phase shift between some extremes of the ENSO and GAO indices. This evidence
strongly supports our hypothesis that the interannual GAO anticipates the occurrence of the El Niño acting as its trigger mechanism.
Figure 3 shows that along with the general similarity of the two indices behavior
they have, at least, one significant difference, namely, the number of extreme points
of the interannual GAO index exceeds the corresponding marks of the ENSO. This
could generally mean that the frequency parameters of the GAO and ENSO may
vary. In such case, the situation is not excluded when the GAO occurs more often
than the ENSO events. However, in any case, as it is clearly seen in Fig. 3, the
signals of all actual ENSO events, distinguished by its index, certainly correspond
to the specific phase of the interannual GAO. Therefore, all events like El Niño and
La Niña should not be considered separately just as anomalous regional features in
the dynamics of the regional Pacific climate system only, although, this approach is
sometimes applied to these phenomena. Nevertheless, according to the previous
discussion, it is not correct to consider these effects beyond the concept of the GAO.
The fact based on the GAO analysis indicates that the signals of the ENSO and
other regional climatic disturbances should not be interpreted otherwise than the
factors of the lower, secondary level.
The bold lines in Fig. 3 provide essential information on the properties and
characteristics of the inter-decadal GAO. First of all, smooth transformation of the
data on the ENSO and GAO indexes, which were converted into the curves of
almost the same form, is worth noting. On this occasion we would assume that such
a result is an actual verification of the adequacy of our understanding of the climate
variability based on the correlations between the signals in the fields of completely
different hydrometeorological characteristics, such as temperature and atmospheric
pressure. These fields indirectly represented here by the corresponding indices of
the GAO and ENSO are distinguished from the quasi-cyclical fluctuations with an
average estimated period of 16 years.
The traces of incompletely filtered interannual GAO (blue curves) and ENSO
(red lines) signals are revealed over the background of the lower frequency fluctuations. The fact that the smoothed ENSO index is similar to the inter-decadal
GAO signal provides evidence that these events are caused by correlated physical
processes. Thus, as it is shown in Fig. 3, the smoothed curves represent, according
to our definition, nothing but the actual inter-decadal GAO. It is clear that the
oscillation frequency characteristics require a further clarification due to the lack of
statistical reliability of its current assessment. Incidentally, we note that even
lower-frequency harmonics of such type of oscillations in the range of periods
about 35–50 years were revealed in our study of the climate change in the North
Atlantic region [11].
356
V. G. Neiman et al.
strongly supports our hypothesis that the interannual GAO anticipates the occurrence of the El Niño acting as its trigger mechanism.
Figure 3 shows that along with the general similarity of the two indices behavior
they have, at least, one significant difference, namely, the number of extreme points
of the interannual GAO index exceeds the corresponding marks of the ENSO. This
could generally mean that the frequency parameters of the GAO and ENSO may
vary. In such case, the situation is not excluded when the GAO occurs more often
than the ENSO events. However, in any case, as it is clearly seen in Fig. 3, the
signals of all actual ENSO events, distinguished by its index, certainly correspond
to the specific phase of the interannual GAO. Therefore, all events like El Niño and
La Niña should not be considered separately just as anomalous regional features in
the dynamics of the regional Pacific climate system only, although, this approach is
sometimes applied to these phenomena. Nevertheless, according to the previous
discussion, it is not correct to consider these effects beyond the concept of the GAO.
The fact based on the GAO analysis indicates that the signals of the ENSO and
other regional climatic disturbances should not be interpreted otherwise than the
factors of the lower, secondary level.
The bold lines in Fig. 3 provide essential information on the properties and
characteristics of the inter-decadal GAO. First of all, smooth transformation of the
data on the ENSO and GAO indexes, which were converted into the curves of
almost the same form, is worth noting. On this occasion we would assume that such
a result is an actual verification of the adequacy of our understanding of the climate
variability based on the correlations between the signals in the fields of completely
different hydrometeorological characteristics, such as temperature and atmospheric
pressure. These fields indirectly represented here by the corresponding indices of
the GAO and ENSO are distinguished from the quasi-cyclical fluctuations with an
average estimated period of 16 years.
The traces of incompletely filtered interannual GAO (blue curves) and ENSO
(red lines) signals are revealed over the background of the lower frequency fluctuations. The fact that the smoothed ENSO index is similar to the inter-decadal
GAO signal provides evidence that these events are caused by correlated physical
processes. Thus, as it is shown in Fig. 3, the smoothed curves represent, according
to our definition, nothing but the actual inter-decadal GAO. It is clear that the
oscillation frequency characteristics require a further clarification due to the lack of
statistical reliability of its current assessment. Incidentally, we note that even
lower-frequency harmonics of such type of oscillations in the range of periods
about 35–50 years were revealed in our study of the climate change in the North
Atlantic region [11].
356
V. G. Neiman et al.