The Global Climate System

Undoubtedly the most important outcome of work in the second half of the twentieth century was the recognition of the existence of the global climate system (see Box 1.1). The climate system involves not just the atmosphere elements, but the five major GLOBAL ATMOSPHERIC RESEARCH PROGRAMME (GARP) AND THE WORLD CLIMATE RESEARCH PROGRAMME (WCRP) The idea of studying global climate through co-ordinated intensive programmes of observation emerged through the World Meteorological Organization (WMO...

Global Circulation

The first attempt to explain the global atmospheric circulation was based on a simple convectional concept. In 1686 Halley associated the easterly trade winds with low-level convergence on the equatorial belt of greatest heating (i.e. the thermal equator). These flows are compensated at high levels by return flows aloft. Poleward of these convectional regions, the air cools and subsides to feed the northeasterly and southeasterly trades at the surface. This simple mechanism, however, presented...

Bifurcation In Climate And Weather

MT WILHELM * < CENTRAL Figure 4.19 The relationship between precipitation (broken line) and relief in the 800 tropics and mid-latitudes. (A) The highly saturated airmasses over the Central Highlands of Papua New Guinea give seasonal maximum precipitations on the windward slopes of the mountains with changes in the monsoonal circulation (B) Across the Jungfrau massif in the Swiss -400 T Alps the precipitation is much less than in A (A) and is closely correlated with the 0 topography on the...

The Atmosphere

The atmosphere, vital to terrestrial life, envelops the earth to a thickness of only 1 per cent of the earth's radius. It had evolved to its present form and composition at least 400 million years ago by which time a considerable vegetation cover had developed on land. At its base, the atmosphere rests on the ocean surface which, at present, covers some 70 per cent of the surface of the globe. Although air and water share somewhat similar physical properties, they differ in one important...

Atmospheric motion principles

When you have read this chapter you will Know the basic laws of horizontal motion in the atmosphere, Know how the Coriolis force arises and its effects, Be able to define the geostrophic wind, Know how friction modifies wind velocity in the boundary layer, Understand the principles of divergence convergence and vorticity and their roles in atmospheric processes, Understand the thermodynamic, dynamic and topographic factors that lead to distinctive local wind regimes. The atmosphere is in...

The interior southeastern United States

The climate of the subtropical southeastern United States has no exact counterpart in Asia, which is affected by the summer and winter monsoon systems (discussed in Chapter 11). Seasonal wind changes are experienced in Florida, which is within the westerlies in winter and lies on the northern margin of the tropical easterlies in summer. The summer season rainfall maximum (see Figure 10.20 for Jacksonville) is a result of this changeover. In June, the upper flow over the Florida peninsula...

Pressure and wind conditions

The dominant features of the mean North Atlantic pressure pattern are the Icelandic Low and the Azores High. These are present at all seasons (see Figure 7.9), although their location and relative intensity change considerably. The upper flow in this sector undergoes little seasonal change in pattern, but the westerlies decrease in strength by over half from winter to summer. The other major pressure system influencing European climates is the Siberian winter anticyclone, the occurrence of...

The lee cyclone

Westerly airflow that is forced over a north-south mountain barrier undergoes vertical contraction over the ridge and expansion on the lee side. This vertical movement creates compensating lateral expansion and contraction, respectively. Hence there is a tendency for divergence and anticyclonic curvature over the crest, and convergence and cyclonic curvature in the lee of the barrier. Wave troughs may be set up in this way on the lee side of low hills (see Figure 6.13) as well as major mountain...

C Precipitation and the moisture balance

Longitudinal influences are apparent in the distribution of annual precipitation, although this is in large measure a reflection of the topography. The 600-mm annual isohyet in the United States approximately follows the 100 W meridian (Figure 10.19), and westward to the Rockies is an extensive dry belt in the rain shadow of the western mountain ranges. In the southeast, totals exceed 1250 mm, and 1000 mm or more is received along the Atlantic coast as far north as New Brunswick and...

Frontogenesis

The first real advance in our understanding of mid-latitude weather variations was made with the discovery that many of the day-to-day changes are associated with the formation and movement of boundaries, or fronts, between different airmasses. Observations of the temperature, wind direction, humidity and other physical phenomena during unsettled periods showed that discontinuities often persist between impinging airmasses of differing characteristics. The term 'front' for these surfaces of...

El Nio And The Southern Oscillation

El Ni o episodes of warm coastal currents with accompanying disastrous consequences for marine life and birds recur about every four to seven years and consequently were long known along the west coast of South America. The related Southern Oscillation (SO) of sea-level pressure between Tahiti (normally high pressure) and Jakarta (or Darwin) (normally low pressure) was identified by Sir Gilbert Walker in 1910 and reinvestigated in the mid-1950s by I. Schell and H. Berlage and in the 1960s by A....

Above the thermocline a Vertical

Meteorological And Oceanographic Process

The major atmosphere-ocean interactive processes (Figure 7.26) involve heat exchanges, evaporation, density changes and wind shear. The effect of these processes is to produce a vertical oceanic layering that is of great climatic significance 1 At the ocean surface, winds produce a thermally mixed surface layer averaging a few tens of metres deep poleward of latitude 60 , 400 m at latitude 40 and 100 to 200 m at the equator. 2 Below the relatively warm mixed layer is the thermocline, a layer in...

Articles

C. (1997) The North American monsoon. Bull. Amer. Met. Soc. 78, 2197-213. Axelrod, D. I. (1992) What is an equable climate Palaeogeogr., Palaeoclim., Palaeoecol. 91, 1-12. Balling, R. C. Jr. (1985) Warm seasonal nocturnal precipitation in the Great Plains of the United States. J. Climate Appl. Met. 24, 1383-7. Barry, R. G. (1963) Aspects of the synoptic climatology of central south England. Met. Mag. 92, 300-8. Barry, R. G. (1967) The prospects for synoptic...

