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The term speleothem refers to carbonate deposits in caves: mainly stalactites, stalagmites and stalagmite floors.

The climate archives found at low latitudes are mostly sedimentary or geomorphological. Their formation and preservation depend fundamentally on favorable geomorphological and climatic conditions.

Author(s): Dibb, JE; Albert, M; Anastasio, C; Atlas, E; Beyersdorf, AJ; Blake, NJ; Blake, DR; Bocquet, F; Burkhart, JF; Chen, G; Cohen, L; Conway, TJ; Courville, Z; Frey, MM; Friel, DK; Galbavy, ES; Hall, S; Hastings, MG; Helmig, D; Greg Huey, L; Hutterli, MA; Jarvis, JC; Lefer, BL; Meinardi, S; Neff, W; Oltmans, SJ; Sherwood Rowland, F; Sjostedt, SJ; Steig, EJ; Swanson, AL; Tanner, DJ

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) were quantified in 67 high volume air samples taken concurrently in a forest and a clearing in southern Ontario, Canada from October 2001 to November 2002. Air concentrations were comparable between the two sites. Gaseous PCBs ranged from 6.4 to 150 pg x m(-3), and gaseous PBDEs ranged from below method detection limit (BDL) to 55 pg x m(-3) (with two extreme events up to 290 pg x m(-3)). Particulate PBDEs ranged from BDL to 40 pg x m(-3). Gaseous concentrations of PCBs and PBDEs were highly temperature dependent, suggesting a relatively strong influence of re-evaporation. Air concentrations of highly chlorinated PCBs in the forest were more temperature dependent than those in the clearing, whereas no difference was observed for the less-chlorinated PCBs. Forest filtering may have enriched highly chlorinated PCBs in the forest soil relative to the soil in the clearing, resulting in a higher contribution of re-evaporation for highly chlorinated PCBs at the forest. Compared to measurements conducted a decade earlier at a nearby site, PCB air concentrations were generally less temperature dependent, indicative of a reduction in the contribution of re-evaporation in the region. Furthermore, a significant correlation was found between temperature dependence and degree of chlorination, which had not been apparent in the previous study. This is presumably because depuration from soils occurred slower for highly chlorinated PCBs, resulting in their relatively higher abundance in terrestrial surfaces and, therefore, higher contribution from re-evaporation. Contrasting with the PCBs, the temperature dependence of PBDE air concentrations did not differ between congeners or between forest and clearing site. This could be a result of different usage and emission history: PCBs were banned approximately three decades ago, whereas PBDEs are currently still in use. Consequently, the influence of primary emissions on air concentrations is expected to be more important for PBDEs than for PCBs.

A field survey of 54 dwellings and 21 points outdoors around Zhuhai area was carried out using a newly developed integrating monitor in the spring of 2001 for a preliminary exposure assessment on 222Rn and 220Rn progeny, focusing especially on 220Rn progeny levels and its contribution to the general public. The flux rates of 222Rn and 220Rn from ground soil and soil nuclide contents were measured simultaneously. The average EECRn and EECTn were 52:9±39:1 Bq-m-3 and 4:0±2:3 Bq-m-3 for dwellings and 7:5±3:6 Bq-m-3 and 0:6±0:2Bq-m−3 for outdoor air, respectively. Rather high 220Rn flux rates from ground surface were measured, the mean value was 2;645:1 + 1;667:6 mBq-m−2-s1. The estimated radiation exposures from the exhalation of 222Rn and 220Rn progeny were 3.3 mSv-a−1 and 1.1 mSv-a−1, respectively. The exposure from 220 Rn progeny was some 1/3 that of 222 Rn progeny, and ought not to be ignored from the viewpoint of radiation protection in Zhuhai area.

Reported here are modeling results based on ISCAT (Investigation of Sulfur Chemistry of Antarctic Troposphere) 2000 observations recorded at the South Pole (SP) during the Austral Summer of 2000. The observations included a comprehensive set of photochemical parameters, e.g., NO, O3, and CO. It is worthy to note that not only were OH and HO2 observed, but also HOx precursor species CH2O, H2O2, and HONO were measured. Previous studies have suggested that HONO is the major source of OH/HOx in the Arctic; however, observed HONO levels at SP induced dramatic model overprediction of both HOx and NOx when used to constrain the model calculations. In contrast, model predictions constrained by observed values of CH2O and H2O2 are consistent with the observations of OH and HO2 (i.e., within 20%) for more than half of the data. Significant model overpredictions of OH, however, were seen at the NO levels lower than 50 pptv or higher than 150 pptv. An analysis of HOx budget at the median NO level suggests that snow emissions of H2O2 and CH2O are the single most important primary source of SP HOx, contributing 46% to the total source. Major sinks for HOx are found to be dry deposition of HO2NO2 and HNO3 as well as their reactions with OH. Although ISCAT 2000 led to a major progress in our understanding of SP HOx chemistry, critical aspects of this chemistry are still in need of further investigation.

