Amazon/Africa precip biases #42
islasimpson
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2. Model bias
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We can gather information that we have here on the Amazon and West Africa precip biases. The too-dry amazon and too-wet West Africa is still a problem in 122. It is there in both the piControl and in the satellite era period of our coupled runs. It isn't there in AMIP mode so it's either associated with SST biases or needs coupled interactions to manifest. Below is a figure showing precipitation in JJA.
Here is the temperature bias in our 121 historical simulation for 1979-2012.
We're too warm in the NH, too cold in the SH. A guess would be that this is pulling precipitation too far North over Africa and making it absent over the Amazon.
CESM2 did have a dry bias over the Amazon but it wasn't as extensive. Neither was the wet bias over West Africa
Here are the JJA temperature biases that we had in CESM2.
The next figure is using the 2000 years from the CESM2 piControl and taking an index of interannual variability in the difference in precipitation between west africa and the amazon, given by the average over the boxes. It shows that in interannual variabilty when you have more precip over west Africa relative to the Amazon, it's warmer in the North tropical Atlantic and cooler in the South.
The next shows the same but for 20 year running means. On these timescales variability in the sub-polar North Atlantic dominates.
So, from the natural variability, we know that when the North Atlantic is warmer, precipitation is higher over West Africa and lower over the Amazon.
We maybe should think about what we can do to try and reduce these biases in the inter-hemispheric temperature gradient.
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