Nature Of The Source Area

Frontal Zone Cross Section

The basic idea of airmass formation is that radiative and turbulent transfers of energy and moisture, between the land or ocean surface and the atmosphere, give rise to Figure 9.1 A schematic height cross-section for the northern hemisphere showing barotropic airmasses and a baroclinic frontal zone (assuming that density decreases with height only). Figure 9.1 A schematic height cross-section for the northern hemisphere showing barotropic airmasses and a baroclinic frontal zone (assuming that...

Cool ocean currents

Between the western coasts of the continents and the eastern rims of the subtropical high-pressure cells the ocean surface is relatively cold (see Figure 7.33). This is the result of the importation of water from higher latitudes by the dominant currents the slow upwelling (sometimes at the rate of about 1 m in twenty-four hours) of water from intermediate depths due to the Ekman effect (see Chapter 7D.1) and the coastal divergence (see Figure 7.31). This concentration of cold water gently...

Further Reading Books

J. et al. (1995) Images in Weather Forecasting, Cambridge University Press, Cambridge, 499pp. Extensive collection of imagery illustrating all types of synoptic phenomena. Barry, R. G. and Carleton, A. M. (2001) Synoptic and Dynamic Climatology, Routledge, London, 620pp. Browning, K. A. (ed.) (1983) Nowcasting, Academic Press, New York, 256pp. Treats the design of forecast systems, new remote sensing tools, and simple and numerical forecasts. Conway, E. D. and the Maryland Space grant...

Teleconnections

Teleconnections are defined as linkages over great distances of atmospheric and oceanic variables clearly the linkages between climatic conditions in the eastern and western tropical Pacific Ocean represent a 'canonical' teleconnection. Figure 11.52 illustrates the coincidence of ENSO events with regional climates that are wetter or drier than normal. In Chapter 7C.1, we have referred to Walker's observed teleconnection between ENSO events and the lower than normal monsoon rainfall over South...

C Human heat production

Numerous studies show that urban conurbations now produce energy through combustion at rates comparable with incoming solar radiation in winter. Solar radiation in winter averages around 25 W m-2 in Europe, compared with similar heat production from large cities. Figure 12.26 illustrates the magnitude and spatial scale of artificial and natural energy fluxes and projected increases. In Cincinnati, a significant proportion of the energy budget is generated by human activity, even in summer (see...

Coalescence theories

Theories of raindrop growth use collision, coalescence and 'sweeping' as the growth mechanisms. It was originally thought that cloud particle collisions due to atmospheric turbulence would cause a significant proportion to coalesce. However, particles break up just as easily if subject to collisions. Langmuir offered a variation of this simple idea. He pointed out that falling drops have terminal velocities (typically 1 to 10 cm s-1) directly related to their diameters, such that the larger...

Diurnal variations

Diurnal weather variations are particularly evident at coastal locations in the trade wind belt and in the Indonesia-Malaysian Archipelago. Land and sea breeze regimes (see Chapter 6C.2) are well developed, as the heating of tropical air over land can be up to five times that over adjacent water surfaces. The sea breeze normally sets in between 08 00 and 11 00 hours, reaching a maximum velocity of 6 to 15 m s-1 about 13 00 to 16 00 and subsiding around 20 00. It may be up to 1000 to 2000 m in...

Formation Of Precipitation

The puzzle of raindrop formation has already been noted. The simple growth of cloud droplets by condensation is apparently an inadequate mechanism and more complex processes have to be envisaged. Various early theories of raindrop growth can be discounted. Proposals were that differently charged droplets could coalesce by electrical attraction, but it appears that distances between drops are too great and the difference between the electrical charges too small for this to happen. It was...

Preface to the eighth edition

When the first edition of this book appeared in 1968, it was greeted as being 'remarkably up to date' (Meteorological Magazine). Since that time, several new editions have extended and sharpened its description and analysis of atmospheric processes and global climates. Indeed, succeeding prefaces provide a virtual commentary on recent advances in meteorology and climatology of relevance to students in these fields and to scholars in related disciplines. This revised and expanded eighth edition...

Tropical urban climates

A striking feature of recent and projected world population growth is the relative increase in the tropics and subtropics. Today there are thirty-four world cities with more than five million people, twenty-one of which are in the less-developed countries. By ad 2025 it is predicted that, of the thirteen cities that will have populations in the twenty to thirty-million range, eleven will be in less-developed countries (Mexico City, Sao Paulo, Lagos, Cairo, Karachi, Delhi, Bombay, Calcutta,...

Numerical models of the general circulation climate and weather prediction

When you have read this chapter you will Know the basic features of atmospheric general circulation models GCMs , Understand how simulations of the atmospheric circulation and its characteristics are performed, Be familiar with the basic approaches to weather forecasting on different time scales. Fundamental changes in our understanding of the complex behaviour of the atmosphere and climate processes have been obtained over the past three decades through the development and application of...

Satellite Meteorology

The launching of meteorological satellites revolutionized meteorology, in terms of the near-global view they provided of synoptic weather systems see Plate H . The first meteorological satellite transmitted pictures on 1 April I960. The early television and infra-red observing satellites TIROS carried photographic camera systems and, due to their spin about an axis parallel to the earth's surface, they photographed the surface only part of the time. The types of images that were collected had...

Urban Climates

There was recognition of the role of cities in modifying local climate during the 1920s and 1930s. In his classic book Climate near the Ground Rudolf Geiger drew attention to many such findings. However, dedicated urban climate studies began in the 1950s. To supplement data from the few existing city weather stations, T. J. Chandler examined urban-rural temperature differences around London, England, at different times of the day and year by making traverses in an instrumented vehicle. By...

