The second issue causes large differences in chemical and shortwave heating

The second issue causes large differences in chemical

This preview shows page 17 - 19 out of 19 pages.

than SC-WACCM. The second issue causes large differences in chemical and shortwave heating rates in the thermosphere. Although these differences in heating rates are large, the percentage differences are less than 6 5% due to large climatological heating rates in the thermosphere. Figure 17. (a) Mean power spectrum and (b) probability density distributions of the NINO 3.4 index for WACCM (black), SC-WACCM (red) and CCSM4 (blue). Thin gray, pink and blue lines in Figure 17a show individual 50 year spectra for WACCM, SC-WACCM, and CCSM4, respectively. The NINO 3.4 index is the time series of sea surface temperature anomaly averaged over the tropical Pacific region, 5 ² S–5 ² N and 170 ² W–120 ² W. Journal of Advances in Modeling Earth Systems 10.1002/2014MS000346 SMITH ET AL. V C 2014. The Authors. 899
Image of page 17
In spite of these differences, in the lower stratosphere and troposphere, WACCM and SC-WACCM have almost identical climatologies. We examined the zonal mean temperatures and winds, the seasonal evolu- tion of the polar vortices, the Brewer-Dobson circulation and the tropical water vapor tape recorder, all of which show remarkable similarities between the two models. At the surface, the mean climate of WACCM and SC-WACCM, diagnosed using surface air temperature, sea-level pressure, precipitation and sea ice extent, are also indistinguishable. Thus, prescribing middle atmosphere chemistry in SC-WACCM does not appear to degrade the simulation of the mean climate of the lower stratosphere, troposphere and surface relative to WACCM. Perhaps more surprisingly, we found that the stratospheric variability in both WACCM and SC-WACCM is also comparable. We examined the probability density distributions of stratospheric meridional eddy heat fluxes and temperatures and found only small differences. Consequently, the frequency, seasonal distribu- tion and composite characteristics of stratospheric sudden warmings are also similar across the two models. In the troposphere, we limited our analysis to the NAO and ENSO and again found no significant difference between WACCM and SC-WACCM. Throughout the paper, we also presented CCSM4 diagnostics along with the WACCM and SC-WACCM diag- nostics as a means of comparing stratosphere-resolving (‘‘high-top’’) and non-stratosphere-resolving (‘‘low- top’’) models. Although it is not a clean ‘‘high-top’’-‘‘low-top’’ comparison, since CCSM4 has other configura- tional differences, such as a finer horizontal resolution and differences in physical parameterizations such as turbulent mountain stress (TMS) and gravity waves, we included these diagnostics because CCSM4 is the main scientifically validated configuration of CESM1 for CMIP5. There are clear differences between the ‘‘high-top’’ models, WACCM and SC-WACCM, and CCSM4, notably the lack of stratospheric variability in CCSM4 in the Northern Hemisphere. At the surface, the lack of TMS in CCSM4 results in weaker (stronger) sea-level pressures in the Northern (Southern) Hemisphere extratropics and less (more) extensive Arctic (Antarctic) sea ice.
Image of page 18
Image of page 19

You've reached the end of your free preview.

Want to read all 19 pages?

  • Spring '20
  • Janet

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes