Apologies for cross-postings
Applications are currently sought for a Postdoctoral Research Assistant
and a graduate student to carry out the National Environment Research
Council (NERC) funded project outlined below.
The project is due to start in October 2004 in the School of
Environmental Sciences at the University of East Anglia jointly
supervised by Prof. John M. C. Plane and Dr Stephen H. Ashworth.
All interested candidates should contact Prof. Plane ([log in to unmask])
in the first instance. (Applications from nationals of all EU member
states are encouraged.)
CALCIUM CHEMISTRY IN THE UPPER ATMOSPHERE
About 100 tonnes of interplanetary dust enters the earth’s atmosphere
every day at velocities ranging between 11 and 72 km s-1. Most of this
dust vaporizes completely, producing layers of metal atoms such as Na
and Fe that occur globally in the upper mesosphere (between 80 and 105
km). These metal atoms can be observed by ground-based lidar (laser
radar), and their ions are measured by rocket-borne mass spectrometers.
Calcium is a major constituent of meteorites (1% by mass), and Ca atoms
should have a similar abundance in the atmosphere to Na atoms.
Surprisingly, Ca is depleted by a factor of between 100 and 300,
depending on season. There are two other very curious aspects to
calcium. First, the Ca abundance peaks in the summer, opposite to the
layers of Na and Fe. Second, the abundance ratio of Ca+ ions to Ca is
about 2, whereas the Na+/Na and Fe+/Fe ratios are between 0.1 and 0.2.
The reasons for these completely unexpected observations remain to be
explained satisfactorily. It appears that calcium does not ablate as
efficiently from molten meteoroids entering the atmosphere as Na and Fe,
but there must also be substantial differences in the chemistries of the
three metals.
The objective of this project is to understand these long-standing
anomalies, using a combination of laboratory studies of reactions of
neutral and ionic calcium species, atmospheric modelling, and lidar
measurements at the U.S. radio telescope observatory in Arecibo, Puerto
Rico (http://www.naic.edu/aisr/sas/sashomeframe.html). The studentship
includes funding for a trip to Arecibo to carry out work there.
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