Global annual cycle

F Kucharski

Fred Kucharski, Abdus Salam ICTP, Earth System Physics Section, Climate Variability Group, Trieste, Italy

http://www.windows2universe.org/earth/climate/cli_seasons.html

External forcing

Longitude average ofSolar surface radiationIn W/m^2

This clearly drivesour seasons

Of course, this translates Into seasonal variations of surface temperature(here in degrees C)

However, note that the north-south excursions are much smaller……..and there is a 1-2 month shift -> Inertia of Oceans

May be a more interestingfield: Sea-level pressure(shown here in hPa)

As you know, it rainswhere the pressure is low…

But first have a look At the consequencesFor the zonal mean Winds [m/s].

Trades

Interesting interruptionsof trades: Monsoons!

Extratropical westerlies

And finally precipitation:

The extratropical rainbelts

The tropical ITCZ

(precip in mm/day)

Diff temp djf-jja

Cool, why?

Even the global men surface temperature has a seasonal cycle(due to heat capacity differences between ocean and land)

Diff slp djf-jja

MediterranianClimates

Subtropicalmonsoons

MediterranianClimates

Subtropicalmonsoons

Diff prec djf-jja

Picture can be quite different if we zoom into specific regions: Indian Monsoon

Seasonality of Indian Monsoon

Mechanism 2 : Different heat capacity of land and sea (land-sea breeze)

Mechanism 2 : Different heat capacity of land and sea (land-sea breeze)

Zoom into Mediterranean

Surface pressure: Azores high moving northwards

Zoom into the Mediterranean

Also Carbon Dioxide has a seasonal Cycle……..

SUMMARY

•The annual cycle is the largest climate variation on Earth.• It is forced by the Earth axis tilt with respect to the rotation axis around the sun.•The surface temperature reacts to this forcing with some delay, depending on the total heat capacity (land/ocean). •The responses of other climatic fields, such as surface pressure, winds and rainfall, is also very clear, but more complicated.•Usually the annual cycle is stronger in high latitudes than in low latitudes, particularly for temperature.•The climate in the mediterranean region is strongly influenced by the seasonal cycle, but also the climate in monsoon regions (i.e. Indian Monsoon).

THANK YOU!