Modeled impacts of changes in tundra snow thickness on ground thermal regime and heat flow to the atmosphere in Northernmost Alaska

Seasonal snow covers the tundra surface for up to nine months of each year on the Alaskan North Slope. Variations in the snow thickness could strongly influence the thermal regime of the underlying soil and permafrost, and the surface energy balance. The impacts of increases and decreases in the tundra snow thickness on the thermal regime of snow surface, active layer, and permafrost, and on the conductive heat flow to the atmosphere were investigated numerically, by using an improved surface energy balance approach based one-dimensional heat transfer model. The baseline inputs for the numerical model are mean daily meteorological data and surface albedos collected at Barrow, Alaska from 1995 through 1999. Based on a study for the long-term mean daily maximum and minimum snow thickness distributions at Barrow in the snow season of 1948 through 1997, a snow thickness factor was defined and five simulation cases were run for the snow season of 1997–1998 by changing the snow thickness factor. The modeled results indicate that changes in snow thickness have significant impacts on ground thermal regimes and conductive heat flow to the atmosphere. Decreasing the snow thickness by 50% led to the maximum ground temperature decrease of 1.48 °C at 0.29 m depth, and 0.72 °C at 3.0 m depth; the magnitude of the mean conductive heat flow to the atmosphere for December increase of 4.3 Wm^− 2. Increasing the snow thickness by 50% resulted in the maximum ground temperature increase of 1.44 °C at 0.29 m depth, and 0.66 °C at 3.0 m depth; the magnitude of the mean conductive heat flow to the atmosphere for December decrease of 1.57 W m^− 2. On an annual basis, variation in the snow thickness by 50%, the ground temperature variations of more than 0.25 °C occurred as deep as 8.0 m below the ground surface. The modeled results also show that changes in snow thickness have a relatively small influence on the snow surface temperature.     

Transient projections of permafrost distribution in Canada during the 21st century under scenarios of climate change

Most general circulation models (GCMs) project that climate will be warmer in the 21st century, especially in high latitudes. Climate warming will induce permafrost degradation, which would have great impacts on hydrology, ecosystems and soil biogeochemistry, and could destabilize the foundations of infrastructure. In this study, we simulated transient changes of permafrost distribution in Canada in the 21st century using a process-based permafrost model driven by six GCM-generated climate scenarios. The results show that the area underlain by permafrost in Canada would be reduced by 16.0–19.7% from the 1990s to the 2090s. This estimate was smaller than equilibrium projections because the ground thermal regime was in disequilibrium at the end of the 21st century and permafrost degradation would continue. The simulation shows significant permafrost thaw from the top: On average for the area where permafrost exists in all the years during 1990–2100, active-layer thickness increased by 0.3–0.7 m (or 41–104%), the depth to permafrost table increased by 1.9–5.0 m, and the area with taliks increased exponentially. Permafrost was also thawed from the bottom in southern regions.     

On the relationship between ground temperature histories and meteorological records: a report on the Pomquet station

An experimental air–ground climate station is operating in Pomquet, Nova Scotia, monitoring meteorological (surface air temperatures at three heights, wind velocity and direction, incoming solar radiation, precipitation, snow depth and relative humidity) and ground thermal variables (soil temperatures at depths of 0, 5, 10, 20, 50 and 100 cm). Readings are taken every 30 s and 5 min averages are stored, in order to characterize the energy exchanges at the air ground interface. Here, I report on the first year of operation. For spring, summer and fall, we find that soil temperatures track surface air temperatures with amplitude attenuation and phase lag with depth confirming that heat conduction adequately describe the soil thermal field at the Pomquet site. For winter conditions, we find that heat transfer is dominated by latent heat released during soil freezing and to a lesser extent by the insulating affect of snow cover. A numerical model of heat conduction was used in order to estimate the magnitude of the heat released by freezing during the winter months. I also show that there is an inverse correlation for the difference between soil (100 cm) and air temperatures and the incoming solar radiation at the site.     

