The Eastern Mediterranean in the 80s and in the 90s: the big transition in the intermediate and deep circulations

We present definitive observational evidence that the startling change of the Eastern Mediterranean deep circulation observed in winter 1995 and documented by [Roether, W., Manca, B.B., Klein, B., Bregant, D., Georgopoulos, D., Beitzel, V., Kovacevich, V., Luchetta, A., 1996. Recent changes in the Eastern Mediterranean deep water. Science 271, 333–335.] actually started before October 1991. This change involved not only the deep water mass pathways but also the origin and pathways of the water mass spreading in the intermediate layer. We carry out the first unified analysis of the POEMBC-O91 data set, which shows that, differently from the previous decade of the 80s, the Cretan/Aegean Sea was in 1991 the `driving' engine of the intermediate, transitional and deep layer circulations, with Cretan Intermediate Water (CIW), transitional water and Cretan Deep Water (CDW) spreading out from the Cretan Sea into the basin interior. The most important new results are: (a) the Levantine Intermediate Water (LIW) formed inside or at the periphery of the Rhodes gyre is blocked in its traditional westbound route on its density horizons σ_θ=29.05 and 29.10 kg/m³ by a three-lobe strong anticyclonic structure in the Southern Levantine, which induces a substantial LIW recirculation in the Levantine basin itself; (b) the CIW exiting from the Western Cretan Arc Straits spreads into the Ionian interior on the σ_θ=29.05–29.10 kg/m³ isopycnal surfaces, thus replacing the LIW confined in the Levantine basin. A branch of CIW flows eastward in the Cretan passage and is entrained by the Ierapetra anticyclone to flow again into the Cretan Sea through the Eastern Cretan Arc Straits; (c) on the horizons σ_θ=29.15 and 29.18 kg/m³ a transitional water mass of Cretan origin, denser than CIW, and CDW are observed to spread out massively from the Cretan Arc Straits both into the Ionian and Levantine interiors. These isopycnal surfaces rise to much shallower depths in 1991 than in 1987, increasing the salt content of the intermediate, transitional and deep layers. This leads to a massive salt increase in the Ionian below 1200 m, clearly related to lateral advection of the new denser waters of Cretan/Aegean origin, thus contradicting the hypothesis of a vertical salt redistribution proposed by Roether et al.     

Fluctuations of snow accumulation in the Antarctic and sea level pressure in the Southern Hemisphere in the last 100 years

This paper summarizes the long-term fluctuations of snow accumulation in the Antarctic and analyzes its correlation with the sea level pressure (SLP) in the middle latitude (40°–50° S) of the Southern Hemisphere. Stratigraphic data which were compiled from studies on ice cores and snow-pits at eight stations in the Antarctic were used in the present study. It was found that the data concerning fluctuations in snow accumulation for East Antarctica showed correlations, whereas no such correlation was observed for the data from West Antarctica.This study shows possible relationships between snow accumulation in the Antarctic and SLP in the middle latitudes. The fluctuations of accumulation at South Pole, Dome C, Wilkes and South Ice Point show correlations with SLP over a large area in the 40°–50° S latitudinal zone. For the long-term fluctuations of SLP in the 40°–50 ° S latitudinal zone, a zonal fluctuation with wave number zero structure and a longitudinal variation of SLP anomalies due to their out-of-phase-fluctuation between the Pacific and the Indian Oceans were observed. The temporal scales for these fluctuations were found to be in the order of 20–30 years and 40–60 years, respectively. The influences of these two modes on the behaviour of snow accumulation in the Antarctic is also discussed.Now at Kitami Institute of Technology, Kitami, Hokkaido, Japan.     

Fronts in the vicinity of the tropopause

Summary From a study of five cases of pronounced fronts in the upper troposphere, it is concluded that the waterspout model offers the most satisfactory solution to the problem of connecting frontal boundaries and tropopauses. Composite cross sections of temperature, potential temperature, normal wind component and potential vorticity are presented for the five cases. On the basis of the potential vorticity measurements it is suggested that the most likely explanation for the formation of the high-level front is a folding of the tropopause.

