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How Close is Modeled Precipitation to Measured Precipitation?

Reference
Song, H., Lin, W., Lin, Y., Wolf, A.B., Neggers, R., Donner, L.J., Del Genio, A.D. and Liu, Y. 2013. Evaluation of precipitation simulated by seven SCMs against the ARM observations at the SGP site. Journal of Climate 26: 5467-5492.
Song et al. (2013) begin their work by noting that precipitation is one of the most poorly parameterized physical processes in general circulation models (GCMs). In fact, they say that it is difficult for them to simulate precipitation features as fundamental as diurnal variation, frequency and intensity.

To see what progress may have recently been made along these lines, Song et al. evaluated the performances of seven single-column models (SCMs) by comparing model-simulated surface precipitation with observations made during the Atmospheric Radiation Measurement (ARM) Program at the Southern Great Plains (SGP) site from January 1999 to December 2001.

The results of the comparison were troubling. The eight researchers report that (1) "in the warm season, most SCMs produce more rain events in the daytime than in the nighttime, while the observations have more rain events in the nighttime," (2) "the mean intensities of rain events in most SCMs are much stronger (weaker) in the daytime (nighttime) than the observations," (3) "in the daytime, most SCMs have a higher frequency of moderate-to-strong precipitation events than the observations for both the warm and cold seasons," (4) "for the precipitation events [for which] all the SCMs simulate the total precipitation well, different SCMs achieve the good performance by different combinations of compensating errors between the number of precipitation events and the mean precipitation intensity," (5) "most SCMs produce a spurious precipitation peak around the regime of weak vertical motions," (6) "model underestimation events occur in the strong ascending regimes with negative low-level horizontal heat and moisture advection," while (7) "model overestimation events occur in the weak (in the daytime) or moderate (in the nighttime) ascending regimes with positive low-level horizontal heat and moisture advection."

Given such findings, it is clear that it will be quite some time before proper confidence can be placed in these single-column models.

Archived 19 November 2013