Showing papers in "Weather in 2000"

North Atlantic climate c.ad 1000: Millennial reflections on the Viking discoveries of Iceland, Greenland and North America

Abstract: “The country seemed to them so kind that no winter fodder would be needed for the livestock: There was never any frost all winter and the grass hardly withered at all.” (A description of Vinland from Granlendinga saga.) It has been suggested that the North Atlantic region experienced a relatively mild climate around the time of the Vikmg expansion (c. AD 800-1 100) and thus during the Norse settlement of Iceland (LAD 870) and Greenland (CAD 985) and during the voyages of the

Solar Variability and Climate

Abstract: Solar radiation is the fundamental energy source for the atmosphere and the global average equilibrium temperature of the Earth is determined by a balance between the energy acquired by the solar radiation absorbed and the energy lost to space by the emission of heat radiation. The interaction of this radiation with the climate system is complex but it is clear that any change in total solar irradiance (TSI) has the potential to influence climate. In the past, although many papers were written on relationships between sunspot numbers and the weather, the topic of solar influences on climate was often disregarded by meteorologists. This was due to a combination of factors of which the key was the lack of any robust measurements indicating that solar radiation did indeed vary. There was also mistrust of the statistical validity of the evidence and, importantly, no established scientific mechanisms whereby the apparent changes in the Sun might induce detectable signals near the Earth’s surface. Another influence was a desire by the meteorological profession to distance itself from the Astrometeorology movement popular in the 19th century (anderson1999). Nowadays, with improved measurements of solar and climate parameters, evidence for an influence of solar variability on the climate of the lower atmosphere has emerged from the noise. This article provides a brief review of the observational evidence and an outline of the mechanisms whereby rather small changes in solar radiation may induce detectable signals near the Earth’s surface is not possible to review here all potential mechanisms for solar-climate links. What is presented offers, necessarily, a personal perspective but, of the areas that are not covered, two may be pertinent: the effects of solar energetic particles on stratospheric composition (see e.g. jackman et al. 2005) and the possible influence of galactic cosmic rays on clouds through ionisation processes (see Marsh, this volume).

Meteorological effects of the solar eclipse of 11 August 1999

Abstract: A rare and spectacular total solar eclipse crossed the south-west tip of Britain, sweeping swiftly onwards into continental Europe, during the late morning of 11 August 1999 (Fig. 1). (The last total solar eclipse in the UK barely clipped Shetland in 1954, and the next will not occur until 2081, in the Channel Islands.) The rest of the country was subjected to a deep partial eclipse. For most of Britain, the eclipse lasted from about 1000 to 1235 BST, with maximum obscuration of the Sun by the Moon between about 1112 and 1122BST, exact timings being later further east (Bell 1997). Unfortunately the surface pressure analysis (Fig. 2) shows a weak low approaching Ireland, with an associated cloudy trough hitting the south-west peninsula just at the crucial hour when avid eclipse watchers could well have done without this nuisance! Ahead of the front, winds were light in a slack south or south-east airflow resulting from a weak transient ridge. Cloud conditions further east and north in Britain were still patchy but generally clearer (Fig. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA3). While many of the south coast resorts east of the Isle of Wight had largely clear skies, with typically 7 or 8 hours of bright sunshine, those further west were mainly cloudy with only an hour or less of sunshine.

The ‘Sunday Effect’ and weekly cycles of winter weather in the UK

Abstract: ’National Center for Atmospheric Research, Boulder. USA ’Division of Geography, University of Derby It has been recognised for some time that urban centres have strong weekly air pollution cycles, and that these cycles have meteorol- ogical consequences. For example, Ashworth (1 929) used ten years of daily rainfall data for Rochdale, 19 18-27, to demonstrate that aver- age Sunday rainfall totals were 13% less than the average of all days of the week, and that this effect was most pronounced in winter. The lesser rainfall of Sunday was attributed to lower emissions of “smoke and hot gases from mill chimneys” on that day of the week. On weekdays, hot gases were thought to stimulate “slight uplift to the air” and to provide “an abundance of nuclei which promote the formation of rain”. In comparison, Sunday rainfall amounts at Stonyhurst (a site with less smoke) were not significantly different from those of weekdays. Subsequent analyses have established the existence of weekly cycles for other parameters including: the loss of bright sunshine; the frequency of fog days; and parti- culate, ozone (0,) and sulphur dioxide (SO2) concentrations in industrial urban centres (Bach 1972; Bruntz