Topographic effects

In various parts of Europe, topography has a marked effect on the climate, not only of the uplands themselves but also of adjacent areas. Apart from the more obvious effects on temperatures, precipitation amounts and winds, the major mountain masses also affect the movement of frontal systems. Frictional drag over mountain barriers increases the slope of cold fronts and decreases the slope of warm fronts, so that the latter are slowed down and the former accelerated. The Scandinavian mountains...

Potential Evapotranspiration Precipitation

Figure 4.7 The average annual moisture budget for stations in western, central and eastern Britain determined by Thornthwaite's method. When potential evaporation exceeds precipitation soil moisture is used at Berkhamsted in central England and Southend on the east coast, this is depleted by July to August. Autumn precipitation excess over potential evaporation goes into replenishing the soil moisture until field capacity is reached. Source From Howe 1956 . Reprinted from Weather, by permission...

Multiples Of Shelter Belt Height

Figure 12.13 The influence of shelter belts on wind-velocity distributions expressed as percentages of the velocity in the open . A The effects of one shelter belt of three different densities, and of two back-coupled medium-dense shelter belts. B The detailed effects of one half-solid shelter belt. Sources A After Nageli, and Geiger 1965 . B After Bates and Stoeckeler, and Kittredge 1948 . c Modification of the humidity environment The humidity conditions within forest stands contrast...

Discussion Topics

What are the essential differences between mesoscale and synoptic scale systems Using an appropriate website with synoptic weather maps see Appendix 4D , trace the movement of frontal and non-frontal lows troughs and high-pressure cells over a five-day period, determining rates of displacement and changes of intensity of the systems. In the same manner, examine the relationship of surface lows and highs to features at the 500-mb level. Consider the geographical distribution and seasonal...

Synoptic anomalies

The mean climatic features of pressure, wind and seasonal airflow regime provide only a partial picture of climatic conditions. Some patterns of circulation occur irregularly and yet, because of their tendency to persist for weeks or even months, form an essential element of the climate. Blocking patterns are an important example. It was noted in Chapter 7 that the zonal circulation in mid-latitudes sometimes breaks down into a cellular pattern. This is commonly associated with a split of the...

Cyclonic type precipitation

Precipitation characteristics vary according to the type of low-pressure system and its stage of development, but the essential mechanism is ascent of air through horizontal convergence of airstreams in an area of low pressure see Chapter 6B . In extra-tropical depressions, this is reinforced by uplift of warm, less dense air along an airmass boundary see Chapter 9D.2 . Such depressions give moderate and generally continuous precipitation over very extensive areas as they move, usually...

Acknowledgements

J. Dunn for his considerable contribution to the first edition the late Professor F. Kenneth Hare of the University of Toronto, Ontario, for his thorough and authoritative criticism of the preliminary text and his valuable suggestions Alan Johnson, formerly of Barton Peveril School, Eastleigh, Hampshire, for helpful comments on Chapters 2 to 6 and to Dr C. Desmond Walshaw, formerly of the Cavendish Laboratory, Cambridge, and R. H. A. Stewart of the Nautical...

Midlatitude synoptic and mesoscale systems

When you have read this chapter you will Understand the airmass concept, the characteristics of the major airmasses and their geographical occurrence, Know the mechanisms of frontogenesis and the various frontal types, Understand the relationships between upper air and surface processes in forming frontal cyclones, Know the major types of non-frontal cyclone and how they form, Be familiar with the role of mesoscale convective systems in severe weather. This chapter examines the classical ideas...

Atmosphere Weather and Climate

Chorley Taylor amp Francis Croup LONDON AND NEW YORK First published 1968 by Methuen amp Co. Ltd Eighth edition 2003 by Routledge 11 New Fetter Lane, London EC4P 4EE Simultaneously published in the USA and Canada by Routledge 29 West 35th Street, New York, NY 10001 Routledge is an imprint of the Taylor amp Francis Group This edition published in the Taylor amp Francis e-Library, 2004. 1968, 1971, 1976, 1982, 1987, 1992, 1998, 2003 Roger G. Barry and Richard J....

Circulations in the vertical and horizontal planes

There are two possible ways in which the atmosphere can transport heat and momentum. One is by circulation in the vertical plane as indicated in Figure 7.18, which shows three meridional cells in each hemisphere. The low-latitude Hadley cells were considered to be analogous to the convective circulations set up when a pan of water is heated over a flame and are referred to as thermally direct cells. Warm air near the equator was thought to rise and generate a low-level flow towards the equator,...

G Thunderstorms Development

In mid-latitudes the most spectacular example of moisture changes and associated energy releases in the atmosphere is the thunderstorm. Extreme upward and downward movements of air are both the principal ingredients and motivating machinery of such storms. They occur 1 due to rising cells of excessively heated moist air in an unstable airmass 2 through the triggering of conditional instability by uplift over mountains or 3 through mesoscale circulations or lifting along convergence lines see p....

Divergence

Different types of horizontal flow are shown in Figure 6.6A. The first panel shows that air may accelerate decelerate , leading to velocity divergence convergence . When streamlines lines of instantaneous air motion spread out or squeeze together, this is termed diffluence or confluence, respectively. If the streamline pattern is strengthened by that of the isotachs lines of equal wind speed , as shown in the third panels of Figure 6.6A, then there may be mass divergence or convergence at a...