Cryospheric change in China

This paper provides an overview of the current status of the cryosphere in China and its changes. Up-to-date statistics of the cryosphere in China are summarized based on the latest available data. There are 46,377 glaciers in China, covering an area of 59,425 km². The glacier ice reserve is estimated to be about 5600 km³ and the annual glacier runoff is about 61.6 × 10⁹ m³. The continuous snow cover extent (> 60 days) in China is about 3.4 × 10⁶ km² and the maximum water equivalent is 95.9 × 10⁹ m³ yr^− 1. The permafrost area in China is about 1.72 × 10⁶ km². The total ground ice reserve on the Qinghai–Tibetan Plateau is estimated to be about 10,923 km³. Recent investigations indicated that glacier areas in China have shrunk about 2–10% over the past 45 yr. Total glacier area has receded by about 5.5%. Snow mass has increased slightly. Permafrost is clearly degrading, as indicated by shrinking areas of permafrost, increasing depth of the active layer, rising of lower limit of permafrost, and thinning of the seasonal frost depth. Some models predict that glacier area shrinkage could be as high as 26.7% in 2050, with glacier runoff increasing until its maximum in about 2030. Although snow mass shows an increasing trend in western China, in eastern China the trend is toward decreasing snow mass, with increasing interannual fluctuations. Permafrost degradation is likely to continue, with one-third to one-half of the permafrost on the Qinghai–Tibetan Plateau anticipated to degrade by 2100. Most of the high-temperature permafrost will disappear by then. The permafrost in northeastern China will retreat further northward.     

Past and recent changes in air and permafrost temperatures in eastern Siberia

Air and ground temperatures measured in Eastern Siberia has been compiled and analyzed. The analysis of mean annual air temperatures measured at 52 meteorological stations within and near the East-Siberian transect during the period from 1956 through 1990 demonstrates a significant and statistically significant (at 0.05 level) positive trend ranging from 0.065 to 0.59 °C/10 yr. A statistically significant (at 0.05 level) positive trend was also observed in mean annual ground temperatures for the same period. The permafrost temperature reflects changes in air temperature on a decadal time scale much better than on an interannual time scale. Generally, positive trends in mean annual ground temperatures are slightly smaller in comparison with trends in mean annual air temperatures, except for several sites where the discordance between the air and ground temperatures can be explained by the winter snow dynamics. The average trend for the entire region was 0.26 °C/10 yr for ground temperatures at 1.6 m depth and 0.29 °C/10 yr for the air temperatures. The most significant trends in mean annual air and ground temperatures were in the southern part of the transect, between 55° and 65° N. Numerical modeling of ground temperatures has been performed for Yakutsk and Tiksi for the last 70 yr. Comparing the results of these calculations with a similar time series obtained for Fairbanks and Barrow in Alaska shows that similar variations of ground temperatures took place at the same time periods in Yakutsk and Fairbanks, and in Tiksi and Barrow. The decadal and longer time scale fluctuations in permafrost temperatures were pronounced in both regions. The magnitudes of these fluctuations were on the order of a few degrees centigrade. The fluctuations of mean annual ground temperatures were coordinated in Fairbanks and Yakutsk, and in Barrow and Tiksi. However, the magnitude and timing of these fluctuations were slightly different for each of the sites.     

Ice table depth variability near small rocks at the Phoenix landing site, Mars: A pre-landing assessment

We combine thermal simulations of ground ice stability near small rocks with extrapolations of the abundance of rocks at the Phoenix landing site based on HiRISE rock counts to estimate the degree of ice table depth variability within the 3.8 m² workspace that can be excavated during the mission. Detailed predictions of this kind are important both to test current ground-ice theory and to optimize soil investigations after landing. We find that Phoenix will very likely have access to at least one rock in the diameter range 5 cm to 1 m. Our simulations, which assume the ice to be in diffusive equilibrium with atmospheric water vapor, indicate that all rocks in this size range are associated with an annulus of deep ice-free soil. Ice table depth variability of 1-5 cm is very likely at the landing site due to the presence of small rocks. Further, there are scenarios in which Phoenix might exploit the presence of individual large rocks and/or the arrangement of small rocks to sample soils at depths >10 cm below the average depth predicted from orbit (∼4 cm). Scale analysis to constrain uncertainties in simulation results indicates that estimates of maximum depths may be somewhat conservative and that ice table depressions associated with individual rocks could be deeper and laterally more extended than indicated by formal predictions by mm to cm.     