In February 2000, a detailed measurement campaign was conducted over a 9-day period within a mercury (Hg) cell chlor-alkali plant in the southeastern United States (US). The principal focus of this study was to determine the fugitive (non-ducted) airborne Hg emissions from the main production equipment located in the “cell building” during extended period operations, including maintenance events. Other Hg monitoring conducted in and around the plant also included surveys of process areas surrounding the cell building, measurement of Hg fluxes from soil and other exposed surfaces, and speciated Hg measurements of ambient air both “upwind” and “downwind” of the production area as well as the determination of Hg contained in output products and wastes. The study was a collaborative effort among scientists from the US Environmental Protection Agency, the US Department of Energy's Oak Ridge National Laboratory, and the University of Michigan. This paper provides a description of the facility, the rationale and design of the study, and an introduction to companion papers containing the observational data.

We propose a theoretical formula of the time dependence of the resuspension factor, a quantity which indicates the degree of ground-surface contamination. The formula, K(t)∼t−4/3, agrees well with the empirical law of the resuspension factor, and conforms to the data of short periods such as 0.1 s in wind-tunnel experiments, as well as very long period, such as field observations in Chernobyl over years. We use the formula to estimate the date when pollutants were deposited on the ground. The estimated date is close to the date when the site was actually contaminated. Using this formula, the date when a pollution occurred can be estimated even if the actual date is unknown.

Surface–atmosphere mercury fluxes are difficult to measure accurately. Current techniques include dynamic flux chambers and micrometeorological gradient and aerodynamic approaches, all of which have a number of intrinsic problems associated with them. We have adapted conditional sampling (relaxed eddy accumulation), a micrometeorological technique commonly used to measure other trace gas fluxes, to measure surface–air mercury fluxes. Our initial flux measurement campaign over an agricultural soil consisted of two 1-week measurement periods, and was longer in duration than previously reported mercury flux measurement periods. Fluxes during both measurement periods ranged between 190.5 (evolution) and –91.7 ng m −2 h −1 (deposition) with an average evolution of 9.67 ng m −2 h −1 . The data showed significant diurnal trends, weakly correlated with shallow soil temperatures and solar radiation. This initial trial run indicates that conditional sampling has much promise for the accurate quantification of both short and long-term mercury fluxes.

Equipment and procedures are developed and implemented to measure nitric oxide (NO) emissions from unamended and municipal wastewater treatment plant biosolids-amended soil in controlled laboratory...

L’amelioration de la modelisation des processus physiques mis en jeu dans le cycle de l’eau comme dans celui du carbone passe aujourd’hui par une description fine des surfaces continentales et des echanges a l’interface sol-vegetation-atmosphere. Cet article illustre les potentialites de la teledetection, qui permet d’observer de fac on reguliere et a des echelles spatiales toujours plus fines, pour retrouver des parametres physiques caracterisant les surfaces observees. Les parametres consideres sont : la vegetation (type et densite), le contenu en eau du sol, et la rugosite du sol (microtopographie et couverture en cailloux).

A tall passive flux chamber with a height significantly greater than its horizontal dimensions is proposed for measuring fluxes of volatile organic compounds (VOCs) at the soil surface. The main feature of this tall chamber is the presence of a vertical concentration gradient of the target gas in the chamber. The emission and transport behavior of the target gas in the soil-chamber system are analyzed using the diffusion theory. A mathematical model is developed to estimate the flux from the soil into the tall chamber, providing the target gas establishes a detectable vertical concentration gradient in the chamber. To obtain the data required for calculating flux, only two gas concentrations (C1 and C2) at two heights (h1 and h2) within the chamber need to be measured at the end of a short chamber placement time (tp). To evaluate the applicability of the tall chamber for measuring flux, several laboratory tests have been conducted, using CH2Cl2 and CH3Br as the target gases. The results indicate that the proposed tall chamber has promising potential as a method for measuring fluxes of VOCs at the soil surface.

