7. A quick search of previous monthly weather reports for Mawson found the lowest pressure reading to be 954hPa in September last year (2010), which coincided with 135km/h winds but was surprisingly warm (-3.8C). I was expecting ultra cold for that pressure, why is it warmer?
Low pressure systems form north of the Antarctic coast and move west to east. Occasionally they bounce off the coast as they move to the East. The air in the low is rotating clockwise so most of the wind associated with a low when it hits the coast has its origin to the north where there is relatively warmer waters surrounding the frozen continent. This warmer air shows on the weather map as a warm front. See the weather map below. Note that the closer the lines on the map (isobars) the stronger is the wind at that point on the map.
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| The red arrows follow the trajectory of the wind around the Low pressure system. |
6. Why are temperatures warmer at Mawson when the wind is blowing strongly?
Temperatures are usually coldest when we have high pressure and clear sky’s similar to Australia. In those conditions the heat from the surface is lost to space and the surface becomes very cold. The cold surface cools the air in contact with it. That cooled air is heavier (warm air rises and cool air sinks) and sinks to the lowest point. Because the Antarctic continent is like a big dome, all the cooled air slides down hill toward the coast. It is quite a shallow layer but very cold. This type of wind is called katabatic wind. At Mawson the katabatic wind comes from the SE so when wind associated with a low pressure system is blowing generally from the same direction the speed of the katabatic wind is added to speed of the wind from the low pressure system. That is when Mawson has its strongest winds and blizzards. But the air from the low is being drawn from further north and is relatively warmer. This warm air which also contains more moisture and produces cloud and snow. The warmer air from the north mixes with the colder katabatic air and warms it. See the weather map above.5. With decreasing exposure to sunlight, what are you doing about vitamin D and calcium levels - are you all on supplements?
Vitamin D is used by the body to enable calcium and phosphorous levels in the blood stream to build and repair bone. As we get less sunlight less vitamin D is made by the body. It is recommended that expetitioners wintering in Antarctica take Vitamin D supplements during the winter months.
4. What is the geodesic dome used for?
The geodesic dome houses the ANARESAT satellite receiving antenna and other communications equipment. It points toward a geostationary communications satellite located above the equator. The Antenna points to the North of Mawson at a very low elevation angle. For a satellite to remain stationary it needs to orbit the earth at the same velocity as the earth rotates on its axis.All phone, email, Internet and data are sent and received to Australian antarctic bases via the ANARESAT link. There are alternative satellites that can be used as a backup if necessary. The outer layer of the dome is a thin membrane wrapped over and attached to the internal lattice frame.
3. Looking at barometric pressure data for Mawson, the current reading of 981.5 seems quite low (and still going down). There are two readings, one which is continuous (QNH) and the other every 3 hours (MSL), but both numbers are typically very close (within 0.2mm). Why 2 measurements?
The short answer.
MSL is observed each three hours and is used to prepare mean sea level weather charts, The QNH value is for aviation users. Both values are different ways of measuring air pressure at Mean Sea Level. See the more detailed explanation below.
The Long answer.
Air pressure is related to the weight of the atmosphere above that point. The higher in altitude the lower the pressure from the atmosphere above.
The air pressure at sea level is called Mean Sea Level Pressure (MSLP) however most barometers are located above mean sea level. The pressure measured at the barometer is called station level pressure (SLP). A correction based on height above sea level, temperature, time etc. is applied to SLP to reduce it to MSLP. This is the pressure that is used for drawing synoptic maps like those in newspapers and on TV. These maps are drawn every 3 hours at what is called the synoptic hour. - 00, 03, 06, 09, 12, 15, 18, 21 UTC. That is the time that weather observations are taken. (UTC is equivalent to GMT)
For aviation purposes the reduction to MSLP uses different correction factors that results in a slightly different pressure value and is called QNH.
Why QNH? - Well when telephony was very new the 'Q' code was devised as a way of abbreviating messages. Later when aviation and radio where both developing the 'Q' code was used to improve understanding of radio communication. If you know anyone with a ham radio set they talk about QSL cards - confirmation that they were able to speak to a particular operator in a distant location. The 'Q' code has many code values for all sorts of things: see http://en.wikipedia.org/wiki/Q_code
'Q' code for other pressure values.
QFF is the pressure at the station barometer which is usually called Station Level Pressure (SLP).
QNH settings are used by pilots to set their altimeter so they know their height when flying and more importantly landing. http://en.wikipedia.org/wiki/International_Standard_Atmosphere
Mawson or any airfield where the BoM takes observations the altitude of the helipad is somewhere between the station barometer and sea level. The pilot uses the altimeter as a guide to knowing the altitude of the ground when landing.
QFE is calculated by adjusting the station level pressure for the difference between the barometer level and the aerodrome reference level, assuming International Standard Atmosphere (ISA) conditions. An Altimeter set to QFE will read zero when the aircraft is on the runway.
2. How thick is the sea ice before you can walk on it?
From the Australian Antarctic Division Field Manual:
Foot or ski travel - 20cm of good quality uniform ice.
Quad Bike - 40cm
Hagglund - 60cm
At Mawson sea ice measurements are taken each week at a number of sites around the nearby islands. Sea ice travel is not permissible before May 1st due to possible break out of ice in heavy sea or storm conditions.
1. Where in the sky is the Southern Cross at Mawson and how can you find south.?
The position of the southern cross at Mawson varies through the night but is easily found at about 45 degrees at its highest point up from the horizon when looking to the south. The southern Cross can be used to find South Celestial Pole. There are a couple of methods.1. Follow the line 4.5 times the length of long axis of cross toward the horizon.
2. The intersection of the line through long axis toward the horizon and the line perpendicular with pointers. (see http://www.csiro.au/helix/sciencemail/activities/crux.html)
