CHAPTER 1: THE CLIMATE

CHAPTER 1: THE CLIMATE

Definitions of CLIMATE include the following:

The meteorological conditions, including temperature, precipitation, and wind, that characteristically prevail in a particular region.¹

The composite or generally prevailing weather conditions of a region, as temperature, air pressure, humidity, precipitation, sunshine, cloudiness, and winds, throughout the year, averaged over a series of years.²

The weather conditions prevailing in an area in general or over a long period³.

So weather means ‘Climate conditions which prevail in an area, or quoting the Oxford English dictionary definition:

The state of the atmosphere at a particular place and time as regards heat, cloudiness, dryness, sunshine, wind, rain, etc

The common feature of all these definitions is that both Climate and Weather are essentially local and largely confined to a particular region or area.

A region or area may be quite small (there is even such a thing as a microclimate) and local topography has an important influence on wind and storm patterns.

Some climate properties are regional or even global. Changes in the sun and in the earth’s axis have a global influence. Volcanic eruptions, ocean oscillations and cyclones influence several regions. Local climates can be very different. It is not possible to combine all of them to provide a meaningful global average. There is no such thing as a global climate.

It is very difficult, even in a more or less uniform region, to derive a scientifically or mathematically acceptable average for any of the climate properties. Climate observations hardly ever comply with requirements for uniformity and symmetry which are needed to make use of standard statistical models. The observations are often irregular, bimodal or skewed. Attempts to apply the popular normal distribution often claim a false uniformity or run into problems with rare events for which there are too few samples or assess regularity The term average, therefore, often applies only to a “range” or to an opinion as to what is typical, normal, or unusual.

WEATHER FORECASTING

Measurement of climate properties has developed from very early beginnings with the aim of attempting to forecast its future behaviour.

Measurements are now made of a large number of properties, both near the surface and at various levels in the atmosphere using radiosondes and satellites. These properties are incorporated into numerical models made up of complex equations incorporating thermodynamics and fluid dynamics of the atmosphere and the ocean.

No part of the climate is ever in equilibrium. Climate is an interrelationship with a large number of meteorological and geological influences which provide a pattern and for individual properties a field which is continually varying.

The climate depends on the behaviour of fluids, of the atmosphere and of the ocean. The physics of fluids involves the use of non linear equations with second order differential quantities demanding great accuracy in defining boundary conditions.

Edward Lorenz⁴  showed that if these methods are applied to the climate a very slight error in the  boundary conditions (for example, the movement of a butterfly’s wing) would be escalated by the equations, making a long term forecast impossible. Lorenz concluded that for the climate the prediction of the sufficiently distant future is impossible by any method.There are also errors arising from the accuracy of the measurements and of the physics and the intervals in space and time of the observations.

Despite these limitations the weather forecasting services are possibly the most widely used of any scientific service. It is a necessary guide to the activity of many enterprises and individuals.

The accuracy of local weather forecasts has been recently studied by Ripley & Archibald. ⁵  

They give a very useful summary of previous studies. They say

The present limit of deterministic weather predictability is a few weeks at most

(Hoskins and Sardeshmukh 1987; Ripley 1988). The major limiting factors are incomplete knowledge of the atmosphere’s initial state (Gilchrist 1986) and imperfect understanding of atmospheric processes (Somerville 1987). The first factor is most important at short lead times while modelling errors become the dominant limitation in longer forecasts (Anthes and Baumhefner 1984).

Their own study covers the entire Canadian system for the year 2000. They say:

In this analysis, we assess the accuracy of short- and medium-range forecasts of minimum and maximum temperatures and precipitation for lead times of 1 to 5 days, issued daily by the Meteorological Service of Canada (MSC, formerly the Atmospheric Environment Service) for selected cities during 2000.