The changes in the atmospheric response (e.g., in the variables of state, the amount of cloud-and precipitating particles, the water- and energy fluxes) to concurrent land-use changes are exemplarly examined for various landscape scenarios since the cessation of open-pit mining. The principle of superposition is applied to detect areas where the atmospheric response is either enhanced or diminished according to concurrent land-use changes as compared to simple land-use changes. The results show that nonlinear behavior of a given quantity may occur in areas without significant changes in this quantity and that a quantity may be significantly changed without finding nonlinearity. Moreover, the concurrent land-use changes do not necessarily yield a stronger atmospheric response than simple land-use changes. In addition to the size of the patches, where land-use changes, the contrast in the hydrologic and thermal behavior of the changes is decisive in measuring the magnitude of the response. Enhancement and diminish ment seem also to depend on the land-use adjacent to the altered land-use.

Attempts to create models of surfaceߚ;atmosphere interactions with greater physical realism have resulted in land surface schemes (LSS) with large numbers of parameters. The hope has been that these parameters can be assigned typical values by inspecting the literature. The potential for using the various observational data sets that are now available to extract plot-scale estimates for the parameters of a complex LSS via advanced parameter estimation methods developed for hydrological models is explored in this paper. Results are reported for two case studies using data sets of typical quality but very different location and climatological regime (ARM-CART and Tucson). The traditional single-criterion methods were found to be of limited value. However, a multicriteria approach was found to be effective in constraining the parameter estimates into physically plausible ranges when observations on at least one appropriate heat flux and one properly selected state variable are available.

Evidence indicates that for homes within a geographically small area, indoor radon can be predicted using soil radon and soil permeability. In northern Virginia, an area of temperate climate and rolling topography, soil measurements taken adjacent to and under 150 homes were compared to their indoor radon. Indoor radon above 5 picoCuries/Liter (pCi/L) occurred in homes with soil radon in excess of 2000 pCi/L, but it also occurred with soil radon as low as 1000 pCi/L if the permeability exceeded 0.5 inches/hour.

As part of the Integrated Atmospheric Deposition Network (IADN), we have measured gas-phase polychlorinated biphenyl (PCB) concentrations in the atmosphere around the Great Lakes since November of ...

A brief error analysis associated with the use of the new method to determine the zero-plane displacement proposed by De Bruin and Verhoef has been performed. It is shown that use of temperature fluctuation data is more suited to determining the zero-plane displacement data over a heterogeneous surface.

Published estimates of removal of atmospheric methyl bromide (CH3Br) by agricultural soils are 2.7 Gg yr−1 (Gg = 109 g) [Shorter et al., 1995] and 65.8 Gg yr−1 [Serca et al., 1998]. The Serca et al. estimate, if correct, would suggest that the current value for total removal of atmospheric CH3Br by all sinks of 206 Gg yr−1 (based on Shorter et al., 1995) would be 30% too low. We have calculated a new rate of global agricultural soil uptake of atmospheric CH3Br from a larger sampling of cultivated soils collected from 40 sites located in the United States, Costa Rica, and Germany. First order reaction rates were measured during static laboratory incubations. These data were combined with uptake measurements we reported earlier based on field and laboratory experiments [Shorter et al. 1995]. Tropical (10.2°–10.4°N) and northern (45°–61°N) soils averaged lower reaction rate constants than temperate soils probably due to differing physical and chemical characteristics as well as microbial populations. Our revised global estimate for the uptake of ambient CH3Br by cultivated soils is 7.47±0.63 Gg yr−1, almost three times the value that we reported in 1995.

Since the ban on the use of trichloroacetic acid (TCAA) as a herbicide in several countries, TCAA is still found ubiquitously in the environment. The presence of TCAA nowadays is suggested to originate mainly from the atmospheric degradation of tetrachloroethene. Our mass balance calculations indicate that this may be true for the presence of TCAA in the atmosphere. However, our mass balance calculations also provide tentative evidence for the formation of TCAA in soil. If our calculated production fluxes are realistic estimates, a very large source of TCAA in soil has been identified.

The First ISLSCP Field Experiment (FIFE) provided an opportunity to test the concept of data publication for long-term access to valuable scientific data. In analogy with the procedures used in research publication, the FIFE Information System and NASA’s Pilot Land Data System adapted the functions performed by authors, editors, and publishers to an information management environment. Procedures and standards were developed to organize, quality check, document, and review data and associated supporting information for publication on a series of five CD-ROM volumes. The CD-ROM series has been successfully published and is in widespread use in the scientific community. The preliminary indications are that this publication will pass the “20-year test” recommended by a committee of the National Research Council for preserving global change data. It is concluded that the data publication approach, using near-permanent distributable publication units like CD-ROMs, is an important addition to the tools ...

