the two vertical patterns described above can be observed.

Influence of Environmental Factors on the Structure of Soil Microfungi of Vietnamese Tropical Forests

Results of a multiyear complex study of species diversity, features and patterns of distribution, substrate colonization, and ecology of soil microscopic fungi in the lowland, piedmont, and mountain monsoon rain forests of Vietnam are presented for the first time. In 97 forest habitats studied within 13 specially protected areas of Vietnam in the Northern, Central, and Southern parts of the country, 510 species of micromycetes from 148 genera have been identified. The influence of environmental factors (climatic features, relief, soils, forest types, etc.) on the formation of complexes of micromycetes has been analyzed. As a result, the dependence of the number of colony-forming units (CFUs) on the type of the substrate and the season (wet/dry) is established: significantly more species are detected in the dry season (October–March) (p < 0.05) in comparison with the wet one; many species are associated with certain plant species. Indicators of species diversity decrease with an increase above sea level altitude (p < 0.01). Herewith, the ratio of the taxonomic groups of micromycetes also consistently changes. A latitudinal–zonal trend of the change of the species composition of microscopic fungi, determined by a combination of environmental factors, has been revealed.

Estimation of uncertainty in surface air temperature climatic trends related to the internal dynamics of the atmosphere

The variability of zonal trends of surface air temperature for the period 1979–2012 is analyzed using ensemble simulations with a general atmospheric circulation model (AGCM) with identical prescribed conditions at the lower boundary of the atmosphere and different initial conditions. It is shown that the dependence of the variability of intra-ensemble zonal temperature trends on the variability of zonal fluctuations of temperature anomalies (associated with the internal variability of atmospheric circulation in the AGCM) is described quite well in terms of the stationary stochastic process model. In such a model, the dependence of the standard deviation of intra-ensemble trends can be approximated by a linear function of the standard deviation of temperature fluctuations, which agrees well with the AGCM results.

재분석자료들을 활용한 아시아-북태평양 상층제트의 강도(풍속) 및 3차원적 위치 변화 경향

In this study, trends of upper jet stream characteristics (intensity, altitude, latitude, and longitude) over the Asia-North Pacific region during the recent 30 (1979~2008) years were analyzed by using four reanalysis datasets (CFSR, ERA-Int., JRA-55, MERRA). We defined the characteristics of upper jet stream as the averages of mass weighted wind speed, mass-flux weighted altitude, latitude and longitude between 400 and 100 hPa. Due to the vertical averaging of jet stream characteristics, our results reveal a weaker spatial variabilities and trends than previous studies. In general, the four reanalysis datasets show similar jet stream properties (intensity, altitude, latitude and longitude) although the magnitude and trends are slightly different among the reanalysis datasets. The altitude of MERRA is slightly higher than that of others for all seasons. The domain averaged intensity shows a weakening trend except for winter and the altitude of jet stream shows an increasing trend for all seasons. Also, the meridional trend of jet core shows a poleward trend for all seasons but it shows a contrasting trend, poleward trend in the continental area but equatorward trend in the Western Pacific region during summer. The zonal trend of jet core is very weak but a relatively strong westward trend in jet core except for spring and winter. The trends of jet stream characteristics found in this study are thermodynamically consistent with the global warming trends observed in the Asia-Pacific region.

Assessment of source of information for polio supplementary immunization activities in 2014 and 2015, Somali, Ethiopia.