Warming permafrost in European mountains

Here we present the first systematic measurements of European mountain permafrost temperatures from a latitudinal transect of six boreholes extending from the Alps, through Scandinavia to Svalbard. Boreholes were drilled in bedrock to depths of at least 100 m between May 1998 and September 2000. Geothermal profiles provide evidence for regional-scale secular warming, since all are nonlinear, with near-surface warm-side temperature deviations from the deeper thermal gradient. Topographic effects lead to variability between Alpine sites. First approximation estimates, based on curvature within the borehole thermal profiles, indicate a maximum ground surface warming of +1 °C in Svalbard, considered to relate to thermal changes in the last 100 years. In addition, a 15-year time series of thermal data from the 58-m-deep Murtèl–Corvatsch permafrost borehole in Switzerland, drilled in creeping frozen ice-rich rock debris, shows an overall warming trend, but with high-amplitude interannual fluctuations that reflect early winter snow cover more strongly than air temperatures. Thus interpretation of the deeper borehole thermal histories must clearly take account of the potential effects of changing snow cover in addition to atmospheric temperatures.     

Numerical modelling of permafrost in bedrock in northern Fennoscandia during the Holocene

The occurrence of permafrost in bedrock in northern Fennoscandia and its dependence on past and presently ongoing climatic variations was investigated with one- (1D) and two-dimensional (2D) numerical models by solving the transient heat conduction equation with latent heat effects included. The study area is characterized by discontinuous permafrost occurrences such as palsa mires and local mountain permafrost. The ground temperature changes during the Holocene were constructed using climatic proxy data. This variation was used as a forcing function at the ground surface in the calculations. Several versions of the present ground temperature were applied, resulting in different subsurface freezing–thawing conditions in the past depending on the assumed porosity and geothermal conditions.Our results suggest that in high altitude areas with a cold climate (present mean annual ground temperature between 0°C and −3°C), there may have been considerable variations in permafrost thickness (ranging from 0 to 150 m), as well as periods of no permafrost at all. The higher is the porosity of bedrock filled with ice, the stronger is the retarding effect of permafrost against climatic variations.Two-dimensional models including topographic effects with altitude-dependent ground temperatures and slope orientation and inclination dependent solar radiation were applied to a case of mountain permafrost in Ylläs, western Finnish Lapland, where bedrock permafrost is known to occur in boreholes to a depth of about 60 m. Modelling suggests complicated changes in permafrost thickness with time as well as contrasting situations on southern and northern slopes of the mountain.Extrapolating the climatic warming of the last 200 years to the end of the next century when the anticipated increase in the annual average air temperature is expected to be about 2 K indicates that the permafrost occurrences in bedrock in northern Fennoscandia would be thawing rapidly in low-porosity formations. However, already a porosity of 5% filled with ice would retard the thawing considerably.     

Permafrost and climatic change in China

The permafrost area in China is about 2.15×10⁶ km², and is generally characterized by altitudinal permafrost. Permafrost in China can be divided into latitudinal and altitudinal types, the latter can be further divided into plateau and alpine permafrost. Altitudinal permafrost also can be divided into five thermal stability types. The permafrost environment has changed significantly since the Late Pleistocene. In northeastern China, the southern limit of permafrost extended to 41–42°N during the last glaciation maximum; in the Holocene megathermal, it retreated northward. The ice wedges and permafrost formed during the Late Pleistocene are still present in the northern part of the Da-Xing'anling Mountains. The inactive ice wedges at Yitulihe indicate a cooling and subsequent permafrost expansion during the Late Pleistocene. The lower limit of altitudinal permafrost in western China has elevated from 800 to 1500 m since the last glaciation maximum. Compared with that in northern Europe and North America, latitudinal permafrost in northeastern China is less sensitive to climatic warming, but altitudinal permafrost, especially permafrost on the Qinghai–Tibet Plateau (QTP), is sensitive to climatic warming. Since the early 20th century, significant permafrost degradation has occurred and is occurring in most permafrost regions in China. Due to the combined influence of climatic warming and increasing anthropogenic activities, substantial retreat of permafrost is expected on the QTP and in northeastern China during the 21st century. Permafrost degradation has and will cast great influence on engineering construction, water resources and environments in the cold regions of China. The wetlands in the cold regions of China emit significant amounts of CH₄ and N₂O to the atmosphere and uptake atmospheric CO₂ at a considerable rate, which might contribute to the global atmospheric carbon budget and feedback to climatic systems. However, uncertainties about permafrost changes, rates of changes and their environmental impacts are still large and call for intensive studying.     

