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From drought to flood down under: Part I--The need for rain


In December 2007, I arrived in Australia for the first time ever.  It was a critically dry period for the region, as they were in the midst of a terrible drought.  Immediately upon my arrival, there were signals of a community in dire straits.  Instead of advertisements for products and services, the signs in the airport were encouraging water conservation.  My hotel bathroom had a message affixed to the mirror asking me to limit my shower time and water usage.  The dams were drying up and many communities faced running out of water in just mere months.  As a result, the local governments had enacted extreme water restrictions, and whether you were a resident or a visitor, you could not escape the reality of the situation: water was scarce.

The reason I was visiting Australia was not for a vacation to see kangaroos and koalas and drive on the left side of the road (although I certainly had several opportunities for all of this during my visit).  Rather, I had been given the exciting opportunity to participate in a field campaign that was taking place along the coast in southeast Queensland, based out of Brisbane.  The purpose of the field campaign was to study how rain forms in the local clouds and investigate if seeding the clouds with giant salt particles could help enhance the amount of rain that they produce [For more about this topic, see About Cloud Seeding].

The field campaign involved an aircraft outfitted with a variety of instruments to measure the clouds from the inside and a sophisticated, dual-polarization weather radar to remotely measure properties of the clouds.  Every day I went to our project airport hangar and briefed the pilots and flight crew on the weather forecast for the day, and then I went to the radar facility to watch the day’s weather unfold.  When the clouds started to form, I got on the radio and spoke to the pilots to direct them to the clouds.  The aircraft flew below the clouds and then into the clouds at a variety of heights, sampling the atmosphere and cloud properties along the way.

Photos of research aircraft and instruments
Research aircraft with close-ups of the instruments mounted under the wings.
Research aircraft about to fly through cloud.
Photo of a cloud that the research aircraft is about to fly through.

This was a typical day for me during two austral summers between December 2007 and March 2009.  We are still analyzing all of the data that was collected during the field campaign, but one thing that we learned is that aerosol particles in the region are quite variable from day-to-day.  The aerosol conditions in this coastal region are sometimes influenced by the adjacent ocean (which brings clean maritime air, with few aerosol particles, onshore) and on other days the aerosol concentrations are higher due to influences from urban pollution, sugar cane fires, and dust from the interior of the continent.  Because cloud droplets cannot form in our atmosphere completely on their own (they need an aerosol particle to condense onto), aerosol conditions can have impacts on the way a cloud, and rain, forms.  The dual-polarization radar data from the field campaign is showing signs of just that: the sizes of the raindrops are forming differently under maritime influences than the influence of the city or interior continent.  Working to understand these kinds of local impacts on rainfall is important when rain is desperately needed.

CP2 dual-polarization radar.
CP2 dual-polarization radar antenna.

Suggested activity: Monitor drought with long-term precipitation measurements.  Use a long-term observation station near your school and look at precipitation trends over the past few decades and calculate the normal (average) precipitation over that period (for climatological studies use at least a 30-year period of data).  The GLOBE website provides long-term data via Google Earth.  Was there an extended period of below normal precipitation?

-ST

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