Cooler Surface Temperatures Research Articles

수평 실린더에서의 서리 생성에 대한 환경 변수들의 영향

It is known that frost formation on surfaces of the heat exchanger seriously affects the performance of the refrigeration system. Accordingly, defrosting should follow, and effective defrosting is possible only when both analytic tools and comprehensive experimental data on frost formation are assailable. An experimental investigation was undertaken to characterize the effect of environmental parameters on frost formation on a horizontal cylinder in cross uniform flow. Several experiments were carried out with various environmental parameters such as inlet air temperature, inlet air humidity, air velocity and cooling surface temperature. Frost thickness, mass, surface temperature and cylinder inner and outer temperature were measured at front and rear positions of the cylinder. Thickness, mass, density, and effective thermal conductivity of the frost layer were obtained from measured data and effects of environmental parameters on the frost formation were analyzed. Data from experiments were correlated using dimensionless variables.

Long-term climate patterns in Alaskan surface temperature and precipitation and their biological consequences

Mean monthly climate maps of Alaskan surface temperature and precipitation produced by the parameter-elevation regression on independent slopes model (PRISM) were analyzed. Alaska is divided into interior and coastal zones with consistent but different climatic variability separated by a transition region; it has maximum interannual variability but low long-term mean variability. Pacific decadal oscillation (PDO)- and El Nino Southern Oscillation (ENSO)-type events influence Alaska surface temperatures weakly (1-2/spl deg/C) statewide. PDO has a stronger influence than ENSO on precipitation but its influence is largely localized to coastal central Alaska. The strongest influence of Arctic oscillation (AO) occurs in northern and interior Alaskan precipitation. Four major ecosystems are defined. A major eco-transition zone occurs between the interior boreal forest and the coastal rainforest. Variability in insolation, surface temperature, precipitation, continentality, and seasonal changes in storm track direction explain the mapped ecosystems. Lack of westward expansion of the interior boreal forest into the western shrub tundra is influenced by the coastal marine boundary layer (enhanced cloud cover, reduced insolation, cooler surface and soil temperatures).

Zooplankton spatial distributions in coastal waters of the northern Arabian Sea, August, 1995

Abstract The spatial distribution of zooplankton biomass was surveyed in coastal waters of the northern Arabian Sea during the 1995 Southwest Monsoon (August) on cruise MB 95-06 of the NOAA Ship Malcolm Baldrige . Vertical patterns of displacement volumes from a limited set of paired day–night MOCNESS tows suggest there was little diel vertical migration in the coastal waters off the southern Arabian Peninsula. Zooplankton biomass varied from 5.2 to 15.1 g dw m −2 (178–517 mM C m −2 ) in the upper 200–300 m of Omani coastal waters. Distributions of acoustic backscatter were mapped in eight daytime acoustic Doppler current profiler transects in coastal waters off Oman and Somalia. Several transects contained maxima in acoustic backscatter that coincided with cool, fresh surface features that were several tens of kilometers wide. Although there was considerable scatter in the relationship between acoustically determined biomass (ADB) of zooplankton and surface temperature, there was a trend of increased biomass in the cool surface temperatures of the Omani upwelling zone. Acoustic transects crossed two filaments that extended seaward from upwelling centers off Oman and Somalia. Estimated zooplankton ADB exported from the upwelling zones in the surface features was on the order of 300 kg dw s −1 . The physical and biological characteristics of filaments maintain zooplankton associated with upwelling areas, such as Calanoides carinatus , as they are advected offshore from coastal upwelling zones.

Looking for the Role of the Ocean in Tropical Atlantic Decadal Climate Variability*

Abstract Ocean models are used to investigate how variations in surface heat fluxes and ocean heat transports contribute to variations of tropical Atlantic SSTs on decadal timescales. The observed patterns of variability, deduced from reanalyses of the National Centers for Environmental Prediction (NCEP), are found to involve the ocean’s response to variations in the strength of the northeast and southeast trades. Stronger trade winds are associated with anomalously cool surface temperatures. The trade winds and surface temperatures in each hemisphere appear to behave independently but each is associated with anomalous cross-equatorial flow. A numerical model is used in an attempt to simulate this variability. The model is an ocean general circulation model coupled to a simple model of the atmospheric mixed layer and is forced by NCEP winds from 1958 to 1998. The model reasonably reproduces the observed variability. Analysis of the ocean model’s mixed layer energy budget shows that, on decadal timescales,...