An empirically derived lunar gravity field

The heat-flow experiment is one of the Apollo Lunar Surface Experiment Package (ALSEP) instruments that was emplaced on the lunar surface on Apollo 15. This experiment is designed to make temperature and thermal property measurements in the lunar subsurface so as to determine the rate of heat loss from the lunar interior through the surface. About 45 days (1 1/2 lunations) of data has been analyzed in a preliminary way. This analysis indicates that the vertical heat flow through the regolith at one probe site is 3.3 × 10^–6 W/cm² (±15%). This value is approximately one-half the Earth's average heat flow. Further analysis of data over several lunations is required to demonstrate that this value is representative of the heat flow at the Hadley Rille site. The mean subsurface temperature at a depth of 1 m is approximately 252.4K at one probe site and 250.7K at the other. These temperatures are approximately 35K above the mean surface temperature and indicate that conductivity in the surficial layer of the Moon is highly temperature dependent. Between 1 and 1.5m, the rate of temperature increase as a function of depth is 1.75K/m (±2%) at the probe 1 site. In situ measurements indicate that the thermal conductivity of the regolith increases with depth. Thermal-conductivity values between 1.4 × 10^–4 and 2.5 × 10^–4 W/cm K were determined; these values are a factor of 7 to 10 greater than the values of the surface conductivity. If the observed heat flow at Hadley Base is representative of the moonwide rate of heat loss (an assumption which is not fully justified at this time), it would imply that overall radioactive heat production in the Moon is greater than in classes of meteorites that have formed the basis of Earth and Moon bulk composition models in the past.Lamont-Doherty Geological Observatory Contribution Number 1800.     

Permafrost warming in the Tien Shan Mountains, Central Asia

The general features of alpine permafrost such as spatial distribution, temperatures, ice content, permafrost and active-layer thickness within the Tien Shan Mountains, Central Asia are described. The modern thermal state of permafrost reflects climatic processes during the twentieth century when the average rise in mean annual air temperature was 0.006–0.032 °C/yr for the different parts of the Tien Shan. Geothermal observations during the last 30 yr indicate an increase in permafrost temperatures from 0.3 °C up to 0.6 °C. At the same time, the average active-layer thickness increased by 23% in comparison to the early 1970s. The long-term records of air temperature and snow cover from the Tien Shan's high-mountain weather stations allow reconstruction of the thermal state of permafrost dynamics during the last century. The modeling estimation shows that the altitudinal lower boundary of permafrost distribution has shifted by about 150–200 m upward during the twentieth century. During the same period, the area of permafrost distribution within two river basins in the Northern Tien Shan decreased approximately by 18%. Both geothermal observations and modeling indicate more favorable conditions for permafrost occurrences and preservation in the coarse blocky material, where the ice-rich permafrost could still be stable even when the mean annual air temperatures exceeds 0 °C.     

Recent organic matter accumulation in relation to some climatic factors in ombrotrophic peat bogs near heavy metal emission sources in Finland

Accumulation of organic matter (OM) was studied in four ombrotrophic peat bogs in Finland: Harjavalta (vicinity of a Cu–Ni smelter), Outokumpu (near a closed Cu–Ni mine), Alkkia (Ni-treated site) and Hietajärvi (a pristine site). At each sampling site, two peat cores (15 × 15 × 100 cm) were taken. Age-dating of peat was determined using ²¹⁰Pb method (CRS model). The local annual temperature sum and precipitation for the past 125 years were modeled. The objective was to compare recent net accumulation rates of heavy metal polluted ombrotrophic peat bogs with those of a pristine bog, and to study the relationship between weather and net accumulation rates. Based on ²¹⁰Pb age-dating, the upper 16-cm peat layer at Harjavalta, 35 cm at Outokumpu and 25 cm at Hietajärvi represents 125 years of peat formation, yielding the following average peat accumulation rates: Harjavalta 1.3 mm year^− 1, Outokumpu 2.8 mm year^− 1 and Hietajärvi 2.0 mm year^− 1. At the Alkkia site, the Ni treatment in 1962 had completely stopped the peat accumulation. Net accumulation rates were related to precipitation at Outokumpu, Harjavalta and Hietajärvi sites. In addition, emissions released from the nearby located Cu–Ni smelter could have affected negatively net OM accumulation rate at Harjavalta site.     

