Characterization of seasons over the extratropics based on the annual daily mean temperature cycle

LÓPEZ DE LA FRANCA AREMA, N; SANCHEZ, E.; MENENDEZ C.G.; CARRIL A. F.; ZANINELLI P.; FLOMBAUM P.

INTERNATIONAL JOURNAL OF CLIMATOLOGY

JOHN WILEY & SONS LTD

Año: 2022

0899-8418

A proposal to characterize seasons based on the annual cy-cle of daily mean temperature over extratropical regions ispresented. Four metrics are computed, based on the datesalong the year when the maximum and minimum tempera-ture values and their corresponding derivatives (when tem-perature changes are maximum and minimum) are obtained.These four metrics are computed for 1980-2014 period forERA-Interim, JRA-55 and NCEP2 reanalysis products. Re-sults indicate that these four metrics are able to representaccurately, with geographical coherence over any extrat-ropical region, the start and end of subperiods along theyear that can be seen and used as a consistent procedureto define seasons along the year. The two more extrememetrics (date for the maximum and minimum temperature)are closely influenced by radiative process and thermal ad-vection. When physical mechanisms than can help to ex-plain the obtained metrics are studied related to the differ-ent land-atmosphere coupling conditions (wet, transition ordry regions), some clear features are obtained. Over wetregions, radiative summer processes are essential for datesrelated to maximum temperature values, being circulationpatterns more relevant for minimum temperature metric.When transitional regions are analyzed, surface budgets playa key role to explain the obtained results. Radiative pro-cesses seem also to be the more relevant feature for dryregions. Therefore, a robust methodology to establish sea-sons based on the annual cycle temperature is presented,and also the physical mechanisms behind the obtained re-sults to characterize seasons are inspected.