However, sea level also varies on other time scales due to other causes. Direct measurements of sea level with tide gauges provides one of the largest sets of available records on ocean variability, extending over many decades, and complementing more modern techniques, such as global estimates of sea level variation using satellite altimetry heights. Experience has shown that large-scale events like ENSO, occurring on time scales from months to years and over spatial scales of several thousand kilometers, can be conveniently documented by monthly mean sea level deviations that are observable with data from tide gauges. Using data from this network of gauges, Professor Klaus Wyrtki presented the first detailed descriptions of the oceanic ENSO cycle in the tropical Pacific. Since June 1984, monthly maps of the Pacific sea level variations have been published without fail, drawing from monthly mean sea level data from a present count of 93 stations in 35 countries throughout the Pacific basin.
Oceans are also substantial.
Sea level maps for the first four months of 1997 appear below, and show the beginnings of warm water movement from the wesern Pacific eastward, with sea levels dropping in the west and rising in the central and eastern tropical Pacific. Typically, the upper layer volume is at a peak preceding an ENSO warm event, then decreases over the course of the event as warm water moves from the western Pacific toward the east, and then north and south along the coasts of the Americas and out of the region. The ENSO cycle is defined by trends in oceanic and atmospheric conditions, which in turn affect climate by changing normal weather patterns. As such, the SOI gives information on the strength or weakness of normal easterly surface wind patterns in the tropical Pacific, compared to the long-term average. These changes in upper layer volume are a result of the ENSO cycle, and therefore cannot be used to predict it.