PCB mixtures in surface deposits composed of core sand and ash from an aluminum foundry are enriched (3.6–9.4%) in chlorine percentage relative to deeper horizons. The deeper materials closely match (R2 = 0.902–0.962) Aroclor 1248, the aroclor used on-site and recovered from the floor inside the foundry (R2 = 0.998). This similarity suggests the more deeply buried PCBs have been stable and immobile for a 20–40 yr period. Chlorine enrichment upward is interpreted as the result of volatilization of lower and orthochlorinated congeners from surficial materials during repeated water evaporation. These results suggest surficial deposits contaminated by PCBs may be a significant source of lower ortho-chlorinated PCB congeners to the atmosphere and that buried PCBs can remain unchanged for decades. Comparison with sediments contaminated with Aroclor 1248 and known to have undergone anaerobic microbial dechlorination, indicates that Aroclor 1248 can be transformed to PCB mixtures enriched or depleted in chlorine by environmental processes.

Air and surface soil samples were taken at three stations downwind of a strip of soil fumigated with injected methyl bromide. Integrated horizontal flux of methyl bromide at each sampling station showed the removal of ∼46% of the methyl bromide mass from the plume by the time it reached 30–60 m downwind. Based on the U.S. EPA's dispersion model SCREEN-3, a mass loss of ∼42% was estimated. Analysis of the surface soil samples indicated the presence of methyl bromide residues that declined in concentration with distance downwind from the source. Laboratory tests confirmed the first-order rapid uptake (2–4 minutes) of methyl bromide by field soil.

A field experiment was conducted to study the effectiveness of a high-barrier plastic film (Hytibar) and reduced methyl bromide (MeBr) application dosages in decreasing MeBr emission from soil fumi...

A detailed description of basic premises as well as the structure and implementation principles of a new programme developed within the IGBP and addressing a comprehensive study of land-ocean interactions in the coastal zone with respect to natural and anthropogenic impacts is given.

Measurements of the atmospheric concentration gradients of mercury (Hg) vapor over soils can be used to determine the direction and magnitude of exchange rates of Hg if certain assumptions are met. However, these gradients are quite small and require highly precise sampling to achieve accurate data. We have developed a sampling and analysis procedure which allows quantification of gradients over background soils. With this procedure we can now measure atmospheric Hg at ambient levels with a precision of ∼0.5 to 2% (expressed as relative standard error). This level of precision is well above those published in earlier gradient studies. In our recent studies, gradients measured between 25 and 165 cm above background forest soils at Walker Branch Watershed, Tennessee were quite small, ranging from 0.02 to 0.39 ng/m3 (expressed as concentration differences). These gradients indicated that Hg emission was about 3 times more frequent than dry deposition. Gradients measured over soils at Lake Gardsjon, Sweden were generally smaller but also indicated bidirectional fluxes. By comparison, gradients above Hg-contaminated soils in Tennessee were far larger as expected, ranging from 0.12 to 5.60 ng/m3. These gradients consistently indicated emission of Hg. A number of tests were performed to validate that these gradients were true indications of Hg exchange rates.

The soil resistivity is an important parameter to consider when dealing with the lightning stroke electric field calculation. The usual methodologies were developed considering the soil as a homogeneous and isotropic medium but the actual soil is usually better represented by horizontal layers of different resistivities. This paper presents a PSpice based methodology for the calculation of the horizontal electric field component originated in the soil resistivity considering a multilayered stratified soil.

There have hand-held GPR systems and vehicle-mounted GPR systems, which are offset from the air-ground interface by a nonnegligible distance, developed for landmine detection. Vehicle-mounted systems have exclusive advantage that can show subsurface imaging in horizontal slices based on grid GPR data set. Hand-held GPR system is one of advantageous technologies in mountain district etc. But handheld GPR system usually cannot display subsurface imaging in horizontal slices because human being operator cannot precisely control GPR sensor to scan the measurement area along the regular survey line and observation positions are random. For both hand-held GPR systems and vehicle-mounted GPR systems, clutter reduction is very challenging due to these physical limitations. We used the technique of CMP antenna array and migration processing to improve the imaging quality for vehicle-mounted GPR systems, and used the modified migration algorithm to perform both interpolation and migration for hand-held GPR systems.

