412
As a rule, climatic records show a repetitive basic pattern upon which apparently
random fluctuations are observed which do not modify the overall structure. This structure is
usually known as an "attractor", which is roughly equivalent to the existence of a slow scale
variable. There exist algorithms to identify such structures from time series records
(Grass berger and Procaccia, 1983; Short, 1993). Therefore, a new non classical modelling is
available. The idea behind the attractor reconstruction implies embedding of the time series in
an adequate n-dimensional vector space, where similar -in a way to be precisely definedfragments of n consecutive terms build sets of close vectors. Predictive capabilities of the
reconstructed attractor depend on its fractal dimension and shortcomings of the method appear
if the time series is not long enough.
In the Canary Islands this study has not been done, though records of air temperatures
and precipitation are kept for agricultural and trade reasons since the 1850' s. It must be noted
here that problems related with water supplies are a constant in the culture of the Islanders. On
the other hand, longer range studies are more difficult to do because of the lack of records
originated by two main reasons: The first is overexploitation of the aquifers that has changed a
large amount of fossile waters (more than 5000 years) into brackish water due to marine
intrusions and to local chemical interactions thus loosing an invaluable climatic record. The
second is systematic deforestation, which is the cause that tree-ring analyses are impossible
due to the lack of old enough trees in most of the Islands.
2. The Climatic cycle.
The energy cycle in the Earth starts with the incoming shortwave (less than 4!!m
wavelength) Solar radiation. Atmospheric water and water vapor are transparent to it, as well
as the first few centimeters of seawater. A substantial part of the Solar energy reaching the sea
surface is stored in this thin layer (Pelegrf et al., 1995; Stephens et ai., 1993). Radiation
reaching the continental land mass comes back to the atmosphere, for the calorific capacity of
land materials is quite low. A part of this reflected radiation, now of a longer wavelength,
remains trapped under the cloud cover: This is called the greenhouse effect. There are also local
anthropic effects contributing to the conservation of heat in the lower atmosphere, the so called
heat island effects. C02 concentration in the atmosphere is closely related with radiative
properties, so this is a basic variable in climate change experiments.
The role of ocean dynamics is a basic one in the global distribution of heat (Bindoff and
McDougal, 1994; Drijfhout, 1994), for sea water has a heat capacity some three orders over
that of the land. Heat transport has two main mechanisms:
a) Within the sea, currents originated by temperature and salinity gradients. These are
responsible of the origin of North Atlantic polar water, which is later on distributed along the
world ocean by a kind of global conveyor belt (Hughes and Weaver, 1994; Weaver and
Hughes, 1994) (Figure 4).
b) Within the atmosphere, the release of latent heat is the main cause of heat transfer to the
upper atmosphere through the mechanisms of evaporation and precipitation (Hernandez,
Pacheco and Garcia, 1983b and 1987; Zeng and Pielke, 1993).
The cycle is closed by the mechanic energy transfer from the atmosphere to the sea
surface via wind stresses (Charney, 1955), giving rise to the wave system and to some types
of surface currents. Winds are generated by temperature and density gradients in the
atmosphere, and a continuous feedback is achieved between the two parts of the climate system
(Pereira and Mascarenhas, 1994). A history of this mechanical interaction is stored in the finer
structures of the thermocline (Liu and Pedlosky, 1994), below which atmospheric interaction is
negligible. No good measurements of the amount of mechanical energy transferred to the sea
surface are known, only rough estimates with great variability. Thus, the choice of the bottom
As a rule, climatic records show a repetitive basic pattern upon which apparently
random fluctuations are observed which do not modify the overall structure. This structure is
usually known as an "attractor", which is roughly equivalent to the existence of a slow scale
variable. There exist algorithms to identify such structures from time series records
(Grass berger and Procaccia, 1983; Short, 1993). Therefore, a new non classical modelling is
available. The idea behind the attractor reconstruction implies embedding of the time series in
an adequate n-dimensional vector space, where similar -in a way to be precisely definedfragments of n consecutive terms build sets of close vectors. Predictive capabilities of the
reconstructed attractor depend on its fractal dimension and shortcomings of the method appear
if the time series is not long enough.
In the Canary Islands this study has not been done, though records of air temperatures
and precipitation are kept for agricultural and trade reasons since the 1850' s. It must be noted
here that problems related with water supplies are a constant in the culture of the Islanders. On
the other hand, longer range studies are more difficult to do because of the lack of records
originated by two main reasons: The first is overexploitation of the aquifers that has changed a
large amount of fossile waters (more than 5000 years) into brackish water due to marine
intrusions and to local chemical interactions thus loosing an invaluable climatic record. The
second is systematic deforestation, which is the cause that tree-ring analyses are impossible
due to the lack of old enough trees in most of the Islands.
2. The Climatic cycle.
The energy cycle in the Earth starts with the incoming shortwave (less than 4!!m
wavelength) Solar radiation. Atmospheric water and water vapor are transparent to it, as well
as the first few centimeters of seawater. A substantial part of the Solar energy reaching the sea
surface is stored in this thin layer (Pelegrf et al., 1995; Stephens et ai., 1993). Radiation
reaching the continental land mass comes back to the atmosphere, for the calorific capacity of
land materials is quite low. A part of this reflected radiation, now of a longer wavelength,
remains trapped under the cloud cover: This is called the greenhouse effect. There are also local
anthropic effects contributing to the conservation of heat in the lower atmosphere, the so called
heat island effects. C02 concentration in the atmosphere is closely related with radiative
properties, so this is a basic variable in climate change experiments.
The role of ocean dynamics is a basic one in the global distribution of heat (Bindoff and
McDougal, 1994; Drijfhout, 1994), for sea water has a heat capacity some three orders over
that of the land. Heat transport has two main mechanisms:
a) Within the sea, currents originated by temperature and salinity gradients. These are
responsible of the origin of North Atlantic polar water, which is later on distributed along the
world ocean by a kind of global conveyor belt (Hughes and Weaver, 1994; Weaver and
Hughes, 1994) (Figure 4).
b) Within the atmosphere, the release of latent heat is the main cause of heat transfer to the
upper atmosphere through the mechanisms of evaporation and precipitation (Hernandez,
Pacheco and Garcia, 1983b and 1987; Zeng and Pielke, 1993).
The cycle is closed by the mechanic energy transfer from the atmosphere to the sea
surface via wind stresses (Charney, 1955), giving rise to the wave system and to some types
of surface currents. Winds are generated by temperature and density gradients in the
atmosphere, and a continuous feedback is achieved between the two parts of the climate system
(Pereira and Mascarenhas, 1994). A history of this mechanical interaction is stored in the finer
structures of the thermocline (Liu and Pedlosky, 1994), below which atmospheric interaction is
negligible. No good measurements of the amount of mechanical energy transferred to the sea
surface are known, only rough estimates with great variability. Thus, the choice of the bottom