Their detailed results are tabulated. They found that temperature forecasts had a bias of about ±1ºC and were rarely better than ±2ºC

The results are plotted in Figure1.1⁵

Figure 1.1 Forecasting errors in different places⁵

The British Met Office⁶  comes to a similar conclusion. They say: 

Temperature

Forecasts for both maximum and minimum temperature are compared to the actual values observed at an agreed list of 119 sites across the UK. The sites used for verification are those where we have quality-controlled data and where we produce forecasts for. The early morning forecast on our website is used to produce a percentage number of the times when the forecast is accurate to within +/- 2°C. This is based over a rolling 36-month period to smooth out extremes and give a representative average.

Temperature forecast - performance

This information will be updated every month.

Maximum temperature - first day of forecast

93.8% of maximum temperature forecasts are accurate to within +/- 2°C on the current day (36-month average).

Target for 2013/14 is 85.0%.

Minimum temperature - first night of forecast

84.3 % of minimum temperature forecasts are accurate to within +/- 2°C on the first night of the forecast period (36-month average).

Target for 2013/14 is 80%.

These results are examples of current practice in advanced Western countries. Accuracy is bound to be lower in less developed countries, and in the western countries in 1950, 1900 and 1850.

The accuracy of the average of a daily maximum and a minimum temperature, the so-called daily average, is unknown, as it has no mathematical derivation. Any manipulations of this quantity thus has unknown and very large inaccuracies.

    

 Climate is essentially local. Numerical climate models have to be supplemented with specific local characteristics to provide a reliable local forecast. Attempts may be made to obtain averages of individual observations such as temperature and precipitation, but it is much more difficult to average wind or air pressure patterns. as influenced by more general features.

 The Global Climate as an array of the climate properties at each individual and regional locality is portrayed to us every day by the press and TV weather forecasts.⁷

Figure 1.2  The Climate as a Heat Engine

Since Global climate properties have to be obtained at present from an assembly of individual local and regional determinations there is no possibility of a plausible global climate model which could be capable of taking all these into account. Any scientific organisation or individual scientist who claims the ability to predict the temperature change of the local or global climate beyond a few weeks, even to decimals of a degree, has to be dismissed as deluded or fraudulent.⁸

CLIMATE AS A HEAT ENGINE

The Climate is a heat engine. Energy input is mainly short wave radiation from the sun. Energy output is mainly long wave radiation from every surface on the earth and from every level in the atmosphere, including clouds and aerosols.

Figure1.2 shows only transfer of heat by radiation. Much of the absorbed heat is distributed by conduction, convection and latent heat transfer.

The whole function of the climate is to provide the energy necessary for the preservation and development of living organisms. In the process there is a complex interaction between all the climate properties

The following diagram which appeared in Climate Change 1995⁹ shows the main features of the climate.

Figure 1.3  Elements of the climate⁹

CLIMATE PROPERTIES 

Observations from many instruments which are processed by the numerical climate models are obtained from a large variety of the following climate properties. 

SOLAR IRRADIANCE¹⁰

Radiation from the sun is only received during each day, as the earth rotates on its axis and follows its orbit around the sun. It ceases altogether at night. The sun passes through the atmosphere at the edge of the earth and its interaction with cloud causes the effects of sunrise and sunsets.

The energy that arrives on a square metre of the earth’s surface with the sun at zenith and at its average distance is referred to as the solar constant: which has an average of 1370 Wm^-2 

The actual direct solar irradiance at the top of the atmosphere fluctuates by about 6.9% during a year (from 1.412 kW/m² in early January to 1.321 kW/m² in early July) due to the Earth's varying distance from the Sun, and typically by much less than 0.1% from day to day.

Thus, for the whole Earth (which has a cross section of 127,400,000 km²), the power is 1.740×10¹⁷ W ±3.5%.This amount falls to zero as it approaches each horizon and each amount actually received depends on absorption by the atmosphere, clouds and overcast. 

Direct measurement of solar irradiance began with Pouillet in 1838 (see Chapter 2) and now is measured continuously by satellites. Its variability is shown in Figure 2 since 1610.

Figure 1. 4 Solar irradiance since 1610¹¹

This graph shows the Maunder Minimum c1645-1715 and the Dalton minimum in 1811.