Rption

10 20 40 60 100 400 1000 4 000 10.000 10 20 40 60 100 400 1000 4 000 10.000 Figure 3.6 Percentage of reflection, absorption and transmission of solar radiation by cloud layers of different thickness. Source From Hewson and Longley 1944 . Reprinted with permission. Copyright CRC Press, Boca Raton, Florida. 2 90 S 60 S 30 S Eq 30'N 60N 90N Figure 3.7 The average receipt of solar radiation with latitude at the top of the atmosphere and at the earth's surface during the June solstice. The effect of...

Interior and eastern North America

Central North America has the typical climate of a continental interior in mid-latitudes, with hot summers and cold winters Figure 10.17 , yet the weather in winter is subject to marked variability. This is determined by the steep temperature gradient between the Gulf of Mexico and the snow-covered northern plains also by shifts of the upper wave patterns and jet stream. Cyclonic activity in winter is much more pronounced over central and eastern North America than in Asia, which is dominated...

Discovery Of The Tropopause And Stratosphere

Early scientific exploration of the upper atmosphere began with manned balloon flights in the mid-nineteenth century. Notable among these was the ascent by J. Glaisher and H. T. Coxwell in 1862. Glaisher last consciousness due to lack of oxygen at about 8800-m altitude and they barely survived the hypoxia. In 1902 L. Teisserenc de Bort in France reported a totally unexpected finding that temperatures ceased decreasing at altitudes of around 12 km. Indeed, at higher elevations temperatures were...

Terrestrial Infrared Radiation And The Greenhouse Effect

Radiation from the sun is predominantly short-wave, whereas that leaving the earth is long-wave, or infra-red, radiation see Figure 3.1 . The infra-red emission from the surface is slightly less than that from a black body at the same temperature and, accordingly, Stefan's Law see p. 33 is modified by an emissivity coefficient e , which is generally between 0.90 and 0.95, i.e. F eoT4. Figure 3.1 shows that the atmosphere is highly absorbent to infra-red radiation due to the effects of water...

Short green crops

Crop Height And Transpiration

Short green crops, up to a metre or so in height, supplied with sufficient water and exposed to similar solar radiation conditions, all have a similar net radiation Rn balance. This is largely because of the small range of albedos, 20 to 30 per cent for short green crops compared with 9 to 18 per cent for forests. Canopy structure appears to be the primary reason for this albedo difference. General figures for rates of energy dispersal at noon on a June day in a 20-cm high stand of grass in the...

Rock and sand

The energy exchanges of dry desert surfaces are relatively simple. A representative diurnal pattern of energy exchange over desert surfaces is shown in Figure 12.3. The 2-m air temperature varies between 17 and 29 C, although the surface of the dry lake-bed reaches 57 C at midday. Rn reaches a maximum at about 13 00 hours when most of the heat is transferred to the air by turbulent convection in the early morning the heating goes into the ground. At night, this soil heat is returned to the...

Forests

Wind Profiles And Forests

The vertical structure of a forest, which depends on the species composition, the ecological associations and the age of the stand, largely determines the forest microclimate. The climatic influence of a forest may be explained in terms of the geometry of the forest, including morphological characteristics, size, cover, age and stratification. Morphological characteristics include amount of branching bifurcation , the periodicity of growth i.e. evergreen or deciduous , together with the size,...

A Continental and oceanic influences

Fog Effect

The large annual temperature range in the interior of the continent shown in Figure 3.24 demonstrates the pattern of continentality of North America. The figure illustrates the key role of the distance from the ocean in the direction of the prevailing westerly winds. The topographic barriers of the western Cordilleras limit the inland penetration of maritime airstreams. On a more local scale, inland water bodies such as Hudson Bay and the Great Lakes have a small moderating influence -cooling...

Tropical weather and climate

When you have read this chapter you will Understand the characteristics and significance of the intertropical convergence zone, Be familiar with the principal weather systems that occur in low latitudes and their distribution, Know some of the diurnal and local effects that influence tropical weather, Know where and how tropical cyclones tend to occur, Understand the basic mechanisms and characteristics of El Ni o and La Ni a events. Tropical climates are of especial geographical interest...

Midlatitude Disturbances

Theoretical ideas about the atmosphere and its weather systems evolved in part through the needs of nineteenth-century mariners for information about winds and storms, especially predictions of future behaviour. At low levels in the westerly belt approximately 40 to 70 latitude there is a complex pattern of moving high and low pressure systems, while between 6000 m and 20,000 m there is a coherent westerly airflow. Dove 1827 and 1828 and Fitz Roy 1863 supported the 'opposing current' theory of...

Mean upperair patterns

Global Waerming Wheatrher Pattern

The patterns of pressure and wind in the middle troposphere are less complicated in appearance than at the surface as a result of the diminished effects of the landmasses. Rather than using pressure maps at a particular height, it is convenient to depict the height of a selected pressure surface this is termed a contour chart by analogy with topographic relief map see Note 1 . Figure 7.3 and 7.4 show that in the middle troposphere of the southern hemisphere there is a vast circumpolar Figure...

Info

Volcanic Activity 1600 1700

M i i i i i i i i i i i I i l i i i ' i i i i r i i 11 i i i i i i i i i l 1300 1400 1500 1600 1700 i h i i i ri It i i i i i I n i i l l m i i i i i i i i i i i I i l i i i ' i i i i r i i 11 i i i i i i i i i l 1300 1400 1500 1600 1700 i h i i i ri It i i i i i I n i i l l Figure 2.11 Record of volcanic eruptions in the GISP 2 ice core and calibrated visible optical depth for ad 1300 to 2000, together with the names of major volcanic eruptions. Note that the record reflects eruptions in the...

