Variables Minimum Temperature Research Articles

Is the Sonoran Desert losing its cool?

Freezing temperatures strongly influence vegetation in the hottest desert of North America, in part determining both its overall boundary and distributions of plant species within. To evaluate recent variability of freezing temperatures in this context, minimum temperature data from weather stations in the Sonoran Desert are examined. Data show widespread warming trends in winter and spring, decreased frequency of freezing temperatures, lengthening of the freeze-free season, and increased minimum temperatures per winter year. Local land use and multidecadal modes of the global climate system such as the Pacific decadal oscillation and the Atlantic multidecadal oscillation do not appear to be principal drivers of this warming. Minimum temperature variability in the Sonoran Desert does, however, correspond to global temperature variability attributed to human-dominated global warming. With warming expected to continue at faster rates throughout the 21st century, potential ecological responses may include contraction of the overall boundary of the Sonoran Desert in the south-east and expansion northward, eastward, and upward in elevation, as well as changes to distributions of plant species within and other characteristics of Sonoran Desert ecosystems. Potential trajectories of vegetation change in the Sonoran Desert region may be affected or made more difficult to predict by uncertain changes in warm season precipitation variability and fire. Opportunities now exist to investigate ecosystem response to regional climate disturbance, as well as to anticipate and plan for continued warming in the Sonoran Desert region.

A seasonally resolved bottom‐water temperature record for the period AD 1866–2002 based on shells of Arctica islandica (Mollusca, North Sea)

AbstractExisting studies on recent global warming are almost exclusively based on environmental data from the Earth's surface. Seasonal information on the effects of climate change on subsurface settings of mid to high latitudes is extremely scarce. Here, we present the first temperature proxy record from bottom (c. 50 m) water settings of the North Sea employing the oxygen isotope composition of ocean quahog shells. Results indicate that δ18Oaragonite measured across shells of Arctica islandica can provide reliable estimates (±0.25 to ±0.4 °C) of the ambient bottom water temperatures. Over the period AD 1880–2001, warming trends in bottom waters are of the order of 0.042 to 0.138 °C/decade. Apparently, the annual maximum‐temperature trend shows a twofold increase over the past four decades (0.236 °C/decade) while the minimum‐temperature trend has remained relatively stable (0.042 °C/decade). During the same time interval, however, annual maximum temperatures at the sea surface quadrupled. Shell oxygen‐isotope‐derived winter temperatures also provide a proxy for the winter North Atlantic oscillation index (WNAO). Some 28 to 50% of the variability in minimum temperatures below the thermocline can be explained by changes of the WNAO. Our new tool enables testing and verification of climate models prior to the 20th century greenhouse forcing. Copyright © 2005 Royal Meteorological Society

Temporal variability in the maternal environment and its effect on seed size and seed quality in Flourensia cernua DC. (Asteraceae).

The biological phenomenon commonly referred to as maternal effect occurs whenever the environment exerts an influence upon the mother that is later expressed in characteristics of her offsprings. For example, the environmental conditions experienced by a mother plant during flowering and fruiting can modify the quality of her descendants (seeds), and even interrupt their development. Between-year variation in minimum temperature and the classic, between-year variation in precipitation represent an unpredictable environment for winter blooming plants in arid zones. In this study, we investigated the effect of maternal environment (temperature and precipitation) on seed size and seed quality in F. cernua, over a 5-year period. Results indicated that the proportion of filled seeds, as well as their size, increased with higher absolute minimum temperatures during seed formation, and that, to a lesser extent, both the precipitation occurred during the same period and the annual precipitation also have a positive influence on seed size. In this way, environmental conditions prevailing during seed formation exerted a strong maternal effect on the size and quality of seeds produced and, probably also, in the developmental possibilities of F. cernua seedlings. This effect was subject to important, between-year variation.

Spatial interpolation‐based mapping of the spring frost hazard in the Champagne vineyards

AbstractThe Champagne vineyards, famous worldwide, are located at the northern limit of viticulture. Consequently, they are very sensitive to spring frosts that can occur after bud burst. These spring frosts occur mainly in radiative atmospheric situations (low speed wind, clear sky) where spatial variations in minimum temperatures are very important. The latter depend on several factors at different scales: from the macroclimatic scale, where the geographical location (latitude/longitude) has a strong influence, to the topoclimatic scale, where environmental and topographical factors play an important role. After a brief recall of the definition of these different factors extracted from a Digital Elevation Model and a land‐use database, we propose a spatial interpolation of minimum temperatures in the Champagne vineyards based on multiple regression. From this interpolation, we can map the frost hazard for the whole vineyard from data measured over five spring seasons (1998–2003) and for about 20 weather stations. In this paper, we present this mapping technique and compare it with the data for spring 2003 when particularly strong frosts occurred. Copyright © 2005 Royal Meteorological Society.

