Solar Radiation Receipt Research Articles

Assessing the control factors upon glacial valley development in southernmost Patagonia (Fuegian Andes of Argentina)

Research on landscape glacial modelling provides particularly relevant information about the complex connection between climate change and relief evolution. Glacial valleys – the most distinctive landforms in alpine-type settings – were systematically mapped across the Fuegian Andes of Argentina, southernmost Patagonia, and quantitatively investigated in terms of the geoenvironmental agents that controlled their formation. A total of 646 troughs were identified and studied in four sub-areas with contrasting past glacial cover. Our observations demonstrate that longer valleys are also the deeper, less steep (in long profile), more sinuous and lower, and that maximum elevation was the main control of altitudinal range, mean and maximum slope, and minimum depth. Overall, it is considered that valley development was subject to conditioning by pre-glacial topography, geological structure and climatic forcings. Specifically, valley's spatial arrangement indicates that glaciers responsible for their erosion (possibly during the early Pleistocene) adjusted to a fluvial drainage network organized according to a marked structural control, mainly associated with Magallanes-Fagnano and Canal Beagle regional strike-slip systems. The predominance and higher degree of development of southern slope valleys reveal that north-south differential insolation effect was determinant in the Fuegian glaciers' balance during extensive time-lapses in glacial cycles, likely reflecting a scenario of relative aridity and comparatively clear skies. Morning-afternoon contrasts in solar radiation receipt and, specially, humid winds from the west (regional westerlies) would have also produced a moderate eastward bias in valley direction. In the western and central sectors, formerly covered by the Cordillera Darwin Icefield, the surface of Fagnano and Beagle outlet palaeolobes and other major collectors constituted a comparatively high base level for mountain glaciers' incision during full glacial conditions, leading to the creation of profuse, short hanging valleys. In the eastern domain, on the contrary, glaciers appear to have been essentially regulated by the topoclimatic factors, attaining greater dimensions and flowing down to lower altitudes in south- and southeast-facing slopes. Finally, in marginal, lower mountains (away from the main chain axis) ice is thought to have formed only under the most severe glacial episodes in the zone.

Spatial distribution and controls of snowmelt runoff in a sublimation-dominated environment in the semiarid Andes of Chile

Abstract. Sublimation is the main ablation component of snow in the upper areas of the semiarid Andes (∼ 26 to ∼ 32∘ S and ∼ 69 to ∼ 71∘ W). This region has elevations up to 6000 m, is characterized by scarce precipitation, high solar radiation receipt, and low air humidity, and has been affected by a severe drought since 2010. In this study, we suggest that most of the snowmelt runoff originates from specific areas with topographic and meteorological features that allow large snow accumulation and limited mass removal. To test this hypothesis, we quantify the spatial distribution of snowmelt runoff and sublimation in a catchment of the semiarid Andes using a process-based snow model that is forced with field data. Model simulations over a 2-year period reproduce point-scale records of snow depth (SD) and snow water equivalent (SWE) and are also in good agreement with an independent SWE reconstruction product as well as satellite snow cover area and indices of winter snow absence and summer snow persistence. We estimate that 50 % of snowmelt runoff is produced by 21 %–29 % of the catchment area, which we define as “snowmelt hotspots”. Snowmelt hotspots are located at mid-to-lower elevations of the catchment on wind-sheltered, low-angle slopes. Our findings show that sublimation is not only the main ablation component: it also plays an important role shaping the spatial variability in total annual snowmelt. Snowmelt hotspots might be connected with other hydrological features of arid and semiarid mountain regions, such as areas of groundwater recharge, rock glaciers, and mountain peatlands. We recommend more detailed snow and hydrological monitoring of these sites, especially in the current and projected scenarios of scarce precipitation.

