Atmospheric Science for Environmental Scientists

C. Nick Hewitt, Andrea V. Jackson

• Publisher: Wiley-Blackwell
• Year: 2019
• ISBN:
  9781119515272
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Meteorology & Climatology

Enlightens readers on the realities of global atmospheric change, including global warming and poor air quality

Climate change and air pollution are two of the most pressing issues facing Mankind. This book gives undergraduate and graduate students, researchers and professionals working in the science and policy of pollution, climate change and air quality a broad and up-to-date account of the processes that occur in the atmosphere, how these are changing as Man's relentless use of natural resources continues, and what effects these changes are having on the Earth's climate and the quality of the air we breathe.

Written by an international team of experts, Atmospheric Science for Environmental Scientists, 2 nd Edition provides an excellent overview of our current understanding of the state of the Earth's atmosphere and how it is changing. The first half of the book covers: the climate of the Earth; chemical evolution of the atmosphere; atmospheric energy and the structure of the atmosphere; biogeochemical cycles; and tropospheric chemistry and air pollution. The second half looks at cloud formation and chemistry; particulate matter in the atmosphere; stratospheric chemistry and ozone depletion; boundary layer meteorology and atmospheric dispersion; urban air pollution; and global warming and climate change science.

• Provides succinct but detailed information on all the important aspects of atmospheric science for students
• Offers the most up-to-date treatment of key issues such as stratospheric chemistry, urban air pollution, and climate change
• Each chapter includes basic concepts, end-of-section questions, and more in-depth material
• Features contributions from the best experts and educators in the field of atmospheric science

Atmospheric Science for Environmental Scientists, 2 nd Edition is an invaluable resource for students, teachers, and professionals involved in environmental science. It will also appeal to those interested in learning how the atmosphere works, how humankind is changing its composition, and what effects these changes are leading to.

1
The Climate of the Earth

John Lockwood

Formerly University of Leeds, Leeds, United Kingdom

The causes, history, and distributions of the Earth's climates are introduced in this chapter. The combination of the distribution of incoming solar radiation across the Earth's surface and the Earth's rotation both drive and shape the observed atmosphere–ocean circulation. Important factors determining changes in climate include palaeogeography, greenhouse gas concentrations, changing orbital parameters, and varying ocean heat transport. One of the major controls of climatic changes is the greenhouse gas concentration of the atmosphere, in particular that of carbon dioxide. Before the Eocene–Oligocene boundary (≈34 Myr ago) the atmosphere–ocean circulation supported a warm atmosphere and ocean, with both poles free of permanent ice. At the Eocene–Oligocene boundary, the atmosphere–ocean circulation changed to a form similar to the present, and the first evidence of an Antarctic ice sheet is found. Falling atmospheric carbon dioxide levels probably caused this change. The waxing and waning of massive temperate latitude continental ice sheets characterize the climate of the past million years. This chapter discusses recent climate changes and evidence that they are largely driven by anthropogenic generated atmospheric carbon dioxide. In particular, recent climate changes are causing the expansion of the tropical zone and a retreat of the polar zones.

The major climate zones of the world are described, with particular attention to interannual variability, and the causes of droughts and heavy rainfalls. This includes discussions of the climatic effects of the North Atlantic Oscillation (NAO) and El Niño‐Southern Oscillation (ENSO).

For more specific information on global warming and climate change science, the reader is referred to Chapter 11 in this book and to the latest reports of the Intergovernmental Panel on Climate Change, available at www.ipcc.ch.

1.1 Basic Climatology

The climate of a particular place is the average state of the atmosphere observed as the weather over a finite period (e.g. a season) for a number of different years. The so‐called climate system, which determines the weather, is a composite system consisting of five major interactive adjoint components: the atmosphere, the hydrosphere, including the oceans, the cryosphere, the lithosphere, and the biosphere (Figure 1.1). All the subsystems are open and not isolated, as the atmosphere, hydrosphere, cryosphere, and biosphere act as cascading systems linked by complex feedback processes. The climate system is subject to two primary external forcings that condition its behaviour: solar radiation and the Earth's rotation. Solar radiation must be regarded as the primary forcing mechanism, as it provides almost all the energy that drives the climate system.

Figure 1.1 The climate system (Houghton 2005).

The distribution of climates across the Earth's surface is determined by its spherical shape, its rotation, the tilt of the Earth's axis of rotation in relation to a perpendicular line through the plane of the Earth's orbit around the Sun, the eccentricity of the Earth's orbit, the greenhouse gas content of the atmosphere, and the nature of the underlying surface. The spherical shape creates sharp north–south temperature differences, whilst the tilt is responsible for month‐by‐month changes in the amount of solar radiation reaching each part of the planet, and hence the variations in the length of daylight throughout the year at different latitudes and the resulting seasonal weather cycle.

