The response of future projections of the North American monsoon when combining dynamical downscaling and bias correction of CCSM4 output
- 315 Downloads
A 20-km regional climate model (RCM) dynamically downscaled the Community Climate System Model version 4 (CCSM4) to compare 32-year historical and future “end-of-the-century” climatologies of the North American Monsoon (NAM). CCSM4 and other phase 5 Coupled Model Intercomparison Project models have indicated a delayed NAM and overall general drying trend. Here, we test the suggested mechanism for this drier NAM where increasing atmospheric static stability and reduced early-season evapotranspiration under global warming will limit early-season convection and compress the mature-season of the NAM. Through our higher resolution RCM, we found the role of accelerated evaporation under a warmer climate is likely understated in coarse resolution models such as CCSM4. Improving the representation of mesoscale interactions associated with the Gulf of California and surrounding topography produced additional surface evaporation, which overwhelmed the convection-suppressing effects of a warmer troposphere. Furthermore, the improved land–sea temperature gradient helped drive stronger southerly winds and greater moisture transport. Finally, we addressed limitations from inherent CCSM4 biases through a form of mean bias correction, which resulted in a more accurate seasonality of the atmospheric thermodynamic profile. After bias correction, greater surface evaporation from average peak GoC SSTs of 32 °C compared to 29 °C from the original CCSM4 led to roughly 50 % larger changes to low-level moist static energy compared to that produced by the downscaled original CCSM4. The increasing destabilization of the NAM environment produced onset dates that were one to 2 weeks earlier in the core of the NAM and northern extent, respectively. Furthermore, a significantly more vigorous NAM signal was produced after bias correction, with >50 mm month−1 increases to the June–September precipitation found along east and west coasts of Mexico and into parts of Texas. A shift towards more extreme daily precipitation was found in both downscaled climatologies, with the bias-corrected climatology containing a much more apparent and extreme shift.
KeywordsRegional climate modeling North American monsoon GCM bias correction Community Climate Model System version 4
This work was supported by the National Science Foundation Microsystem Program Project NSFEF-1065730. The authors would like to acknowledge and thank Drs. Lawrence Hipps, Scott Jones, and Bruce Bugbee of the Utah State University department of Plants, Soils and Climate for their comments and guidance regarding this work, as well as Dr. Patrick Belmont of the Utah State University Department of Watershed Science. We also wish to extend our appreciation to the anonymous reviewers who helped during the review process.
- Berbery EH (2001) Mesoscale moisture analysis of the North American monsoon. J Clim 14(2):121–137. doi: 10.1175/1520-0442(2001)013%3C0121:mmaotn%3E2.0.co;2 CrossRefGoogle Scholar
- Broccoli AJ, Manabe S (1992) The effects of orography on midlatitude Northern Hemisphere dry climates. J Clim 5(11):1181–1201. doi: 10.1175/1520-0442(1992)005%3C1181:teooom%3E2.0.co;2 CrossRefGoogle Scholar
- Douglas MW, Maddox R, Howard K, Reyes S (1995) The summertime low level jet over the Gulf of California. Mon Weather Rev 123:2334–2347. doi: 10.1175/1520-0493(1995)123%3C2334:tslljo%3E2.0.co;2 CrossRefGoogle Scholar
- Higgins RW, Yao Y, Wang XL (1997) Influence of the North American monsoon system on the US summer precipitation regime. J Clim 10:2600–2622. doi: 10.1175/1520-0442(1997)010%3C2600:iotnam%3E2.0.co;2 CrossRefGoogle Scholar
- Higgins RW, Mo KC, Yao Y (1998) Interannual variability of the U.S. Summer Precipitation regime with emphasis on the Southwestern Monsoon. J Clim 11:2582–2606. doi: 10.1175/1520-0442(1998)011%3C2582:ivotus%3E2.0.co;2 CrossRefGoogle Scholar
- Misra V, Kanamitsu M (2004) Anomaly nesting: a methodology to downscale seasonal climate simulations from AGCMs. J Clim 17:3249–3262. doi: 10.1175/1520-0442(2004)017%3C3249:anamtd%3E2.0.co;2 CrossRefGoogle Scholar
- Mitchell DL, Ivanova D, Rabin R, Brown TJ, Redmond K (2002) Gulf of California sea surface temperatures and the North American monsoon: mechanistic implications from observations. J Clim 15(17):2261–2281. doi: 10.1175/1520-0442(2002)015%3C2261:gocsst%3E2.0.co;2 CrossRefGoogle Scholar
- Skamarock WC, Klemp JB, Dudhia J, Gill DO, Barker DM, Wang W, Powers JG (2005) A description of the advanced research WRF version 2 (No. NCAR/TN-468+STR). National Center For Atmospheric Research Boulder Co Mesoscale and Microscale Meteorology DivGoogle Scholar
- Stensrud DJ, Gall RL, Nordquist MK (1997) Surges over the Gulf of California during the Mexican monsoon. Mon Weather Rev 125(4):417–437. doi: 10.1175/1520-0493(1997)125%3C0417:sotgoc%3E2.0.co;2 CrossRefGoogle Scholar