Showing posts with label lightning. Show all posts
Showing posts with label lightning. Show all posts
Tuesday, March 22, 2016
Physical Principles: Electricity in the Atmosphere
Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward Aguado, James E. Burt
Friday, November 6, 2015
Focus on Aviation: Lightning and Aircraft
Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward Aguado, James E. Burt
Monday, July 20, 2015
Meteorological Measurements
Ø Surface
Measurements
̶
Most locations report hourly automated measurements
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Non-automated measurements are reported every 3
hours
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U.S. national weather service stations are
called ASOS (Automated Surface Observing Systems)
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Federal aviation administration and department
of defense are called AWOS (Automated Weather Observing Systems)
̶
ASOS reports cloud height and amount, visibility,
precipitation type, intensity, and accumulation, obstructions to vision such as
fog or haze, dewpoint temperatures, and wind direction, speed, and character
(gusts, squalls)
̶
Data available on the internet
̶
Original data are coded using Meteorological
Aviation Report format called METAR
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Data also plotted on meteograms (graphs that
show how several atmospheric properties change with time)
̶
Meteorologists use meteograms to analyze the
structure of hazardous weather events and track their progress as they move
between stations
Ø Rawinsondes
̶
Rawinsondes are primary instrument packages
used to make these measurements (through the depth of the troposphere and well
into the stratosphere)
̶
Is a balloon-borne instrument system that
measure pressure, temperature, dewpoint temperature, wind direction, and speed?
̶
Launched worldwide twice a day at 0000 UTC and
1200 UTC
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Data collected are plotted on a diagram that
depicts pressure on the vertical axis and temperature (Celsius) on the
horizontal axis
Ø Radar
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A device that transmits pulses of microwave
energy
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When microwaves encounter objects, such as
raindrops and hailstones, some of the energy is scattered back toward the
antenna.
̶
The antenna gathers its energy (radar echo) and
passes it through other electronic device called a receiver
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The amount of energy that returns to the radar
depends on 3 parameters:
1. Size
of precipitation particles
2. Type
of particles (ice crystals, rain, hail)
3. Number
of particles in the beam
̶
Radar reflectivity allows meteorologists to
estimate the rain rate
̶
To display radar reflectivity meteorologists
use logarithmic or decibel scale which is denoted as dBZ
Ø Wind Profiling
̶
Type of Doppler radar that operates with very high frequency (VHF)
and ultra high frequency (UHF) radio bands.
̶
Antenna is an array of cables called a Phased Array Antenna
̶
Array transmits electromagnetic radiation with a slight time delay
from one side to the other across the array - delay creates a beam of radiation
that points in a specific direction
̶
By using three beams and trigonometry a vertical profile of the
wind can be obtained
̶
RASS (Radio Acoustic Sounding System) transmits an acoustic
(sound) wave in the vertical direction
̶
Speed of sound is related to the temperature of the air through
which the acoustic wave is passing
̶
WSR-88D (Doppler) radar are obtained through mathematical
manipulation of the radial velocity measurements all around the radar
̶
WSR-88D can also detect motion within about 20 km of the radar
site
Ø Satellites and Satellite
Imagery
̶
Found in 2 types of orbits (Geostationary orbits and Low-Earth
orbits)
̶
Geostationary Orbits: circular orbit lying in the earth’s equatorial plane in which a
satellite has the same rotational velocity as the earth, must be 35,800 km up
̶
Low-earth Orbits: several hundreds of thousands of km up, near polar orbit (crosses
the equator), view small part of the earth, clear view of polar regions
̶
Three primary channels are used when weather monitoring:
1. Visible: measures solar
radiation reflected from the earth or atmosphere at a frequency visible to the
human eye (like sitting on a satellite viewing the earth in black and white)
2. Infrared: Tuned to be sensitive
to infrared electromagnetic radiation that the earth emits. Lower clouds are
warmer so they give off more radiation then the cooler higher clouds in the
troposphere
3. Water Vapor Channels: Measures radiation at a
specific infrared frequency that is sensitive to radiation emitted from water
vapor molecules in the atmosphere, allows meteorologists to monitor during both
clear and cloudy situations
Ø Commercial Aircraft Measurements
̶
Various types of systems used are collectively named AMDAR
(aircraft meteorological data reporting) systems
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Meteorological data is reported to the National Weather Service
(NWS) and is used to develop weather forecasts
Ø Lightning Detection
̶
NLDN (national lightning detection network) and CLDN (Canada LDN)
map out the location of all cloud-to-ground lightning strikes in the US and
Canada
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Consists of remote, ground based sensing stations
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Direction, time of arrival, and other characteristics of
electromagnetic waves created
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Triangulates using three or more receivers to determine the
position, time, strength, and polarity
Friday, May 8, 2015
Earth Science (Meteorology)
Temperatures and Temperature Patterns
- Measured in: Fahrenheit, Celsius, Kelvin (no negatives)
- Should be above ground (5ft, ~1.5 meters), natural surface, and shaded
- Normal ≤ 30years worth of data
Influences/Factors: LOCALS
- Latitudes
o Variations in solar angle and day length depend on latitude
o Increased latitude = increased range
o Related to net radiation
§ Net gain – tropics and subtropics
§ Net loss – poleward of 38°
- Ocean currents
o Warm vs. cold
- Cloud cover
o Daily range is dependent on humidity and cloudiness (less clouds = more range; more clouds = less range)
- Altitude
o Decrease temperature, air pressure, and ______
o On average, temp decreases at 6.5°C/km in the troposphere. Therefore, it’s expected to be cooler at greater heights.
