Laboratory of Computer and Information Science / Neural Networks Research Centre CIS Lab Helsinki University of Technology

Most prominent interannual phenomena with seasonally changing effects

Slow climate phenomena such as ENSO are known to interact with the annual cycle. One can say that slow phenomena modify the seasonal variations such that, for example, temperature conditions become colder or warmer in specific regions. In other words, seasonal variations change the effect of the slow climate phenomena. These interactions are likely to be small in the equatorial regions where the seasonal variability is small. Therefore, for example, El Niño (whose effect is most noticeable in the equatorial regions) is easily observable in the data. However, slow climate variations can exist in the polar regions as well. They could be discovered by investigating consistent slow changes in seasonal variations because of the dominancy of the annual cycle in those regions.

In the following experiment, we analyze surface temperature data in order to find climate variations prominent in the interannual timescale. The experiment is similar to the one presented here except that the interactions with the annual cycle are now taken into account. The same temporal filter shown on the right was used to emphasize the timescale of interest.

Surface temperature

You can click on the averaged maps to see a movie of the seasonally changing effect.
Time course Average effect, °C Winter-Summer effect, °C Spring-Autumn effect, °C

For comparison, the results of the analysis without taking into account the seasonal effects are reproduced below.

Surface temperature, °C

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