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Order of Business
1.
2.
3.
4.
5.
Homework 3: due Monday
Observing Project - questions? keys
Questions?
Lecture
Computer stuff
Today’s topic: Weather
Text: Chapter 7
Wednesday, February 15, 2017
Isoplanatic Patch region of the atmosphere through
which parallel light rays have the same
speckle characteristics
= smearing component of the
atmosphere
r0 : Fried parameter
H : avg height of seeing layer
For r0≈10cm (V-band), H=5km → θIP≈1.2” (V-band)
but for K-band, r0≈60cm → θIP≈7.4”
Wednesday, February 15, 2017
Isokinetic area
Isokinetic Patch region of the atmosphere through
which parallel light rays have the
same motion characteristics
= motion component of the
atmosphere
D : telescope diameter
H : avg height of seeing layer
For a 4m telescope and typical conditions, θkin≈50” in optical
θkin larger at longer wavelengths
Wednesday, February 15, 2017
Coherence time characteristic timescale of variation
r0 : Fried parameter
V0 : avg velocity of turbulence layer
If most seeing effects caused by
ground layer, then
V0 ~ surface wind speed
for V0 = 2 m/s (~5mph), r0 =10cm → τ0 ≈16ms
Wednesday, February 15, 2017
Exosphere
air molecules won’t collide with each other;
no boundary between here and outer space
Thermosphere or Ionosphere
where aurora (Northern lights) occur
also where objects in “low Earth orbit” are
i.e., space shuttle and Hubble Space Telescope
Mesosphere
Stratosphere: where the ozone layer lives
Tropopause - boundary, associated with jet stream
Troposphere: where weather occurs and planes fly
Wednesday, February 15, 2017
Temperature Structure of the Atmosphere:
Sun heats & ionizes atoms
heated by stratosphere
ozone stores heat from Sun
heated by Earth
Wednesday, February 15, 2017
inversion layer cold air at surface with warmer air above
VERY stable air because convection shuts down --however, causes poor visibility from fog, smog, etc, can also cause freezing rain
Wednesday, February 15, 2017
Practical Meteorology
Wednesday, February 15, 2017
Absolute humidity amount of water vapor in a
particular sample of air (e.g., g/kg)
Relative humidity amount of water vapor in air
amount needed to saturate air
expressed as a %
water vapor condenses more easily in cold air,
so cold air “holds” less water vapor than warm air
remember definition of temperature
Wednesday, February 15, 2017
Dewpoint temperature at which the
water vapor in the air will
condense into a liquid
RULE OF THUMB:
if temperature - dewpoint < 2 °C,
it will soon be very wet outside
Keep in mind: humidity is measured at the ground,
but clouds usually form well above the ground
→ always keep an eye on the radar map
Wednesday, February 15, 2017
wind movement of air from areas of high
pressure to areas of low pressure
wind direction - where the wind
is coming from
Does the wind direction above
make sense given the atmospheric
pressure map for the US today?
Wednesday, February 15, 2017
front boundary between two masses of air
with different properties
warm front
mass of warm air is
advancing into region of
cold air
cold front
mass of cold air is advancing
into region of warm air
symbol is on advancing side of front
stationary front
unmoving boundary
between warm region and
cold region
Wednesday, February 15, 2017
Front type
Associated weather
warm front
mass of warm air is
advancing into region of
cold air
variable winds
steady T increase
stratus clouds
cold front
mass of cold air is advancing
into region of warm air
gusty winds
sudden T drop
cumulonimbus clouds (thunderstorms)
stationary front
unmoving boundary between
warm region and cold region
large T difference on either side of front
noticeable wind shift on either side
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Wednesday, February 15, 2017
Wednesday, February 15, 2017
Prediction of the hourly conditions based on North America
weather conditions and expected trends
Click on any box to see forecast map
Wednesday, February 15, 2017
Wednesday, February 15, 2017
Telescope Weather Limits
Put in place to protect the telescope from dangerous conditions
Your data are never more important than the safety of the telescope!
Typical Limits
Wind speed: 40mph
Humidity: 85%
Condensation on metal surfaces
Dust in flashlight beam
Remember that when the dew point and T get close, the
humidity will rise and likely go over the safety limits
--- be proactive and start closing down!
Lightning in the region can require special shutdown procedures to
isolate and protect the electronics
Wednesday, February 15, 2017
Final Thoughts
There is no substitute for LOOKING OUTSIDE
and observing the current weather conditions
while also keeping one eye on your weather instruments
Wednesday, February 15, 2017
Wednesday, February 15, 2017
Linux Operating System
Command-line operations
(similar to MS-DOS)
Wednesday, February 15, 2017
Some GUI-based support
(clickable icons and button controls, like
Windows)
Linux Directory Structure Example
home
Desktop
data
hlco
biases
bias01.fits
bias02.fits
Wednesday, February 15, 2017
iraf
kittpeak
cals
standards
darks
flats
stuff
Linux laptops: password is “student” (same as account name)
New to Linux or command line OS?
1. Start laptop
2. Log into CatChat2x wireless
3. Open web browser
4. Open Linux tutorial at
http://ryanstutorials.net/linuxtutorial/
5. Work through tutorial
Today’s Goal:
SHARE YOUR DATA FILES AMONG GROUP MEMBERS!
Wednesday, February 15, 2017