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Her heartbeat is "up": The El Nino - Southern Oscillation is more frequent and more intensive
_________________________________________________________________________________________ J.R.E.Harger _________________________________________________________________________________________
The "El Nino-Southern Oscillation" (ENSO) consists of a sympathetic movement of the waters along the equatorial region of the Pacific, in the form of a so called "Kelvin Wave" in association with the atmosphere. This combination acts in such a way that significant areas of the globe experience consequential extended droughts or alternatively, periods of heavy rainfall. Over the last 20-30 years or so, the frequency and intensity of this massive movement of water along the equator in the Pacific has increased. The system is moving in a more agitated manner as the system strives to redistribute the incoming heat throughout the depths of the oceans. In essance the action can be likened to that of a simple "heat pump". The following account is based on analysis of long-term temperature records from Indonesia (1866-1994).
The major features in development of the "El Nino - Southern Oscillation" (ENSO) involve oscillation of the Pacific ocean and the related atmosphere in an unpredictable (chaotic) fashion. The system moves between extremes of so called "warm events" lasting one or two years where warm sea water moves from the western Pacific along the equator to impact on the west coast of the American continent and "cold-events", associated with easterly trade-winds, induced flows of colder water from the eastern Pacific towards the west. Historical data indicate that ENSO years as experienced by the Island of Java are either much warmer than non-ENSO years or are only slightly, if at all, warmer than normal (non-ENSO) years. Along the equator, particularly in southeast Asia, hot-dry years within the ENSO warm event cycle are almost always followed by cooler wet years and vice-versa. This alternating pattern also extends to include the year immediately following the terminal year of an ENSO warm event set. The initial year of an ENSO warm event set may be either hot with a long dry season or relatively cool (nearer to the temperature of a non-ENSO year) and having a short dry season. In recent years, since 1950, of the 9 ENSO warm events, the initial year tends to have been hot and dry for 6 (1951, 1957, 1963, 1972, 1982, 1991) and neutral or cool and wet for 3 (1968, 1976, 1986).
There is an increasing annual trend in air-temperature exhibited by the mean monthly values over the period 1866-1993, for Java (Jakarta and Semarang data taken together) and is 1.64 deg C (0.0132 deg C per year from 25.771 deg C to 27.409 deg C). The major industrial development in infrastructure for Jakarta has been significant only since 1980 or so and was not apparent before 1970 when the city had the aspect of an extended village with few large buildings (greater than 3-4 stories) and no extensive highways. The 1.65 degree difference between 1866-1991 can presumably be partitioned into: 1) urban heat-island effect, 2) effect of deforestation, 3) effect of secular micro-climate shift, 4) influence of general global warming with particular reference to the tropics.
When the blocks of non-ENSO years in themselves are considered, the deviations from the secular trend for warmest month mean temperatures in successive years are correlated with that of the next immediate year deviation so that either continual warming or cooling appears to take place from the termination of one ENSO to the initiation of the next. When the deviations around the time-based trend shown by the warmest month average temperatures are summed for the inter-ENSO intervals (the separate non-ENSO years) the resultant "heat-loading" index is positively correlated with the following (initial) ENSO warmest month deviation from the overall ENSO warmest month secular trend. This provides an immediate predictive mechanism for the likely strength of an ENSO, in terms of the dry season impact to the Island of Java, should one occur in the next year to break a non-ENSO sequence. The length of the build-up and the build-up achieved seems not to be related. The relationship does not in itself however, predict the occurrence of the "next" ENSO.
The data show that a consistent structure underlies ENSO events for the last century and a quarter. However, as a process monitored by mean monthly air-temperature measurements at Jakarta-Semarang, the system is changing in character with time in association with an overall atmospheric temperature increase in a way that involves increased intra-annual temperature fluctuations. In general ENSO years are associated with higher temperatures than non-ENSO years, with a significant negative correlation between subsequent years which are thereafter systematically cooler. This is because the ENSO event actively mixes excess heat energy into the ocean-sink to an extent that is in direct proportion to the outstanding positive temperature deviation. A weak ENSO, preceded by a relatively modest temperature build-up in the lead-up non-ENSO years, then results in limited mixing which leads to a relatively warm subsequent year while a strong event leads to extensive mixing and so generally results in a following very much cooler year. Atmospheric temperature build-up possibly associated with the greenhouse effect may be coupled to an increasingly wider temperature swing in west and central Java associated with the warm pool influence but anchored by the ocean-sink.
Teleconnections
The influence of the ENSO (warm events) are apparently far reaching. During such situa- tions in the Pacific seasonal rainfall is increased for Kiribati, Tuvalu and the northern Cooks but decreased in southern Cooks, Fiji, and Tonga. The "great dry event" of 1877-1878 was associated with global impact being the proximal cause of millions of deaths from famine in India and China. Particular effects were associated with the 1982-1983 ENSO (warm) event and these are called ENSO-climate teleconnections, defined as "climate anomalies which tend to occur during most if not all ENSO events".