Daily temperature extremes for Britain

Abstract: The utmost care has been taken in checking available records and conditions of thermometer exposure in order to provide tables of Britain’s extreme temperatures for every date of the year. The stages at which comparable standards of exposure (including site exposure) were implemented, following the invention of the Stevenson screen in 1866, have been discussed by Webb and Meaden (1993) and Parker (1994). Table 1 lists Britain’s highest recorded temperatures for every date of the year. This covers the period beginning with the introduction of standardised thermometer exposure in the mid-1870s and ending on the last day of 1999. It fully updates the list published by Meaden and Webb (1984), and revised by Webb and Meaden (1997). The distinction between ‘standard’ and ‘representative’ stations must be noted. Camden Square, although not quite meeting the criteria for an ideal standard station, was probably very representative of inner London. Likewise, the early twentieth-century stations at Epsom and Beddington were, then, quite representative of town gardens in the home counties. Table 2 includes a fully updated version of the table of daily extreme minimum temperatures for the eight months October to May inclusive, first published by Webb (1 985). The extremes listed are limited to sites below 500 m, excluding ‘high-level’ weather stations which are not at permanently inhabited heights (e.g. Ben Nevis Observatory!). The highest village in England is Flash (Staffordshire) at 463m. Reported minima for June to September include many readings from such upland sites, making the compilation of a daily list of minima for this period of the year impracticable. Moreover, comprehensive summer ‘lows’ would arguably be of only technical interest, as it is cold summer days which stick in the public awareness (and which attract media attention). However, recorded lows for each 10-day period in these four warmest months have been included in Table 2, in order to answer questions such as “what is the lowest temperature on record in late June”, or “in early September”. Table 2 covers the 125 years ending in 1999. Local factors (adiabatic warming, relative altitude, soil type, etc.) can raise summer maxima by up to about 2 degC above general levels. The fohn effect in winter (Lockwood 1962) can account for larger anomalies downwind of mountain ranges. Otherwise highs more than 2 degC above adjacent stations (at comparable altitudes) must be treated with scepticism. Potential pitfalls in the study of temperature (and other) extremes are discussed by Dukes and Eden (1 997). The larger local variations in extreme minimum temperatures make it less appropriate to reject the authenticity of such readings on the basis of support from other stations alone, especially as their occurrence has often been in areas with a low density of climatological stations. Over the past 20 years, remote sensing of surface temperatures has been effectively used to identify very localised extreme minima, e.g. in 198 1-82 (Roach and Brownscombe 1984). This has highlighted the fact that we probably do not know the absolute range of British temperatures, because it is unlikely that orthodox thermometer screens have always been sited at the coldest spots (McClatchey et al. 1987)! From earlier in the period under discussion, there remain some sites for which full details are elusive, e.g. the site at Aviemore (certainly a cold location) from which several low minima were quoted for 1895 (Bayard and Marriott 1895). As discussed in Webb and Meaden

An appraisal of precipitation distribution around the Everest and Kanchenjunga peaks in the Himalayas

Abstract: The Himalayan range has been described as the greatest physical feature on earth. Because of its enormous size and altitude it is also called the 'third Pole'. It runs from Mount Namche Barua (7756m) in the east to Mount Nanga Parbat (8126m) in the west for a distance of about 2400km in the form of an arc with convexity towards the south. In the northwest, the Himalayan foothills start from about 34 ON and in the east this lofty mountain range runs down to about 28"N (see Fig. 1). The Himalayan range consists of three broad ranges parallel to each other:

Sensing and mis‐sensing the eclipse

Abstract: Morton, F. I. (1984) What are the limits on forest evaporation? J. Hydrol., 14, pp. 373-398 (1985) What are the limits on forest evaporation? Reply. J. Hydrol., 82, pp. 184-1 92 Verdecchia, M., Visconti, G., Giorgi, F. and Marinucci, M. R. (1994) Diurnal temperature range for a double carbon dioxide concentration experiment: analysis of possible physical mechanisms. Geophys. Res. Lett., 21, pp. 1527-1530 and night-time temperatures. Weather, 53, pp. 7278 Mayes, J. and Sutton, G. (1997) Eastern England. In: Wheeler, D. and Mayes, J. (Eds.) Regional climates of the British Isles. Routledge, London, pp. 89-1 10 Monteith, J. L. (1999) Physical and physiological feedback constraining evaporation from land surfaces. In: Browning, K. A. and Gurney, R. J. (Eds.) Global energy and water cycles. Cambridge University Press, pp. 155-160 Monteith, J. L. and Unsworth, M. H. (1990) 1%ciples of environmental physics. Edward Arnold, Correspondence to: Dr J. G. Lockwood, 4 London Woodthorne Croft, Leeds LS 17 8XQ.

Back to basics: Coriolis: Part 2 — The Coriolis force according to Coriolis

Abstract: In his professional activity Gaspard Gustave Coriolis (Fig. 1) was never concerned with the atmosphere, not even with the rotating earth. His interest was to promote the Industrial Revolution in early nineteenth-century France. It was during his study of machines, their forces and energy exchanges, that he made his discovery of the deflective force. Coriolis was both a victim and an offspring of the French Revolution. He was born on 21 May in the fateful year 1792 in Paris to a small aristocratic family. His father, Jean-BaptisteElzear, who had been a captain in Louis XVI’s guard, was ruined by the political turmoil and, to save his own life, had to flee to Nantes, where he became a businessman. The young Gaspard showed early remarkable mathematical gifts. At 18 he was admitted to 1’Ecole Polytechnique and at 20 he continued as an engineering student at 1’Ecole Ponts et Chaussees. He showed great talent as a teacher, and in 1816 was employed by the school (see Persson 1998a,b for more details about Coriolis’s life).