Soil air normally contains elevated levels of CO 2 relative to the atmosphere. The primary source of soil C is plant-root and microbial respiration. The exchange of soil and atmospheric CO 2 is important to many environmental concerns, such as acid rain, global warming and waste management. Proposed disposal of high-level nuclear wastes containing primarily inorganic 14 C may provide a source of 14 CO 2 to the atmosphere

We suggest that the atmosphere–ocean–earth system is unlikely to be intransitive, i.e. to admit two or more possible climates, any one of which, once established, will persist forever. Our reasoning is that even if the system would be intransitive if the external heating could be held fixed, say as in summer, the new heating patterns that actually accompany the advance of the seasons will break up any established summer circulation, and an alternative circulation may develop during the following summer, particularly if chaos has prevailed during the intervening winter. We introduce a very-low-order geostrophic baroclinic “general circulation” model, which may be run with or without seasonal variations of heating. Under perpetual summer conditions the model is intransitive, admitting either weakly oscillating or strongly oscillating westerly flow, while under perpetual winter conditions it is chaotic. When seasonal variations of heating are introduced, weak oscillations prevail through some summers and strong oscillations prevail through others, thus lending support to our original suggestion. We develop some additional properties of the model as a dynamical system, and we speculate as to whether its behaviour has a counterpart in the real world. DOI: 10.1034/j.1600-0870.1990.t01-2-00005.x

The concentration of atmospheric CO 2 was measured continuously in the suburbs of Sendai, Japan for the period December 1978-June 1981. The diurnal CO 2 variation was greatest in July and August and was barely observable during the cold months from November to April. The seasonal CO 2 variation was highly irregular and a decrease of CO 2 concentration with height was found throughout the year, presumably reflecting a substantial influence of local soil respiration. Daily minimum values of CO 2 concentration, however, showed a fairly regular seasonal trend and an average rate of CO 2 increase of 1.6 ppmv yr -1 . which are very close to the results of our aircraft measurements in the lower troposphere for the same period. DOI: 10.1111/j.1600-0889.1985.tb00042.x

In using GPR images for landmine detection it is often useful to identify the air-ground interface in the GPR signal for alignment purposes. A number of algorithms have been proposed to solve the air-ground interface detection problem, including some which use only A-scan data, and others which track the ground in B-scans or C-scans. Here we develop a framework for comparing these algorithms relative to one another and we examine the results. The evaluations are performed on data that have been categorized in terms of features that make the air-ground interface difficult to find or track. The data also have associated human selected ground locations, from multiple evaluators, that can be used for determining correctness. A distribution is placed over each of the human selected ground locations, with the sum of these distributions at the algorithm selected location used as a measure of its correctness. Algorithms are also evaluated in terms of how they affect the false alarm and true positive rates of mine detection algorithms that use ground aligned data.

An attempt is made to construct a model, coupling land surface and atmospheric processes in the planetary boundary layer (PBL). A grassland strip in a semi-desert (hereinafter called desert) is presupposed, so as to simulate the case of heterogeneous vegetation cover.

One way to reduce carbon dioxide (CO2) emissions to the atmosphere is to recover it from an energy conversion process (e.g. from stack gases) and to store it in an aquifer (a permeable, mainly sandy, underground layer). The main goal of this study was a preliminary evaluation of this kind of storage. Allowing for a large uncertainty in the geological properties, we arrived at the following tentative results. The average cost of disposal is $1.4 per ton CO2 stored. The enclosing layer of most aquifers seems impermeable enough to prevent the CO2 from rising to the surface within at least 10 000 years. The main technical uncertainty is whether the water in the reservoir can be pushed aside fast enough to prevent an intolerable pressure build-up in the reservoir. The disposal of CO2 in aquifers seems to be a feasible option in the light of existing geological knowledge. If it is a practical possibility, the opportunities are large and the costs appear to be relatively low. However, uncertainties remain in the technical sphere. These uncertainties have to be studied and dispelled before the disposal of CO2 in aquifers can be said to be called technically feasible.

The sensitivity of short-term climate to soil moisture parameterization has been investigated using the Florida State University Global Spectral Model. This is done through the implementation of a simple and realistic soil moisture availability in a prognostic equation for the surface temperature.

This Horton Memorial Lecture reviews the approach of Robert Horton (1875–1945) to key problems in hydrology, meteorology, and geography and then speculates on how Horton might today approach the problem of analyzing the sensitivity of catchment runoff to climate change. It is suggested that the techniques used by Horton can give us an insight into the nature of the latter problem through a partial analysis of the phenomena involved.