A comparison of surface and rectal temperatures between sheared and non-sheared alpacas ( Lama pacos)

The objective of this research was to determine if whole-body shearing would effect gross thermoregulation in alpacas. Eight mature, intact male alpacas were randomly assigned to one of two groups and maintained in outdoor pastures with adequate artificial shade from June through August (summer climate) in east central Alabama, USA. Group one animals ( N=4) were sheared to remove all fiber to within 2 cm of their skin. Group 2 animals ( N=4) were left non-sheared. Sheared alpacas tended to have lower rectal temperatures during high ambient temperatures than did non-sheared alpacas ( P=0.06). Thermographic studies of the scrotum revealed cooler surface temperatures in sheared versus non-sheared alpacas ( P=0.05). Temperatures in the right medial thigh of sheared animals were 0.9°C cooler than the thigh region of non-sheared animals in the morning ( P<0.03). Right medial thigh temperatures were 1.6°C cooler in sheared alpacas in the afternoon ( P<0.01). Significant positive correlations were found in non-sheared animals between ambient temperature and rectal temperature in the morning ( r=0.612, P=0.014). In sheared animals during the morning significant positive correlations were established between the Heat Stress Index (HSI) and the right medial thigh surface temperatures ( r=0.648, P=0.003), the HSI and rectal temperature ( r=0.729, P=0.0003), the ambient temperature and right medial thigh surface temperature ( r=0.485, P=0.04), and the ambient temperature and the rectal temperature ( r=0.823, P<0.0001). In the afternoon a significant positive correlation was found in the sheared alpacas between the HSI and the right medial thigh surface temperature, rectal temperature and surface scrotal temperature ( r=0.538, P=0.02, r=0.543, P=0.019 and r=0.522, P=0.045), respectively. These data indicate that whole-body shearing of alpacas could have a beneficial effect on thermoregulation when used as a preventative measure against heat stress. Shearing may assist heat dissipation resulting in a cooler surface body temperature and rectal temperature in alpacas when challenged by the heat and humidity experienced in the summer months in the southeastern United States.

Recovery of dilute acetone–butanol–ethanol (ABE) solvents from aqueous solutions via membrane distillation

The simultaneous recovery of dilute acetone–butanol–ethanol (ABE) solvents from aqueous solutions by air gap membrane distillation was theoretically assessed. A previously developed and validated Stefan–Maxwell based mathematical model was used for this purpose. It was found that membrane distillation could successfully be used for the recovery of these solvents. Interestingly it was found that butanol could be separated with the highest selectivity and flux though it has the highest boiling point. The effect of operating conditions such as feed and cooling surface temperatures, air gap width, and individual component concentration on the flux and selectivity of these solvents was examined and discussed in this paper.

Heat transfer analysis of a non‐Newtonian fluid on a power‐law stretched surface with suction or injection for uniform and cooled surface temperature

Heat transfer characteristics of a non‐Newtonian fluid on a power‐law stretched surface with suction or injection were investigated. Similarity solutions of the laminar boundary layer equations describing heat transfer flow in a quiescent fluid were obtained and solved numerically. Temperature profiles as well as the Nusselt number Nu, were obtained for two thermal boundary conditions; namely, uniform surface temperature (b=0) and cooled surface temperature (b=–1), for different governing parameters such as Prandtl number Pr, injection parameter d and power‐law index n. It was found that decreasing injection parameter d and power‐law index n and increasing Prandtl number Pr enhanced the heat transfer coefficient.

