Weather forecasting & Optical Phenomena

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1 Weather forecasting & Optical Phenomena

2 Weather forecasting

3 Weather forecasting

4 Weather forecasting National Weather Service (NWS) is a branch of the National Oceanic and Atmospheric Administration (NOAA). The mission statement of NWS is to provide weather and climate forecasts and warnings to the U.S., territories, and waters for the protection of life and property and enhancement of the economy. National Centers for Environmental Prediction: This branch of the NWS collects weather data from all over world. Information is disseminated to 125 regional Weather Forecast Offices, which prepare local forecasts.

5 Weather forecasting In Canada Environment Canada has its Weather Office, which is responsible for weather information on land and the adjoining ocean. Their website ( provides not only forecasts for cities and towns in Canada and a marine forecast, but also for air traffic. Furthermore, the website provides satellite information, historical data, and analyses and modeling data In general, their forecasts are more accurate than most other sources in Canada

6 Weather analysis Weather analysis: The forecaster must collect, transmit, and compile billions of pieces of observational data. Gathering data: The World Meteorological Organization (WMO), which is part of United Nations is responsible for the international exchange of weather data. Surface observations: The NWS and the Federal Aviation Administration (FAA) operate ~900 automated surface observation systems (ASOS). Worldwide, more than 10,000 land observation stations, 7000 ships at sea, and hundreds of data buoys and oil platforms report conditions four times daily.

7 Weather analysis

8 Weather analysis

9 Weather analysis

10 Weather analysis

11 Weather analysis Observations aloft: Weather balloons are launched twice daily at midnight and noon GMT. They contain radiosondes, which are lightweight instrument packs measuring temperature, humidity, and pressure.

12 Weather analysis Weather maps: pictures of the atmosphere The collected information is displayed in a format that can be comprehended easily by forecasters. The information is placed on synoptic weather maps, which means coincident in time.

13 Weather analysis Weather maps: pictures of the atmosphere

14 Weather analysis Weather maps: pictures of the atmosphere

15 Weather forecasting using computers Numerical weather prediction: This technique uses mathematical models. It begins by entering temperature, wind speed and direction, pressure, and humidity. The NWS produces generalized forecast maps, called prognostic charts (or progs).

16 Weather forecasting using computers Numerical weather prediction: A statistical analysis of progs compares the accuracy of previous forecasts. This approach is known as Model Output Statistics

17 Weather forecasting using computers Ensemble forecasting: This method produces a number of forecasts using the same computer model. It alters initial conditions while remaining within error range of the observational instruments.

18 Weather forecasting using computers Role of the forecaster: After progs are sent to the WMOs, forecasters blend information with local conditions and regional weather to produce site-specific forecasts. Forecasters use their knowledge and judgments based on experience. They will sometimes add extra detail to the model forecasts.

19 Other forecasting methods Persistence forecasting: This technique is based on the tendency of weather to remain unchanged for hours or days. Climatological forecasting: This method uses climate data (average weather statistics over many years).

20 Other forecasting methods Analog method: This is based on the assumption that weather repeats itself. Forecasters attempt to find weather patterns. Pattern recognition is an important tool, which helps improve shortrange, computer-generated forecasts. Trend forecasting: This method determines the speed and direction of fronts, cyclones, clouds and precipitation. Forecasters try to extrapolate the future position of weather phenomena.

21 Upper airflow and weather forecasting Upper level maps: These maps are generated twice daily. They are drawn at 850-, 700-, 500-, 300-, and 200-millibar (mb) levels.

22 Upper airflow and weather forecasting 850- and 700-millibar maps: The 850-mb map finds areas of cold-air and warm-air advection. Winds at the 750-mb level are used to predict movement of weather producers.

23 Upper airflow and weather forecasting 500-mb maps: This level is found approximately 5.5 km above sea level. These maps show upper level lows best.

24 Upper airflow and weather forecasting 300- and 200-mb maps: These maps represent zones near the top of the troposphere. The jet stream is best observed at these levels.

25 Upper airflow and weather forecasting The connection between upper-level flow and surface weather: Zonal patterns depict quickly moving westerlies (west to east). Meridional patterns consist of slow moving north to south flows, typically with heavy precipitation.

26 Upper airflow and weather forecasting

27 Upper airflow and weather forecasting An extreme winter

28 Upper airflow and weather forecasting

29 Upper airflow and weather forecasting Long-range forecasts: The Climate Prediction Center, a branch of the NWS, produces 30- and 90-day outlooks

30 Upper airflow and weather forecasting Long-range forecasts: The Climate Prediction Center, a branch of the NWS, produces 30- and 90-day outlooks

31 Upper airflow and weather forecasting

32 Forecast accuracy Percentage probability: Rainfall is the only aspect of a forecast expressed this way. The prediction of occurrence is fairly accurate. The predictions of amount, time, and duration are not as reliable. Short- and medium-range forecasts: Accuracy has improved over the decades. Beyond 8 days: Predictability of day-to-day weather is of low accuracy.

33 Satellites in weather forecasting TIROS 1: Launched in 1960, this was the first weather satellite. Since then, more than 30 versions have been launched through Polar-orbiting: These satellites orbit over the poles. Geostationary: These satellites orbit west to east over the equator.

34 Satellites in weather forecasting What types of images do weather satellites provide? Geostationary Operational Environmental Satellites (GOES) provide visible, infrared, and water-vapor images. They track large weather systems. Visible light imagery records the intensity of light reflected from cloud tops and other surfaces, to help define shapes, patterns, and thicknesses. Infrared images are obtained from radiation emitted from objects. They help to determine which clouds are likely to produce heavy precipitation.