A general account of suspected teleconnections associated with ENSO (warm events) which may be summarized as warm and dry in southeast Asia extending north and south of the equator with a wet area around the equator in the central Pacific with another dry area in the northeast of south America. Wet areas in the southeast and southwest of the U.S.A. as well as northeast of south America, southeast of south America and also east Africa. Warm areas occur in south Asia, east Asia, northwest of north America, southeast Africa, southeast Australia and east of south America.
Indonesia and southeast Asia
Indonesia lies on the western margin of the ENSO interaction and for the most part enjoys a humid tropical climate except in the eastern most regions. Indonesia presently supports extensive tracts of tropical rain forest apparently amounting to some 117.9 million ha in 1990 which accounts for some 6.4% of the global total estimated as 1,838 million ha in 1982. For Indonesia, the ENSO-associated warm event drought of 1991 led to the failure of 190,000 ha in paddy with an overall 843,000 ha affected. This event caused unprece- dented losses in rice production to Indonesia resulting in 600,000 tons being imported to the previously self-sufficient archipelago. In 1982-1983 the ENSO-associated drought of that time, resulted in 420,000 ha of paddy being affected and failure of 158,000 ha and was also accompanied by forest fires which burned 3.7 million ha of generally second-growth timber, mainly in Kalimantan (Borneo). An area of 88,000 ha burned in 1991 (Jakarta Post 30 November 1991) largely in Kalimantan in association with the 1991-1992 ENSO event. An extensive pall of smoke developed over Kalimantan, Singapore and Malaysia during September-October of 1991.
The length of the dry season, as defined above, has progressively increased in central Java (Jakarta, Tegal, Yogyakarta, Surabaya, Banguwangi) from 1909 to the present where all years are considered.
Discussion
The data show that a consistent structure underlies ENSO events for the last century and a quarter. However, as a process monitored by mean monthly air-temperature measurements at Jakarta-Semarang, the system is changing in character with time in association with an overall atmospheric temperature increase in a way that involves increased intra-annual temperature fluctuations. In general ENSO years are associated with higher temperatures than non-ENSO years, with a significant negative correlation between subsequent years which are thereafter systematically cooler.
The warm month Jakarta/Semarang deviates themselves may be directly related to the size and relative movement of the western Pacific warm pool, particularly in the ENSO warm- event years. The most obvious time periods to seek temperature induced changes in biomass burning of southeast Asia would undoubtedly correspond with ENSO warm-event years and particularly those in which marked positive deviations from the overall secular trend are apparent. In recent years these are: 1991, 1987, 1983, 1982, 1972, 1963, 1958(?), 1957, 1953 and 1951. The heat build-up in southeast Asia and the western Pacific presumably commences before the Kelvin wave resurgence from the western to the eastern Pacific which seems to have started in October to mid-December in recent years although in 1993 a Kelvin wave was also detected in August and then in late October. The warmest month of the first ENSO year usually takes place in either September (3 times in the record), October (18) or November (4) and can also show up in May (7) and June (2) as well. In itself, a significant warm deviation above the secular trend in average monthly temperature for any of these months signals an upcoming warmer-than-average ENSO with a hit-ratio of 21:6.
ENSO and drought in Africa
Some measure of a response to the dry season conditions first developing in the Philippines and then in Indonesia might be seen in the instigation of famine-inducing droughts in the Horn of Africa starting in the beginning of the year following the appearance of high- temperature low-rainfall dry-seasons in equatorial southeast Asia. Mr Ayalew of Ethiopia, in a personal communication (1993), indicated that, in recent years, famine-events associated with droughts have occurred in Ethiopia after one year following the warm events terminating the ENSO- blocks of 1952-1953, 1959-1963, 1970-1972, 1975-1983, 1984-1987, 1988-1992. With reference to the Jakarta record, the ENSO blocks ending in 1878, 1891, 1902, 1914, 1951, 1953, 1958, 1963, 1969, 1983 and 1992-1993 were apparently trending warmer than average. It is in association with these last-mentioned peaks that pronounced warm- event teleconnections might have occurred along with the geographical patterns noted earlier and the particular associated impacts on biota such as coral reefs and tropical rain forests. The mean duration between such peak events was 10.6 years (for the instrumental record under consideration) and the longest period without such a peak was 37 years (1914-1951). It may be noted that the last two strong events are separated by 8 years (including an intervening weaker event).
Conclusion
Atmospheric temperature build-up possibly associated with the greenhouse effect may be coupled to an increasingly wider temperature swing in west and central Java associated with the warm pool influence but anchored by the ocean-sink. In southeast Asia, longer dry periods coupled with increased temperatures may thus result from an ENSO-driven mechan- ism which may force increased equatorial aridity as global carbon dioxide concentrations increase resulting in a change from "ever-wet" conditions. Forest fires have become a persistent problem in Kalimantan, Indonesia in the ENSO-associated droughts of recent years. The warm event years seem to provide the driving mechanism. The temperature record shown by the southeast Asian cities studied to date indicates a progressive annual warming for the region of around 0.013 deg C over the last century. This is almost an order of magnitude greater than the global mean cited above.
