Spaceborne Solar Observations

Modern observations of the Sun are also based on satellite-borne instruments and space probes which eliminate the problems associated with atmospheric disturbances as the observations are no longer made through the atmosphere. Magnetism may still affect instruments if they are not thoroughly shielded, as the electronics may be subject to a Hall effect. best-fit to Rz independent prediction de-trend fit + trend de-trend prediction best-fit to Rz independent prediction de-trend fit + trend...

The aurora and the geomagnetic field

The aurora depends on the state of the geomagnetic field. The geomagnetic field lines are closed at low latitudes, which means that the lines flow out from the southern hemisphere and into the surface at the northern hemisphere (Figure 7.1). There are open structures near the poles, where only one end is attached to Earth's surface and the other end is somewhere out in space.3 If the IMF has an orientation which is opposite to the geomagnetic field, then this will close the magnetic field lines...

The diurnal cycle

The fact that the insolation varies diurnally (with the day and night) is a trivial example of how the atmosphere responds to changes in the available solar energy. Every 24 hours, the Earth makes a complete rotation about its own axis and the sunlight varies as the Sun is nearly above the equator. The atmosphere tends to cool during night, with greatest differences between day and night-time in the low-latitude, mid-altitude regions with continental climate (spring and autumn) and the smallest...

Chapter

8.1 Discuss the scientific criteria. 8.2 What are parametric tests, null-hypotheses, and null-distributions 8.3 Describe the basics and purpose of Monte-Carlo simulations. 8.4 Give an account of the first ideas about feedback mechanisms in solar-terrestrial relationships (Blandford) 8.5 (a) Describe the early relationships established between sunspots and temperature on Earth (before 1910). (b) How do these compare with current knowledge 8.6 What was the established view of the relationship...

Pacific Decadal Oscillation And Solar Activity

Recently, attention in climate research has been on decadal variations in the North Pacific and a possible discovery of a new mode of natural variability (Zhang et al., 1997 Mantua et al., 1997). Variations with timescales of the order of 10 years may potentially be related to the 11-year solar cycle. Figure 9.13 shows a comparison between an index of the Pacific Decadal Oscillation (PDO) and the sunspot record. Gulf Stream latitude & sunspot number Gulf Stream latitude & sunspot number...

Entropy

The climate system obeys the laws of thermodynamics. The first law of thermodynamics states that when heat is added to a gas (Q), the gas may do work (W), and the change in the internal energy is the difference between the heat added and the work done AU Q W. The internal energy change is independent of how the change was achieved. The second law of thermodynamics states that the total energy of a closed system is always transformed into more disorderly forms until a state of maximum disorder...

Correlation studies and pitfalls

An example illustrating the dangers associated with correlation studies is given in Figure 8.17 (see colour plate section) which shows the correlation map between the SCL and temperatures from a climate model. The temperatures in the climate model have realistic timescales, but are not related to the SCL because variations in solar activity are not taken into account by the model. There are some regions where the correlation is high, and 9 of the area in the upper panel is associated with...

Sea level pressure

The 17th-century scientist Torricelli discovered that the air has a mass, and Otto v. Guericke demonstrated that the air pressure could keep two hemispheres together by strong forces when the space between them is evacuated. As a consequence of the atmospheric mass and Earth's gravity, the atmospheric pressure decreases with height. The legend tells of Pascal dispatching his brother with a barometer to the top of Puy de Dome in France to demonstrate this height dependency of the air pressure....

Sunspot Groups

The sunspots often appear in groups in which the individual spots are associated with the same magnetic field structures. Some sunspots are referred to as leading and following spots, meaning spots in a group leading or following in terms of the Sun's rotation. Hale and Nicholson (1938) devised a magnetic classification scheme for the sunspot groups (Table 4.2) with three different types unipolar, bipolar and complex. Bipolar groups are sunspot groups which consist of two members associated...

Stochastic ENSO models

Lau (1985) proposed that intra-seasonal (intra-seasonal timescale of 40-50 days) variability associated with the Madden-Julian Oscillation (MJO) may play a central role in triggering ENSO events. Westerly inflow to the west of enhanced convective regions over the western Pacific may affect the SSTs in the eastern Pacific through remote forcing. This hypothesis may therefore involve oceanic intra-seasonal Kelvin waves that link the forcing in the west with the ocean response in the east. Wyrtki...