Cirque morphology and palaeo-climate indications along a south-north transect in High Mountain Asia

Cirques preserve important palaeo-climate information and have been investigated in various areas around the world. High Mountain Asia (HMA) contains the largest modern glacier inventory outside of polar regions, and tens of thousands of cirques. We analyzed 2831 largely ice-free cirques from five areas along a south-north transect in HMA, including central Himalayas (C. Himalayas), western Gangdise (W. Gangdise), eastern Tian Shan (E. Tian Shan), southern Altai (S. Altai), and northern Altai (N. Altai). These cirques are large relative to those in many parts of the world, and in the Himalayas, Tian Shan, and Altai their vertical dimensions are considerable. Their size variations show weakly allometric relations. The poleward decreasing trend in cirque floor altitudes is consistent with the reducing temperature trend toward high latitudes. Although just north of C. Himalayas, W. Gangdise is in their precipitation shadow and its cirque floors are higher. Relatively shallow cirques in W. Gangdise probably reflect low subglacial erosion associated with limited precipitation received from either the Indian monsoon or Westerlies due to this orographic effect. Lower cirque floor altitudes for north-facing cirques were likely caused by their lesser receipt of solar radiation. Because most mountains rose well above equilibrium-line altitudes of glaciers and were heavily glaciated, cirque aspects show symmetric vector strengths except in the lowest area, N. Altai. Eastward aspects in N. and S. Altai show the strong effects of Westerly winds in the past, as for present glaciers. Similarly, cirque aspects in C. Himalayas are more northeast-ward than modern glacier aspects, suggesting a stronger west wind influence in the past. North-facing cirques are lower and more frequent than south-facing, showing the general importance of solar radiation receipt, which is especially dominant in E. Tian Shan.

The form, distribution and palaeoclimatic implications of cirques in southwest Turkey (Western Taurus)

The Taurus Mountains of southwest Turkey are split into numerous separated ranges, of which eleven supported former glaciers. We describe cirques and related moraines in four new locations, as well as those in seven ranges where glaciation was previously known. This gives a complete inventory of the 85 cirques in southwest Turkey. These are comparable in size to those elsewhere, but narrower and often less developed. Lengths averaging 672 m are high relative to widths of 542 m. Overall axial gradients average 22.4°. Cirque floor altitudes are controlled largely by altitudes of the mountains above, but they also vary in relation to precipitation, in sympathy with ELAs (Equilibrium Line Altitudes) of former glaciers. In most ranges where glaciers were short (extending little beyond cirques), ELA can be predicted from mean mid-floor altitude. Our observations demonstrate lower ELAs than in previous literature. Both ELAs and cirque floors rise eastward in the west, and northward inland from the coast. This supports the importance of winds from the west and southwest, off the Mediterranean Sea, bringing LGM (Last Glacial Maximum) conditions wetter than present to mountains near the coast. Cirques face on average a little east of north, showing the effects of shade and differential solar radiation receipt.

РОЗРОБКА БАЗИ ДАНИХ ДЛЯ ПРОГНОЗУВАННЯ СОНЯЧНОЇ ГЕНЕРАЦІЇ В ПРОГРАМНО-ТЕХНІЧНОМУ КОМПЛЕКСІ УПРАВЛІННЯ ЕЛЕКТРОСПОЖИВАННЯМ ЛОКАЛЬНОГО ОБ’ЄКТА

An informational database of clear days for forecasting of electricity generation in software and hardware complex of energy consumption management of a local facility in real operating conditions based on use of statistical meteorological data from open sources is developed. The comparison of clear days solar radiation data for photoelectric systems located at points with different geographical coordinates on the territory of Ukraine is carried out. The high consistency of clear days solar radiation data and total electricity generation data of photoelectric systems for selected geographical coordinates is justified. It is shown that the analysis of solar radiation data that receipt in clear days during the period of meteorological observations can be carried out for geographical coordinates of Kiev. The analysis of clear days solar radiation data during the period of meteorological observations is carried out and the time step of data sampling is determined. It is shown that calendar month can be considered the data sampling period by clear days in the database. The exception is the winter period, when calendar month can be divided into two halves, for each of which its own time level of solar radiation receipt is determined. A generalized structure of predicting system of solar radiation receipt in real conditions for software and hardware complex of energy consumption management of local facility is developed. The cloudless sky model was chosen as the basic model for predicting of solar radiation. The input and output data of forecasting system are determined. It is established that to increase the accuracy of forecast, the clear days database should be supplemented by a stochastic model that takes into account real cloudiness. It is shown that further research direction is accounting of cloudiness influence for hourly forecast of solar radiation on surface of photoelectric module with a certain spatial orientation, and for calculations of energy generated by the photoelectric system is temperature of solar panels

