Monday, December 24, 2012

Summer's here!

 Last week it was humid, rainy, and cool -
well cool for Panama.

Just like that!  It's summer.    

And this week it is bright, blue and breezy.
It’s always confusing here when we talk about summer.  The gringos usually mean June-August, the summer holidays for universities in the north; the summer field season for hard-working graduate students; the busy season for the field stations. 

But here, for Panamanians, summer starts in the weeks before or after Christmas.  It’s not a date you can find in the calendar. There’s no gradual spring warming.  It switches almost from one day to the next. 

What happens is this…..the Inter-Tropical Convergence Zone (ITCZ) is a thin strip of low pressure between two areas of high pressure, one in the subtropical part of the northern hemisphere and the other in the southern hemispheres.  You can see the ITCZ from satellite photos.  It’s the band of clouds and storms swirling around the equator.  During the dry season the northern hemisphere areas of high pressure push the ITCZ south keeping it south of Panama and we get blue skies and breezy dry days.  The rest of the year it is closer to us and keeps things wet and cloudy.
Red arrow points to us in Panama, orange arrows show the
line of clouds and rain.  Photo from NASA.

Biologically this has large effects.   In the dry season it doesn’t rain for weeks or even months.  Trees lose their leaves. Dry grassy areas burn.  Residents spend time watering their lawns. 

For us marine biologists things are different. The strong winds cause upwelling of cool water, so it’s cold for marine life in Panama.  Plankton blooms in the Bay of Panama. Tuna and dolphins arrive to take advantage of the little fish that thrive in upwelling.  And the animals we work on in the intertidal have to cope with wild fluctuations between the cold water and the scorching sun as the tide goes in and out.

Click for more information about the ITCZ in the news

No comments:

Post a Comment