The Northeast Monsoon's impact on mixing, phytoplankton biomass and nutrient cycling in the Arabian Sea

In the northern Arabian Sea, atmospheric conditions during the Northeast (winter) Monsoon lead to deep convective mixing. Due to the proximity of the permanent pycnocline to the sea surface, this mixing does not penetrate below 125 m. However, a strong nitracline is also present and the deep convection results in significant nitrate flux into the surface waters. This leads to nitrate concentrations over the upper 100 m that exceed 4 μM toward the end of the monsoon. During the 1994/1995 US JGOFS/Arabian Sea expedition, the mean areal gross primary production over two successive Northeast Monsoons was determined to be 1.35 gC/m 2/d. Thus, despite the deep penetrative convection, high rates of primary productivity were maintained. An interdisciplinary model was developed to elucidate the biogeochemical processes involved in supporting the elevated productivity. This model consisted of a 1-D mixed-layer model coupled to a set of equations that tracked phytoplankton growth and the concentration of the two major nutrients (nitrate and ammonium). Zooplankton grazing was parameterized by a rate constant determined by shipboard experiments. Model boundary conditions consist of meteorological time-series measured from the surface buoy that was part of the ONR Arabian Sea Experiment's central mooring. Our numerical experiments show that elevated surface evaporation, and the associated salinization of the mixed layer, strongly contributes to the frequency and penetration depth of the observed convective mixing. Cooler surface temperatures, increased nitrate entrainment, reduced water column stratification, and lower near-surface chlorophyll a concentrations all result from this enhanced mixing. The model also captured a dependence on regenerated nitrogen observed in nutrient uptake experiments performed during the Northeast Monsoon. Our numerical experiments also indicate that variability in mean pycnocline depth causes up to a 25% reduction in areal chlorophyll a concentration. We hypothesize that such shifts in pycnocline depth may contribute to the interannual variations in primary production and surface chlorophyll a concentration that have been previously observed in this region.

Effects of diagenesis on the isotopic record of late paleogene tropical sea surface temperatures

Oxygen isotope records of planktonic foraminifera indicate that Late Eocene and Oligocene tropical sea surface temperatures were as much as 8°C lower than present at a time when high latitude sea surface temperatures were higher than present. Using a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate, the effects of diagenesis on bulk carbonate δ18O records for the Cenozoic are quantified for four tropical sites. Most of the observed variations in measured δ18O values at all sites can be accounted for by diagenetic effects. There are no systematic trends that support substantial variations in tropical sea surface temperatures beyond diagenetic effects, with the possible exception of the Early Eocene for which the data are consistent with slightly higher sea surface temperatures. Reconstructions based on oxygen isotope records of planktonic foraminifera which indicate cooler tropical sea surface temperatures for the Eocene and Oligocene may be artifacts of diagenetic recrystallization as such records are particularly sensitive to diagenetic effects.

Southern High-Latitude Ocean Climate Drift in a Coupled Model

Abstract Climate drift in coupled models affects the response of the coupled system to an external forcing. In most existing coupled models that employ flux adjustments, the southern high latitudes, in particular, are still affected by some climate drift. In the CSIRO coupled model, within 100 years following coupling, the Antarctic Circumpolar Current (ACC) intensifies by about 30 Sv (Sv ≡ 106 m3 s−1). This happens despite the use of flux adjustments. Many other model fields such as sea ice, surface albedo, and heat fluxes of the coupled system also experience drift from the precoupled spinup states. It is therefore important to study the processes that give rise to these drifts. The primary cause of drift in the CSIRO model is due to changes in the pattern of convection in the Southern Ocean relative to the spinup steady state. Upon coupling, the pattern of convection alters systematically regardless of surface boundary conditions. Consequently, overturning at shallow to intermediate depths (from the surface to about 2000 m) weakens, while that below these depths intensifies. The decline of overturning at shallow to intermediate depths leads to reduced surface temperatures because a lesser amount of warm subsurface water is mixed up into the colder surface mixed layer. The cooler surface temperature leads to an initial increase in sea ice, which is exacerbated by a significant albedo–temperature–sea ice feedback. The resulting increase in sea ice formation at the higher southern latitudes leads to increased brine rejection and a general increase in salinity throughout much of the high-latitude water column. This increase in salinity intensifies deep convection and bottom water formation, driving a stronger ACC. Several additional experiments are performed to trace various oceanic and ocean–atmosphere feedbacks that give the drift its character. It is demonstrated that the feedbacks significant to the drift in the present model are the positive albedo–temperature–sea ice feedback and a negative feedback between sea ice and overturning. The role of these two feedbacks in the interconnection between the drifts in various model fields is discussed.