Phased Patagonian Ice Sheet response to Southern Hemisphere atmospheric and oceanic warming between 18 and 17 ka

The onset of deglaciation in the Southern Hemisphere mid-latitudes has been attributed to the southward transmission of climate anomalies in response to slow-down of Atlantic meridional overturning circulation (AMOC) during Heinrich Stadial 1 (HS-1; 18–14.6 ka). However, inferences on the response of former ice sheets to sub-millennial palaeoclimate shifts are limited by a shortage of high-resolution terrestrial archives. Here we use a ~1000-year duration, annually-resolved lake sediment record to investigate the deglacial retreat dynamics of the Lago General Carrera–Buenos Aires ice lobe (46.5°S) of the former Patagonian Ice Sheet. We attribute the onset of glacier retreat at 18.0 ± 0.14 cal ka BP to abrupt southward migration of the Southern Westerly Winds that enhanced solar radiation receipt (and ablation) at the ice sheet surface. We infer that accelerated retreat from 17.77 ± 0.13 cal ka BP represents a lagged Southern Hemisphere response to gradual ocean-atmosphere warming associated with the centennial-scale transmission of Northern Hemisphere climate anomalies through the oceanic bipolar seesaw. By 17.38 ± 0.12 cal ka BP, the glacier margin had receded into a deepening proglacial lake, instigating sustained calving losses and more rapid ice recession.

Aspect controls the survival of ice cliffs on debris-covered glaciers

Supraglacial ice cliffs exist on debris-covered glaciers worldwide, but despite their importance as melt hot spots, their life cycle is little understood. Early field observations had advanced a hypothesis of survival of north-facing and disappearance of south-facing cliffs, which is central for predicting the contribution of cliffs to total glacier mass losses. Their role as windows of energy transfer suggests they may explain the anomalously high mass losses of debris-covered glaciers in High Mountain Asia (HMA) despite the insulating debris, currently at the center of a debated controversy. We use a 3D model of cliff evolution coupled to very high-resolution topographic data to demonstrate that ice cliffs facing south (in the Northern Hemisphere) disappear within a few months due to enhanced solar radiation receipts and that aspect is the key control on cliffs evolution. We reproduce continuous flattening of south-facing cliffs, a result of their vertical gradient of incoming solar radiation and sky view factor. Our results establish that only north-facing cliffs are recurrent features and thus stable contributors to the melting of debris-covered glaciers. Satellite observations and mass balance modeling confirms that few south-facing cliffs of small size exist on the glaciers of Langtang, and their contribution to the glacier volume losses is very small ([Formula: see text]1%). This has major implications for the mass balance of HMA debris-covered glaciers as it provides the basis for new parameterizations of cliff evolution and distribution to constrain volume losses in a region where glaciers are highly relevant as water sources for millions of people.

Relationships Between Epidermal Browning, Girdling, Damage, and Bird Cavities In a Military Restricted Database of 12,000+ Plants of the KeystoneCarnegiea giganteaIn the Northern Sonoran Desert

An exceptional dataset for over 12,000 Carnegiea gigantea collected by the Arizona Department of Game and Fish over two field seasons on a restricted military reservation was released to the authors for analysis, including a variety of variables for which little empirical evidence exists. Data on epidermal browning, physical damage due to fire, lightning, gunshot or topping, rodent girdling, bird cavities and other variables were assessed using primarily chi-square analysis. The main findings of this study include: (1) Plants with high amounts of epidermal browning were rather evenly distributed across height classes, although the very smallest plants (0–0.9 m) had substantially less epidermal browning. (2) Although past work has shown that epidermal browning is surely a function of solar radiation receipt, other variables (bird cavities, girdling, damage, branching) are statistically linked with browning, raising the possibility that other biotic and abiotic factors may hasten browning. (3) Bird cavities are better predicted by height than branches, likely due to decreased visibility and exposure to thermally tempering winds caused by branches, and improved defensive position and reduced exposure to heating from the surface associated with taller plants.