The present orbit of the Earth is slightly elliptical with the Sun at one focus of the ellipse, and as a consequence the strength of the solar beam reaching the Earth varies about its mean value. At present, the Earth is nearest to the Sun in January and farthest from the Sun in July. This makes the solar beam near the Earth about 3.5% stronger than the average mean value in January, and 3.5% weaker than average in July. The gravity of the Sun, the Moon, and the other planets causes the Earth to vary its orbit around the Sun (over many thousands of years). Three different cycles are present, and when combined, produce the rather complex changes observed. These cycles affect only the seasonal and geographical distribution of solar radiation on the Earth's surface, yearly global totals remaining constant. Surplus in one season is compensated by a deficit during the opposite one; surplus in one geographical area is compensated by simultaneous deficit in some other zone. Nevertheless, these Earth orbital variations can have a significant effect on climate and are responsible for some major long‐term variations.

Firstly, there are variations in the orbital eccentricity. The Earth's orbit varies from almost a complete circle to a marked ellipse, when it will be nearer to the Sun at one particular season. A complete cycle from near circular through a marked ellipse back to near circular takes between 90 000 and 100 000 years. When the orbit is at its most elliptical, the intensity of the solar beam reaching the Earth must undergo a seasonal range of about 30%. Second, there is a wobble in the Earth's axis of rotation causing a phenomenon known as the precession of the equinoxes. That is to say, within the elliptical orbits just described, the distance between Earth and Sun varies so that the season of the closest approach to the Sun also varies. The complete cycle takes about 21 000 years. Lastly, the tilt of the Earth's axis of rotation relative to the plane of its orbit varies at least between 21.8° and 24.4° over a regular period of about 40 000 years. At present, it is almost 23.44° and is decreasing. The greater the tilt of the Earth's axis, the more pronounced the difference between winter and summer. Technically, these three mechanisms are known as the Milankovitch mechanism.

If the Earth did not rotate relative to the Sun – that is, it always kept the same side towards the Sun – the most likely atmospheric circulation would consist of rising air over an extremely hot, daylight face and sinking air over an extremely cold, night face. The diurnal cycle of heating and cooling obviously would not exist, since it depends on the Earth's rotation. Surface winds everywhere would blow from the cold night face towards the hot daylight face, whilst upper flow patterns would be the reverse of those at lower levels. Whatever the exact nature of the atmospheric flow patterns, the climatic zones on a nonrotating Earth would be totally different from anything observed today. Theoretical studies suggest that if this stationary Earth started to rotate, then as the rate of rotation increased, the atmospheric circulation patterns would be progressively modified until they resembled those observed today. In very general terms, these circulation patterns take the form of a number of meridional overturning cells in the atmosphere, with separate zones of rising air motion at low and middle latitudes, and corresponding sinking motions in subtropical and polar latitudes.

1.2 General Atmospheric Circulation

A schematic representation of the mean meridional circulation between Equator and pole is shown in Figure 1.2. A simple direct circulation cell, known as the Hadley cell, is clearly seen equatorward from 30° latitude (Lockwood 2003). Eastward angular momentum is transported from the equatorial latitudes to the middle latitudes by nearly horizontal eddies, 1000 km or more across, moving in the upper troposphere and lower stratosphere. This transport, together with the dynamics of the middle latitude atmosphere, leads to an accumulation of eastward momentum between 30° and 40° latitude, where a strong meandering current of air, generally known as the subtropical westerly jet stream, develops (Figure 1.3). The cores of the subtropical westerly jet streams in both hemispheres and throughout the year occur at an altitude of about 12 km. The air subsiding from the jet streams forms the belts of subtropical anticyclones at about 30° to 40° N and S (Figure 1.4). The widespread subsidence in the descending limb of the Hadley cell should be contrasted with the rising limb, where ascent is restricted...

Table of contents

• Cover
• Table of Contents
• List of Contributors
• Preface
• Abbreviations, Constants, and Nomenclature
• 1 The Climate of the Earth
• 2 Chemical Evolution of the Atmosphere
• 3 Atmospheric Energy and the Structure of the Atmosphere
• 4 Biogeochemical Cycles
• 5 Tropospheric Chemistry and Air Pollution
• 6 Cloud Formation and Chemistry
• 7 Particulate Matter in the Atmosphere
• 8 Stratospheric Chemistry and Ozone Depletion
• 9 Boundary Layer Meteorology and Atmospheric Dispersion
• 10 Urban Air Pollution
• 11 Global Warming and Climate Change Science
• Appendix: Suggested Web Resources
• Index
• End User License Agreement