IntroductionCommunication is key for the successful implementation of polio vaccination campaigns. The purpose of this study is to review and analyse the sources of information utilized by caregivers during polio supplementary immunization activities (SIAs) in Somali, Ethiopia in 2014 and 2015.MethodsData on sources of information about the polio campaign were collected post campaign from caregivers by trained data collectors as part of house to house independent monitoring. The sources of information analysed in this paper include town criers (via megaphones), health workers, religious leaders, kebele leaders (Kebele is the lowest administrative structure in Ethiopia), radio, television, text message and others. The repetition of these sources of information was analysed across years and zones for trends. Polio vaccination campaign coverage was also reviewed by year and zones within the Somali region in parallel with the major sources of information used in the respective year and zones. 57,745 responses were used for this analysis but the responses were received from < or = 57,745 individuals since some of them may provide more than one response. Moreover, because sampling of households is conducted independently during each round of independent monitoring, the same household may have been included more than once in our analysis. The methodology used for independent monitoring does not allow for the calculation of response rates. Monitors go from house to house until information from 20 households is received.ResultsFrom the total 57,745 responses reviewed, over 37% of respondents reported that town criers were their source for information about the 2014 and 2015 polio SIAs. Zonal trends in using town criers as a major source of information in both study years remained consistent except in two zones. 87.5% of zones that reported at least 90% coverage during both study years had utilized town criers as a major source of information while the rest (12.5%) used health workers.ConclusionWe found that town criers were consistently the major source of information about the polio campaigns for Somali region parents and caregivers during polio immunization days held in 2014 and 2015. Health workers and kebele leaders were also important sources of information about the polio campaign for parents.

Time-to-Detect Trends in Precipitable Water Vapor with Varying Measurement Error

Abstract This study determined the theoretical time-to-detect (TTD) global climate model (GCM) precipitable water vapor (PWV) 100-yr trends when realistic measurement errors are considered. Global trends ranged from 0.055 to 0.072 mm yr−1 and varied minimally from season to season. Global TTDs with a 0% measurement error ranged from 3.0 to 4.8 yr, while a 5% measurement error increased the TTD by almost 6 times, ranging from 17.6 to 22.0 yr. Zonal trends were highest near the equator; however, zonal TTDs were nearly independent of latitude when 5% measurement error was included. Zonal TTDs are significantly reduced when the trends are analyzed by season. Regional trends (15° × 30°) show TTDs close to those in the 15° latitude zones (15° × 360°). Detailed case study analysis of four selected regions with high population density—eastern United States, Europe, China, and India—indicated that trend analysis on regional spatial scales may provide the most timely information regarding highly populated regions when comparing detection time scales to global and zonal analyses.

Soil formation in the quarries for limestone and clay production in the Ukhta region

The soils forming on the overgrowing technogenic dumps of quarries for limestone and clay production were investigated in the northern taiga (the Ukhta region). The soils are formed under sparse herbaceous plant communities. In the soils on calcareous technogenic eluvium and clay dumps, the processes of humus formation and accumulation predominate. In the soils of the clay dumps, the leaching of carbonates is expressed to a greater extent than in the soils of the limestone quarries. The nitrogen content of organic matter is low in the soils on the technogenic lime substrates and very low on the clay ones. Fulvic acids predominate in the humus composition. At the stages of the soil restoration studied, the zonal trend of pedogenesis is manifested only in the humus accumulation. The calcareous technogenic eluvium is found to be more favorable for the development of microbial communities as compared to the clay substrates with their small microbial biomass. However, there are no features pointing to the development of zonal soil profiles. This fact attests that, in the first 20–30 years, the soil-forming potential in the northern taiga is insufficient for the initiation of the zonal processes.

Latitudinal dependence of variations in stratospheric NO2 content

Diurnal and annual variations in the NO2 total content (TC), the effect of its decrease owing to the products of the eruption of Mt. Pinatubo, its variations during an 11-year cycle of solar activity, and its linear trends are analyzed on the basis of data obtained from the ground-based spectrometric measurements of the NO2 TC in stratospheric vertical columns over the stations of the Network for the Detection of Atmospheric Composition Change. Latitudinal dependence of the indicated variations and trends is revealed. The annual estimates of the linear trends of the NO2 TC are found to be mostly positive for the middle and low latitudes of the Southern Hemisphere and negative for the middle and low latitudes of the Northern Hemisphere. The maximum values of the positive and negative trends amount to ∼10% per ten years. In the high and polar latitudes of both hemispheres, the annual trend estimates are statistically insignificant. Seasonal estimates of the trends may differ from their annual estimates. The trends and solar-activity effect in the NO2 TC, which were estimated by using the two-dimensional model SOCRATES, as well as the analytical estimates of a zonal mean trend of the NO2 TC, on the whole, significantly differ from the estimates obtained from the measurements.