Southern High-Latitude Ocean Climate Drift in a Coupled Model

Climate drift in coupled models affects the response of the coupled system to an external forcing. In most existing coupled models that employ flux adjustments, the southern high latitudes, in particular, are still affected by some climate drift. In the CSIRO coupled model, within 100 years following coupling, the Antarctic Circumpolar Current (ACC) intensifies by about 30 Sv (Sv ≡ 106 m3 s−1). This happens despite the use of flux adjustments. Many other model fields such as sea ice, surface albedo, and heat fluxes of the coupled system also experience drift from the precoupled spinup states. It is therefore important to study the processes that give rise to these drifts. The primary cause of drift in the CSIRO model is due to changes in the pattern of convection in the Southern Ocean relative to the spinup steady state. Upon coupling, the pattern of convection alters systematically regardless of surface boundary conditions. Consequently, overturning at shallow to intermediate depths (from the surface to about 2000 m) weakens, while that below these depths intensifies. The decline of overturning at shallow to intermediate depths leads to reduced surface temperatures because a lesser amount of warm subsurface water is mixed up into the colder surface mixed layer. The cooler surface temperature leads to an initial increase in sea ice, which is exacerbated by a significant albedo–temperature–sea ice feedback. The resulting increase in sea ice formation at the higher southern latitudes leads to increased brine rejection and a general increase in salinity throughout much of the high-latitude water column. This increase in salinity intensifies deep convection and bottom water formation, driving a stronger ACC. Several additional experiments are performed to trace various oceanic and ocean–atmosphere feedbacks that give the drift its character. It is demonstrated that the feedbacks significant to the drift in the present model are the positive albedo–temperature–sea ice feedback and a negative feedback between sea ice and overturning. The role of these two feedbacks in the interconnection between the drifts in various model fields is discussed.

High resolution windows into early Holocene climate: [formula omitted] coral records from the Huon Peninsula

High-precision measurements of Sr Ca ratios are reported for Porites corals from the uplifted Holocene coral terraces at Huon Peninsula, Papua New Guinea. The early Holocene Porites have UTh mass spectrometric ages of 8920 ± 60 yr and 7370 ± 50 yr, and δ 234U(t) values of 145 ± 2, similar to modern seawater. The Sr Ca coral records provide 5–6 year high resolution (near weekly) time windows into early Holocene sea surface temperatures. Seasonal temperature fluctuations are generally in the range of ± 1°C, with occasional excursions of ± 2°C, which may indicate the more frequent recurrence of very strong ENSO (El Niño-Southern Oscillation) events. Mean annual Sr Ca temperatures of 24.2 ± 1.1°C and 22.9 ± 0.8°C have been obtained, which are ∼ 2–3°C cooler than that exhibited by a modern Porites. These results indicate that, during the early Holocene, the equatorial western Pacific ocean was at least several degrees cooler than present-day temperatures. This is consistent with late glacial coral records from the Caribbean that indicate lower (∼ 6°C) sea surface temperatures for the equatorial oceans. The Huon Peninsula corals also indicate that SSTs were several degrees cooler than those in the Caribbean during the early Holocene. Thus, although the northern hemisphere summer radiation maximum occurred at ∼ 10 ka, there appears to have been a significant lag in the response of the equatorial western Pacific ocean to this warming. Cooler early Holocene sea surface temperatures in the western Pacific may have been due to changing patterns of ocean-atmosphere circulation, resulting from the exposure of large areas of continental shelf in the southeast Asia region, a consequence of lower glacial sea levels. It is likely that ocean temperatures in the Huon Peninsula were influenced by the opening at ∼ 7 ka of the Torres Strait, that now separates New Guinea from the Australian mainland.