Patterns and sources of thermal heterogeneity in small mountain streams within a forested setting

Spatial thermal patterns and the sources of those patterns were examined in four mountain streams in northeast Oregon and Idaho during hot summer days in 2001. Summer baseflow ranged from <0.007 to 0.22 m 3/s. Maximum and minimum temperatures increased in the downstream direction, with the diurnal range decreasing with increasing stream size. Each stream was thermally diverse spatially, diurnally, and seasonally, with unique landform and geologic influences on the daily temperature maxima. Insolation was the most important predictor for maximum temperature at each stream. Minimum daily temperatures were less variable than maxima and followed a seasonal and elevation gradient, with minimum air temperature a more important predictor than either the insolation from the previous day or channel features. Models for each stream using insolation and physical habitat characteristics explain 32 to 67% of maximum temperature and 17 to 51% of minimum temperature variability. Groundwater inputs moderated thermal conditions, particularly local maxima, but did not subsume the predominant temperature range controls of insolation and air temperature.

Urbanization and seasonal temperature trends: observational evidence from a data‐sparse part of North America

AbstractViewed from the continental or hemispheric perspective, the evidence of warming trends in surface temperatures continues to accumulate. Here, we focus on the detection of seasonal temperature trends at regional and sub‐regional space scales. The study region is transnational, extending from the border areas of New Mexico and Texas in the USA, southward into the altiplano of north central Mexico. The analysis considers maximum and minimum temperature records (1941–2000) from 21 stations located in a variety of land‐use environments ranging from large urban settings to rural areas. The analysis demonstrates that a significant part of the variability in minimum temperatures for stations located in large urban areas is captured by positive linear trend, and thus is likely associated with rapid urbanization within the region. A similar, but comparatively minor, urban effect is also apparent in the maximum temperature records for the warm season (June–September). Aside from the urban influence, the most consistent feature emerging from the analysis is the tendency for station records to exhibit a recent (post—1970) warming trend. It is present across all place sizes, i.e. from large urban to rural stations, and is particularly pronounced for cool‐ and warm‐season minimum temperatures and for warm‐season maximum temperatures. This behaviour generally mirrors the temperature trends detected on continental and hemispheric space scales, and thus the onset of this warming regime is broadly consistent with documented changes in large‐scale climate modes such as the North Atlantic oscillation and the Atlantic multi‐decadal oscillation. Copyright © 2003 Royal Meteorological Society

Spatial and Seasonal Variations of Air Temperature Lapse Rates in Alpine Regions

Air temperature decrease with altitude was estimated by simple linear regression for several regions around northern Italy for minimum, maximum, and mean monthly temperatures. The comparison of the gradients with previous works revealed the absence of a lapse rate seasonal pattern in most earlier studies. Such inconsistencies in other analyses were demonstrated to be largely due to insufficient climatic stations in each area, and incomplete temporal coverage. These problems were solved here by using 269 stations in northern Italy, 205 in the Tyrol area, and 166 in the Trentin–Upper Adige region, covering a wide range of elevations and based on at least 30-yr means. Yearly lapse rates ranging from −0.54° to −0.58°C (100 m)−1 were obtained. As hypothesized, a seasonal pattern in monthly gradient variations was observed, regardless of location, and with higher lapse rates during summer. Weather stations on valley bottoms were distinguished from those located on slopes, the former group being heavily influenced by a cold-air drainage process. Both differences in temperatures at sea level and lower lapse rates on valley bottoms explained minimum temperature variation with exposure, mainly due to temperature inversions. On the other hand, maximum temperature changes with topography mostly imply differences among the lapse rates themselves, attributed to a stronger sun warming of slopes. Since lapse rates may be used for monthly temperature spatial interpolation, an analysis of cross-validated interpolation errors was performed, to assess the method accuracy. The highest interpolation reliability was founded for maximum temperature, especially for summer values, and even when topographic information was not available (with an accuracy about 1°C in most cases). The degree to which topographic differences influence the lapse rate determination was also quantified. The addition of topographic information appeared to significantly increase the temperature interpolation reliability, especially for slope sites, and was required for both minimum and winter temperature reconstruction. Thus, the interpolation error of January minimum temperature in slope stations was reduced from 2.8° to 1.1°C by using such a technique. Finally, the lapse rate's spatial variability was shown to be a potential source of error, especially when the region exceeds a 1° width latitude area, whereas longitude role was shown to be less crucial.