Sunspots are dark spots on the sun compared to surrounding regions. They represent concentrations of magnetic field of reduced surface temperature. Sunspots usually appear as pairs, with each spot having the opposite magnetic polarity of the other³. It is rather a crude way to assess solar variability but the recently revised sunspot record⁴ shows similar variability to the irradiance measurements:

Figure 1.5 Revised sunspot number¹²

The Sun⁹contains 74.9% hydrogen which is being converted into helium by nuclear fusion heating the surface to around 6000°K. The Sun then radiates energy outwards. It has the following spectral composition:

Figure 1.6 The Solar Spectrum¹³

Figure 1.7 Daily input and output of radiation¹⁴

The amount of radiation from the sun begins at dawn from zero to a maximum at noon and declines to zero at sunset and depends on latitude and the  seasons.

The radiation received follows several different paths.

Some is absorbed by the surface and is transmitted into it, depending on its local thermal conductivity. Over ice or snow some energy may form liquid water. Over the oceans, or lakes, transmission is disturbed by fluid motion in the area, both above and below the surface.

Some of the energy absorbed will transfer heat by conduction to the neighbouring layers of the atmosphere, which will rise by convection, influenced by local topology and by local wind speed and direction. 

Some heat is removed by evaporation of water from damp ground or from oceans and lakes. Wind speed and direction enhances the process, so that when combined with convection the air may sometimes be warmer than the ground.

Some energy is radiated perpendicularly from the surface. It will be greatest after it has been heated by the sun and will fall progressively through the night.

At night, radiation depends on heat absorbed the previous day. Energy is radiated from every level of the atmosphere both up and down, but as it cools and the atmosphere becomes less dense the amount fall rapidly. Most radiation loss from the atmosphere takes place close to the surface, the part that  causes the weather

Atmospheric circulation distributes heat and moisture across and around. the surface, reducing the difference between the tropics and the poles and up into the atmosphere as far as the tropopause.

At night, circulated air may reduce heat loss by conduction or by deposition of dew or frost.

Heat is also distributed by ocean currents which form in recognised fluctuating patterns. Water vapour from the earth condenses to clouds as soon as it reaches the dew point. The latent heat is deposited in the atmosphere at this region, thus increasing the slope of the lapse rate.

Some clouds form rain, hail or snow which is deposited on the earth’s surface, but not necessarily in the place where it came from. Since it comes from a cool part of the atmosphere it usually cools the surface on which it falls. With snow this may persist over time, abstracting further latent heat when a period of thaw ensues.

THE LAPSE RATE

The density of the atmosphere falls with height from reduced gravity and it cools adiabatically This fall of temperature with height is called the Lapse Rate.

The actual lapse rate varies considerably, and depends somewhat upon the moisture content of the air and other factors, which are the actual change in temperature with height, and the conditions of air at the surface. If the air at the surface is warmer than the actual lapse rate, then a parcel of air will begin to rise in the air that surrounds it. This rising air will cool off primarily by expansion at a rate known as the dry adiabatic lapse rate. When this parcel of air reaches its dewpoint however, the rate of cooling will decrease due to the heat released when water vapour condenses to a liquid. This is known as the saturated adiabatic lapse rate.

The height where the parcel of air becomes saturated also is the height at which cloud starts to form. When the parcel of air can rise no higher or has released all of its moisture, the top of the cloud is reached.

Figure 1.8 The nominal lapse rate¹⁵

The return of latent heat by clouds causes a decrease in this rate. In addition, there are effects from convection, radiation loss and latitude.  As with all other  climate properties, the lapse rate profile changes continuously. It is affected by the diurnal and seasonal variability and by the general movement of the atmosphere., clouds precipitation and with cyclones and anticyclones.

Figure 9 shows examples of measurements made in different places¹⁷

Figure 1.9  Lapse Rate  in different places¹⁶

Various simplifying attempts have used the concept of a Standard Atmosphere¹⁷.