Cloud albedo feedback and the super greenhouse effect in a global coupled GCM

Two competing cloud-radiative feedbacks identified in previous studies i.e., cloud albedo feedback and the super greenhouse effect, are examined in a sensitivity study with a global coupled ocean-atmosphere general circulation model. Cloud albedo feedback is strengthened in a sensitivity experiment by lowering the sea-surface temperature (SST) threshold in the specified cloud albedo feedback scheme. This simple parameterization requires coincident warm SSTs and deep convection for upper-level cloud albedos to increase. The enhanced cloud albedo feedback in the sensitivity experiment results in decreased maximum values of SST and cooler surface temperatures over most areas of the planet. There is also a cooling of the tropical troposphere with attendant global changes of atmospheric circulation reminiscent of those observed during La Nina or cold events in the Southern Oscillation. The strengthening of the cloud albedo feedback only occurs over warm tropical oceans (e.g., the western Pacific warm pool), where there is increased albedo, decreased absorbed solar radiation at the surface, stronger surface westerlies, enhanced westward currents, lower temperatures, and decreased precipitation and evaporation. However, the weakened convection over the tropical western Pacific Ocean alters the large-scale circulation in the tropics such that there is increased upper-level divergence over tropical land areas and the tropical Indian Ocean. This results in increased precipitation in those regions and intensified monsoonal regimes. The enhanced precipitation over tropical land areas produces increased clouds and albedo and wetter and cooler land surfaces. These additional contributions to decreased absorbed solar input at the surface combine with similar changes over the tropical oceans to produce the global cooling associated with the stronger cloud albedo feedback. Increased low-level moisture convergence and precipitation over the tropical Indian Ocean enhance slightly the super greenhouse effect there. But the stronger cloud albedo feedback is still the dominant effect, although cooling of SSTs in that region is less than in the tropical western Pacific Ocean. The sensitivity experiment demonstrates how a regional change of radiative forcing is quickly transmitted globally through a combination of radiative and dynamical processes in the coupled model. This study points to the uncertainties involved with the parameterization of cloud albedo and the major implications of such parameterizations concerning the maximum values of SST, global climate sensitivity, and climate change.

Early Earth's climate: Cloud feedback from reduced land fraction and ozone concentrations

Two features of early Earth—reduced ozone (O3) concentration and land fraction are investigated with a general circulation model (GCM). These features are components of a paradox (Faint‐Young Sun paradox) which has intrigued researchers for more than two decades. In this study, land fraction and O3 concentrations are uniformly reduced by 100 percent. The reduction in O3 takes place in the troposphere and stratosphere with all other variables held constant including present‐day land fraction. Two sensitivity tests under global ocean conditions are reported: one case with implied oceanic poleward transports of heat, the other case with no implied oceanic poleward transports of heat. The results show that the removal of land under present‐day conditions increases cloud fractions and cool surface temperatures, unless heat is transported poleward by oceans. In a third sensitivity test with zero O3 concentrations, global mean air temperatures are increased by 2 K because of an increase in upper tropospheric and lower stratospheric clouds. The clouds enhance the greenhouse effect within the troposphere, increasing downward longwave radiation to the surface, melting sea ice and snow. Similar studies using radiative‐convective models which do not include interactive clouds do not show such surface warming.

