Recent fluctuations of tropospheric temperature and water vapour content in the tropics

Summary During the last decades the average temperature of the tropical troposphere (200/850 hPa layer) has steadily increased, between 1965 and 1984 by about 0.8°C in the whole equatorial belt. Data series from a section of individual stations verify this trend as seasonally constant, but decreasing from the equator towards both hemispheres. Further evidence is presented by selected mountain stations and glacier retreat in all equatorial mountains.Above the equatorial Pacific, the same stations indicate an increase of moisture content in the middle troposphere (500/700 hPa layer) expressed in precipitable water as well as in relative humidity. This coincides with increasing sea surface temperature in the area around Indonesia and northern Australia. Above Africa the trend is (if real) quite patchy. Due to the short residence time of water vapour in the atmosphere the horizontal (zonal ) distances between its sources and sinks remain near 2000 km, which may explain, in addition to instrumental differences, large regional deviations.With 7 Figures     

A discharge flow mass-spectrometric study of the reaction between the NO3 radical and isoprene

The kinetics and mechanism of the reactionNO₃+CH₂=C(CH₃)–CH=CH₂productswere studied in two laboratories at 298 K in the pressure range 0.7–3 torr using the discharge-flow mass-spectrometric method. The rate constant obtained under pseudo-first-order conditions with excess of either NO₃ or isoprene was: k ₁=(7.8±0.6)×10^–13 cm³ molecule^–1 s^–1. The product analysis indicated that the primary addition of NO₃ occurred on both -bonds of the isprene molecule.     

Observation of DMSO and CH3S(O)OH from the gas phase reaction between DMS and OH

Products and mechanisms have been investigated for the reactions between dimethylsulfide (DMS) and dimethylsulfoxide (DMSO) and the hydroxyl radical (OH) in the presence of NO_x. All of the experiments were performed in a 480 L reaction chamber, applying Fourier transform infrared spectroscopy (FT-IR) and ion chromatography as the analytical techniques.In addition to the sulfur containing products that are known to be produced from the gas phase reaction between DMS and OH (SO₂, dimethylsulfone, methylsulfonyl peroxynitrate, methanesulfonic acid, H₂SO₄), DMSO and methanesulfinic acid (CH₃S(O)OH) were also observed as products. Only SO₂, DMSO₂ and methylsulfonyl peroxynitrate were found as sulfur containing products in the reaction between DMSO and OH. Based on these new results we propose a mechanism for the atmospheric oxidation of DMS and DMSO by OH radical.     

Zonally resolved water vapour coupling with tropical tropopause temperature: Seasonal and interannual variability,and influence of the Walker circulation

Climate Dynamics - Global stratospheric water vapour is strongly coupled to the tropical cold-point tropopause temperatures. We quantified the coupling between temperature and water vapour in the...     

The atmospheric chemistry of dimethylsulfoxide (DMSO) kinetics and mechanism of the OH+DMSO reaction

We have employed a pulsed laser photolysis-pulsed laser induced fluorescence technique to study the kinetics and mechanism of the reaction of OH with dimethylsulfoxide and its deuterated analogue. A rate coefficient of (1.0±0.3)×10^-10 cm³ molecule^-1 s^-1 was obtained ar room temperature. The rate coefficient was independent of pressure over the range 25–700 Torr, showed no dependence on the nature of the buffer gas and showed no kinetic isotope effect. A limited study of the temperature dependence indicated that the reaction displays a negative activation energy. The gas phase ultraviolet absorption spectrum was obtained at room temperature and showed a strong absorption feature in the far ultraviolet. The absolute absorption cross-section at 205 nm, the absorption peak, is (1.0±0.3)×10^-17 cm², where the large uncertainty results from experimental difficulties associated with the low vapor pressure and stickiness of DMSO.     

