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MOSQTRAK output

Simulations performed with RegCM3 contained large warm biases in daily summer (June, July, August-JJA) 2m temperatures over Iraq and Kuwait.  For example, observations show average Kuwait JJA daily temperatures of 35 oC whereas model values were closer to 39 oC.  Several important surface features in RegCM3 are corrected to address the warm bias.  We are able to show that surface characteristics such as albedo, land use practices such as irrigation, and natural processes such as dust emissions, all help to reduce summertime temperatures in semiarid regions.  All of these features are important in correctly simulating arid climates across regional and global models.

JJA surface (2m) temperatures for observations (upper left), original RegCM3 (upper right), and difference between observations and RegCM3 (bottom).

Comparing surface albedo values in RegCM3 to NASA’s Earth Radiation Budget Experiment’s (ERBE) Solar Radiation Budget (SRB) satellite, revealed that RegCM3 underestimates surface albedo by 3% in the region.  SRB estimates albedo at 0.30 whereas RegCM3 value is 0.27.  With too much shortwave radiation absorbed at the surface, this error causes RegCM3 to warm the surface too much.  By matching RegCM3 albedo values to that of ERBE/SRB, we find the increased reflection causes nearly 1oC cooling over the area.

Resulting average JJA temperature cooling when correcting (raising) albedo of RegCM3 to match ERBE/SRB observations.

The Fertile Crescent of Mesopotamia has been extensively irrigated for the past 6,000 years.  Original simulations performed with RegCM3 did not include irrigation or the Mesopotamian marshlands.  By including these land surface features, dramatic decreases in temperature occurs due to increased latent heat fluxes at the surface.  Resulting temperature decreases on the order of 1-1.2oC throughout the domain including regions where no irrigated land is present.

Resulting average JJA temperature cooling when including irrigation and marshlands of the region.

Dust emissions is another important land process absent in the original simulations performed with RegCM3.  Dust storms are quite common in the region, particularly during the spring and summer seasons.  Mineral aerosols (dust) have been shown to reflect incoming shortwave radiation, causing surface cooling.  RegCM3 has a full aerosol/tracer chemistry model.  When forcing this model to match observations for dust load over the Middle East, a 1oC cooling is observed.

Resulting average JJA temperature cooling when dust model (and hence dust emissions) are included.

Lastly, bias within the interpolated observational dataset may exist due to station locations.  Since most measurements are taken in cooler valleys outside desert regions, it is possible that the actual temperatures are somewhat warmer over desert areas.  Therefore, we compare reanalysis data to CRU observations---reanalysis data merges model output and observations.  We find that ERA40 (ECMWF’s reanalysis dataset) is nearly 1oC warmer than CRU.  As a result, combining these four features we are able to eliminate RegCM3’s summertime warm bias.  It is believed that to properly simulate summer climate in arid regions, accurate representation of all these features are necessary across all models.

Difference between JJA surface temperatures in ERA40 and CRU observations.

- graduate students on this project:  Marc Pace Marcella