Orbital and internal forcing of climate on the Yucatan Peninsula for the past ca. 36 ka

A 19.6 m sedimentary sequence from Lake Quexil, Guatemala, is presented as a proxy record of climatic change on the low-lying Yucatan Peninsula over the last ca. 36 ka. Long-term climatic fluctuations are attributed to orbital forcing of insolation, while abrupt changes during the late glacial period are the result of internal forcing mechanisms that remain imperfectly modelled. GCMs simulating meltwater cooling of the Gulf of Mexico may predict some but not all climatic responses in the Circum-Caribbean. Lake Quexil did not experience greater aridity than predicted by orbital forcing during late glacial zones Q-LG 1 and 2, which were drier only in comparison with Holocene conditions. Q-LG 1 appears to have been colder than expected based on insolation alone, and is contemporary with the Younger Dryas event between meltwater pulses 1A and 1B. Thus, other feedbacks also may have cooled surface temperatures in the Gulf of Mexico, such as unique late glacial circulation patterns, increased albedo for the Florida and Yucatan Peninsulas, or surface temperatures on the North American continent. Additional terrestrial sequences are needed to improve the chronology and confirm the distribution of sub-regional climatic variability in the Circum-Caribbean.

Molluscan diversification and extinction on opposite sides of the Isthmus of Panama

Molluscs are the most diverse and abundant tropical American macrofossils, but their distributions and evolution are not well understood. Classic studies by Olsson and Woodring documented a rich Late Miocene to Early Pliocene “Gatunian” fauna throughout the Caribbean and tropical Eastern Pacific, with many species in common between the oceans. This fauna was divided by formation of the Isthmus of Panama, and diverged into distinct Pacific and Caribbean faunas sometime thereafter. Diversity also decreased by about half in the Caribbean. However, the timing, rates and correlation of these major biological changes with changes in environmental conditions have not been resolved because of imprecise dating and taxonomy and failure to consider problems of sampling and biofacies in biological comparisons. We used the newly revised late Neogene stratigraphy for Panama and Costa Rica to date for the first time the radiation and extinction of molluscs on opposite sides of the Isthmus. Data include occurrences throughout tropical America for nearly 100 species of the Strombina-group (Gastropoda, Columbellidae) and for more than 500 gastropod and bivalve genera from 240 Late Miocene to Pleistocene isthmian collections.All evidence suggests that final closure of the Isthmus of Panama occurred between 3.5 and 2.5 My. Subgeneric divergence between the oceans was well developed, and trans-isthmian species were rare by the Early Pliocene, at least 2 Ma before final closure. Caribbean diversity remained high until 1.8 to 1.5 Ma when massive but selective extinction occurred. This was at least 1 Ma after final closure of the Isthmus, and may be correlated with onset of slightly cooler Caribbean sea surface temperatures in the Pleistocene. In contrast, Eastern Pacific diversity did not decline, and even increased during the Pleistocene.

Energy Balance Studies and Plasma Catecholamine Values for Patients with Healed Burns

We report heat balance studies and plasma catecholamine values for 49 children and young adults with healed burn wounds (age range 0.6 to 31 years and burn range 1% to 82% body surface area burned; mean 41%). All measurements were made during the week of discharge. Heat production for patients with healed burns was not significantly different from predicted normal values. However, compartmented heat loss demonstrated a persistent increment in evaporative heat loss that was secondary to continued elevation of cutaneous water vapor loss immediately after wound closure. A reciprocal decrement in dry heat loss was demonstrated (as a result of a cooler average surface temperature, 0.84 degree C cooler than the average integrated skin temperature of five normal volunteers who were studied in our unit under similar environmental conditions). Mean values for plasma catecholamines were in the normal range: epinephrine = 56 +/- 37 pg/ml, norepinephrine = 385 +/- 220 pg/ml, and dopamine = 34 +/- 29 pg/ml. In conclusion, patients with freshly healed burn wounds have normal rates of heat production; however, there is a residual increment in transcutaneous water vapor loss, which produces surface cooling and decreased average surface temperature, which in turn lowers dry heat loss by an approximately equivalent amount.