British airflow patterns and their climatic characteristics

Continentality Britain

The daily weather maps for the British Isles sector 50 to 60 N, 2 E to 10 W from 1873 to the present day have been classified by H. H. Lamb according to the airflow direction or isobaric pattern. He identified seven major categories westerly W , northwesterly NW , northerly N , easterly E and southerly S types Figure 10.2 Continentality in Europe. The indices of Gorczynski dashes and Berg solid lines are explained in the text. Source Partly after Bluthgen 1966 . Figure 10.2 Continentality in...

Air Stability And Instability

Tephigram Unstable Air

If stable unstable air is forced up or down it has a tendency to return to continue to move away from its former position once the motivating force ceases. Figure 5.3 shows the reason for this important characteristic. The environment temperature curve A lies to the right of any path curve representing the lapse rate of an unsaturated air parcel cooling dry adiabatically when forced to rise. At any level, the rising parcel is cooler and more dense than its surroundings and therefore tends to...

Mountain and valley winds

Valley Climate Day Anabatic Breeze

Terrain features give rise to their own special meteorological conditions. On warm, sunny days, the heated air in a valley is laterally constricted, compared with that over an equivalent area of lowland, and so tends to expand vertically. The volume ratio of lowland valley air is typically about 2 or 3 1 and this difference in heating sets up a density and pressure differential, which causes air to flow from the lowland up the axis of the valley. This valley wind Figure 6.10 is generally light...

Condensation Level

Figure 5.2 illustrates an important property of the tephigram. A line along a dry adiabat 6 through the dry-bulb temperature of the surface air TA , an isopleth of saturation mixing ratio xs through the dew-point Td , and a saturated adiabat 6w through the wet-bulb temperature Tw , all intersect at a point corresponding to saturation for the airmass. This relationship, known Figure 5.2 Graph showing the relationships between temperature T , potential temperature 6 , wet-bulb potential...

Boundary layer

Ekman Boundary Layer Convergence

The last force that has an important effect on air movement is that due to friction from the earth's surface. Towards the surface i.e. below about 500 m for flat terrain , friction begins to reduce the wind velocity below its geostrophic value. The slowing of the wind towards the surface modifies the deflective force, which is dependent on velocity, causing it also to decrease. Initially, the frictional force is opposite to the wind velocity, but in a balanced state - when the velocity and...

The Intertropical Convergence

Streamline Convergence

The tendency for the trade wind systems of the two hemispheres to converge in the equatorial low-pressure trough has already been noted see Chapter 7B . Views on the exact nature of this feature have been subject to continual revision. From the 1920s to the 1940s, the frontal concepts developed in mid-latitudes were applied in the tropics, and the streamline confluence of the northeast and southeast trades was identified as the intertropical front ITF . Over continental areas such as West...

Autumn

India Retreating Monsoon

Autumn sees the southward swing of the equatorial trough and the zone of maximum convection, which lies immediately to the north of the weakening easterly jet see Figure 11.16 . The breakup of the summer circulation systems is associated with the withdrawal of the monsoon rains, which is much less clearly defined than their onset Figure 11.34 . By October, the easterly trades of the Pacific affect the Bay of Bengal at the 500mb level and generate disturbances at their confluence with the...

Mean Sea Level Pressure Wind.sp

Thus, at any given pressure, an increase in temperature causes a decrease in density, and vice versa. Air is highly compressible, such that its lower layers are much more dense than those above. Fifty per cent of the total mass of air is found below 5 km see Figure 2.13 , and the average density decreases from about 1.2 kg m-3 at the surface to 0.7 kg m-3 at 5000 m approximately 16,000 ft , close to the extreme limit of human habitation. Pressure is measured as a force per unit area. A force of...

Fronts Jet Streams And The Tropopause 1990 Qeii

E. 1952 Characteristics of air masses over the British Isles. Meteorological Office, Geophysical Memoirs 11 87 , 34pp. Bennetts, D. A., Grant, J. R. and McCallum, E. 1988 An introductory review of fronts Part I Theory and observations. Met. Mag. 117, 357-70. Blanchard, D. O. 1990 Mesoscale convective patterns of the southern High Plains. Bull. Amer. Met. Soc., 71 7 , 994-1005. Boucher, R. J. and Newcomb, R. J. 1962 Synoptic interpretation of some TIROS vortex patterns a preliminary...

Southern Africa

Southern Africa lies between the South Atlantic and Indian Ocean subtropical high-pressure cells in a region subject to the interaction of tropical easterly and extratropical westerly airflows. Both of these high-pressure cells shift west and intensify see Figure 7.10 in the southern winter. Because the South Atlantic cell always extends 3 latitude further north than the Indian Ocean cell, it brings low-level westerlies to Angola and Zaire at all seasons and high-level westerlies to central...

The temperate west coast and Cordillera

Cordillera Climate Chart

The oceanic circulation of the North Pacific closely resembles that of the North Atlantic. The drift from the Kuroshio current off Japan is propelled by the westerlies towards the west coast of North America and it acts as a warm current between 40 and 60 N. Sea-surface temperatures are several degrees lower than in comparable latitudes off western Europe, however, due to the smaller volume of warm water involved. In addition, in contrast to the Norwegian Sea, the shape of the Alaskan coastline...

Winter

Air Flow Over India During Winter

Near the surface, this is the season of the out-blowing 'winter monsoon', but aloft westerly airflow dominates. This reflects the hemispheric pressure distribution. A shallow layer of cold high-pressure air is centred over the continental interior, but this has disappeared even at 700 mb see Figure 7.4 where there is a trough over East Asia and zonal circulation over the continent. The upper westerlies split into two currents to the north and south of the high Tibetan Qinghai-Xizang Plateau 10...