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Zusammenfassung Auf Grund einer Untersuchung von fünf Fällen ausgesprochener Fronten in der höheren Troposphäre wird der Schluß gezogen, daß die Wasserhosen-Vorstellung am besten den Zusammenhang zwischen Fronten und Tropopausen darstellt. Kombinierte Querschnitte von Temperatur, potentieller Temperatur, normaler Windkomponente und potentieller Vorticity werden für die fünf Fälle vorgelegt. Auf Grund der Bestimmungen der potentiellen Vorticity wird dargelegt, daß die wahrscheinlichste Erklärung für die Entstehung einer Front in der Höhe in der Annahme einer Faltung der Tropopause besteht.

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Résumé En se fondant sur cinq cas de fronts très nets de la haute troposphère, les auteurs concluent que le schéma de trombe constitue la meilleure solution pour représenter la liaison entre zones frontales et tropopause. Ils donnent des profils combinés de température, de température potentielle, de composantes normales du vent et de vorticity potentielle pour les cinq cas. Ils montrent à l'aide de mesures de la vorticity potentielle que l'explication la plus probable de la formation d'un front en altitude consiste à admettre un plissement de la tropopause.

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With 11 Figures

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Contribution No. 37, Department of Meteorology and Climatology. —The research reported in this article has been supported by the Geophysical Research Directorate, Air Force Cambridge Research Center, under Contract No. AF 19 (604)-1811.     

Partial pressure of carbon dioxide in the peter the great bay surface water in the autumn

During the hydrological survey from November 4 to 9, 2009, the underway measurements of pH, temperature, and salinity of the surface water in the Peter the Great Bay were carried out using the cell without the liquid junction in the running system. Using the measurement data, the partial pressure of carbon dioxide (pCO₂) was computed which was below its atmospheric value and varied from 290 to 360μatm. Thus, during the period under study, the surface water of the bay forms the runoff for the atmospheric carbon dioxide. The minimum values of pCO₂ are associated with the warm stream entering the bay from the southwestern part of the open sea. The maximum values of pCO₂ are associated with the local upwelling of bottom waters. It is suggested that the horizontal convection caused by the nonuniform cooling of coastal water in the autumn forms the revealed mesoscale dynamic structures.     

Light hydrocarbons in the surface water of the mid-Atlantic

During a cruise of RV Polarstern over the Atlantic in September/October 1988, C₂–C₄ hydrocarbons were measured in surface sea water. The ship passed through three different ocean regions divided by divergences at 8° N and 3° S. Hydrocarbon concentrations differed considerably in these regions. The highest values were obtained for ethene with mean concentrations of 246 pMol/l between 35° N and 8° N, 165 pMol/l between 8° N and 3° S, and 63 pMol/l between 3° S and 30° S. Low values were found for i- and n-butane and acetylene between 32 pMol/l and 1 pMol/l. The alkene concentrations were in general higher than the concentrations of their saturated homologs. Concentrations decreased with increasing carbon numbers. The various alkenes were well correlated with one another as were the various alkanes. Oceanic emission rates of the light hydrocarbons were calculated from their sea water concentrations using an ocean atmosphere exchange model. The averaged fluxes ranged from about 10⁸ molec cm^-2 s^-1 for the alkenes and ethane to less than 10⁷ molec cm^-2 s^-1 for the C₄ alkanes. Acetylene emissions were below 3×10⁶ molec cm^-2 s^-1. Based upon these rates budget estimates of NMHC in the ocean surface layer were made with a simple model considering production and destruction processes in the water. The emissions to the atmosphere appear to be the dominant loss process between 35° N and 8° N, whereas destruction in the water seems to be dominant in the latitude ranges 8° N-3° S and 3° S-30° S.     

Turbulence spectra in the near-neutral surface layer over the Loess Plateau in China

We present the power spectra of wind velocity and the cospectra of momentum and heat fluxes observed for different wind directions over flat terrain and a large valley on the Loess Plateau. The power spectra of longitudinal (u) and lateral (v) wind speeds satisfy the −5/3 power law in the inertial subrange, but do not vary as observed in previous studies within the low frequency range. The u spectrum measured at 32 m height for flow from the valley shows a power deficit at intermediate frequencies, while the v spectrum at 32 m downwind of the valley reaches another peak in the low frequency range at the same frequency as the u spectrum. The corresponding peak wavelength is consistent with the observed length scale of the convective outer layer at the site. The v spectrum for flat terrain shows a spectral gap at mid frequencies while obeying inner layer scaling in its inertial subrange, suggesting two sources of turbulence in the surface layer. All the spectra and cospectra from the valley direction show a height dependency over the three levels.     