ENSO year warm events vary in their effects as estimated by deviation of warmest month mean air temperature from the secular trend exhibited by the Jakarta/Semarang data set and perhaps more widely throughout southeast Asia. The strength of this temperature deviation from the secular trend for ENSO year provides a quantitative key to understanding the form of the teleconnections passed outwards from the region of southeast Asia and the associated "warm pool" of surface sea water that accumulates against the western margin of the equatorial Pacific.
In general ENSO years are associated with higher temperatures than non-ENSO years, with a significant negative correlation between subsequent years which are thereafter systemat- ically cooler. This is presumably because the ENSO event acts as a heat-pump and actively mixes excess heat energy into the ocean-sink to an extent that is in direct proportion to the outstanding positive temperature deviation. A weak ENSO, preceded by a relatively modest temperature build-up in the lead-up non-ENSO years, then results in limited mixing which leads to a relatively warm subsequent year while a strong event leads to extensive mixing and so generally results in a following very much cooler year. The differentiation between non-ENSO-ENSO blocks showing trends of positive "heat-loading" indices as opposed to those showing decreasing trends suggests that heat build-up alone may not be the only critical variable but that perhaps two sub-categories of ENSO initiating mechanisms may be involved. Those dominated by heat forcing, and those by water-mass forcing. Both however, generating heat re-distribution into the Pacific Ocean.
The warming-pulse effect of the ENSO warm-events observed recently are probably not quantitatively different from the "great dry event" of 1877-1878 however, the overall global temperature is now around 0.5 deg C higher and perhaps as much as 1.5 - 2.0 deg in the region of the equator. The Jakarta air-temperature data, near the equator, show a clear change in amplitude and degree over the 127 year record. It is of course relatively easy to dismiss these changes in a superficial way by attributing them to a "city effect". Similar changes overall throughout the Indonesian and Philippines archipelagos together with those from El Salvador are less easily dismissed. The fact is however, that ecological conditions and vegetation cover have probably also been changed markedly in the same interval making it difficult to ascribe such observed effects entirely to secular responses of a global nature. It is certain that if the instrumental record of the 1877-1878 ENSO event did not exist, the events observed in 1982-1983 and 1991-1992-1993 would appear to be quite extra-ordinarily severe in relation to all activity from 1879 forward.
Information drawn from meteorological records in southeast Asia clearly indicates that each event is unique in terms of the signature which it imposes on the rainfall and temperature from location to location. Never-the-less, a strong underlying pattern within the context of each event, itself apparently initiated or molded by the character of the preceding years, can be detected. This pattern permits relatively circumscribed predictions of forward condi- tions (drought-intensity) for 2 to 3 years, to be made once the event "locks in" for the duration of the warm event and at least one year beyond. The character of the intervening non-ENSO years can also be projected but in a more tenuous, though fairly regular manner.
When the non-ENSO years leading up to a warm event are scored in terms of the extent to which they depart from the secular warming trend for the warmest month using data from Jakarta and Semarang on the north coast of Java, the cumulative temperature deviations signal the character of the upcoming ENSO event. This signal does not however, allow an exact determination to be made with respect to whether or not an ENSO event will occur in the next year. For the available historical instrumental data, all markedly upward-moving traces eventually delivered a hot dry season in east Indonesia. This sort of tendency within non-ENSO blocks can thus serve as a caution in the sense that a very hot ENSO event is likely in the offing. The background data can also be used to actually predict the probable intensity of an ENSO in the upcoming year in terms of its drought potential, should such an event take place in reality. In this respect the correlation between the cumulative tempera- ture deviation of the inter-ENSO blocks in relation to the temperature deviation of the first ENSO year is 0.43.
In the region of southeast Asia represented by Indonesia and the Philippines, relatively secure predictions concerning likely upcoming droughts can be made in specific instances once an ENSO event "locks in" for successive years (2-4) until the warm event set terminates. In the case of Java and within succeeding inter-ENSO years, further predictions can be made with reference to successive years in terms of the character of preceding years. This system, in conjunction with predictions generated by models could form the basis of a crop advisory service for prediction of drought or rainfall within dry seasons from one year to the next. It is anticipated that a broad description of temperature and rainfall patterns associated with space and time with ENSO events will lead to better food security for the region as long as sudden changes do not occur.
Global temperature anomalies are also strongly correlated with the warmest month temper- atures of the Jakarta/Semarang data set (r=0.84, n=121, p<0.00001), for the period of available data, 1958-1990 with Ahuachapan (r=0.81, n=20, p<0.0001) and with Los Andes (r=0.73, n=28, p<0.0001). When the secular trends are removed the residual deviations shown by the Jakarta/Semarang warmest month data are correlated with the deviations shown by the annual global anomalies (r=0.53, n=121, p<0.00001). This is of some interest since the Jakarta/Semarang warmest month indications are obtained usually by May or June (10/35 ENSO-years) or at least by October (31/35) of any one year . The Jakarta/Semarang warmest month temperatures are also closely related to the warmest month temperature deviations in say Manila, the Philippines which develop by April-May.
The temperature of the warmest month of the year in Jakarta Indonesia seems to closely reflect overall global warming and in particular can be used to predict upcoming droughts and global temperatures.
Gaia is running a feaver and her heartbeat is increasing both in frequency and intensity.
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