A note on estimating the effect of a limited fetch on micrometeorological evaporation measurements

A formula for the effective fetch of micrometeorological evaporation measurements is derived by application of diffusion theory, using Calder's approximation of a uniform wind field and neutral atmospheric stability. This simplification allows estimation of the likely sampling error, which would result from an upwind step-change in evaporation rate, without change in roughness.     

The Hadley circulation: assessing NCEP/NCAR reanalysis and sparse in-situ estimates

 We present a comparison of the zonal mean meridional circulations derived from monthly in situ data (i.e. radiosondes and ship reports) and from the NCEP/NCAR reanalysis product. To facilitate the interpretation of the results, a third estimate of the mean meridional circulation is produced by subsampling the reanalysis at the locations where radiosonde and surface ship data are available for the in situ calculation. This third estimate, known as the subsampled estimate, is compared to the complete reanalysis estimate to assess biases in conventional, in situ estimates of the Hadley circulation associated with the sparseness of the data sources (i.e., radiosonde network). The subsampled estimate is also compared to the in situ estimate to assess the biases introduced into the reanalysis product by the numerical model, initialization process and/or indirect data sources such as satellite retrievals. The comparisons suggest that a number of qualitative differences between the in situ and reanalysis estimates are mainly associated with the sparse sampling and simplified interpolation schemes associated with in situ estimates. These differences include: (1) a southern Hadley cell that consistently extends up to 200 hPa in the reanalysis, whereas the bulk of the circulation for the in situ and subsampled estimates tends to be confined to the lower half of the troposphere, (2) more well-defined and consistent poleward limits of the Hadley cells in the reanalysis compared to the in-situ and subsampled estimates, and (3) considerably less variability in magnitude and latitudinal extent of the Ferrel cells and southern polar cell exhibited in the reanalysis estimate compared to the in situ and subsampled estimates. Quantitative comparison shows that the subsampled estimate, relative to the reanalysis estimate, produces a stronger northern Hadley cell (∼20%), a weaker southern Hadley cell (∼20–60%), and weaker Ferrel cells in both hemispheres. These differences stem from poorly measured oceanic regions which necessitate significant interpolation over broad regions. Moreover, they help to pinpoint specific shortcomings in the present and previous in situ estimates of the Hadley circulation. Comparisons between the subsampled and in situ estimates suggest that the subsampled estimate produces a slightly stronger Hadley circulation in both hemispheres, with the relative differences in some seasons as large as 20–30%. 6These differences suggest that the mean meridional circulation associated with the NCEP/NCAR reanalysis is more energetic than observations suggest. Examination of ENSO-related changes to the Hadley circulation suggest that the in situ and subsampled estimates significantly overestimate the effects of ENSO on the Hadley circulation due to the reliance on sparsely distributed data. While all three estimates capture the large-scale region of low-level equatorial convergence near the dateline that occurs during El Nino, the in situ and subsampled estimates fail to effectively reproduce the large-scale areas of equatorial mass divergence to the west and east of this convergence area, leading to an overestimate of the effects of ENSO on the zonal mean circulation. Received: 16 September 1998 / Accepted: 22 April 1999     

Undulation and anomaly estimation using Geos-3 altimeter data without precise satellite orbits

The paper describes results obtained from the processing of 53 Geos-3 arcs of altimeter data obtained during the first weeks after the launch of the satellite in April, 1975. The measurement from the satellite to the ocean surface was used to obtain an approximate geoid undulation which was contaminated by long wavelength errors caused primarily by altimeter bias and orbit error. This long wavelength error was reduced by fitting with a low degree polynomial the raw undulation data to the undulations implied by the GEM 7 potential coefficients, in an adjustment process that included conditions on tracks that cross. The root mean square crossover discrepancy before this adjustment was ±12.4 meters while after the adjustment it was ±0.9 m. These adjusted undulations were used to construct a geoid map in the Geos-3 calibration area using a least squares filter to remove remaining noise in the undulations. Comparing these undulations to ones computed from potential coefficients and terrestrial gravity data indicates a mean difference of 0.25 m and a root mean square difference of ±1.92 m. The adjusted undulations were also used to estimate several 5^o, 2^o, and 1^o anomalies using the method of least squares collocation. The resulting predictions agreed well with known values although the 1^o x 1^o anomalies could not be considered as reliably determined.     

鄱阳湖水龄季节性变化特征

基于环境水动力学模型EFDC源程序,建立了染色剂模型和水龄模型,在将模型与航测水文数据验证吻合的基础上,分别计算了鄱阳湖自然条件下春、夏、秋、冬季的水龄和倒灌前后鄱阳湖染色剂和水龄分布的变化,以及五河水系各分支河流水龄.分季节的水龄计算表明鄱阳湖水体交换受季节性来水影响明显.夏、秋季的水龄相对较小,在多数年份又受到长江水倒灌的影响导致水龄有所增大;冬、春季水龄较大,亦无长江水倒灌现象,相较于夏、秋季,水域面积明显减少.分支流的水龄计算表明,西南湖区的水体交换主要受到赣江的影响,西北湖区水体交换主要受到修水和赣江的影响,南部湖区主要受到抚河与信江的影响,东部湖区主要受到饶河的影响,湖心区和入江水道则受到五河水系的综合影响.同时水龄的研究表明拟建的鄱阳湖水利枢纽工程"调枯不调洪"的原则是合理的,为鄱阳湖水利枢纽工程论证提供了重要的参考依据.     