Spatial and temporal variability of annual glacier equilibrium line altitudes in the Southern Alps, New Zealand

Assessments of the contribution of meltwater to sea-level rise from mountain glaciers cannot presently account for the considerable spatial inter-catchment and temporal inter-annual variations in annual net glacier mass balance. We therefore analyse annual equilibrium line altitudes (ELAs) to infer the controls on annual net glacier mass-balance variability for 34 glaciers in the central Southern Alps, New Zealand. Elevation, curvature and mean solar radiation receipt (both direct and indirect) during the ablation season can in combination account for up to 95% of the (temporal) variability in the long term ELA and up to c. 85% for a given year. It appears that long-term glacier net mass balance in the Southern Alps is controlled by ablation processes as a function of air temperature which decreases with elevation, and shortwave radiation which causes a positive feedback in ablation by reducing snow and ice cover and increasing albedo. In detail however, the degree to which local topographic variables can explain the differences in (i) the patterns and (ii) in the magnitudes of departures from the trend varies considerably from year to year and across the study region. At least 15–35% of annual ELA temporal variability is apparently associated with regional weather patterns. Our basic quantification of the interaction on multiple scales of topographic influences on annual ELA and ELAo (steady-state ELA) has implications for understanding inter- and intra-catchment variability in glacier responses to climatic change.

Glacier distribution and direction in Svalbard, Axel Heiberg Island and throughout the Arctic: General northward tendencies

Glacier distribution and direction in Svalbard, Axel Heiberg Island and throughout the Arctic: General northward tendenciesArctic glaciers depend on supply of moisture, mostly from the Atlantic. The snowline is remarkably high in northeast Siberia, remote from this source. Because of differential solar radiation receipt, local glaciers have a northward-facing tendency throughout the Arctic. This is weaker than in dry mid-latitudes but low sun angles enhance the effects of shading, compensating for the broader range of aspects (i.e.slope directions) illuminated in summer. Statistics from the World Glacier Inventory and other sources show that mass balance differences between slopes of different aspects give both more glaciers, and lower glaciers, facing the favoured direction: usually North. This is clear, for example, for local glaciers (and for all small glaciers) in central Spitsbergen and in Axel Heiberg Island. Wind effects (drifting snow to leeward slopes) are much less important, except in northwest Europe from Norway to Novaya Zemlya which is under the strong influence of westerly winds, greatest in the Polar and Sub-polar Urals. A thorough analysis is provided of aspect data for local glaciers within and near the Arctic Circle, and of variation in glacier mid-altitude with aspect and position. There is consistency between mean glacier aspect (in terms of numbers) and aspect with lowest glaciers, everywhere except in Wrangel Island.

MODIS‐derived NDVI Characterisation of Drought‐Induced Evergreen Dieoff in Western North America

AbstractVegetation stress or mortality can be the result of many factors including drought‐induced water deficit, insect infestations and failures of, or fluctuations in, precipitation sources typical to an area. Reduction of cover and reduced health are identifiable in remotely‐sensed multispectral satellite images. A suite of images from NASA's MODIS sensor was used to calculate the Normalised Difference Vegetation Index (NDVI) during the 2000–2006 North American growing seasons. Fluctuations in NDVI over this period show a significant decline in vegetative health in the region with specific areas showing changes linked to moisture sources, prevailing wind patterns, slope aspect and solar radiation receipt. Ground‐truthing of these areas has confirmed the extent and magnitude of the dieoff signal. Historically, dieoff has been reversed through regeneration as climate conditions return to a normal regime. However, quantification of recent vegetative change in western North America suggests that the degree of change may be too severe for regrowth to occur and may have far‐reaching impacts on a scale unseen in modern times. The loss of vegetative habitat and native species in semi‐arid regions and lack of regeneration in these marginal ecosystems due to prolonged drought are growing global problems. Similar drought stress impacts on marginal ecotypes have also been observed in semi‐arid regions of Australia, South America, Asia and Africa. Observations of the spatial pattern of temperate forest vegetation globally can be used to develop a precise picture of vegetative health in these regions and how they are reacting to global climate change.