Tropospheric methane in the mid-latitudes of the Southern Hemisphere

Results of more than 800 new measurements of methane (CH₄) concentrations in the Southern Hemisphere troposphere (34–41° S, 130–150° E) are reported. These were obtained between September 1980 and March 1983 from the surface at Cape Grim, Tasmania, through the middle (3.5–5.5 km) to the upper troposphere (7–10 km). The concentration of CH₄ increased throughout the entire troposphere over the measurement period, adding further support to the view that CH₄ concentrations are currently increasing on a global scale. For data averaged vertically through the troposphere the rate of increase found was 20 ppbv/yr or 1.3%/yr at December 1981. In the surface CH₄ data a seasonal cycle with a peak to peak amplitude of approximately 28 ppbv is seen, with the minimum concentration occurring in March and the maximum in September–October. A cycle with the same phase as that seen at the surface, but with a significantly decreased amplitude, is apparent in the mid troposphere but no cycle is detected in the upper tropospheric data. The phase and amplitude of the cycle are qualitatively in agreement with the concept that the major sink for methane is oxidation by hydroxyl radicals. Also presented is evidence of a positive vertical gradient in methane, with a suggestion that the magnitude of this gradient has changed over the period of measurements.     

Meteorological singularities in the Czech Republic in the period 1961–2002

Summary Based on the mean daily values of air temperature, air pressure, and precipitation totals at 13 climatological stations within the territory of the Czech Republic in the period 1961–2002, a statistical analysis of “meteorological singularities” (i.e., calendar-dependent deviations from the mean annual variation for selected meteorological elements) was performed. At the 13 stations analysed, a total of 45 meteorological singularities (37 singularities in air temperature, 35 in air pressure, and 30 in precipitation) were found. The singularities detected correlate well with cases traditionally recognised in the Czech Republic as well as with the results of analyses performed for Germany. Despite the considerable variability of singularities in time and space, most of them are found across the entire territory of the Czech Republic and can be observed for the most part in all three elements processed. The majority of the singularities detected may be explained on the basis of circulation mechanisms, by relating them to a significantly higher occurrence of certain groups of synoptic situations characterised by anomalous temperature or precipitation effects. Cases of “competition” between singularities, when different singularities may occur on the same calendar day, were found.     

Verification of the Contribution of Vehicular Traffic to the Total NMVOC Emissions in Germany and the Importance of the NO3 Chemistry in the City Air

In 1997 and 1998 several field campaigns for monitoring non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO_x) were carried out in a road traffic tunnel and in the city center of Wuppertal, Germany. C₂–C₁₀ aliphatic and aromatic hydrocarbons were monitored using a compact GC instrument. DOAS White and long path systems were used to measure aromatic hydrocarbons and oxygenated aromatic compounds. A formaldehyde monitor was used to measure formaldehyde. Chemiluminescence NO analysers with NO₂ converter were used for measuring NO and NO₂. The high mixing ratios of the NMVOCs observed in the road traffic tunnel, especially 2.9 ppbv phenol, 1.5ppbv para-cresol and 4.4 ppbv benzaldehyde, in comparison with themeasured background concentration clearly indicate that these compounds were directly emitted from road traffic. Para-Cresol was for the first timeselectively detected as primary pollutant from traffic. From the measured data a NMVOC profile of the tunnel air and the city air, normalised to benzene (ppbC/ppbC), was derived. For most compounds the observed city air NMVOC profile is almost identical with that obtained in the traffic tunnel. Since benzene originates mainly from road traffic emission, the comparison of the normalised emission ratios indicate that the road traffic emissions in Wuppertal have still the largest impact on the city air composition, which is in contrast to the German emission inventory. In both NMVOC profiles, aromatic compounds have remarkably large contributions of more than 40 ppbC%. In addtion, total NMVOC/NO_x ratios from 0.6 up to 3.0ppbC/ppb in the traffic tunnel air and 3.4± 0.5 in the city air of Wuppertal were obtained. From the observed para-cresol/toluene and ortho-cresol/toluene ratios in the city air, evidence was found thatalso during daytime NO₃ radical reactions play an important role in urban air.     