Injection of dust into the martian atmosphere: Evidence from the viking gas exchange experiment

It is proposed that dust storms on Mars that develop during predawn hours may be triggered by a freeze/thaw dust injection process. The model is based on a phenomenon that was observed during the Viking Gas Exchange experiments on Mars, in which adsorbed gas was catastrophically desorbed from soil samples when exposed to humidification at ∼5°C. Similar conditions may develop at midlatitude locations on Mars near perihelion, and a similar humidification-driven desorption process might occur in the soil column. If soils are dampened during humikification, desorbed gases in confined pore spaces could possibly reach 8.6 bar. Diurnal freezing may possibly cause H₂O to crystallize within the pores, possibly producing cohesive soil failure, release of the trapped gas, and explosive injection of freeze-dried powdery overburden dust into the atmospheric column. The process could potentially occur at 5–20 cm depth, and the freeze/thaw dust injection event may initiate after 10:00 PM local time (20°S lat). Dust would be injected at velocities approaching 450 m sec⁻¹ and it would remain in the atmosphere for several hours before settling out. The plumes could potentially regenerate diurnally until the growing atmospheric dust load produced sufficient dampening of the diurnal thermal wave to prevent freeze/thaw. Seasonal replenishment of H₂O could potentially occur by upward migration from depth during the period between 150 and 475 sols after perihelion. The model was experimentally tested and the results were in good agreement with predictions, although a factor of 14 times more gas evolved from the laboratory samples than from the Viking samples. Most of the characteristics of the predawn storms could possibly be adequately explained by the freeze/thaw injection model, including (1) predawn onsets, (2) postperihelion seasonal occurence, (3) daily recurrence during the initial phases of the storms, and (4) generation of blue clouds (H₂O ice) at the storm sites. The process may possibly occur over widespread locations at midlatitudes during seasonal retreat of “tempofrost” from these latitude belts. Permanent low albedo features in these latitude belts may possibly be regions of preferential humidification-induced dust entrainment and net dust removal. The H₂O injected into the atmosphere may potentially be a major source of H₂SO₄ and HCl aerosols, which may possibly chemically react with the regolith to form soluble sulfate and chloride salts. Mg²⁺ may be preferentially depleted from the dust.     

Thermokarst processes and the origin of crater-rim gullies in Utopia and western Elysium Planitia

We have identified a number of gullies that could be aqueous in origin near or at the rim of several impact craters in Utopia Planitia and western Elysium Planitia (30.0°-59.0° N; 241.0°-291.0° W). Based on the sharpness of their incisions and the general absence of superposed craters, we ascribe a relatively recent origin to the gullies. Scalloped depressions are commonplace throughout the region, as well as on the crater walls, rims and floors near the areas of gully issuance. Occasionally, the depressions cross-cut the gully debris-aprons, suggesting that the formation of some depressions is even more recent than that of the gullies. Previous research has proposed that the depressions are collapse basins formed by thermokarst processes. On Earth, thermokarst landforms occur in areas of low gradient topography where the permanently frozen ground (permafrost) is ice rich and has undergone a change in thermal equilibrium. This change can be triggered by long-term or episodic/cyclic climate change and accompanying rises in mean temperatures towards ∼0 °C as well as by rises in seasonally sustained summer temperatures well above ∼0 °C. In order to explain the origin of the rim or near-rim gullies we invoke high obliquity and the possibility that this region of Mars experienced obliquity-driven rises in temperature, atmospheric pressure and humidity sufficient to keep surface water and near-surface ground-ice stable for extended periods of time. We propose that gully formation is closely related to local freeze-thaw processes that, in turn, generate a thermokarst landscape (of which the gullies are a part). This geological and climatological scenario comprises the following steps:

1.

An inundation of meltwater at high obliquity (due to the thawing of an atmospherically-deposited snowpack or ice-sheet) and the subsequent saturation of the underlying regolith to tens of metres of depth.

2.

Loss of water on the surface, perhaps as obliquity decreases slightly, followed by the progressive freezing of the saturated regolith; this creates an aggrading mass of ice-rich regolith.

3.

Obliquity-induced temperature rises that engender the thaw, drainage and partial evaporation of the near-surface, ice-rich regolith.

4.

Localised formation of thermokarst collapse-basins (alases), as water is evacuated from these basins.

5.

Formation of gullies near, or at, some impact-crater rims as the result of meltwater migration from nearby alases through the thawed regolith to the areas of gully issuance.

Although the plains' materials in this region are in part very old (possibly Hesperian or even Noachian), the mantling deposits and their deformation by thermokarst processes appears to be relatively young. This suggests that recent climatic conditions could have been episodically warmer and wetter than had been previously thought.     

