The Figures Behind the Floods

2011 annual rainfall compared against historical rainfall records.

© Australian Bureau of Meteorology.

The past two years have been hard for Australia, with record floods following many years of drought across most of the country.  Last month the Australian Weather Bureau provided the statistics to go with the devastating stories:

The persistent rain of 2010 and 2011 was thanks to La Nina; a shift in ocean currents and temperatures that alters weather patterns across the Equatorial Pacific.  Usually, there’s warm water to the East of Indonesia and Australia, warming the air above, which rises to produce clouds and rain.  When La Nina takes hold, though, sea temperatures are much warmer than normal, creating more convection (rising warm air), and delivering much more rain. 

The effects of La Nina extend much further than the Pacific; the atmosphere’s global circulation is driven by convection at the equator, and changes here can affect the rest of the globe: jet streams shift; patterns of temperature and rainfall on other continents change; and the greatest impact is in the Northern Hemisphere, not the South.

A Week in the Weather of: Brighton

Location of Brighton, UK

Fancy a week at the seaside?  Of course you do, but probably not in the UK at the moment.  The beach is synonymous with summer, but what's it like for the donkeys and ice-cream sellers left behind after the autumn exodus?  Let's find out.... 

Build Your Own Desert

The Mojave Desert, at a latitude of 35^o North

Copyright: Alice Bryant 2010

Consult a map of the globe and you’ll find two bands of desert sandwiching the rainforests that straddle the equator.  Their symmetry is no accident; nor is that of the temperate regions, half-way to each pole, where Britain (amongst others) enjoys its changeable weather.  The deserts and their neighbours are a manifestation of the temperature difference between the equator and the poles.  That such a difference exists in the first place is no surprise: The land at the equator faces the sun head on, whilst the icy tundra can spend months in perpetual darkness.  Warm air at the equator tends to rise, whilst cold air sinks at the poles; and in an idea put forward by George Hadley (an Eighteenth century barrister, and gentleman scientist), these were the two ends of a giant circulation, transporting polar air along the surface to the equator, and taking equatorial air to the poles in the upper atmosphere.  But there was a problem:  It didn’t explain the deserts, or the other patterns of weather found at different latitudes.

A Week in the Weather of: Much Wenlock

Location of Much Wenlock
(Click to Enlarge)

It’s just six months until the start of the 2012 Olympics, so we’re jumping on the bandwagon:  For this week's daily glance at the UK weather, we're in Much Wenlock - the birthplace of Dr William Penny Brookes, who was instrumental in the inception of the modern Olympic Games.

Perched above Wenlock Edge, Much Wenlock is a small medieval English market town in rural Shropshire.  Any geology student, from anywhere in the world, can tell you about Wenlock Edge; at 400 million years old, this giant wall of limestone harks back to the country’s equatorial beginnings,  and still bears fossils of a tropical shoreline.  As for the weather...