First lacustrine varve chronologies from Mexico: impact of droughts, ENSO and human activity since AD 1840 as recorded in maar sediments from Valle de Santiago

We present varve chronologies for sediments from two maar lakes in the Valle de Santiago region (Central Mexico): Hoya La Alberca (AD 1852–1973) and Hoya Rincon de Parangueo (AD 1839–1943). These are the first varve chronologies for Mexican lakes. The varved sections were anchored with tephras from Colima (1913) and Paricutin (1943/1944) and 210Pb ages. We compare the sequences using the thickness of seasonal laminae and element counts (Al, Si, S, Cl, K, Ti, Mn, Fe, and Sr) determined by micro X-ray fluorescence spectrometry. The formation of the varve sublaminae is attributed to the strongly seasonal climate regime. Limited rainfall and high evaporation rates in winter and spring induce precipitation of carbonates (high Ca, Sr) enriched in 13C and 18O, whereas rainfall in summer increases organic and clastic input (plagioclase, quartz) with high counts of lithogenic elements (K, Al, Ti, and Si). Eolian input of Ti occurs also in the dry season. Moving correlations (5-yr windows) of the Ca and Ti counts show similar development in both sequences until the 1930s. Positive correlations indicate mixing of allochthonous Ti and autochthonous Ca, while negative correlations indicate their separation in sublaminae. Negative excursions in the correlations correspond with historic and reconstructed droughts, El Nino events, and positive SST anomalies. Based on our data, droughts (3–7 year duration) were severe and centred around the following years: the early 1850s, 1865, 1880, 1895, 1905, 1915 and the late 1920s with continuation into the 1930s. The latter dry period brought both lake systems into a critical state making them susceptible to further drying. Groundwater overexploitation due to the expansion of irrigation agriculture in the region after 1940 induced the transition from calcite to aragonite precipitation in Alberca and halite infiltration in Rincon. The proxy data indicate a faster response to increased evaporation for Rincon, the lake with the larger maar dimensions, solar radiation receipt and higher conductivity, whereas the smaller, steeper Alberca maar responded rapidly to increased precipitation.

Effects of digital elevation model spatial resolution on distributed calculations of solar radiation loading on a High Arctic glacier

AbstractHigh-resolution airborne lidar data are used to produce digital elevation models (DEMs) of an arctic valley glacier (midre Lovénbreen, Svalbard) at resolutions of 2.5–2000 m, using three different interpolation schemes. These data are used in a distributed model of solar radiation loading for glaciers. When the mean of all lidar measurements within a DEM cell is used to calculate cell height, the differences between the finest- (2.5 m) and coarsest-resolution (2000 m) DEMs for the calculated annual whole-glacier spatial means of total potential direct-beam solar radiation, potential duration of direct-beam solar radiation, and intensity of potential direct-beam solar radiation are 20%, 56% and −23% of the 2.5 m DEM values respectively. A resolution change from 2.5 m to 200 m affects the whole-glacier spatial mean summer net solar radiative flux by an average of 5%, and the summer melt production from the glacier by an average of 3% compared with the 2.5 m DEM values, for the years 2001–03. These changes are largely driven by underestimation of shading by surrounding topography at coarser DEM resolutions. This dependency is reduced in the second and third interpolation schemes, especially at resolutions finer than 50 m, which use the maximum lidar height measurement in some or all DEM cells. These results suggest that resolutions of ∼50 m are the coarsest that should be adopted in high-resolution glacier surface energy-balance models for glaciers of similar size and in similar topographic situations to midre Lovénbreen, and that the impact of DEM resolution on calculated solar radiation receipts can be reduced by an appropriate choice of DEM interpolation scheme.