Effects of Spatial Variations of Soil Moisture and Vegetation on the Evolution of a Prestorm Environment: A Numerical Case Study

To study the effects of spatial variations of soil moisture and coverage coverage on the evolution of a prestorm environment, the Goddard mesoscale model (GMASS) was modified to incorporate a simple evapo-transpiration model that requires them two parameters. Soil moisture was estimated from an antecedent precipitation index. Relative fractional vegetation coverage was estimated from a normalized difference vegetation index (NDVI). The case study, 3–4 June 1980, is of particular interest because of the development of a tornado producing convective complex near Grand Island, Nebraska during a period of relatively weak synoptic-scale forcing. Three model simulators are compared. The first had no spatial variations in either sail moisture or vegetation; the second had soil moisture variability but no vegetation; and in the third, the observed variabilities of both soil moisture and vegetation are simulated. The modeled of effects spatial variations of vegetation and soil moisture include the enhancement of a stationary front oriented northwest-southeast through Grand Island. Prior to sunset, the unstable boundary layer collapses over a zone of cool surface temperature aligned with the observed front and coincident with an observed dry/moist soil boundary. Following the boundary layer collapse, the evolution of the ageostrophic flow exhibits a horizontally differential acceleration that amplifies the isolated upward motion over the frontal boundary. It is shown that the observed stationary front was strongly enhanced by differential heating caused by observed gradients of soil moisture, as acted upon by the vegetation cover. Thus, the run with realistic vegetation and soil moisture produces the best forecast of storm precursor conditions.

Evidence for a mesoscale thermal circulation over dry salt lakes

Because of albedo and thermal conductivity effects, dry salt lakes in central Australia exhibit a characteristics thermal “signature” within the overall landscape, having much cooler daytime surface temperatures and warmer nocturnal temperatures than the surrounding environment. Various aspects of a possible mesoscale thermal circulation arising from such a thermal differentiation have been investigated for The Salt Lake, a moderately sized (70 km 2) dry salt lake in northwestern New South Wales (30° 05′S, 142° 08′E). Surface temperatures across The Salt Lake and surrounding landscape determined by field and polar orbiting (NOAA-9) satellite observations show marked variation, with the salt crust remaining up to 16 K cooler than the surrounding sand country during the day and up to 8 K warmer at night. That this thermal forcing can provide a horizontal pressure gradient sufficiently strong to induce air motion is confirmed by analysis of hourly output from a network of anemographs which were established around the perimeter of The Salt Lake during a five-month autumn and winter period. An extremely regular pattern of nocturnal near-surface convergence (lake warm) and daytime divergence (lake cool) is shown, a pattern which is enhanced when data are stratified for anticyclonic conditions with a weak pressure gradient (∼24% of total observations). Wind roses produced for a number of sites around the lake show a distinct diurnal reversal in near-surface airflow, with generally onshore flow by day and offshore flow at night. Confirmation that a diurnally reversing thermal circulation does operate under certain conditions at The Salt Lake is provided by pilot balloon analysis of winds aloft and by preliminary mesoscale modelling of airflow. This circulation, which has not previously been described in the literature, may have important environmental and climatic implications in the Australian context.

A review of factors affecting minimum temperature reached on clear, windless nights.

A mathematical model of heat flux in which net flux was assumed to be proportional to the surface temperature was used to examine the effects of important environmental variables on minimum surface temperatures reached during cloudless nights. Variables considered were altitude, atmospheric water content, surface emissivity, soil heat capacity and conductivity, length of night, and initial starting temperature. Final temperatures reached were especially sensitive to changes in soil thermal conductivity and heat capacity. Both these parameters are affected by moisture content (particularly when low), making this the single most important factor affecting the severity of frost. Lower initial starting temperatures and longer nights increase the severity of frosting, as does any decrease in the depth of the atmosphere (as happens with changes in altitude) or reductions in the water content of the atmosphere. Emissivity of the radiating surface is relatively unimportant. Temperature profiles in the soil were similar, but extended to greater depths as heat capacitance declined, whereas lower thermal conductivity resulted in cooler surface temperatures while the decline in temperature did not extend as deep. The model was shown to be an improvement on one in which net flux was assumed to remain constant, and allows for a more instructive sensitivity analysis.