Correlation and detrending the data

One common mistake is to apply correlation and regression analysis to series which contain long-term trends if it is not known a priori that these are part of the signal. Such trends may bias the analysis by, for instance, inflating the correlation scores if they are caused by external factors, especially for short data series. It is often wise to de-trend the data (here the least-squares fit linear trend has been subtracted) in order to reduce such biases. De-trending can be justified in terms...

Sunspots and the solar irradiation

Although the individual dark sunspots reduce Sun's total radiative output, the Sun tends to be brighter when there are many sunspots because other factors such as plages and faculae also affect the solar brightness. Lean and Rind (1998) show that these variations are evident as 27-day variations with magnitudes as much as ''a few tenths of percent'' in the total solar irradiance in addition to the prominent 11-year cycle (0.1 ). The short-term variations are measured accurately but space-borne...

Ekman pumping

A schematic illustration of the coupled mode. The physical mixed layer processes present may be crucial for the coupled Kelvin modes. The mixed layer temperature has a strong relation to the thickness of the mixed layer (Kraus and Turner, 1967). The depth of the base of the mixed layer is in turn affected by the turbulent mixing (wind stress) and the buoyant stability (insolation). Pacanowski and Philander (1981) proposed that the mixing also depends on the Richardson number of the...

Bibliography

E. (1908) Radiation and Terrestrial Temperature. Annals of the Astrophysical Observatory of the Smithsonian Institute. Abbot, C. G. and Fowle, F. E. (1913) Volcanoes and climate. Ann. of the Astrophys. Observ. Smithson. Inst. Abetti, G. (1957) The Sun. Faber & Faber, London. Adler, R. (2001) Melting away. New Scientist, 15 December, 15. Alfven, H. (1942) Ark. f. Mat. Astr. och Fys, 29B(2). Ambaum, M. H. P., Hoskins, B. J. and Stephenson, D. B. (2001) Arctic...

Testing for nonhomogeneity

It is always a good idea to test a time-series for non-homogeneity.3 How does one do this A simple test for homogeneity can involve looking for changes in the difference between two neighbouring climate stations. Jumps, discontinuities or trends in the time-series of station differences can be a sign of non-homogeneity. To illustrate this, 2 Changes to the landscape properties as a result of urbanisation also contribute to the urban heat effect. 3 Changes in observational practices or a...

Satellite altimetry

Satellite altimetry measures surface heights. The ERS-1 and Topex-Poseidon satellites observe variations in the sea level height to an accuracy of around 5 cm. The Topex-Poseidon programme started in 1992, and gridded altimeter data may be constructed with a temporal resolution of 15 days and a high spatial resolution. The sea level height anomalies (SLA) are important quantities since they reflect the geostrophically5 driven currents. Furthermore, the sea level height may also give an...

Ice and snowalbedo feedback

Ice and snow can only exist in cold regions as temperatures above freezing point favour melting and sublimation (direct transition from solid to gas phase such as from snow to vapour). Ice also reflects a large fraction of the sunlight and is therefore associated with a high albedo. The albedo of open sea and sea-ice differ by approximately 0.50 Aoce 0.10, whereas Aice 0.60 (Hartmann, 1994). The more light reflected back to space, the less absorbed by the climate system, and the less available...

Correlation and filtering the data

Low-pass-filtering may introduce spurious results if care is not taken. Low-pass-filtered signals tend to give too high correlation, and sometimes low-pass-filtering may produce spurious undulation, an effect known as the Slutsky-Yule effect. It is therefore important to examine the sensitivity of the analysis to the filter type and width. The effect of low-pass-filtering9 on the correlation analysis is easy to demonstrate on a home computer by repeating the analysis many times but after...

The Influence Of Corpuscular Clouds

Ludmany and Baranyi (2000) argue that the energy transferred to the Earth system by corpuscular clouds cannot be neglected and can in some instances be as important as the variations in the solar irradiation. The mean total energy flux associated with the TSI is around 107 times the energy associated with the corpuscular clouds. But the variations in the latter are proportionally much larger than the variations in TSI. The plasma in the corpuscular clouds is thought to interact with the...