The Global Wind Belts

The importance of the subtropical high-pressure cells is evident from the above discussion. Dynamic, rather than immediately thermal, in origin, and situated between 20 and 30 latitude, they seem to provide the key to the world's major wind belts, shown by the maps in Figure 7.12. In the northern hemisphere, the pressure gradients surrounding these cells are strongest between October and April. In terms of actual pressure, however, oceanic cells experience their highest pressure in summer, the...

D Heat islands

Heat Island Chandler

The net effect of urban thermal processes is to make city temperatures in mid-latitudes generally higher than in the surrounding rural areas. This is most pronounced after sunset during calm, clear weather, when cooling rates in the rural areas greatly exceed those in the urban areas. The energy balance differences that cause this effect depend on the radiation geometry and thermal Table 12.2 Energy budget figures W m-2 for the Cincinnati region during the summer of 1968. Table 12.2 Energy...

Pressure systems

Pressure Systems Map Asia

The mean pressure pattern for the middle troposphere displays a prominent trough over eastern North America in both summer and winter see Figures 7.3A and 7.4A . In part, this is a lee trough caused by the effect of the western mountain ranges on the upper westerlies, but at least in winter the strong baroclinic zone along the East Coast of the continent is a major contributory factor. As a result of this mean wave pattern, cyclones tend to move southeastward over the Midwest, carrying...

Central And Southern Africa

Equatorial Westerlies Rain Summer

The annual climatic regime over West Africa has many similarities to that over South Asia, the surface airflow being determined by the position of the leading edge of a monsoon trough see Figure 11.2 . This airflow is southwesterly to the south of the trough and easterly to northeasterly to its north Figure 11.38 . The major difference between the circulations of the two regions is due largely to the differing geography of the land to sea distribution and to the lack of a large mountain range...

Atmospheric Energy And Horizontal Heat Transport

Poleward Heat Transfer

So far, we have given an account of the earth's heat budget and its components. We have already referred to two forms of energy internal or heat energy, due to the motion of individual air molecules, and latent energy, which is released by condensation of water vapour. Two other forms of energy are important geopotential energy due to gravity and height above the surface, and kinetic energy associated with air motion. Geopotential and internal energy are interrelated, since the addition of heat...

Early summer

Severe Midlatitude Climate

Generally, during the last week in May the southern branch of the high-level jet begins to break down, becoming intermittent and then gradually shifting northward over the Tibetan Plateau. At 500 mb and below, however, the plateau exerts a blocking effect on the flow and the jet axis there jumps from the south to the north side of the plateau from May to June. Over India, the equatorial trough pushes northward with each weakening of the upper westerlies south of Tibet, but the final burst of...

East Asian And Australian Summer Monsoons

China has no equivalent to India's hot, pre-monsoon season. The low-level, northeasterly winter monsoon reinforced by subsiding air from the upper westerlies persists in north China, and even in the south it begins to be replaced by maritime tropical air only in April to May. Thus at Guangzhou Canton , mean temperatures rise from only 17 C in March to 27 C in May, some 6 C lower than the mean values over northern India. Westerly depressions are most frequent over China in spring see Figure...

Modification of surface characteristics a Airflow

Effect Roughness Windspeed

On average, city wind speeds are lower than those recorded in the surrounding open country owing to the sheltering effect of the buildings. Average city-centre wind speeds are usually at least 5 per cent less than those of the suburbs. However, the urban effect on air motion varies greatly depending on the time of day and the season. During the day, city wind speeds are Figure 12.29 Details of urban airflow around two buildings of differing size and shape. Numbers give relative wind speeds...

B Other tropical disturbances

Not all low-pressure systems in the tropics are of the intense tropical cyclone variety. There are two other major types of cyclonic vortex. One is the monsoon depression that affects South Asia during the summer. This disturbance is somewhat unusual in that the flow is westerly at low levels and easterly in the upper troposphere see Figure 11.27 . It is described more fully in C.4, this chapter. The second type is usually relatively weak near the surface, but well developed in the middle...

Condensation nuclei

Hygroscopic Nuclei

Remarkably, condensation occurs with utmost difficulty in clean air moisture needs a suitable surface upon which it can condense. If clean air is cooled below its dew-point it becomes supersaturated i.e. relative humidity exceeding 100 per cent . To maintain a pure water drop of radius 10-7 cm 0.001 mm requires a relative humidity of 320 per cent, and for one of radius 10-5 cm 0.1 mm only 101 per cent. Usually, condensation occurs on a foreign surface this can be a land or plant surface in the...

Tropical cloud clusters

Mesoscale convective systems MCSs are widespread in tropical and subtropical latitudes. The mid-latitude mesoscale convective complexes discussed in Chapter 9.I are an especially severe category of MCS. Satellite studies of cold high cloud-top signatures show that tropical systems typically extend over a 3000 to 6000 km2 area. They are common over tropical South America and the maritime continent of Indonesia-Malaysia and adjacent western equatorial Pacific Ocean warm pool. Other land areas...

Zones Of Wave Development And Frontogenesis

Advection Potential Absolute Vorticity

Fronts and associated depressions tend to develop in well-defined areas. The major zones of frontal-wave development are areas that are most frequently baro-clinic as a result of airstream confluence Figure 9.18 . This is the case off East Asia and eastern North America, especially in winter, when there is a sharp temperature gradient between the snow-covered land and warm offshore currents. These zones are referred to as the Pacific polar and Atlantic polar fronts, respectively Figure 9.19 ....

The polar easterlies

This term is applied to winds that occur between polar high pressure and subpolar low pressure. The polar high, as has already been pointed out, is by no means a quasi-permanent feature of the Arctic circulation. Easterly winds occur mainly on the poleward sides of depressions over the North Atlantic and North Pacific Figure 7.12 . If average wind directions are calculated for entire high-latitude belts there is found to be little sign of a coherent system of polar easterlies. The situation in...

