Measurements of natural airflow within a Stevenson screen

Climate science depends upon accurate measurements of air temperature and humidity, the majority of which are still derived from sensors exposed within passively-ventilated louvred Stevenson-type thermometer screens. It is well-documented that, under certain circumstances, air temperatures measured within such screens can differ significantly from ‘true’ air temperatures measured by other methods, such as aspirated sensors. Passively-ventilated screens depend upon wind motion to provide ventilation within the screen, and thus airflow over the sensors contained therein. Consequently, instances of anomalous temperatures occur most often during light winds when airflow through the screen is weakest, particularly when in combination with strong or low-angle incident solar radiation. Adequate ventilation is essential for reliable and consistent measurements of both air temperature and humidity, yet very few systematic comparisons to quantify relationships between external wind speed and airflow within a thermometer screen have been made. This paper addresses that gap by summarising the results of a three month field experiment in which airflow within a UK-standard Stevenson screen was measured using a sensitive sonic anemometer, and comparisons made using simultaneous wind speed and direction records from the same site. The average in-screen ventilation rate was found to be 0.2 m s−1, well below the 1 m s−1 minimum assumed in meteorological and design standard references, and only about 7 % of the scalar mean wind speed at 10 m. The implications of low in-screen ventilation on the uncertainty of air temperature and humidity measurements from Stevenson-type thermometer screens are discussed, particularly those due to the differing response times of dry- and wet-bulb temperature sensors, and ambiguity in the value of the psychrometric coefficient.

Insights from 20 years of temperature parallel measurements in Mauritius around the turn of the 20^th Century

There is considerable import in creating more complete, better understood, holdings of early meteorological data. Such data permit an improved understanding of climate variability and long-term changes. Early records are particularly incomplete in the tropics, with implications for estimates of global and regional temperature. There is also a relatively low level of scientific understanding of how these measurements were made and, as a result, of their homogeneity and comparability to more modern techniques and measurements. Herein we describe and analyse a newly rescued set of long-term, up to six-way parallel measurements, undertaken over 1884–1903 in Mauritius, an island situated in the southern Indian Ocean. Data include: i) measurements from a well-ventilated room, ii) a shaded Thermograph; iii) instruments housed in a manner broadly equivalent to a modern Stevenson Screen; iv) a set of measurements by a Hygrometer mounted in a Stevenson Screen; and for a very much shorter period v) two additional Stevenson Screen configurations. All measurements were undertaken within roughly 80 metre radius. To our knowledge this is the first such multidecadal multi-instrument assessment of meteorological instrument transition impacts ever undertaken, providing potentially unique insights. The intercomparison also considers the impact of different ways of deriving daily and monthly averages. The long-term comparison is sufficient to robustly characterise systematic offsets between all the instruments and seasonally varying impacts. Differences between all techniques range from tenths of a degree Celsius to in excess of a degree Celsius and are considerably larger for maximum and minimum temperatures than for means or averages. Systematic differences of several tenths of a degree also exist for the different ways of deriving average / mean temperatures. All differences bar two average temperature series pairs are significant at the 0.01 level using a paired t-test. Given that all thermometers were regularly calibrated against a primary Kew standard thermometer this analysis highlights significant impacts of instrument exposure, housing, siting and measurement practices in early meteorological records. These results reaffirm the importance of thoroughly assessing the homogeneity of early meteorological records.

Thermometer screens and the geographies of uniformity in nineteenth-century meteorology

By the 1860s a number of thermometer stands, screens and boxes were being used at public observatories and in private settings. The ultimate object of these humble pieces of scientific infrastructure was to protect the thermometers from precipitation and radiation. In response to concerns over the quality of designs and the comparability of results a trial of the various apparatuses was staged at Strathfield Turgiss, Hampshire, in 1868, and subsequent discussions were organized by Britain's Meteorological Society (from 1883 the Royal Meteorological Society). In an attempt to guarantee uniformity of exposure, the Society recommended the adoption of the Stevenson screen, a double-louvred box designed by Thomas Stevenson in 1866. It was promoted as an essential part of the Society's network of second-order and climatological stations across England. Despite the Meteorological Society's aim of overcoming the idiosyncrasies of geography through recourse to a uniform pattern screen, their chosen design ended up embodying a particular geography: the aesthetic and moral codes of the suburban domestic garden.

