They can be seen in the diagram below (of the CERES radiation dataset - supposedly they contribute a lot to the total variance in net radiation, which is the sum of SW and LW) - just west of Peru and Mexico (my supervisor, Dargan Frierson, said these are stratocumulus regions). I'm just wondering - why are stratocumulus clouds so abundant there?

(the diagram is taken after taking the 12-month running mean of the dataset, which smoothes out a lot of features).

enter image description here

  • 1
    $\begingroup$ What year is the 12-month running mean from? $\endgroup$ Jul 23, 2014 at 16:52
  • $\begingroup$ 2011? 2012? 2013? 2014? $\endgroup$ Aug 28, 2014 at 22:02
  • $\begingroup$ What year is it from? $\endgroup$ Nov 20, 2014 at 22:02
  • $\begingroup$ Or even better, a source for the data/image. $\endgroup$ Nov 20, 2014 at 22:03
  • $\begingroup$ Any update on the sources and date information? $\endgroup$ May 8, 2016 at 13:41

1 Answer 1


On the east side of the Pacific Ocean, there are cold currents coming the poles going towards the equator. The cold currents makes it so there is almost a permanent cold air mass above the eastern portion of the ocean. As warmer air is blown over this colder air, it must go above the colder air. The warmer air expands, temperature decreases, becomes saturated and the stratus clouds form!

The cold currents are there because of the semi-permanent high pressure system in the mid-latitudes of the ocean. The winds are equator-ward on the east side of high pressure systems. This drives the ocean currents to be equator-ward on the east side of the ocean.


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