Topographic controls on the surface energy balance of a high Arctic valley glacier

This paper presents the results of a distributed, two‐dimensional surface energy balance model used to investigate the spatial and temporal variations in the surface energy balance of Midre Lovénbreen, a small valley glacier in northwest Spitsbergen, Svalbard, over the summer of 2000. We utilize high‐resolution airborne lidar data to derive a digital elevation model of the glacier and surrounding topography, on which a surface energy balance is computed, driven by meteorological data obtained from a meteorological station located on the glacier and a synoptic station maintained at the nearby Ny‐Ålesund research base. Given the high‐resolution topographic data, we focus particularly on whether the long duration of sunshine at high latitudes compensates for the higher solar zenith angles on the season‐long energy balance and whether shading by the surrounding topography plus glacier surface slope and aspect play an increased role in the patterns of solar radiation receipt (and hence melt) over the glacier surface. The model results are validated using a combination of mass balance data from the glacier, measured surface lowering at the glacier meteorological station, and by comparing a derived energy balance component from the model with a measured energy flux. Overall, the model performance is very good. Glacier topography is found to play a fundamental role in determining the surface energy balance; topographic shading, slope, and aspect and correction of the surface albedo for high solar zenith angles are found to play a crucial role in determining spatial patterns of surface energy balance and therefore melt.

The Role of Airmass Types and Surface Energy Fluxes in Snow Cover Ablation in the Central Appalachians

Abstract A one-dimensional snowpack model, a unique airmass identification scheme, and surface weather observations are used to investigate large ablation events in the central Appalachian Mountains of North America. Data from cooperative observing stations are used to identify large ablation events within a 1° latitude × 1° longitude grid box that covers the majority of the Lycoming Creek basin in northern Pennsylvania. All 1-day ablation events greater than or equal to 7.6 cm (3 in.) are identified for the period of 1950 through 2001. Seventy-one events are identified, and these days are matched with a daily airmass type derived using the Spatial Synoptic Classification technique. Average meteorological characteristics on ablation days of each airmass type are calculated in an effort to understand the diverse meteorological influences that led to the large ablation events. A one-dimensional mass and energy balance snowpack model (“SNTHERM”) is used to calculate surface/atmosphere energy fluxes responsible for ablation under each airmass type. Results indicate that large ablation events take place under diverse airmass/synoptic conditions in the central Appalachians. Five airmass types account for the 71 large ablation events over the 52-yr period. Forty-three of the events occurred under “moist” airmass types and 28 under “dry” airmass conditions. Large ablation events under dry airmass types are driven primarily by daytime net radiation receipt, especially net solar radiation. These events tend to occur early and late in the snow cover season when solar radiation receipt is highest and are characterized by relatively clear skies, warm daytime temperatures, and low dewpoint temperatures. Moist airmass types are characterized by cloudy, windy conditions with higher dewpoint temperatures and often with liquid precipitation. During these events sensible heat flux is most often the dominant energy flux to the snowpack during ablation episodes. However, in many cases there is also a significant input of energy to the snowpack associated with condensation. Combinations of high sensible and latent heat fluxes often result in extreme ablation episodes, similar to those witnessed in this area in January 1996.

Extrapolation of solar irradiation measurements: Case study over Egypt

Relationships for determining the maximum permissible distance for extrapolating daily totals of solar irradiation from measurement sites are established for mesoscale monitoring networks in Egypt. The proposed method involves calculation of the standard deviation of the daily differences in solar radiation receipt for each couple of measurement stations to determine the variability coefficient. This is related to distance between station pairs to establish relationship due to extrapolation distance. Results indicate that the solar climate has much greater spatial coherence which permit data extrapolation of data over long distances. A comparison to temperature extrapolated data confirm the same finding.

SPATIAL COHERENCE OF SOLAR RADIATION FOR REGIONS IN THE CENTRAL AND EASTERN UNITED STATES

Information from the National Climatic Data Center's Solar and Meteorological Surface Observation Network CD-ROM data set is used to study the spatial coherence of incoming solar radiation for selected regions in the United States for the 30-year period 1961–1990. Networks of nine sites are analyzed for each of five regions: North Central, Ohio Valley, New England, East Texas, and Southern Piedmont. The spatial coherence of solar radiation is examined by calculating the standard deviation of daily differences in solar radiation receipt for paired stations and subsequently determining a coefficient of variability. These are plotted as a function of distance between station pairings to establish absolute and relative solar radiation spatial-variation relationships. Comparisons are made among the five regions with the Southern Piedmont showing the most spatial coherence and New England generally having the greatest variation (i.e., greater standard deviation and coefficient of variability values with distance). Interdecade analyses reveal that the relationships are temporally stable, with only slight differences in the three separate decade solar radiation relationships for each region. [Key words: solar radiation, solar climate.]