Studying the stability of the Antarctic slope front in the Commonwealth Sea

In 2004–2007 and 2011–2013, oceanography sections with the high spatial resolution were carried out on the shelf and continental slope of the Commonwealth Sea and in the Prydz Bay in the Antarctic. In combination with a fine vertical resolution, this provides an advanced interpretation of the obtained data. It becomes possible to analyze the local thermohaline structure of the baroclinic Antarctic slope front (the ASF) and to investigate its stability. The reliable determination of the ASF characteristics enables to apply the parameterizations and criteria obtained during laboratory experiments for analysis of its stability. The ASF instability is preceded by the local vertical dramatic intensification of the front, where the ASF approaches the pure baroclinic state. Therefore, the local baroclinic instability in the ASF area prevails over the barotropic one at the significant mutual impact of layers (δ = H _ASF/H _b ≈ ≈ 0.3–0.6, H _b is the total depth) and accompanied with the hydrostatic instability. Instability conditions in the frontal zone with a width of ～(1–2)Rd _L (Rd _L is local baroclinic deformation radius) relative to the wide ASF (L _ASF ≈ (3–5)Rd _L ) coincide with those of the narrow (intensified) ASF (L _ASF ≈ Rd _L* ). In the case of the runoff of dense Antarctic shelf water, on the shelf edge the realization is possible of the self-oscillatory mechanism of the ASF instability caused by the topographic beta-effect as well as the periodic generation of baroclinic vortices.     

On the Scale-dependence of the Gradient Richardson Number in the Residual Layer

We present results of a technique for examining the scale-dependence of the gradient Richardson number, Ri, in the nighttime residual layer. The technique makes use of a series of high-resolution, in situ, vertical profiles of wind speed and potential temperature obtained during CASES-99 in south-eastern Kansas, U.S.A. in October 1999. These profiles extended from the surface, through the nighttime stable boundary layer, and well into the residual layer. Analyses of the vertical gradients of both wind speed, potential temperature and turbulence profiles over a wide range of vertical scale sizes are used to estimate profiles of the local Ri and turbulence structure as a function of scale size. The utility of the technique lies both with the extensive height range of the residual layer as well as with the fact that the sub-metre resolution of the raw profiles enables a metre-by-metre ‘sliding’ average of the scale-dependent Richardson number values over hundreds of metres vertically. The results presented here show that small-scale turbulence is a ubiquitous and omnipresent feature of the residual layer, and that the region is dynamic and highly variable, exhibiting persistent turbulent structure on vertical scales of a few tens of metres or less. Furthermore, these scales are comparable to the scales over which the Ri is less than or equal to the critical value of Ri _c of 0.25, although turbulence is also shown to exist in regions with significantly larger Ri values, an observation at least consistent with the concept of hysteresis in turbulence generation and maintenance. Insofar as the important scale sizes are comparable to or smaller than the resolution of current models, it follows that, in order to resolve the observed details of small Ri values and the concomitant turbulence generation, future models need to be capable of significantly higher resolutions.     

Cyclogenesis in the Mediterranean region

A statistical study is made of cyclones originating in the Mediterranean region in the months October through May from 1929 to 1939 and 1945 to 1952. The following features are summarized: synoptic type, points of origin, monthly and geographic frequencies, relation of displacement to topography and deepening, 24-hr deepening, isobar direction at 3 km at time and place of origin, relation between 3-km isobar direction and cyclone trajectory, and relation between vertical temperature distribution and central pressure.

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Zusammenfassung Es wird eine statistische Untersuchung der Zyklonen durchgeführt, die sich während der Perioden 1929 bis 1939 und 1945 bis 1952 (jeweils in den Monaten Oktober bis Mai) im Mittelmeergebiet gebildet haben. Dabei wird über folgende Gesichtspunkte zusammenfassend berichtet: Synoptische Wetterlage, zyklogenetische Ursprungsstellen, monatliche und geographische Häufigkeitsverteilung Beziehung zwischen Verlagerung einerseits und topographischen Einflüssen und Vertiefung anderseits, Depressionsvertiefung innerhalb 24 Stunden, Isobarenrichtung in 3 km Höhe im Zeitpunkt und Ort der Zyklonenentstehung, Beziehung zwischen der Isobarenrichtung in 3 km und der Zyklonenbahn, Beziehung zwischen der vertikalen Temperaturverteilung und dem Luftdruck im Zyklonenzentrum.