Fundamentals Of The

In the GCM, all dynamic and thermodynamic processes and the radiative and mass exchanges that have been treated in Chapters 2 to 7 are modelled using five basic sets of equations. The basic equations describing the atmosphere are 1 The three dimensional equations of motion i.e. conservation of momentum see Chapter 6A,B . 2 The equation of continuity i.e. conservation of mass or the hydrodynamic equation, p. 118 . 3 The equation of continuity for atmospheric water vapour i.e. conservation of...

Atmospheric moisture budget

When you have read this chapter you will Be familiar with the major atmospheric components of the hydrological cycle, Know the main controls of evaporation and condensation, Be aware of the spatial and temporal characteristics of moisture in the atmosphere, evaporation and precipitation, Know the different forms of precipitation and typical statistical characteristics, Know the major geographical and altitudinal patterns of precipitation and their basic causes, Understand the nature and...

Singularities and natural seasons

Popular weather lore expresses the belief that each season has its own weather for example, in England, 'February fill-dyke' and 'April showers' . Ancient adages suggest that even the sequence of weather may be determined by the conditions established on a given date. For example, forty days of wet or fine weather are said to follow St Swithin's Day 15 July in England sunny conditions on 'Groundhog Day' 2 February are claimed to portend six more weeks of winter in the United States. Some of...

Land and sea breezes

Sea And Land Breezes

Another thermally induced wind regime is the land and sea breeze see Figure 6.11 . The vertical expansion of the air column that occurs during daytime heating over the more rapidly heated land see Chapter 3B.5 tilts the isobaric surfaces downward at the coast, causing onshore winds at the surface and a compensating offshore movement aloft. Typical land-sea pressure differences are of the order of 2 mb. At night, the air over the sea is warmer and the situation is reversed, although this...

Surface Receipt Of Solar Radiation And Its Effects

1 Energy transfer within the earth-atmosphere system So far, we have described the distribution of solar radiation as if it were all available at the earth's surface. This is, of course, unrealistic because of the effect of the atmosphere on energy transfer. Heat energy can be transferred by three mechanisms 1 Radiation Electromagnetic waves transfer energy both heat and light between two bodies, without the necessary aid of an intervening material medium, at a speed of300 X 106m s-1 i.e. the...

Radar Meteorology

Radio detection and ranging radar , developed for aircraft detection during the Second World War, was swiftly applied to tracking precipitation areas from the radar echoes. Radio waves transmitted by an antenna in the cm wavelength range typically 3 and 10 cm are back-scattered by raindrops and ice particles, as well as by cloud droplets, particulates, insect swarms and flocks of birds. The return signal and its time delay provide information on the objects in the path of the beam and their...

The vertical variation of pressure systems

The air pressure at the surface, or at any level in the atmosphere, depends on the weight of the overlying air column. In Chapter 2B, we noted that air pressure is proportional to air density and that density varies inversely with air temperature. Accordingly, increasing the temperature of an air column between the surface and, say, 3 km will reduce the air density and therefore lower the air pressure at the surface without affecting the pressure at 3 km altitude. Correspondingly, if we compare...

A The Arctic

Eurasian Arctic Weather

At 75 N, the sun is below the horizon for about ninety days, from early November until early February. Winter air temperatures over the Arctic Ocean average about -32 C, but they are usually 10-12 C higher some 1000 m above the surface as a result of the strong radiative temperature inversion. The winter season is generally stormy in the Eurasian sector, where low-pressure systems enter the Arctic Basin from the North Atlantic, whereas anticyclonic conditions predominate north of Alaska over...

The centripetal acceleration

Supergeostrophic Winds

Observations in the free atmosphere above the level affected by surface friction up to about 500 to 1000 m show that the wind blows more or less at right angles to the pressure gradient i.e. parallel to the isobars with, for the northern hemisphere, high pressure on the right and low pressure on the left when viewed downwind. This implies that for steady motion the pressure-gradient force is balanced exactly by the Coriolis deflection acting in the diametrically opposite direction Figure 6.3A ....

Condensation Levell

Mixing Condensation Level

Figure 5.4 Schematic adiabatic chart used to determine the convective condensation level see p. 91 . T0 represents the early morning temperature Tp T2 and T3 illustrate daytime heating of the surface air. downward it will warm at the dry adiabatic rate the parcel will always be warmer and less dense than the surrounding air, and tend to return to its former position unless prevented from doing so . However, if local surface heating causes the environmental lapse rate near the surface to exceed...

Oceanicity and continentality

Winter temperatures in northwest Europe are some 11 C or more above the latitudinal average see Figure 3.18 , a fact usually attributed to the presence of the North Atlantic current. There is, however, a complex interaction between the ocean and the atmosphere. The current, which originates from the Gulf Stream off Florida strengthened by the Antilles current, is primarily a wind-driven current initiated by the prevailing south-westerlies. It flows at a velocity of 16 to 32 km per day and thus,...

Mesoscale Convective Systems

Linear Mesoscale Convective Complex

Mesoscale convective systems MCSs are intermediate in size and life span between synoptic disturbances and individual cumulonimbus cells see Figure 9.26 . Figure 9.27 shows the movement of clusters of convective cells, each cell about 1 km in diameter, as they crossed southern Britain with a cold front. Each individual cell may be short-lived, but cell clusters may persist for hours, strengthening or weakening due to orographic and other factors. MCSs occur seasonally in middle latitudes...

Solar Radiation

Main Atmospheric Absorption Bands

The source of the energy injected into our atmosphere is the sun, which is continually shedding part of its mass by radiating waves of electromagnetic energy and high-energy particles into space. This constant emission represents all the energy available to the earth except for a small amount emanating from the radioactive decay of earth minerals . The amount of energy received at the top of the atmosphere is affected by four factors solar output, the sun-earth distance, the altitude of the...

