La Niña (Jan 2000)542 Views
Satellite observation from space are especially useful to investigate large areas (e.g. the marine environment) which are otherwise not or only difficult to explore. Furthermore, large scale phenomena like El Niño and El Niña events, causing changes in global weather patterns, can only be fully comprehended in their entire dimension using observations from space.
This examples presents a combination of Chlorophyll biomass in the oceans and of the "Normalized Difference Vegetation Index" (NDVI) over land masses. NDVI is an indicator of "greenness" and hence, can bee seen as an indicator of land-based Plant biomass. The occurrence of a La Niña (Jan-2000) event as monthly average is shown. These phenomena can be directly detected from space e.g. by measuring the Sea Surface Temperature in the marine environment. Indirect evidence, however, can be gained by measuring the chlorophyll biomass, which strongly correlates with nutrient rich waters, upwelled from the deep ocean due to a change in the dominant wind patterns. Both, El Niño and La Niña, cause global changes of both temperatures and rainfall. The different effects (described below) caused by El Niño and La Niña can be distinguished in the greenness of the respective areas when comparing the two globes.
La Niña (Jan-2000) - During La Niña increased stronger upwelling (cold, nutrient rich water rising from the deep ocean to the surface) occurs fostering an increase in Chlorophyll biomass (algal growth) which is transported westward across Pacific. This can be seen in the imagery as a green, elongated band across the entire equatorial Pacific. La Niña results in wetter-than-normal conditions in Southern Africa (December-February), and drier-than-normal conditions over equatorial East Africa over the same period; over eastern and northern Australia an increase of rainfall occurs.
Imagery: OceanColor NASA
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