Validation of parameterized convective fluxes with DIAMOD

Summary A diagnostic model (DIAMOD) for the atmosphere over Europe is use at the University of Vienna. Central parameters in each diagnostic column (horizontal resolution 100 km, time resolution 12 hours) are the vertical moisture plus heat flux (the total convective heat fluxh) and the vertical rain flux (r); both are functions of pressure. In this study DIAMOD is applied to validate the output of a forecast model for the simulation of acid deposition (EURAD) which is in use at the University of Cologne. The basic equations of both DIAMOD and EURAD models are summarized with emphasis on the sub-gridscale hydrologic components.First, the nontrivial problem of validating model output versus observations is discussed. Two different validation techniques based upon the budget equations are indentified. The fully prognostic technique compares the forecast of EURAD for the total verification period with the corresponding DIAMOD output. The semiprognostic validation technique involves only one-time-step tendencies. Neither yields an exact correspondence between EURAD and DIAMOD; however, the semiprognostic technique comes somewhat closer to the ideal of an objective validation. The quantities investigated are: The fields, the time tendencies and the fluxesh andr.Second, EURAD is validated versus DIAMOD with both techniques for the EUMAC Joint Wet Case (the Chernobyl episode) in April 1986; the output fields include selected profiles ofh(p) over France (a moist night situation) and over Greece (a dry day situation). The comparison demonstrates for both that the EURAD forecasts are acceptable for ther-fluxes but are relatively poor for theh-fluxes. Reasons for the differences are discussed.With 11 Figures     

Identifying Key Sources of Uncertainty in Climate Change Projections

What sources of uncertainty shouldbe included in climate change projections and whatgains can be made if specific sources of uncertaintyare reduced through improved research?DIALOGUE, anintegrated assessment model, has been used to answerthese questions. Central in the approach of DIALOGUEis the concept of parallel modeling, i.e., for eachstep in the chain from emissions to climate change anumber of equivalent models areimplemented. The followingconclusions are drawn:The key source of uncertainty in global temperatureprojections appears to be the uncertainty inradiative forcing models. Within this group ofmodels uncertainty within aerosol forcing models isabout equal to the total forcing of greenhouse gasmodels. In the latter group CO₂ is dominant.The least important source of uncertainty appears tobe the gas cycle models. Within this group of modelsthe role of carbon cycle models is dominant.Uncertainty in global temperature projections hasnot been treated consistently in the literature.First, uncertainty should be calculated as a productof all uncertainty sources. Second, aparticular choice of a base year for global warmingcalculations influences the ranking of uncertainty.Because of this, a comparison of ranking resultsacross different studies is hampered. We argue that`pre-Industrial' is the best choice for studies onuncertainty.There is a linear relationship between maximumuncertainty in the year 2100 and cumulativeemissions of CO₂ over the period 1990–2100:higher emissions lead to more uncertainty.     

On the evaluation of an integral connected with the thermonuclear reaction rate in closed form

The standard expression of the reaction rate for low-energy, nonresonant nuclear reactions in nondegenerate plasma contains a parameter-dependent integral which in all previous calculations with physical or astrophysical background is considered as not capable of being evaluated in a closed form. So one usually resorts to approximation methods concerning large values of the parameter. At first we point out that CONSUL (1964) has given a series representation of the integral which was identified with a MEIJER 's G-function by MATHAI (1971). Next, in view of a physically more exact determination of the reaction rate formula, especially in connection with calculations concerning stellar energy generation, we consider a more general integral containing the mentioned one as special case and give an approximation-free representation by means of MEIJER 's G-function. The G-function so obtained may be conceived as complex-valued continuation of CONSUL 's series representation of a certain class of integrals contained in the considered one. From the series we extract a small parameter approximation of the special integral.     

Search for optical identifications in the 5C4 radio survey

With the aid of a statistical approach regarding only the nearest optical object to a given radio position we have found identification rates of nearly 30 per cent up to the blue and red limits of the Palomar Sky Survey prints covering the region of the 5C4 radio survey. Roughly 60 per cent of these identifications are blue starlike objects and therefore possible quasar candidates. The remainig identifications are galaxies. Probabilities for the first neighbours to be an optical counterpart and finding charts for highly reliable objects are given.     

Further notes on the associated alpha-functions and related integrals in the theory of the light changes of eclipsing variables

With a view to furthering the theory of the light changes of eclipsing variables, developed before systematically by Z. Kopal, this paper presents a number of new (and computable) expressions for the associated alpha-function _n ⁰ ,(r₁,r₂,) (and also for its partial derivatives), where _n ⁰ ,(r₁,r₂,) represents the fractional loss of light suffered by an eclipse of a circular disc of fractional radiusr ₁ (and darkened at the limb to thenth degree) by an opaque disc of radiusr ₂, with their centres separated by a fractional (projected) distance , provided that the transparency of the occulting disc increases with the angle of foreshortening in the same manner as the limb-darkening of the eclipsed star (that is, when the transparency functiong(, ) of the second aperture is given by Equation (4) below). Many of the explicit expressions derived here are valid for any type of eclipse, occultation or transit, regardless of whetherr ₁>r ₂ orr ₁<r ₂. and for any degreen of the adopted law of limb-darkening. It is also pointed out how some of the results obtained in this paper are related to the various representations given earlier in the literature for the case =0.