The polar regions

Common to both polar regions is the semi-annual alternation between polar night and polar day, and the prevalence of snow and ice surfaces. These factors control the surface energy budget regimes and low annual temperatures see Chapter 10B . The polar regions are also energy sinks for the global atmospheric circulation see Chapter 7C.1 , and in both cases they are overlain by large-scale circulation vortices in the middle troposphere and above see Figures 7.3 and 7.4 . In many other respects,...

North Africa

High Pressure System Inflow Jet Stream

The dominance of high-pressure conditions in the Sahara is marked by the low average precipitation in this region. Over most of the central Sahara, the mean annual precipitation is less than 25 mm, although the high plateaux of the Ahaggar and Tibesti receive over 100 mm. Parts of western Algeria have gone at least two years without more than 0.1 mm of rain in any twenty-four-hour period, and most of southwest Egypt as much as five years. However, twenty-four-hour storm rainfalls approaching 50...

A Hurricanes and typhoons

Cumulonimbus Clouds Air Circulation

The most notorious type of cyclone is the hurricane or typhoon . Some eighty or so cyclones each year are responsible, on average, for 20,000 fatalities, as well as causing immense damage to property and a serious shipping hazard, due to the combined effects of high winds, high seas, flooding from the heavy rainfall and coastal storm surges. Considerable attention has been given to forecasting their development and movement, so their origin and structure are beginning to be understood....

Winter Monsoon Season

Japan Shurin Weather

Figure 11.36 A Seasonal variation of daily normals at Nagoya, southern Japan, suggesting six natural seasons. B Average ten-day precipitation amounts for a station in southern Japan, indicating in black the proportion of rainfall produced by typhoon circulations. The latter reaches a maximum during the Shurin season. Sources A From Maejima 1967 B after Saito 1959 , from Trewartha 98I . during late July and August, giving a period of more settled sunny weather. The secondary precipitation...

A Zonal index variations

Air Circulation Index Cycle

Variations of three to eight weeks' duration are observed in the strength of the zonal westerlies, averaged around the hemisphere. They are rather more noticeable in the winter months, when the general circulation is strongest. The nature of the changes is illustrated schematically in Figure 7.23. The mid-latitude westerlies develop waves, and the troughs and ridges become accentuated, ultimately splitting up into a cellular pattern with pronounced meridional flow at certain longitudes. The...

The earths rotational deflective Coriolis force

Coriolis Effect Chemistry

The Coriolis force arises from the fact that the movement of masses over the earth's surface is referenced to a moving co-ordinate system i.e. the latitude and Figure 6.1 The Coriolis deflecting force operating on an object moving outward from the centre of a rotating turntable. Figure 6.1 The Coriolis deflecting force operating on an object moving outward from the centre of a rotating turntable. longitude grid, which 'rotates' with the earth . The simplest way to visualize how this deflecting...

Airmass Modification

As an airmass moves away from its source region it is affected by different heat and moisture exchanges with the ground surface and by dynamic processes in the atmosphere. Thus a barotropic airmass is gradually changed into a moderately baroclinic airstream in which isosteric and isobaric surfaces intersect one another. The presence of horizontal temperature gradients means that air cannot travel as a solid block maintaining an unchanging internal structure. The trajectory i.e. actual path...

B Gases

As well as particulate pollution produced by urban and industrial activities involving coal and coke combustion, there is the associated generation of pollutant gases. Before the Clean Air Act in the UK, it was estimated that domestic fires produced 80 to 90 per cent of London's smoke. However, these were responsible for only 30 per cent of the sulphur dioxide released into the atmosphere - the remainder being contributed by electricity power-stations 41 per cent and factories 29 per cent ....

SUMMARY

Ideal airmasses are defined in terms of barotropic conditions, where isobars and isotherms are assumed to be parallel to each other and to the surface. The character of an airmass is determined by the nature of the source area, changes due to airmass movement, and its age. On a regional scale, energy exchanges and vertical mixing lead to a measure of equilibrium between surface conditions and those of the overlying air, particularly in quasi-stationary high-pressure systems. Airmasses are...

The southern westerlies

Heavy Rainfall West Southern Alps

The strong zonal airflow in the belt of the southern westerlies, which is apparent only on mean monthly maps, is associated with a major frontal zone characterized Figure 10.33 Main climatological features of Australasia and the southwest Pacific. Areas with gt 100 mm January and gt 50 mm July mean monthly precipitation for Australia are also shown. Source After Steiner, from Salinger et al. 1995 , copyright John Wiley amp Sons Ltd. Reproduced with permission. Figure 10.33 Main climatological...

Surface pressure conditions

The most permanent features of the mean sea-level pressure maps are the oceanic subtropical high-pressure cells Figures 7.9 and 7.10 . These anticyclones are located at about 30 latitude, suggestively situated below the mean subtropical jet stream. They move a few degrees equatorward in winter and poleward in summer in response to the seasonal expansion and contraction of the two circumpolar vortices. In the northern hemisphere, the subtropical ridges of high pressure weaken over the heated...

Vorticity

Vorticity And Weather

Vorticity implies the rotation, or angular velocity, of small imaginary parcels in any fluid. The air within a low-pressure system may be regarded as comprising an infinite number of small air parcels, each rotating cyclonically about an axis vertical to the earth's surface Figure 6.8 . Vorticity has three elements - magnitude defined as twice the angular velocity, Q see Note 3 , Figure 6.7 Cross-section of the patterns of vertical motion associated with mass divergence and convergence in the...