Summer Solar Radiation in the Canadian High Arctic

The limited number of weather stations in the Canadian Arctic Islands has prevented the mapping of incoming shortwave radiation. A cloud layer model, using cloud observations reported by summer field camps supported by the Polar Continental Shelf Project, allows the computation of solar radiation for these widely scattered arctic sites. The calculated values were combined with the measured data from the weather stations to examine the temporal and spatial variations of summer radiation. For the years studied (1974-93), incoming shortwave radiation was the highest in June and declined afterwards. On a local scale, coastal low clouds that are prevalent during the open-water periods reduce the solar radiation receipt, but local variability is unlikely to mask the regional trends. At a regional level, most field camps are highly correlated with their closest weather stations. The short-term field camp data were adjusted with the long-term means of the weather stations to map the distribution of solar radiation for the months of June to August. Throughout these months, the northern Queen Elizabeth Islands, have relatively high radiation, which decreases towards the western sector. Both seasonal and spatial variations of solar radiation may be related to the distribution of clouds.

Spatial Coherence of Incoming Solar Radiation for the Southern Piedmont

The spatial coherence of incoming solar radiation is examined for a mesoscale network of locations across the Southern Piedmont region of Alabama, Georgia, and South Carolina. Data from the National Climatic Data Center's (NCDC) Solar and Meteorological Surface Observation Network (SAMSON) are used in the analysis for the period 1961-1990. The method involves calculation of the standard deviation of the daily differences in solar radiation receipt for each pair of stations and the determination of a coefficient of variability. These are plotted as a function of distance between station pairs to establish absolute and relative solar radiation spatial variation relationships. In addition to overall annual and decadal analyses, the spatial coherence for different seasons is assessed. Results are compared to similar previous studies in other mesoscale regions, all of which were based on much shorter periods of record.

CROPSIM — WHEAT: A model describing the growth and development of wheat

Crop simulation models consolidate mathematical representations of the various physiological processes underlying crop growth and development into an entity that can be used to predict the outcome of various crop, soil and weather scenarios. For wheat, a number of simulation models are already available, but most of these do not appear to be set-up to facilitate easy comparison of model outputs with experimental data, to allow easy modification for new cultivars, and to facilitate the addition of disease routines, an aspect necessary for models to be useful in the general field situation. Cropsim-wheat was developed to help overcome some of these deficiencies.The model assumes that a crop consists of a collection of uniform plants, and performs calculations on a daily basis. It is driven by daily weather data dealing with solar radiation receipt, maximum and minimum temperatures, and precipitation. Water and nitrogen balance subroutines are included, and the rate of various crop processes is modulated through the use of multipliers that reflect the water and nitrogen states of the crop. Developmental processes are simulated using the concept of "biological days", a time measure that equates to chronological days under optimum conditions. The phases into which the life-cycle is broken relate closely to those in the widely used "Zadoks" scale. Dry matter accumulation is calculated from intercepted radiation, and distributed largely on the basis of demand. A minimum fraction of daily assimilate, however, is reserved for root growth. Leaf area is computed on the basis of potential leaf size and available dry matter, whereas stem and spike areas are calculated from the stem and spike weights. Both leaf and stem area are used in calculating radiation interception. Critical stresses, water saturation during early seedling growth and low temperature during the winter period, can result in plant death. Low temperatures, when they occur around heading, can also result in sterility and reduced grain number.The model performance has been compared with datasets from North America and Europe, and results of these comparisons will be conveyed in companion publications. The model has been set-up, however, on the premise that model development should be a continuing process as new datasets become available and new applications are contemplated. With this in mind, it has been built to use file structures that facilitate the handling and storage of field data, and the easy comparison of field and simulated data. It should thus be useable by experimenters as a tool to help in the analysis of field studies. Key words: Wheat, simulation, nitrogen, water, development, growth