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Résumé Il s'agit d'une étude statistique des dépressions formées en Méditerranée pendant les périodes 1929–1939 et 1945–1952, d'octobre à mai. L'auteur considère les points de vue suivants: situation météorologique générale, régions cyclogénétiques, distribution des fréquences par mois et par régions, relation entre le déplacement et les influences topographiques et le creusement, creusement en24 heures, direction des isobares à 3 km d'altitude au moment et au lieu de formation, relation entre cette même direction et la trajectoire dépressionnaire, relation entre la répartition verticale de la température et la pression au centre de la dépression.

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With 20 Figures.

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Contribution to a research project sponsored by the Geophysics Research Directorate of the Air Force Cambridge Research Center under Contract No. AF 19 (122)-466.     

Direct measurement of the meridional circulation in the stratosphere during the IGY

Summary In this study the horizontal component of the meridional circulation at the 100, 50 and 30 mb levels in the stratosphere is computed for the IGY period July 1957 through June 1958. Radiosonde data from approximately 240 stations, well distributed over the northern hemisphere, are used in the analysis of the north-south component of the wind. Values of the mean meridional circulation for the four seasons are presented at every 5° latitude from the equator to 80°N.In the annual average at 100 mb an apparent three cell pattern is obseered, consisting of a region of strong poleward motion north of 55°N, equatorward motion from 15° to 55°N and weak poleward motion from 0° to 15°N. In the annual averages at 50 and 30 mb poleward motions appear only at high latitudes and diminsih in strength with height. Equatorward motions dominate at 30 mb. A maximum value of the mean meridional circulation of +60 cm sec^–1 is found at 100 mb at 70°N.

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Zusammenfassung In dieser Untersuchung ist für die 100-, 50- und 30 mb-Niveaus die horizontale Komponente der meridionalen Zirkulation in der Stratosphäre im internationalen geophysikalischen Jahr (Juli 1957 bis Juni 1958) berechnet worden. Es werden dabei Radiosonden-Daten von etwa 240 Stationen, die über die nördliche Hemisphäre gut verteilt sind, für die Analyse der Nord-Süd-Windkomponente verwendet. Für jeden fünften Breitengrad vom Äquator bis 80°N werden Werte der durchschnittlichen Meridionalkomponente der Zirkulation für die vier Jahreszeiten mitgeteilt.Im Jahresdurchschnitt zeigt sich im 100 mb-Niveau eine Verteilung der Meridionalkomponente, die anscheinend einem aus drei Zellen bestehenden Zirkulationssystem entspricht, wobei nördlich von 55°N eine starke polwärts gerichtete Bewegung, zwischen 15° und 55°N eine Strömung gegen den Äquator und zwischen 0° und 15°N wieder eine schwache polwärts gerichtete Strömung besteht. In den Jahresdurchschnittswerten aus den Niveaus der 50- und 30 mb-Flächen sind polwärts gerichtete Strömungskomponenten nur in hohen geographischen Breiten festzustellen, die mit zunehmender Höhe an Stärke abnehmen. Im Niveau von 30 mb herrscht eine zum Äquator hin gerichtete Meridionalkomponente der Strömung vor. Ein Maximalwert der durchschnittlichen meridionalen Zirkulation von +60 cm sec^–1 wurde in der 100 mb-Höhenlage bei 70°N festgestellt.

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Résumé Dans cette étude, la composante horizontale de la circulation méridionale dans la stratosphère aux niveaux de 100, 50 et 30mb est calculée pour la période de Juillet 1957au Juin 1958 pour l'Année Géophysique Internationale. Les données de radiosondage d'environ 240 stations bien réparties sur l'hémisphère du nord sont employées dans l'analyse de la composante nord-sud du vent. Les valeurs de la circulation moyenne méridionale des quatre saisons sont présententées pour tous les 5° de latitude de l'équateur jusqu'à 80°N.En moyenne d'un an, on peut apparemment observer, à 100mb, une distribution en trois cellules consistant d'une région de mouvement fort vers le pôle au nord de 55°N, d'un mouvement vers l'équateur de 15° à 55°N et d'un mouvement faible vers le pôle de 0° à 15° N. A 50 et 30 mb en moyenne d'un an des mouvements vers le pôle apparaissent seulement dans les hautes altitudes et ils diminuent en force suivant la hauteur. Dans le niveau de 30 mb, c'est un mouvement vers l'équateur qui domine. Use valeur maxima de la circulation méridionale moyenne de +60 cm·sec^–1 a été constatée à 100 mb à 70°N.