The updated version of SPONSOR land surface scheme: PILPS-influenced improvements

The parameterization scheme SPONSOR (Semi-distributed ParameterizatiON Scheme of the ORography-induced hydrology) participating in PILPS (Project for Intercomparison of Land-surface Parameterization Schemes) experiments since 1993 is described in more detail than before, taking into account a range of recent modifications. Improvement of the scheme in several aspects (e.g., soil water movement) resulted in significantly improved results for the Cabauw site (used for PILPS (2a) experiments). Then, parameterization of cold seasons/regions processes (water phase transformations within soil and snow cover) was developed for PILPS (2d) experiments carried out with Valdai data. Testing of the scheme against the data of Kolyma water balance station shows that it is able to reproduce the main features of heat and water exchange at the land surface in the permafrost zone quite satisfactorily. It was found that the scheme results are rather sensitive to the soil heat conductivity, especially in the cold seasons. The original method for the calculation of this parameter was developed using a square root function. The surface temperature and dates of crossing the 0°C temperature threshold for Kolyma station were reproduced with satisfactory accuracy. The temporal variation of the deep soil layers' temperatures was modelled satisfactorily too, but the seasonal amplitude of deep soil temperatures was overestimated by the scheme. This disadvantage can possibly be improved by inclusion of vertical inhomogeneity of soil thermal and hydraulic properties in the model.     

Estimation of net accumulation rate at a Patagonian glacier by ice core analyses using snow algae

Snow algae in a 45.97-m-long ice core from the Tyndall Glacier (50°59′05″S, 73°31′12″W, 1756 m a.s.l.) in the Southern Patagonian Icefield were examined for potential use in ice core dating and estimation of the net accumulation rate. The core was subjected to visual stratigraphic observation and bulk density measurements in the field, and later to analyses of snow algal biomass, water isotopes (¹⁸O, D), and major dissolved ions. The ice core contained many algal cells that belonged to two species of snow algae growing in the snow near the surface: Chloromonas sp. and an unknown green algal species. Algal biomass and major dissolved ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻, SO₄²⁻) exhibited rapid decreases in the upper 3 m, probably owing to melt water elution and/or decomposition of algal cells. However, seasonal cycles were still found for the snow algal biomass, ¹⁸O, D-excess, and major ions, although the amplitudes of the cycles decreased with depth. Supposing that the layers with almost no snow algae were the winter layers without the melt water essential to algal growth, we estimated that the net accumulation rate at this location was 12.9 m a^− 1 from winter 1998 to winter 1999, and 5.1 m from the beginning of winter to December 1999. These estimates are similar to the values estimated from the peaks of ¹⁸O (17.8 m a^− 1 from summer 1998 to summer 1999 and 11.0 m from summer to December 1999) and those of D-excess (14.7 m a^− 1 from fall 1998 to fall 1999 and 8.6 m a^− 1 from fall to December 1999). These values are much higher than those obtained by past ice core studies in Patagonia, but are of the same order of magnitude as those predicted from various observations at ablation areas of Patagonian glaciers.     

Bearing strength of lunar soil

Bearing load vs penetration curves have been measured on a 1.3 g sample of lunar soil from the scoop of the Surveyor 3 soil mechanics surface sampler, using a circular indentor 2 mm in diameter. Measurements were made in an Earth laboratory, in air. This sample provided a unique opportunity to evaluate earlier, remotely controlled, in-situ measurements of lunar surface bearing properties. Bearing capacity, measured at a penetration equal to the indentor diameter, varied from 0.02–0.04 N cm^–2 at bulk densities of 1.15 g cm^–3 to 30-100 N cm^–2 at 1.9 g cm^–3. Deformation was by compression directly below the indentor at bulk densities below 1.61 g cm^–3, by outward displacement at bulk densities over 1.62 g cm^–3. Preliminary comparison of in-situ remote measurements with those on returned material indicates good agreement if the lunar regolith at Surveyor 3 has a bulk density of 1.6 g cm^–3 at 2.5 cm. depth; definitive comparison awaits both better data on bulk density of the undisturbed lunar soil and additional mechanical-property measurements on returned material.     