The Gulf Stream And Sunspots

The Gulf Stream is known to be responsible for a considerable part of oceanic heat transport and hence influences sea surface temperatures over substantial parts of the North Atlantic Ocean. A comparison between the meridional excursions of the Gulf 8 The NAO has sometimes been dubbed the Noisy Atlantic Oscillation''. 0.2 0.5 1.0 2.0 5.0 20.0 50.0 Time scale (years) 0.2 0.5 1.0 2.0 5.0 20.0 50.0 Time scale (years) Figure 9.9. (a) A comparison between standardised 11-year low-pass-filtered NAOI...

Sunspotirradiance models

One of the best ways of testing a scientific hypothesis is to make predictions. In order to make predictions, one needs a model. In this case, we can develop empirical models based on past statistics. There are several ways of making such models, and one of the most common methods is to apply a linear regression to estimate the best-fit linear relationship between two or more quantities. Linear regression is a method for finding coefficients, m and c, that give the best fit between two...

The Sun As A Star 321 Solar size and mass

Sun Core Gauss

Our Sun is one of many so-called G2 stars.1 The Sun has a diameter that is measured to be 1.39 x 109m and a mass estimated to be 1.989 x 1030 kg. The solar mass and parallax have traditionally been derived indirectly from studies of the orbit of the asteroid Eros. The parallax is the mean angle subtended (in arc-seconds) by Earth's 1 Stars are classified by a letter and a number describing the nature of their spectral lines and their surface temperature. The types are denoted by the letter O,...

Synopsis

The term solar activity comprises photospheric and chromospheric phenomena such as sunspots (Figure 4.1), prominences (see Figure 3.6, on p. 42), and coronal disturbances. Solar activity also refers to the level of solar magnetism, often giving rise to sunspots (Thomas and Weiss, 1992). Prominences and coronal disturbances are often associated with sunspots, but there are also types of solar activity which do not involve sunspots directly, such as the appearance of magnetic flux tubes and...

Corpuscular clouds

Corpuscular clouds are gases of ionised matter being ejected from the Sun during flares with speeds of the order 1,000,000 m s and an extension length typically of 109 m. The clouds get rarefied as they spread out with the distance from the Sun, and their density decreases from typical values in the corona 2 x 1013 protons m3 to a typical density of approximately 106 protons m3 at one astronomical unit.16 The corpuscular beams are also associated with fast-travelling radio-emission sources. It...

Autocorrelation and lagcorrelation

When applying a low-pass filter to a series we increase the autocorrelation by making adjacent data points more similar to each other. Thus in series with non-zero autocorrelation the successive data points are not entirely independent of each other. This means that each data point cannot be regarded as an independent observation and the degrees of freedom associated with the series is less than the number of observations. Successive observations are related to each other because the quantity...

Solar Activity And Preferred Timescales 461 Solar activity and the sunspot cycle

Sunspot 1750 Present

There are various methods for quantifying the solar activity. The classical method is using the Wolf sunspot number, also known as the Zurich sunspot number. Wolf, who was the director of the Zurich observatory, adopted in 1849 the following equation for estimating the sunspot number Rz which is an index The symbol f is the total number of physical sunspots, g is the number of sunspot groups, and k is a scaling factor depending on the observing method. The Wolf sunspot record was extended back...

Spectral analysis

Sun Cycles Power Spectrum

The term spectral analysis'' may have two different meanings, which may cause some confusion, although the two are related. Figure 3.3 in Section 3.2.5.1 shows the spectral analysis obtained through spectroscopy. One example of spectroscopy is a prism that separates the different wavelengths of light by bending the rays at different angles. Spectral analysis can also be carried out numerically through a Fourier transform FT . In this section, the latter type, i.e. FT-based spectral analysis,...

Wavelet analysis

Solar Radio Spectrum

It is also possible to compute how the various frequencies contribute over time through a wavelet analysis Torrence and Compo, 1998 . The wavelet analysis is a method that estimates how important the various timescales are at various times Figure 4.9, see colour plate section . The result of a wavelet analysis applied to a Figure 4.7. The power spectrum of the aa-index indicates the presence of an 11-year cycle in the magnetic field. There are also hints of a cycle with 32-year periodicity, but...

Instruments For Observing The

The only way to study the Sun from the Earth is by examining the solar quantities that reach us, which includes particles, magnetic fields, and electromagnetic radiation. In addition, the action of the Sun's gravity on other bodies in our solar systems may be used to infer the solar mass. There is a great deal to learn from the electromagnetic radiation. The visible light and its directional variation is the foremost source of information on what happens on the Sun. It is through the visible...