Animations

Sea Surface Height

TOPEX/POSEIDON (T/P) sea surface height anomalies are compared with their model equivalent. The clips below differ in period and frame rate. In each animation, upper and lower panels correspond to model simulation and T/P, respectively. Units are cm.

Clip 1:     MPEG [3.7MB]     AVI [11MB]     QuickTime [24MB]

1997-98 covering the last El Nino and La Nina event. (1996/12/01 to 1998/12/30, one frame per 24 hours, 30 frames per second)

This animation highlights sea level changes associated with the 1997-98 El Nino/La Nina event and the "flickering" of large-scale high-frequency variability simulated at high latitudes.

The animation starts with two pulses (January and March '97) of positive anomalies rapidly propagating eastward along the equator in the Pacific Ocean (equatorial Kelvin waves). These waves are followed by large positive and negative anomalies in the eastern and western ends of the tropical Pacific Ocean, respectively, that reflect the El Nino condition (December '97). The anomalies gradually evolve into the La Nina condition, characterized by an opposite pattern of negative anomalies in the central and eastern tropical Pacific and positive anomalies in the western Pacific (November '98). Significant seasonal-to-interannual variability is also evident in the Indian Ocean, which relation to the Pacific variability is an active area of research.

The model simulation demonstrates significant coherence with TOPEX/POSEIDON measurements at seasonal-to-interannual time-scales. However, the magnitude and spatial extent of its estimates are in disagreement with the observations due to various errors in the model. Correcting such deficiencies is one of the aims of data assimilation.

Apart from seasonal-to-interannual changes, the model exhibits high frequency fluctuations at high latitudes (poleward of 30-deg from the equator). These fluctuations correspond to the wind-driven barotropic response   of the ocean. Much of these fluctuations occur at periods shorter than 20-days, and are aliased by TOPEX/POSEIDON due to its 10-day repeat cycle. De-aliasing TOPEX/POSEIDON measurements of these high-frequency variations is discussed in a separate study ("High-Frequency Signal").

Clip 2:     MPEG [3.5MB]     AVI [4.6MB]     QuickTime [10MB]

A detailed (slow-motion) animation of the high frequency variability. (1996/12/01 to 1997/05/31, one frame per 12 hours, 15 frames per second)

This animation runs at a quarter of the speed as Clip 1 and has twice the temporal resolution that allows for  a careful examination of the high-latitude, high-frequency fluctuations. The period corresponds to that of the double Kelvin wave that preceded the 1997-98 El Nino/La Nina event (See Clip 1 caption for details.)

What appears as "flickering" in Clip 1 can now be seen as a continuous fluctuation. Variations in the Southern Ocean display a tendency of eastward propagation reflecting the predominant pathway of storms. Topographic influence is evidenced by abrupt changes near topographic boundaries, such as near the Mid Ocean Ridge   south of New Zealand and Australia. Coherent changes are also evident over the Bellingshausen Basin.

Although not as energetic (fast oscillating) as the model, it is interesting to note some evidence of coherence between the model's high frequency fluctuations and anomalies mapped from TOPEX/POSEIDON. Particular examples can be seen in the southern Indian Ocean (February '97) and the Bellingshausen Sea (January '97).

Clip 3:     MPEG [10MB]     AVI [30MB]

A long animation. (1993/01/01 to 1998/12/30, one frame per day, 30 frames per second)