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The temporal evolution of El Niño and La Niña varies greatly from event to event. To understand the dynamical processes controlling the duration of El Niño and La Niña events, a suite of observational data and a long control simulation of the Community Earth System Model, version 1, are analyzed. Both observational and model analyses show that the duration of El Niño is strongly affected by the timing of onset. El Niño events that develop early tend to terminate quickly after the mature phase because of the early arrival of delayed negative oceanic feedback and fast adjustments of the tropical Atlantic and Indian Oceans to the tropical Pacific Ocean warming. The duration of La Niña events is, on the other hand, strongly influenced by the amplitude of preceding warm events. La Niña events preceded by a strong warm event tend to persist into the second year because of large initial discharge of the equatorial oceanic heat content and delayed adjustments of the tropical Atlantic and Indian Oceans to the tropical Pacific cooling. For both El Niño and La Niña, the interbasin sea surface temperature (SST) adjustments reduce the anomalous SST gradient toward the tropical Pacific and weaken surface wind anomalies over the western equatorial Pacific, hastening the event termination. Other factors external to the dynamics of El Niño–Southern Oscillation, such as coupled variability in the tropical Atlantic and Indian Oceans and atmospheric variability over the North Pacific, also contribute to the diversity of event duration.

The structure of the room-temperature charge density wave (CDW) phase in octahedrally coordinated tantalum disulfide, 1T-TaS2, has been a controversial issue for over 15 years. Large-scale scanning tunneling microscope images of the intralayer structure of this phase exhibit a domain-like pattern defined by a variation in the maximum CDW amplitude. The circular domains, consisting of high-amplitude CDWs, are arranged in a regular hexagonal lattice (period 73+/-3 angstroms) that is rotated relative to the CDWs. In addition, from the analysis of atomic resolution images it was determined that there is a well-defined phase shift between the CDWs in adjacent domains, and that within a domain the CDW superlattice is commensurate with the atomic lattice. These results provide evidence for the hexagonal discommensurate CDW phase in 1T-TaS2 and also suggest an explanation for the long-standing controversy concerning the structure of this phase.

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