Description of epidemics of coffee rust with neural networks

The objective of this paper was to evaluate the potential of neural networks (NN) as an alternative method to the basic epidemiological approach to describe epidemics of coffee rust. The NN was developed from the intensities of coffee (Coffea arabica) rust along with the climatic variables collected in Lavras-MG between 13 February 1998 and 20 April 2001. The NN was built with climatic variables that were either selected in a stepwise regression analysis or by the Braincel® system, software for NN building. Fifty-nine networks and 26 regression models were tested. The best models were selected based on small values of the mean square deviation (MSD) and of the mean prediction error (MPE). For the regression models, the highest coefficients of determination (R²) were used. The best model developed with neural networks had an MSD of 4.36 and an MPE of 2.43%. This model used the variables of minimum temperature, production, relative humidity of the air, and irradiance 30 days before the evaluation of disease. The best regression model was developed from 29 selected climatic variables in the network. The summary statistics for this model were: MPE=6.58%, MSE=4.36, and R²=0.80. The elaborated neural networks from a time series also were evaluated to describe the epidemic. The incidence of coffee rust at four previous fortnights resulted in a model with MPE=4.72% and an MSD=3.95.

Differential variations of maximum and minimum temperatures

We present some analysis which shows generally how maximum (or peak daytime) sensible energy at a given location and minimum (or lowest night-time) sensible energy at the same location vary relative to each other. Then we show that daytime warming is not always in phase with night-time temperature increases. Furthermore we establish both theoretically and by means of actual records that major changes in mean minimum temperature variations at a given location are followed after time τ by (associated) major changes in mean maximum temperature variations at the same location. The value of parameter τ, which is apparently independent of the choice of the location involved, is found to be approximately eight years.

Pattern and controls of reproduction of the southern African rodentGerbillurus paebain the semi-arid Karoo, South Africa

The pattern and controls of reproductive activity of the hairy-footed gerbil,Gerbillurus paeba, were investigated in the semi-arid environment of the Karoo, South Africa. Animals (N = 62) were collected monthly for 14 months. Although some animals appeared to be capable of breeding throughout the year, successful breeding was observed only in summer months. Reproductive activity was related positively to mean monthly rainfall and negatively to actual rainfall and was associated with variations in minimum temperatures and photoperiod. An opportunistic reproductive strategy was proposed with the timing and controls of reproduction being sex, population and habitat specific.

Test methodology for the determination of optimum fusion welding conditions of polyethylene

AbstractThe fusion welding behavior of a medium density polyethylene resin has been studied for a wide range of heating rates using a recently developed test methodology. With this method, the thermal and physical phenomena occurring at the interface of two thin polyethylene pieces assembled by fusion can be studied. It consists of a thermal welding phase and a phase of mechanical separation of the welded assembly. For the mechanical phase, an adaptation of the T‐peel test was used. These conditions make it possible to determine the thermal welding parameters (temperature, time) for optimal mechanical quality of the joint, according to a criterion established by optimization of the peel test used. The variations in minimum temperature required for an optimum weld, as a function of heating rate, can be simulated with a numerical model based on the concept of macromolecular interdiffusion. Consistent with the experimental behavior, the numerical model involves two parameters characteristic of the diffusion behavior of the polyethylene resin. Thus, these parameters characterize the weldability of the polyethylene resin under study.

Local temperature variation in Shillong area

Parry's (1956) and Lysack's (1957) conclusion that substantial local variations, occur due to relief of the place has been tested for local temperature variations in Shillong area for the Winter season for the years 1960-62. The variation of minimum temperature is more pronounced than the maximum temperature. Parry concluded that the influence of relief win be observed when the range of altitude of observatories recording local variation of temperature is small. the present study indicates that this variation is observable even where the range of altitude is of the order of 2000 ft.

Local temperature variations in the Reading area

AbstractThe following paper describes some results of an investigation of local climate — based on a close network of meteorological stations — undertaken over an 18‐month period in the Reading area. Mean and extreme temperatures, and temperature distributions on selected occasions are examined in relation to the local factors involved: these are mainly the relief and the presence of the town. In particular, the relation between weather conditions and variations in minimum temperatures is considered. Diurnal temperature variations at different sites are compared. Although the local relief is slight and the urban area neither closely built up nor heavily polluted, temperature differences of up to 8°F can occur, and differences in minima of 4°–5° are common, during radiation nights. Maximum temperatures vary little.