The surface of the earth and every level of the atmosphere radiates energy according to the Stefan Boltzmann Law, dependent on emissivity multiplied by the fourth power of the absolute temperature. The lapse rate means that the radiated energy from the atmosphere falls very rapidly with height, so that most of it comes from close to the surface

Radiation from the surface is upwards but from the atmosphere it is in all directions, so that half of this radiated energy returns to the surface. By land the amount returned depends on local albedo but there is evidence that this is very low over the ocean where most is reflected.

Energy is consumed by changes in the earth’s surface, by erosion, glaciers, waterfalls and the effects of cyclones and tornadoes.

Energy is used to maintain and increases all the living organisms on the earth, some of whose products can be stored for small or long periods. Stored energy from the past, such as from fossil fuels may be restored. Some energy may also come from within the earth with earthquakes and volcanoes or from nuclear power.

Humans modify their personal climate by erecting buildings which exclude the wind, rain, adjust temperature and lighting, and provide living and sleeping business or recreational facilities. Individual design depend on local climate, availability  of building materials and level of prosperity.

Figure 1.10  The Air Circulation System¹⁸

THE CIRCULATION SYSTEM

The complex patterns of the circulation of the atmosphere are the main determinants of the behaviour of the climate in every locality. The above diagram shows some of the main patterns that have been identified and classified.

Air pressure determines the pattern of air circulation. The basic instrument for air pressure is a barometer. A cyclone is a rotating area of low pressure, where the flow is inward toward the centre. An anti-cyclone is the opposite, where flow is outward from the centre.

For atmospheric cyclones and anticyclones, over the northern hemisphere, air flows counter clockwise around cyclones, and clockwise around anticyclones. In the southern hemisphere, it is just the opposite.

Figure 1.11 The main elements of ocean circulation¹⁹

Circulation of warm and cool currents is influenced by the position of land masses and of the properties of the ocean floor, An oversimplified version of this process is The Great Ocean Conveyor Belt (Figure 9)

Figure 1.12 The Great Ocean Conveyor Belt²¹

OCEAN OSCILLATIONS

The principal oscillations are:

El Niño/Southern Oscillation (ENSO) which is observed in the southern Pacific and has a periodicity of 3 to 8 years.

 

Figure 1.13  The El Niṅo Southern Oscillation Index (ENSO)²¹

Pacific Decadal Oscillation (PDO) which is observed over the whole Pacific hand has a periodicity of two or three decades.

Figure 1.14 Pacific Decadal Oscillation Index²²

North Atlantic Oscillation (NAO) which is observed over the northern Atlantic Ocean and has a period of around one decade

Other oscillations affect the Arctic, Antarctic and Indian Oceans.

ENSO has a global effect on the climate. The PDO influences the Arctic ice cover

METEOROLOGY TODAY

There are now some 8000 official weather stations measuring a very large quantity of local and international climate properties and processing them to supply weather forecasts, which now apply to the entire lower atmosphere, the surface and the oceans. Sophisticated world maps with temperatures for three times a day, air pressure. Wind circulation, wind velocity, precipitation, relative humidity, hours of sunshine, behaviour of clouds, and many other features are presented on television and newspapers all over the world on a continuous basis.

This service is by far the most widely used scientific operation, for individuals, communities, businesses and nations.

Figure 1.15 Typical weather map²³

Figure 1.15 shows a typical weather map of North America²³ showing air pressure and wind direction.

Other maps show temperature measurements, often three times a day.the  progress of cyclones and many other properties on different scales.

Climate science is regional. Each region has climate models which are influenced strongly by the significant local climate effects in that region.

There is, at present, no prospect of an overriding climate model suitable for the entire climate and any claim that such a system exists is spurious.

CLIMATOLOGY 

Meteorology is the discipline mainly concerned with forecasting. Climatology is a related discipline which uses climate  measurements and historical and geological information to assess information about the likely general climate behaviour in a particular place, region or historical or geological epoch.

It is to be regretted that some climatologists have attempted to extend their discipline into attempts to forecast future global climate. So far these attempts have had no useful influence on weather forecasting and no successful future global prediction has ever emerged. Future Chapters will explain why this is so.

REFERENCES

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23. National Weather Forecast Office  http://www.erh.noaa.gov/btv/events/15Jan2009/wx.shtml