The observed relationship between global radiation and actinic flux in a radiation experiment above grassland corresponds well with the theoretical relationship expressed by Madronich.

Computer projections suggest that forests may respond dramatically and rapidly to global warming, with significant and readily observable changes in forests of mid-latitudes occurring by the turn of the century or shortly thereafter. These results raise the question: how reliable are the projections? Sensitivity analyses reported in this paper suggest that projections of forest response to global warming will be generally insensitive to errors of 10% in parameter estimation. Even where projections are sensitive quantitatively, they are not changed in timing. Projections are insensitive to the choice of baseline weather records, unless the warmest or coldest decades of the 20th century are used as baselines.

Soil/air partition coefficients (K(SA)) were measured experimentally on a silty clay loam soil spiked with polychlorinated biphenyls (PCBs) over a wide range of environmentally relevant temperatures (-30 to +30 degrees C). Measured K(SA)-values ranged over 6.4 orders of magnitude, with log K(SA) from 4.3 for PCBs 10/4 at +30 degrees C to 10.7 for PCBs 77/110 at -30 degrees C. Higher than expected, K(SA)-values were observed at subzero temperatures (by up to one order of magnitude, at -30 degrees C). The plots of log K(SA) vs. reciprocal absolute temperature show a change in slope at 0 degrees C. A log-log linear regression of K(SA) vs. octanol/air partition coefficient (K(OA)) has a slope close to 1, indicating that K(OA) is a good descriptor of the interchemical variability in K(SA). Further study showed that K(OA)-based Karickhoff-type equations can perfectly fit experimental K(SA)-values.

Relationships between the bulk Richardson number, B, and other stability parameters were derived for the atmospheric surface layer. Nomograms were constructed, relating the Monin-Obukhov stability parameter, z/L, to B. The nomograms and the graph of Golder (1972) were used to establish various schemes for classifying z/L, B and Ri, in terms of the Pasquill stability classes.

Fluxes of formic (HCOOH) and acetic (CH3COOH) acids between soils and the atmosphere were measured in a scrub-grass savanna and a semideciduous forest of Venezuela. High emissions of both acids were observed from savanna soils during daytime, with a daily contribution to the atmospheric boundary layer of about 0.15 ppb HCOOH and 0.07 ppb CH3COOH. Soil watering, simulating rainfall, produces a significant increase in CH3COOH emissions. Forest soils consumed these acids, with deposition velocities of 0.21 and 0.16 cm s−1. Savanna soils appear to be a significant source of HCOOH and CH3COOH to the tropical savanna atmosphere.

Curvilinear technique has been applied to rice crop in Bhandara district (Maharashtra) to examine effects of rainfall, maximum temperature and relative humidity. Partial regression curves for estimating the rice yield by taking into account the .combined effect of these three factors have been worked out. It is observed that during the period of active growth rainfall is the most significant factor followed by maximum temperature and relative humidity in that order. The optimum value of total rainfall during the active growth phase was found as 1000 mm and those for maximum temperature and relative humidity as 30.5° C and 81% respectively.

Energy exchange between the atmosphere and a melting glacier surface is mediated by the presence of a water layer. Under conditions of rapid melt and/or heavy rainfall, the possibility exists that a supraglacial run-off layer can advect sensible heat and influence the spatial variations of melt. The potential magnitude of such advection was investigated by numerically solving differential equations expressing the mass and energy balances of a two-dimensional run-off layer. Solutions were obtained for conditions typical of rainfall events, in which the potential for supraglacial heat advection should be maximal. The solutions indicate that advection cannot influence macro-scale melt patterns and surface morphology, except perhaps under heavy rainfall and/or rapid melt conditions, but can possibly cause micro-scale variations in ice melt. One-dimensional energy-balance models, which have normally been applied over glacier surfaces, should remain valid for most conditions.

Cet article presente une etude comparative de deux modeles theoriques du champ electromagnetique rayonne par un dipOle electrique vertical elementaire, situe dans l’air au-dessus du sol suppose plan. Des expressions du champ ont ete calculees en suivant la methode de King [3], et confrontees avec le modele bien connu de Norton [6-8]. On definit avec precision les domaines de validite de ces deux modeles. Les deux modeles montrant des differences importantes en champ proche, on les compare avec des resultats de mesures d’amplitude de champ effectuees dans cette zone au moyen de deux antennes quart d’onde verticales a la frequence de 400 MHz.