Surface fluxes of heat and water vapour from sites in the European Arctic

Summary  Measurements of the surface fluxes of heat and water vapour were taken at four sites across the European Arctic as part of the EU funded LAPP project. The sites cover a range of latitudinal, altitudinal and climatic conditions. The most northerly site is near Ny-?lesund, Svalbard, a polar semi-desert with continuous permafrost. A second permafrost site is a fen area in the Zackenberg valley, East Greenland. Finally two sites in northern Finland, Skalluvaara and Kaamanen are on the southern boundary of the region affected by permafrost. At all sites measurements were made of the turbulent fluxes of heat and water vapour using eddy correlation equipment for at least one active season. The net radiation totals for July and August are similar at all sites. At the sites with permafrost a substantial proportion (over 20%) of the net radiation goes into soil heat flux, to thaw the soil moisture in the top metre. Of the remaining energy just over half is used for evaporation. At the Finnish sites the vegetation is largely deciduous and this is seen in the record with higher evaporative ratios in July and August, after the vegetation becomes green. The Finnish sites tend to have higher surface resistance to evaporation; however, the evaporative demand is greater leading to slightly higher evaporation rates. The two Finnish sites have a similar seasonal pattern determined by the water table and seasonality of the vegetation. The two northern sites show a pattern that is determined primarily by the variation of water table only. It is concluded that the water balance through the active season is influenced primarily by the history of snow cover. The seasonality of the vegetation, the permafrost and the depth of water table are also important influences. Received November 1, 1999 Revised April 17, 2000     

Interannual variability of water discharge through the Korea (Tsushima) Strait and its influence on the dissolved oxygen content in the Sea of Japan

The interannual variations of the sea level at the coastal stations of the Sea of Japan and of the water discharge through the Korea (Tsushima) Strait are studied. It is demonstrated that the interannual variations of the water discharge through this strait are determined by the water discharge of the Oyashio (in the subarctic Pacific) and the Kuroshio (in the East China Sea) currents and by the zonal wind stress component over the Sea of Japan in winter period. It is revealed that the variations in the East China Sea water transport through the Korea (Tsushima) Strait cause the interannual variations of the dissolved oxygen content in intermediate (500 m) and deep (1000 m and more, σ_θ = 27.35) waters of the Sea of Japan.     

Further studies of the temperature dependence of the rate coefficients for the reactions of OH with a series of ethers under simulated atmospheric conditions

The following temperature-dependent rate coefficients (k/cm³ molecule^–1 s^–1) of the reactions of hydroxyl radicals with aliphatic ethers have been determined over the temperature range 247–373 K by a competitive flow technique: diethyl ether,k _OH=5.2×10^–12 exp[(262±150)/T]; methyln-butyl ether,k _OH=5.4×10^–12 exp[(309±150)/T]; ethyln-butyl ether,k _OH=7.3×10^–12 exp[(335±150)/T]; di-n-butyl ether,k _OH=5.5×10^–12 exp[(502±150)/T] and di-n-pentyl ether,k _OH=8.5×10^–12 exp[(417±150)/T]. The data have been measured relative to the rate coefficientk(OH + 2,3-dimethylbutane)=6.2×10^–12 cm³ molecule^–1 s^–1 independent of temperature.Previous discrepancies in the room-temperature rate coefficients for the OH reactions with ethyln-butyl ether and di-n-butyl ether, obtained in the flow and static experiments of Bennett and Kerr (J. Atmos. Chem. 8, 87–94, 1989;10, 29–38, 1990) compared with those of Wallingtonet al. (Int. J. Chem. Kinet. 20, 541–547, 1988;21, 993–1001, 1989) and of Nelsonet al. (Int. J. Chem. Kinet. 22, 1111–1126, 1990) have been resolved. The results are considered in relation to the available literature data and evaluated rate expressions are deduced where possible. The data are also discussed in terms of structure-activity relationships.     

Distribution of water vapor content (WVC) and its seasonal variation over the mainland of China

Based on the meteorological data of 105 aerological stations during the period of 1960－1969, the monthly average water vapor content (WVC) in air column over the mainland of China is calculated. Charts showing the distribution of mean WVC for January and July and its seasonal variation associated with the atmos-pheric circulation in the lower troposphere over East Asia are also presented. Results obtained from this anal-ysis will contribute to the assessment of water resources, as well as the studies of the formation of rainfall and climate.     

