Reports from Jasmine
5/11/99 :
5/19/99 :
5/20/99 :
5/23/99
Sample Data
05/11/99
5/20/99
Your class is right about the cloudy/rainy weather. We get bursts of cooler
air during the rainy periods (coolest so far about 23 Cent.). The winds have
been stronger (around 10 m/s) for the last two days and we have had about 2
inches of rain. There are a lot of whitecaps and the ship is bumping around a
lot more. We are presently at about 6 degrees N. latitude, 88.5 degrees E.
longitude. We are chasing a huge glob of a convective storm which we can see on
the satellites and on the ship's C-band Doppler radar. The satellite images
also show a band of clouds and convection coming down from Bangladesh. Our
present plan is to go to about 10 degrees N. and commence a 5-day star pattern
survey similar to the one we did last week. We hope this second survey will be
done under "disturbed" conditions (i.e., stormy).
The students are doing about as well with their forecasts are we are here on
the ship. The question I posed (Why does the air cool of when it rains?) was a
tricky one. The students' answer
The higher the air in the clouds goes, the
more it cools off. When it cools off enough, water condenses out and falls as
rain, along with the cooler, heavier air.
contains some parts of the complete
answer but not others. The processes involved can be fairly complex.
One point
of confusion is the distinction between "cooling off" which is a reduction of
temperature and "loss of heat" which implies heat has been exchanged with the
environment. If you raise a chunk of air it does cool off, but this cooling can
be accomplished with out losing heat (in this case we say it was done
'adiabatically' because that makes us sound a lot smarter than if we said
'didn't exchange heat'). Thus, if you bring it back to its starting point it
will return to its original temperature. The weird part is if you take a parcel
of air up into a cloud, condense some water out, then return it to the surface
leaving the condensed water in the cloud or letting it fall out as rain, it
will arrive warmer than it started. That is because the process of condensation
releases heat (called the latent heat of condensation). To understand this,
imagine you start with a chunk of dry air near the surface and you want to add
water vapor to it. You could do that by boiling water and evaporating it into
the air. To do that, you have to put heat into the liquid water to make vapor.
Thus, when you condense the vapor to liquid again, you get the heat back. In
the tropics, this air is too warm (and therefore buoyant) to return easily to
the surface so it stays up there. The cold air we see in these storms is
actually air that has passed under rain clouds. As the rain falls through,
water evaporates from the raindrops, and this cools both the raindrops and the
air. Then, when that air is brought to the surface (to replace that warm air we
can't get back) it is colder because the evaporation process has removed heat
(i.e., heat was removed from the air to "boil" the water drops). This leads us
to a followup question: Why does snow in the Rocky Mountains warm up Denver?
Here are some more answers for your questions
What are your living quarters like?
The cabins are about the size of a typical home bedroom. Most share a
bathroom with an adjacent cabin. There are 2-3 bunk beds in each cabin, plus
drawers and closets for several people, and a wash basin with a mirror.
Everything is set up with latches so things don't fall out when the ship rolls.
I think some of the crew cabins have TVs (they bring their own), but scientists
are only on board for a month at a time so we just watch in the lounge. We
don't actually get television on this ship because it doesn't have a TV
satellite system.
How cold can that area get?
I don't believe it ever gets to freezing in the Bay of Bengal. It would be
unusual for it to drop below 15 C.
Can you get weather forecasts?
We get several different types of 48-hr forecasts over our communications
links. Unfortunately forecasts for this part of the ocean are notoriously
unreliable because the atmospheric data used for initialization are sparse.
What movies have you seen?
The ship gets a mixture of very recent movies (e.g., Saving Private Ryan,
Rush Hour) and classics like Airplane.
What happens if you cannot find a monsoon?
Our ship must be in Darwin, Australia on the 8th of June regardless of
weather during our cruise. The ship is scheduled to embark on another experiment
in the central equatorial Pacific Ocean, so our cruise cannot be extended. That
means you must carefully study the climatology of the region you wish to study
before designing your field program.
How many people are onboard? What do they do?
The crew of the Brown is 22 people; I think there are three women. The jobs
fall in categories like drive the ship, run the engines and generators, work on
the deck, cook the food, run the computer and instrument systems, etc.
There are 20 scientists (6 are women).
This picture shows two remote sensors on the aft main deck of the
Brown. The small white object (with red lettering) pointed at the sky is a
lidar (laser equivalent of radar) that bounces light beams off clouds to
determine their height (called a ceilometer for 'cloud ceiling'). The smallish
white building with the black letter in the upper right hand corner is a van
that houses the ETL cloud radar and microwave radiometer. The strange looking
metal pedastal with the large disc is a reflector for the radiometer, which
looks sideways out that white box stuck on the side of the van (it is actually a
window with a rain shade). The radiometer is a passive instrument in that it
doesn't send out radiation, it only detects what is coming in. It operates at
frequencies similar to the radar oven in your kitchen. The atmosphere actually
radiates small amounts of thermal radiation at microwave frequencies; the amount
depends on the concentrations of water vapor and water liquid in the sky.
This picture shows two of my instruments on the tall tower (jackstaff)
on the bow of the ship. The tall skinny thing is a sonci anemometer (i.e., a
device that measures wind using ultrasonic sound). The little cage at the top
holds 3 pairs of sound transducers that beep back and forth at each other; from
the difference in time it takes a beep to transect the distance between
transducers, the instrument computes the wind speed in that component. It does
this 20 times a second. The smaller cylinder with the bright red cap in the
lower part of the figure is an infrared device that measures the concentration
of CO2 and water vapor in the path. The red thing is a heater for the mirror
(keeps of water droplets). This system also provides a measurement 20 times a
second. We need this high speed information to evaluate the 'turbulent'
transport of moisture and CO2.
This picture shows about one-third the instruments located at the
top of the scaffold on the bow of the ship. It is difficult to get a picture
that shows everything. In the foreground are two pairs of radiative flux
sensors. The near ones (with the clear glass domes) measure the solar
radiation; the far ones (with the silver domes) measure the infrared radiation.
The two white boxes on the right are optical rain gauges. The other white
object (back on the left) is a different solar radiation instrument that
measures the diffuse radiation from the sun. It does this by blocking the disc
of the sun. The diffuse radiation is highly dependent on the scattering
properties of the clouds, a subject of great interest nowadays because of the
importance of clouds to the earth's climate.
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