35 Satellites in weather forecasting Geostationary Operational Environmental Satellites (GOES)

36 Satellites in weather forecasting Visible: Only during day Higher resolution No temperatures Infrared: Day or night Shows temperature of cloud tops Lower clouds warmer Higher clouds cooler

37 Satellites in weather forecasting Water-vapor images: Most of Earth s radiation with a wavelength of 6.7 micrometers, is emitted by water vapor.

38 Optical phenomena: Rainbows, Mirages, Halos, Aurora

39 Interactions of light and matter Reflection: A portion of the light rays bounce off the surface at the same angle they met the surface.

40 Interactions of light and matter Refraction: Refraction is the change of direction of light as it passes obliquely from one medium to another It can also bend light

41 Interactions of light and matter

42 Mirages Mirage: Mirages result when the bending of light is such that objects appear where they are not

43 Mirages Inferior mirage: The image appears below the true location

44 Mirages Superior mirage: The image appears above the true location

45 Rainbows Rainbow: A rainbow appears as an arch-shaped array of colors in the sky

46 Rainbows Dispersion: Dispersion is the separation of colors by reflection Prisms, as well as water droplets in the atmosphere disperse light They appear red on top and violet inside

47 Double Rainbows

48 Halos A halo appears as a whitish ring centered around the Sun or Moon They can occur in the morning or late afternoon Halos appear when there is a thin layer of cirrus or cirrostratus clouds A 22 halo has a radius of 22 degrees A 46 halo has a radius of 46 degrees

49 Halos Halos appear when there is a thin layer of cirrus or cirrostratus clouds They are caused by differently shaped ice crystals

50 Halos

51 Sun dogs or Parhelia These are features of halos and have two bright regions on opposite sides of the Sun Ice crystals magnify the sunlight

52 Sun pillars Sun pillars appear as vertical shafts of light reflected off ice crystals in high clouds

53 Glories A glory results when a shadow is projected on clouds below They are best observed from the air They consist of shadows surrounded by colored rings Like rainbows, they are the result of backscattered light

54 Other optical phenomena Diffraction: Diffraction happens when light passes close to water droplets Like refraction, diffraction separates light into colors.

55 Other optical phenomena Coronas: A corona appears as a bright white disk centered on the Sun or Moon

56 Other optical phenomena Iridescent clouds: Cloud iridescence is most often associated with altostratus, cirrocumulus, and lenticular clouds They appear as bright colors, such as pink, violet and green They are caused by the Sun behind a cloud or just after the Sun sets behind a building or other topographical feature

57 Other optical phenomena Noctilucent clouds: Tiny crystals of water ice at altitudes of km (highest clouds in atmosphere) Sources of dust and water are unclear; dust could be from micrometeors, moisture may be lifted through gaps in troposphere, or from chemical reactions incl. methane

58 Space Weather - Stellar Wind Flow of gas from the surface of a star into space - generates stellar winds loaded with atomic particles Stellar winds from massive stars often have speeds >2000 km/s

59 The Sun Photosphere Visible surface Sunspots Chromosphere Layer just above photosphere Magnetic activity Corona Extended rare surface Solar flares Solar Wind

60 Space Weather - Solar Wind Flow of gas ( km/sec!) from the surface of the Sun related to: Sun spots, Solar Flares & Coronal Holes

61 Sun Spots In 1610, shortly after viewing the sun with his new telescope, Galileo Galilee made the first European observations of Sunspots Dark regions on the photosphere where T is relatively low (~4,000 o K instead of 6,000 o K) VERY strong magnetic field

62 Sunspot Cycles & 22 year cycle

63 Solar Flares Massive abrupt releases of magnetic energy in the "active region" around a sunspot heat material to millions of degrees release as much energy as a billion megatons of TNT Flares release energy as: electro-magnetic (Gamma rays & X-rays) energetic particles (protons and electrons) mass flows

64 Solar Flares, March 1989 A series of massive intense solar flares started a LOT of space weather related events The particle and magnetometer sensors on satellites show the arrival of an interplanetary shockwave which caused a magnetic storm was the second largest in history The SMM (Solar Maximum Mission) satellite dropped 5 km from its normal orbit due to increased drag Geomagnetically-induced-currents caused a major power failure at Hydro-Quebec 6 million people without electricity for 9 hours

65 Earth s Magnetic Field liquid iron layer just above solid core - as it rotates, it generates a current current is moving charges, charges are either positive or negative large scale fields set up surrounding Earth between N and S poles Poles may flip over long periods of time: ~30,000 to 100,000 s of years

66 Earth s Magnetic Field magnetosphere is the region where particles come under influence of field most particles get deflected around the Earth s magnetosphere those that penetrate through, get trapped by the VAN ALLEN BELTS! discovered by Dr. James Van Allen in 1958 on first flight of a U.S. Earth-orbiting satellite Geiger counter on board!

67 Aurora Aurora Borealis and Aurora??? Sometimes magnetosphere gets overloaded with charged particles Solar wind electrons precipitate into polar regions, ionizing nitrogen and oxygen atoms

68 Aurora Ionosphere is electrically charged layer in thermosphere Molecules of nitrogen and atoms of oxygen are ionized by absorption of high-enery shortwave solar energy Borealis from Alaska Australis from Space aurora are connected to solar flares (magnetic storms) and found near Earth s magnetic poles