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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 Wednesday, February 15, 2017 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