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Earth System Dynamics An interactive open-access journal of the European Geosciences Union

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doi:10.5194/esd-2016-28
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
14 Jul 2016
Review status
A revision of this discussion paper was accepted for the journal Earth System Dynamics (ESD) and is expected to appear here in due course.
Annual and semiannual cycles of midlatitude surface temperature and baroclinicity: reanalysis data and AOGCMs simulations
Valerio Lembo1, Isabella Bordi2,3, and Antonio Speranza2 1Department of Biological and Environmental Sciences and Technologies (DiSTeBA ), University of Salento, Lecce, Italy
2National Interuniversity Consortium for the Physics of the Atmosphere and Hydrosphere (CINFAI), Rome, Italy
3Department of Physics, Sapienza University of Rome, Rome, Italy
Abstract. Seasonal variability of surface air temperature and baroclinicity from the ECMWF ERA-Interim (ERAI) reanalysis and six coupled atmosphere-ocean general circulation models (AOGCMs) participating in the Coupled Model Intercomparison Project phase 3 and 5 (CMIP3 and CMIP5) are examined. In particular, the annual and semiannual cycles of hemispherically averaged fields are studied using spectral analysis. The aim is to assess the ability of coupled general circulation models to properly reproduce the observed amplitude and phase of these cycles, and investigate the relationship between surface temperature and baroclinicity (coherency and relative phase) in such frequency bands. The overall results of power spectra agree in displaying a statistically significant peak at the annual frequency in the zonally averaged fields of both hemispheres. The semiannual peak, instead, shows less power and in the NH seems to have a more regional character, as is observed in the North Pacific Ocean region. Results of bivariate analysis for such a region and Southern Hemisphere midlatitudes show some discrepancies between ERAI and model data, as well as among models, especially for the semiannual frequency. Specifically: (i) the coherency at the annual and semiannual frequency observed in the reanalysis data is well represented by models in both hemispheres; (ii) at the annual frequency, estimates of the relative phase between surface temperature and baroclinicity are bounded between about ±15° around an average value of 220° (i.e., approximately 1 month phase shift), while at the semiannual frequency model phases show a wider dispersion in both hemispheres with larger errors in the estimates, denoting increased uncertainty and some disagreement among models. The most recent CMIP climate models (CMIP5) show several improvements when compared with CMIP3 but a degree of discrepancy still persists though masked by the large errors characterizing the semiannual frequency. These findings contribute to better characterize the cyclic response of current global atmosphere-ocean models to the external (solar) forcing that is of interest for seasonal forecasts.

Citation: Lembo, V., Bordi, I., and Speranza, A.: Annual and semiannual cycles of midlatitude surface temperature and baroclinicity: reanalysis data and AOGCMs simulations, Earth Syst. Dynam. Discuss., doi:10.5194/esd-2016-28, in review, 2016.
Valerio Lembo et al.
Valerio Lembo et al.

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Short summary
The study wishes to better characterise the annual and semiannual cycles of surface temperature and baroclinicity at midlatitudes as observed in ERA-Interim reanalysis data and AOGCMs simulations. Results show that at the semiannual frequency model phases between surface temperature and baroclinicity have wide dispersion in both hemispheres with large errors in the estimates, denoting uncertainty and a degree of disagreement among models.
The study wishes to better characterise the annual and semiannual cycles of surface temperature...
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