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With 6 Figures

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The research reported in this paper has been made possible through the support of the Atomic Energy Commission and of the Geophysics Research Directorate of the U.S. Air Force under contracts No. At (30-2) 2241 and 19(604)-5223.     

Variability of refractive index gradient in the atmospheric boundary layer in the East regions of Russia

On the basis of 10-year series of observations at 30 stations in Eastern Siberia and Far East, features are analyzed of annual and diurnal changes in vertical gradient of refractive index g _n , and of its rms deviation σ in the lower 900-m layer of the atmosphere. It is found that the main type of annual variations of g _n and σ is represented by the annual cycle with two maxima (in winter and summer) and two minima (in spring and fall). The annual cycle with a single high winter maximum of g _n and σ is, for the first time, revealed in the northeastern border region of Russia. The largest amplitude of g _n annual cycle is observed in the northeastern part of the area. The diurnal variations of g _n exhibit maximum amplitudes in spring and summer; diurnal changes of σ are not pronounced but in several stations in the northern part of the area.     

Internal tides in the coastal zone of the Sea of Japan in autumn

The results are presented of hydrological studies in the coastal zone of the Sea of Japan in autumn in different years. It is revealed that the typical density stratification of water is formed there in autumn. The amplitudes are estimated of regular (with the periodicity of tidal harmonic M₂) vertical displacements of isotherms in the intermediate layer and maximum values of flow velocity in the surface and bottom layers. It is demonstrated that temperature perturbations are induced at the shelf edge and propagate to the coastal zone with the velocity that is close to the velocity of the first mode of internal gravity waves with the frequency of the tidal harmonic M₂.     

UV attenuation in the cloudy atmosphere

Ultraviolet (UV) energy absorption plays a very important role in the Earth–atmosphere system. Based on observational data for Beijing, we suggest that some atmospheric constituents utilize or transfer UV energy in chemical and photochemical (C&P) reactions, in addition to those which absorb UV energy directly. These constituents are primarily volatile organic compounds (VOCs) emitted from both vegetative and anthropogenic sources. The total UV energy loss in the cloudy atmosphere for Beijing in 1990 was 78.9 Wm⁻². This attenuation was caused by ozone (48.3 Wm⁻²), other compounds in the atmosphere (26.6 Wm⁻²) and a scattering factor (4.0 Wm⁻²). Our results for a cloudy atmosphere in the Beijing area show that the absorption due to these other compounds occurs largely through the mediation of water vapor. This fraction of energy loss has not been fully accounted for in previous models. Observations and previous models results suggest that 1) a cloudy atmosphere absorbs 25∼30 Wm⁻² more solar shortwave radiation than models predict; and 2) aerosols can significantly decrease the downward mean UV-visible radiation and the absorbed solar radiation at the surface by up to 28 and 23 Wm⁻², respectively. Thus, quantitative study of UV and visible absorption by atmospheric constituents involved in homogeneous and heterogeneous C&P reactions is important for atmospheric models.     

Gravity waves in the atmosphere

Summary Mathematical discussion is restricted to gravity waves of period short enough for the earth's rotation to be neglected, propagated horizontally through air whose horizontal velocity and static stability vary with height in the layers near the ground. The differential equation (15) is derived, describing how the vertical velocity of the wave motion varies with height for waves, of length 2 /k, at rest relative to the coordinate system. Boundary conditions are then applied—at the ground where the motion is horizontal, and above where the kinetic energy is finite—to give the relationship betweenk and the velocity of the wave relative to the air above (–W).This relationship is illustrated for all possible stable waves in fig. 2 for four different airstreams whose profiles of stability and velocity are set out in fig. 1. Remarkably different results are obtained; conclusions about the wave-properties of an airstream therefore depend very much on the model chosen.Two intervening chapters discuss the circumstances under which gravity waves are possible. Some of the conclusions are applicable to long waves also. Unstable waves are a very unusual occurrence, and very special circumstances are necessary to produce them, if they occur at all; they cannot lead to any phenomenon in which one wavelength predominates. Observable stable waves are not propagated over the ground but are at rest relative to their cause, except in the case of compression waves which are accompanied by no phenomena of the weather and travel with about the speed of sound. The most important stable waves are waves in the lee of mountains.

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Zusammenfassung Die mathematische Erörterung beschränkt sich auf Gravitationswellen, deren Periode kurz genug ist, um die Erdrotation unberücksichtigt zu lassen, und zwar speziell Wellen, die sich horizontal durch die Luft ausbreiten, deren horizontale Geschwindigkeit und statische Stabilität in den bodennahen Schichten von der Höhe abhängig sind. Es wird die Differentialgleichung (15) abgeleitet, die beschreibt, wie die Vertikalgeschwindigkeit der Wellenbewegung mit der Höhe bei Wellen variiert, die 2 /k lang und relativ zum Koordinationssystem unbewegt sind. Ferner werden Grenzbedingungen aufgestellt, wonach die Bewegung an der Erdoberfläche horizontal und darüber die kinetische Energie begrenzt ist, um die Beziehung zwischenk und der Wellengeschwindigkeit —W relativ zur oberhalb liegenden Luft anzugeben.Diese Beziehung wird in Abb. 2 für alle möglichen stabilen Wellen für vier verschiedene Luftströme veranschaulicht, deren Stabilitäts- und Geschwindigkeitsprofile in Abb. 1 dargestellt sind. Dabei ergeben sich auffallend verschiedenartige Resultate; Folgerungen über die Welleneigenschaften eines Luftstromes hängen somit stark von dem gewählten Modell ab.In zwei Zwischenkapiteln werden die Bedingungen besprochen, unter denen Gravitationswellen möglich sind. Mehrere Folgerungen daraus sind auch für lange Wellen gültig. Instabile Wellen kommen nur äußerst selten vor, da sie überhaupt nur durch ganz spezielle Bedingungen hervorgerufen werden; dabei können sie zu keiner Erscheinung führen, bei der eine einzelne Wellenlänge überwiegt. Stabile Wellen, die sich über der Erdoberfläche ausbreiten, können nicht beobachtet werden, da sie relativ zu ihrem Ursprung unbewegt sind, mit Ausnahme von Kompressionswellen, die sich ungefähr mit Schallgeschwindigkeit bewegen und keine Witterungserscheinungen verursachen. Die bedeutendsten stabilen Wellen sind auf der Leeseite von Gebirgen zu finden.

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Résumé La discussion mathématique se borne aux ondes de gravité de période assez courte pour qu'on puisse faire abstraction de la rotation de la terre et qui se propagent horizontalement dans l'air dont la vitesse horizontale et la stabilité statique varient avec l'altitude dans les couches voisines de la surface terrestre. On obtient l'équation différentielle (15) qui décrit la façon dont la vitesse verticale du mouvement des ondes varie suivant l'altitude dans le cas d'ondes d'une longueur de 2 /k en repos relativement au système des coordonnées. On tient compte des conditions aux limites — sur le sol d'une part où le mouvement est horizontal, et en haut d'autre part où l'énergie cinétique a une valeur finie — pour donner une relation entrek et la vitesse de l'onde (–W) relativement à l'atmosphère supérieure. Ces relations sont illustrées pour toutes les ondes stables possibles par la fig. 2 pour quatre courants d'air différents dont les profils de stabilité et de vitesse sont représentés dans la fig. 1. On obtient des résultats très variés. Aussi les conclusions que l'on peut tirer à propos des ondes formées dans un courant dépendentelles beaucoup du modèle choisi.Deux chapitres concernent les conditions dans lesquelles les ondes de gravité peuvent se produire. Quelques-unes des conclusions auxquelles on aboutit s'appliquent également aux ondes longues. Les ondes instables ne se produisent que très rarement et résultent de circonstances tout à fait spéciales; elles ne mènent à aucun phénomène où prédomine une seule longueur d'onde. Les ondes stables que l'on peut observer ne se propagent pas relativement à la terre; au contraire, sauf les ondes de compression qui ne sont accompagnées d'aucun phénomène visible du temps et se propagent à peu près à la vitesse du son, elles sont en repos relativement à leur cause. Les ondes stables les plus importantes sont celles qui naissent à l'abri des montagnes.