Spatial modelling of air temperature and precipitation for Andorra (Pyrenees) from daily circulation patterns

Based on the daily sea level pressure (SLP) circulation catalogue obtained by Esteban, Martin-Vide and Mases, Int J Climatol 26:1501–1515, (2006) for Western Europe, high-resolution maps of daily maximum and minimum temperature, mean daily precipitation and daily precipitation probability have been obtained for Andorra (Pyrenees). The 20 daily-circulation patterns cover the period 1960–2001 and were generated using new approaches based on the rotated principal component analysis (PCA) and clustering technique. The final maps of Andorra associated with each circulation pattern have been constructed using altitude, latitude, continentality and solar radiation as multiple regression predictors (Ninyerola, Pons and Roure, Int J Climatol 20:1823–1841, 2000). The daily temperature and rainfall series used from Andorran, French and Catalan/Spanish weather stations have been checked for data quality. The results confirm the complexity of the spatial distribution of meteorological phenomena over mountainous areas such as in Andorra, and show the importance of the Mediterranean and Atlantic influence upon the climate of this country of the Pyrenees. On the other hand, different tests have been made showing that the classification results could improve the resulting interpolated climate maps by the use of the circulation-pattern frequencies.     

Cloud water content effects on computing spectral characteristics of temperature fields and turbulent heat fluxes in the cumulus cloud zones as derived from airborne observations

Analyzed are the earlier obtained data on the dynamic structure of cumulus (convective) clouds in order to estimate cloud water content effects on the air temperature, computed turbulent fluxes, and their spectral characteristics. It is demonstrated that the cloud and precipitation droplets falling to the aircraft temperature sensor provoke an error in temperature measurements. Developed is a method for taking into account these effects and for computing the correct air temperature fluctuations in the cloud, wavelet spectra of the temperature, and wavelet cospectra of heat fluxes. The use of the method enabled to construct a consistent picture of horizontal heat flux distribution in the cumulus zone depending on the wave number and cloud location. It is shown that mesoscale eddies with the scale of more than 500 m are the main factors of heat exchange between clouds and the ambient space, and the role of turbulence consists only in the mixing inside the cloud. The conclusion is made that the temperature adjustment to the water content of the cloud is needed for correct interpretation of the results of aircraft observations of dynamic structure of cumulus clouds.     

Tropospheric Box-Modelling and Analytical Studies of the Hydroxyl (OH) Radical and Related Species: Comparison with Observations

Calculated and observed hydroxyl (OH) fields are presented. Calculated OH was obtained in three ways using (1) a photochemical box-model (2) a simple OH steady state approach and (3) a variant on (2) – the multiple equation steady state approach which assumes steady state for OH, HO2 and RO2 and hence obtains three simultaneous, non linear, equations. All three methods used data collected in June 1995 during the Weybourne Atmospheric Observatory Summer Experiment (WAOSE'95). Julian Days 169, 178, 179 and 180 displayed especially good data capture and were consequently chosen for study. The two steady state methods are essentially driven purely by observations and derive OH from the ratio of the relevant source and sink terms. The box-model was constrained where possible to observations; remaining unmeasured volatile organic compounds (VOCs) were initialised to an arbitrary low value of 10 ppt. Agreement between theory and experiment was usually around 50% and often better than this value, especially on J169, though discrepancies of up to a factor of 3 were occasionally apparent. Despite the inherent scatter, neither the box-model nor the simple steady state method were found to consistently over-estimate OH (a common feature of many numerical approaches) although this did occur to a certain extent using the multiple equation steady state approach, probably due to breakdowns in the steady state approximation. More data spread was evident in the box-model approach compared with the other methods. An analysis of the major sources and sinks of OH is presented for the three methods of calculation. Calculated and observed peroxy radicals are also presented. Calculated peroxy radicals were generally lower than that observed at night yet higher, sometimes by up to a factor of 7, during the day. Possible explanations for this result are explored.     

Studying the wintering conditions of winter crops from the satellite and ground-based observations (A case study for the Belgorod oblast)

The method is proposed for assessing the wintering conditions of winter crops with the accuracy to separate sown areas based on the joint use of the data of remote sensing and ground-based observations. The dependence is revealed between snow depth and snow albedo in the red band (MOD09GQ data). Geoinformation mapping of wintering conditions of winter crops cultivated in the Belgorod oblast is carried out for the winter period of 2012/2013.     