Tropical ice cloud optical depth, ice water path, and frequency fields inferred from the MODIS level-3 data

The 1.375-μm water vapor absorption band included on the space-borne Moderate resolution Imaging Spectroradiometer (MODIS) provides an unprecedented view of ice clouds (e.g., cirrus) on a global scale. In this study the spatial and temporal patterns of ice clouds over the tropics (i.e., the region between ± 30° latitude) are analyzed. Three successive years (July 2002–August 2005) of data acquired from the MODIS instrument aboard NASA's Aqua satellite are used in the analyses. Specifically, the frequency of occurrence of ice clouds and its zonal trends are investigated. We compare the ice cloud frequency results from this study with those obtained from the High Resolution Infrared Radiation Sounders (HIRS). In addition to the HIRS-type frequency of occurrence of ice clouds, we also investigate the average cloud optical depth and ice water path of these clouds, as well as the zonal trends of these parameters. The present analyses reveal that ice clouds are observed quite frequently in the tropics (approximately 67% of MODIS level-3 data points), and have a higher frequency of occurrence over land, 43%, than over the oceans, 32%. Ice cloud optical depth and ice water path have distributions highly skewed toward small values, indicating a large number of thin cirrus observations. Approximately 70% of the tropics has mean ice cloud optical depth below 2.0, and 80% has mean ice water path less than 40 g m − 2 . Moreover, spatial patterns, as well as seasonal cloud migrations, can be clearly seen.

Anisotropic reflection of UV radiation at the top of the atmosphere: Characteristics and models obtained from Meteor 3/TOMS

Reflection of solar radiation usually exhibits a strong dependence on viewing geometry relative to the Sun's position. Such a dependence needs taking into account in remote sensing studies employing satellite measurements made with scanning radiometers. While many investigations have been conducted concerning the angular variation of radiation in the total solar, visible, and IR wavelengths, no study was devoted to the UV radiation whose dependence on viewing geometry may differ from radiation in other spectral regions. On the basis of two and half years of Meteor‐3/TOMS data (from January 1992 to May 1994) the angular characteristics of UV radiation reflected at the top of the atmosphere (TOA) were studied extensively. A set of angular dependence models (ADMs) was developed for UV radiation at 340, 360, and 380 nm over 10 scene types. The results show that the angular dependence of UV‐reflected radiation is strong and rather different from that for total shortwave (SW) radiation as derived for the Earth Radiation Budget Experiment (ERBE). The largest discrepancy occurs under clear conditions over oceans for overhead Sun and large viewing zenith angles. The discrepancy in TOA mean albedos derived using the two sets of ADM can reach up to 48%. The discrepancy diminishes to about 10% for clear land scenes. Comparisons were also made for regional monthly mean TOA albedos over the whole globe derived from the ERBE SW ADM, TOMS UV ADM, and the assumption of isotropic reflection from an independent data set acquired by Nimbus 7/TOMS in January and July 1991. The differences exhibit an apparent zonal trend, large at high latitudes, moderate at midlatitudes, and small in the tropics.

Tropopause pressure change in January during 1979-1992

The global tropopause pressure change for the Januaries 1979 - 1992 is shown. In the extratropics over the North Atlantic-European region there is a marked large scale wave pattern with a pressure decrease of 2 hPa/yr over central Europe. The pattern corresponds well with that of the ozone column trend. A discussion of tropopause pressure change in the zonal mean as well as for the large scale wave structure in the extratropics is given. A counterbalance of zonal mean trends in tropopause pressure between the subtropics and midlatitudes is observed and discussed in dependence on the variability of large scale wave fluxes and the induced residual circulation. In the extratropics the tropopause pressure change wave pattern reflects the known compensation relation of stationary pressure systems between troposphere and stratosphere.