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With 2 Figures.     

Hydroperoxides in the marine troposphere over the Atlantic Ocean

Hydrogen peroxide (H₂O₂) and organic hydroperoxides (ROOH) were measured on board of theRV Polarstern during its cruise across the Atlantic Ocean from 20 October to 12 November 1990 (54° N to 51° S latitude) by the enzyme fluorometric method. The H₂O₂ mixing ratio varied from below the detection limit of about 0.12 ppbv up to 3.89 ppbv, showing a latitudinal dependence with generally higher values around the equator and decreasing values poleward. The shape of the latitudinal H₂O₂ distribution agrees well with an analytical steady state expression for H₂O₂ using the measured H₂O and O₃ distribution and a wind dependent H₂O₂ deposition rate. The ROOH mixing ratio varied from below the detection limit of about 0.08 ppbv up to 1.25 ppbv with qualitatively the same latitudinal dependence as H₂O₂. The observed ratio ROOH/(ROOH + H₂O₂) varied between 0.17 and 0.98 showing higher values at the lowest H₂O₂ mixing ratios at high latitudes. The measured H₂O₂ mixing ratio shows a significant diurnal variation with a maximum around 14:00 local time, explicable by a superposition of the photochemical H₂O₂ production with a constant H₂O₂ deposition rate. Four independent estimations of the average effective H₂O₂ deposition rate inferred from the H₂O₂ decrease in the night, from the midday H₂O₂ production deficit (as derived from comparison with a photochemical model and from the daily ozone loss), and from the offset in the latitudinal H₂O₂ distribution, were consistent. An episode of maximum H₂O₂ concentration suggests the possibility of its formation in clouds.     

An unusual anomaly of ice conditions in the eastern seas of the Russian Arctic and in the arctic basin in summer 2007

It is demonstrated that during the whole annual cycle of ice cover evolution in 2006–2007 in the eastern seas of the Russian Arctic and in the Arctic basin, the factors whose effect led to the formation of an extremely large anomaly of ice conditions in summer 2007 were revealed. By the end of summer, the ice melted on the huge water area of 3500000 km². In September, the ice edge between the meridians of 150° E-170° W reached the parallel of 85° N. The estimates of the open water area being formed due to the ice melting and its drifting edge shift are given.     

Agricultural droughts in the tropics

Summary Irregular droughts are the main reason for serious yield reductions in tropical agriculture, with sometimes very serious consequences. These agricultural droughts are defined and delimited in relation to normal rainfall conditions, to which traditional agricultural production systems are fully adapted. Examples from East Africa and Malaysia, tropical areas which differ climatically and in the availability of climatic data, illustrate that it is necessary to use different statistical methods to estimate the probability of agricultural droughts.Short droughts, often concealed by monthly rainfall figures, can have serious effects, particularly on annual crops with their short root systems. A simple water balance model, based on daily rainfall data, is used to estimate the probability of these dry periods. The same model can be used to predict periods of surplus rainfall, when soils are saturated. These periods can cause severe reduction in agricultural yields.

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Zusammenfassung Unregelmäßig auftretende Trockenperioden sind die Hauptursache von Produktionsverlusten in der tropischen Landwirtschaft, die katastrophale Folgen haben können. Diese landwirtschaftlichen Trockenperioden werden in bezug auf die normalen Niederschlagsverhältnisse definiert und begrenzt, an die die traditionellen tropischen Landwirtschaftssysteme vollständig angepaßt sind. Beispiele aus Ostafrika und Malaysien zeigen, wie die statistischen Methoden zur Ermittlung der Wahrscheinlichkeit landwirtschaftlicher Trockenperioden an die Klimaverhältnisse sowie an die Verfügbarkeit von Klimadaten angepaßt werden müssen.Monatliche Niederschlagsziffern verbergen oft kurze Trockenperioden, die erhebliche Schäden verursachen können, besonders an einjährigen Pflanzen mit ihren kurzen Wurzelsystemen. Ein einfaches Wasserbilanzmodell, basierend auf Tagesziffern der Niederschläge, zeigt die Wahrscheinlichkeit solcher kurzen Trockenperioden an. Dasselbe Modell kann auch Perioden mit saturierten Böden vorhersagen. Diese können schädliche Folgen für die Ernteerträge haben.

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With 13 Figures