The land-surface flux model PROGSURF

The land-surface flux model (PROGSURF) designed jointly at the Universities of Vienna and Budapest is reviewed; it belongs to the broad spectrum of PILPS¹ models. PROGSURF comprises one vegetation layer and three soil layers. Temperature prediction is made by the heat conduction equation in conjunction with the force-restore method. Turbulent heat fluxes are parameterized by gradient laws using the resistance concept. The formula for the canopy surface resistance involves both a parameter describing atmospheric demand and one describing moisture availability. Soil moisture prediction is made with Richards' equation. PROGSURF is tested in off-line mode for the Cabauw data set. The observed annual mean values of the state and flux quantities at the earth's surface are well reproduced. For example, the model yields latent and sensible heat fluxes of −35.3 and −2.4 W/m², respectively; evapotranspiration and runoff is −449 and 326 mm/yr; and root zone soil moisture content is 0.344 m³/m³. Further, the seasonal changes of water and energy balance components are well simulated. The sensitivity of PROGSURF to the canopy resistance formulation is analysed. We find that the atmospheric demand is largely represented by the saturation value of the evapotranspiration/soil moisture curve with maximum summer impact upon the annual value and further that the moisture availability is represented by the slope of the evapotranspiration curve. Both saturation value and slope control the amplitude of the seasonal fluctuation of the water balance components; at Cabauw site the saturation value is the governing parameter. These results fit satisfactorily into the other PILPS models. In particular, we are able to reproduce with PROGSURF the total variability of most other PILPS models by simply changing the atmospheric demand and soil moisture availability parameters. PROGSURF presently serves to simulate observed surface fluxes for an atmospheric diagnostic model.     

Glacier mass balance of tropical Zongo glacier, Bolivia, comparing hydrological and glaciological methods

A glaciological program has been undertaken since 1991 on Zongo glacier in Bolivia (6000–4850 m asl, 2.4 km², 16°S). This program involves mass balance measurements, hydrological studies and energy balance investigations. On outer-tropical glaciers, melting and snow accumulation are both maximum in the wet season (austral summer), whereas the dry season (winter) is a period of low ablation. Errors on each term of the glaciological (stakes, snow-pits and integration method of the measurements) and hydrological (precipitation, discharge and runoff coefficient of free ice areas) methods are investigated to estimate the overall accuracy of the mass balance measurements. The hydrological budget is less than the glaciological one (mean difference: 60 cm w.e. per year), but both methods reproduce similar inter-annual variations. Errors in assessment of evaporation or water storage inside the glacier cannot explain the discrepancy. Errors using the glaciological method are large (around ± 40 cm w.e. per year), but no bias can explain the departure from the hydrological balance. Errors on discharge measurements are small and the uncertainty on the runoff coefficient has a minor effect on the mass balance. We concluded that hydrological budgets are too low due to the catch deficiency of rain gauges and absence of precipitation measurements at high altitudes, emphasizing the difficulty to assess snowfall distribution in high mountainous basins.     

Modeling mineral dust emissions from Chinese and Mongolian deserts

The present study investigates the frequency and intensity of mineral dust emissions over the deserts of eastern Asia from 1996 to 2001. Mineral dust emissions are simulated using a physical dust emission scheme over a region extending from 35.5°N to 47°N and from 73°E to 125°E. The input parameters required by the dust emission model are (1) surface features data including aerodynamic roughness length, soil dry size distribution and texture; and (2) meteorological surface data, mainly wind speed, soil moisture and snow cover. The way by which these surface features and meteorological data can be assessed is described and discussed. The influence of soil moisture and snow cover is taken into account and their effects on simulated dust emission are quantified.The simulations reproduce on a daily basis the location and intensity of the severe events of April 1998 and spring 2001 as recorded by the meteorological stations and/or described in various studies. Based on 6 yr of simulations, the main dust source regions are identified and their relative contributions to the total dust emissions are quantified.The seasonal cycle of the dust storms frequency is well reproduced with a maximum in spring. The simulations suggest that it is mainly controlled by the emissions occurring in the Taklimakan desert in latter spring and in summer, and by those occurring in the northern deserts of China in winter. The Taklimakan desert appears to be the most frequent and steady source of dust emissions during the studied period. On the other hand, in the Gobi desert, only a few dust emission events are simulated, but the dust amount emitted during each event is generally very large. In the northern deserts of China, dust emissions are frequent and their intensity is variable.These results show an important annual and inter-annual variability of the emitted dust (between 100 Mt yr^− 1 and 460 Mt yr^− 1), mainly controlled by the occurrence of severe events in the Gobi desert and in the northern deserts of China.