Patterns of activity and inactivity in echidnas (Tachyglossus aculeatus) free-ranging in a hot dry climate: correlates with ambient temperature, time of day and season

Echidnas occur throughout Australia. They exhibit daily fluctuations in body temperature (Tb) and use torpor to various degrees throughout much of their range. Echidnas elsewhere are commonly diurnal except during hot weather. This study used temperature-sensitive radio-transmitters to investigate the activity patterns and temperature relations of echidnas in the relatively hot, dry climate of south-west Queensland with respect to temperature and photoperiod. During activity, echidnas were characterised by rising, but not necessarily high, Tbs. Activity was seen only within an ambient temperature range (as measured in a nearby Stevenson Screen: Tss) of 9–33�C so that activity was seen during the day and at night during the cool weather but only at night in summer. Echidnas used caves, burrows and logs when inactive. Tbs of inactive echidnas declined except when affected by rising ambient temperatures, as determined within these shelters (Ta). In summer, Tbs of echidnas in these shelters changed little or rose with increasing Ta to levels even higher than in active echidnas.Torpor was used by echidnas for periods up to nine days during winter and occasionally for up to one day during summer. Due to the difficulty of identifying the occurrence of torpor from Tb alone in warm conditions, the possibility that echidnas utilise torpor for less than one day remains inconclusive. Nevertheless, at least five bouts of torpor were identified in four (of eight) echidnas during winter/spring and two bouts of torpor from two echidnas in summer.

Wheat spike temperatures in relation to varying environmental conditions

Most field studies investigating the effect of temperature on growth processes use temperatures recorded within a Stevenson screen. These are likely to deviate from temperatures within the plant. This investigation reports a comparative study of methodologies and applications for measuring temperatures in the field during grain development by comparing Stevenson screen, ambient (air temperatures within the crop canopy), and wheat spike temperatures. Miniature sensors were inserted into wheat spikelets located midway on the spike of a primary tiller at anthesis. Located also within the crop canopy, and at the same height as the spike sensors, were sensors to measure ambient temperatures. Stevenson screen temperatures were also recorded at the site. Temperatures were recorded automatically every 12 min during grain filling from anthesis to maturity. Plants were grown in dryland and irrigated conditions within the same location, with the aim of determining differences in plant temperatures between stressed and non-stressed plants. Stevenson screen temperatures did not relate closely to ambient or spike temperatures. Plants growing in adequate soil moisture conditions had spike temperatures lower than ambient temperatures, but in some dryland trials, where soil moisture was limiting, spike temperatures equalled ambient temperatures, indicating that the plants were under moisture stress. Temperature differences of up to 5˚C were observed between the spikes of irrigated and non-irrigated crops on a hot day. Neither ambient nor screen temperatures gave an accurate measurement of spike temperature on hot days. Spike temperature differences between 2 cultivars, awned and awnless, were investigated. Trends were not consistent over both years; however, in 3 of the 4 environments, the maximum spike temperatures were higher for the awned cultivar (Hartog) than the awnless cultivar (Halberd). On very hot days, when ambient temperatures exceeded 40˚C, spikes of Hartog were cooler than those of Halberd.

DEGREE-DAY RELATIONSHIPS TO THE DEVELOPMENT OF LITHOCOLLETIS BLANCARDELLA (LEPIDOPTERA: GRACILLARIIDAE) AND ITS PARASITE APANTELES ORNIGIS (HYMENOPTERA: BRACONIDAE)

Degree-day relationships in the development of Lithocolletis blancardella (Fab.) and Apanteles ornigis Weed, its major parasite, were established from laboratory and field studies in Ontario apple orchards during 1973, 1974, and 1975. Under constant laboratory conditions, temperature thresholds for development of overwintering pupae were estimated by three methods, and found to be 6.3°, 6.7°, and 5.7°C for L. blancardella, and 10.4°, 10.4°, and 11.3°C for A. ornigis. Degree-day accumulations in the field were calculated by two methods using daily maximum and minimum temperatures recorded from the pupal habitat and a Stevenson screen. Degree-days in the pupal habitat accumulated from 1 January, above 5.7°C for L. blancardella and 11.3°C for A. ornigis were more accurate than Stevenson screen degree-day accumulations for predicting first emergence; however, after emergence, seasonal development was best related to Stevenson screen degree-days accumulated from 1 April, above 6.7°C for L. blancardella and 10.4°C for A. ornigis. This study shows that degree-day relationships can be used in an apple pest management programme to optimize timing of insecticide applications against L. blancardella and preserve A. ornigis, its major natural enemy.