Upper‐stratospheric ozone trends 1979–1998

Extensive analyses of ozone observations between 1978 and 1998 measured by Dobson Umkehr, Stratospheric Aerosol and Gas Experiment (SAGE) I and II, and Solar Backscattered Ultraviolet (SBUV) and (SBUV)/2 indicate continued significant ozone decline throughout the extratropical upper stratosphere from 30–45 km altitude. The maximum annual linear decline of −0.8±0.2 % yr−1 (2σ) occurs at 40 km and is well described in terms of a linear decline modulated by the 11‐year solar variation. The minimum decline of −0.1±0.1% yr−1 (2σ) occurs at 25 km in midlatitudes, with remarkable symmetry between the Northern and Southern Hemispheres at 40 km altitude. Midlatitude upper‐stratospheric zonal trends exhibit significant seasonal variation (±30% in the Northern Hemisphere, ±40% in the Southern Hemisphere) with the most negative trends of −1.2% yr−1 occurring in the winter. Significant seasonal trends of −0.7 to −0.9% yr−1 occur at 40 km in the tropics between April and September. Subjecting the statistical models used to calculate the ozone trends to intercomparison tests on a variety of common data sets yields results that indicate the standard deviation between trends estimated by 10 different statistical models is less than 0.1% yr−1 in the annual‐mean trend for SAGE data and less than 0.2% yr−1 in the most demanding conditions (seasons with irregular, sparse data) [World Meteorological Organization (WMO), 1998]. These consistent trend results between statistical models together with extensive consistency between the independent measurement‐system trend observations by Dobson Umkehr, SAGE I and II, and SBUV and SBUV/2 provide a high degree of confidence in the accuracy of the declining ozone amounts reported here. Additional details of ozone trend results from 1978 to 1996 (2 years shorter than reported here) along with lower‐stratospheric and tropospheric ozone trends, extensive intercomparisons to assess relative instrument drifts, and retrieval algorithm details are given by WMO [1998].

The hydrography of the mid-latitude northeast Atlantic Ocean: I: The deep water masses

The circulation of the deep water masses in the mid-latitude northeast Atlantic Ocean was studied by analysis of the distributions of potential temperature, salinity, dissolved oxygen, phosphate, nitrate, and silicate. Pre-formed nutrients were used to allow a quantitative description of the deep water masses, especially the Northeast Atlantic Deep Water, in terms of four local source water types: Iceland–Scotland Overflow Water, Lower Deep Water, Labrador Sea Water, and Mediterranean Sea Water. Over the Porcupine Abyssal Plain between 2500 and 2900 dbar Northeast Atlantic Deep Water appears to be a mixture of mainly Iceland–Scotland Overflow Water and Labrador Sea Water (∼80%), with minor contributions of Lower Deep Water and Mediterranean Sea Water. When the Northeast Atlantic Deep Water re-circulates in the north-eastern Atlantic and flows southwards towards the Madeira Abyssal Plain, contributions of the former two water types of northern origin diminish to about 50% due to diapycnal mixing with the overlying and underlying water masses. The observed meridional and zonal trends of dissolved oxygen and nutrients in the Northeast Atlantic Deep Water appear to be caused both by diapycnal mixing with the underlying Lower Deep Water and by mineralization of organic matter. The eastward decrease of oxygen and increase of nutrients especially require considerable mineralization of organic matter near the European continental margin. At deeper levels (∼4100 dbar), where the nutrient rich Lower Deep Water is found near the bottom, the meridional gradients of oxygen and nutrients are opposite to those found between 2500 and 2900 dbar. Diapycnal mixing cannot explain this change in gradients, which is therefore considered to be a qualitative indication of ageing of the Lower Deep Water when it flows northwards. A considerable part of the Iceland–Scotland Overflow Water and the Lower Deep Water that enter the northeast Atlantic may be removed by deep upwelling in the Bay of Biscay and eastern Porcupine Plain.