Comparisons of xylem sap flow and water vapour flux at the stand level and derivation of canopy conductance for Scots pine

Summary Simultaneous measurements of xylem sap flow and water vapour flux over a Scots pine (Pinus sylvestris) forest (Hartheim, Germany), were carried out during the Hartheim Experiment (HartX), an intensive observation campaign of the international programme REKLIP. Sap flow was measured every 30 min using both radial constant heating (Granier, 1985) and two types of Cermak sap flowmeters installed on 24 trees selected to cover a wide range of the diameter classes of the stand (min 8 cm; max 17.5 cm). Available energy was high during the observation period (5.5 to 6.9 mm.day^–1), and daily cumulated sap flow on a ground area basis varied between 2.0 and 2.7 mm day^–1 depending on climate conditions. Maximum hourly values of sap flow reached 0.33 mm h^–1, i.e., 230 W m^–2.Comparisons of sap flow with water vapour flux as measured with two OPEC (One Propeller Eddy Correlation, University of Arizona) systems showed a time lag between the two methods, sap flow lagging about 90 min behind vapour flux. After taking into account this time lag in the sap flow data set, a good agreement was found between both methods: sap flow = 0.745^* vapour flux,r ² = 0.86. The difference between the two estimates was due to understory transpiration.Canopy conductance (g _c ) was calculated from sap flow measurements using the reverse form of Penman-Monteith equation and climatic data measured 4 m above the canopy. Variations ofg _c were well correlated (r ² = 0.85) with global radiation (R) and vapour pressure deficit (vpd). The quantitative expression forg _c =f (R, vpd) was very similar to that previously found with maritime pine (Pinus pinaster) in the forest of Les Landes, South Western France.With 6 Figures     

Measurement and investigation of chamber radical sources in the European Photoreactor (EUPHORE)

It is essential to quantify the background reactivity of smog-chambers, since this might be the major limitation of experiments carried out at low pollutant concentrations typical of the polluted atmosphere. Detailed investigation of three chamber experiments at zero-NO _x in the European Photoreactor (EUPHORE) were carried out by means of rate-of-production analysis and two uncertainty analysis tools: local uncertainty analysis and Monte Carlo simulations with Latin hypercube sampling. The chemical mechanism employed was that for methane plus the inorganic subset of the Master Chemical Mechanism (MCMv3.1). Newly installed instruments in EUPHORE allowed the measurement of nitrous acid and formaldehyde at sub-ppb concentrations with high sensitivity. The presence of HONO and HCHO during the experiments could be explained only by processes taking place on the FEP Teflon walls. The HONO production rate can be described by the empirical equation W(HONO)_EUPHORE ^dry = a × j _{NO 2}× exp (− T ₀/T) in the low relative humidity region (RH < 2%, a = 7.3×10²¹ cm⁻³, T ₀ = 8945K), and by the equation W(HONO)_EUPHORE ^humid = W(HONO)_EUPHORE ^dry+ j _{NO 2}× b × RH ^q in the higher relative humidity region (2% < RH < 15%, b = 5.8×10⁸ cm⁻³ and q = 0.36, and RH is the relative humidity in percentages). For HCHO the expression W(HCHO)_EUPHORE = c × j _{NO 2}exp (− T′₀/T) is applicable (c = 3.1×10¹⁷ cm⁻³ and T′₀ = 5686 K). In the 0–15% relative humidity range OH production from HONO generated at the wall is about a factor of two higher than that from the photolysis of 100 ppb ozone. Effect of added NO₂ was found to be consistent with the dark HONO formation rate coefficient of MCMv3.1.     

Technogenic influence on the quality of water resources of small river basins (with a special reference to the Protva river)

The underground waters in small river basins in central Russia are recharged as a result of the atmospheric precipitation infiltration on the catchment and river water inflow to the horizons hydraulically connected with the river. In the first case, the atmospheric precipitation on its way of transit is being enriched in elements of water-bearing rocks, in the second case, of the surface runoff and domestic wastes waters. Both fluxes get mixed at the coastal water withdrawals of underground water. Some regularities in the drinking water quality formation connected with climatic conditions and water use regime were established based on geochemical and hydrodynamic studies of underground waters of the Protva River basin deposits.