- Land & water, proximity to water
- Surface type
2/12/14
Thunderstorms and Severe Weather
Wedge tornado = a tornado that is wider than it is tall
Thunderstorm = a localized storm produced by a cumulonimbus cloud and always accompanied by lightning and thunder
Thunderstorms are most common in Florida because it is a peninsula.
Ingredients for Thunderstorms
Moisture
- Typical source is from the large bodies of water (Atlantic ocean, Pacific ocean, Gulf of Mexico)
- Measurements: dewpoint (TD) and relative humidity (RH)
Lift
- Topography
- 
Air density
Air density
- Drylines
- Outflow boundaries
Instability
- Warm moist air at the surface and cold air above that
- 
CAPE = potential energy of a storm
CAPE = potential energy of a storm
- Warm air rises
Severe Thunderstorms:
To be severe, you have to have...
- Winds >= 58mph
- Hail 1” +
- Tornado
Stages of Thunderstorm Development
- Cumulus Stage
o Dominated by updraft
o Bergeron builds precipitation supported by updraft
- Mature Stage
o Side-by-side updraft and downdraft
o Downdraft has heavy rainfall, cold pool
o Most severe stage
- Dissipating Stage
o Downdrafts dominate
o Light precipitation
Severe Weather:
- 1” hail
- Wind gusts ≥ 58mph
- Tornado
Types of Thunderstorms
- Single Cell (Air Mass)
o Commonly form in warm mT air masses during the summer
o Short lived (less than 30mins)
o Weak
o Rarely produce severe weather
- Multicellular
o Single cells lumped together
o Squall line forms ahead of a cold front as a line of thunderstorms
o MSC – Mesoscale Convective Systems
§ Thunderstorm complex about the size of the state of Iowa
§ Flood and severe weather producers
§ Tend to dominate summer months in U.S.
o Often more intense than single-cells
- Squall-line
- Supercell
o Rotating updraft
o Speed + directional shear
o Produce damaging winds, grapefruit size hail, and tornadoes
Lightning
- Electrical discharge between 2 charge centers
- Can be within a cloud
- Travels at the speed of sound (1000ft/s, 1 mile every 5 seconds)
- Distance = time(sec)/5
- Average temp is hotter than the surface of the sun
Bow Echoes and Derechos
- Strong winds and downdrafts
- Last a long time and cover large areas
Hail
- Ice
- Forms by recycling up into the updraft
Tornadoes
- Violently rotating column of air descending from a thunderstorm and in contact with the ground
- Most are brief, lasting only a few minutes. Sometimes last for more than an hour
- On average 100 people a year are killed by tornadoes (30yrs average of 65)
- 45% of all fatalities occurred in mobile homes
- Most rotate counter-clockwise
- Typical diameter is 300-2000 ft
- Usually move SW to NE
- Winds rage 75-250mph
- Can consist of one or multiple vortices
- Fujita Intensity Scale
Why does the south have a disproportionate number of fatalities?
- More tornadoes during nighttime hours
o between sunset and sunrise
o more difficult to spot
o days are shorter à more likely to occur at night
- More forest cover
- Strong tornadoes
- Storm move faster (stronger wind shear)
- Lower base clouds
- Higher population density
- Lack of a focus on “tornado season”
o Complacency
- More mobile homes/weak frame housing structure (reduce visibility)
- Other
o Education
o Coping styles
o Warning distribution systems
Instability = CAPE (has the potential to be unstable) more CAPE, mean more instability
Lift = convergence, low pressure, mountains
Wind Shear = speed/direction (between0 & 6km if >= 35knots+ you’re going to get supercells)
Floods
Tropical Weather
- Occurs between 0 and 23.5 degrees N & S
- Differs from midlatitue weather:
o No major air mass differences (lots of heat & humidity)
o Easterly winds
o Not much temperature differences
Hurricane
- An intense storm of tropical origin with sustained winds exceeding 74mph
- Conditions for development
o >27C or 80F (june through November)
o Convergence
o Forms 5-20degrees latitude
- Will not form 0-5degrees N & S of equator
- Cannot pass through the hemisphere
- DO NOT LIKE WIND SHEAR
- Stages of development
1. Tropical disturbance
2. Tropical depression
3. Tropical storm
4. Hurricane
- Weakening
o Move over cooler water
o Move onto land
o Move into very strong wind shear
- Official season June – November
- Peaks: Aug, Sep, Oct (80% of Hurricanes)
- Saffir-Simpson Intensity Scale
- Hazards
o High wind speed
o Flooding
o Storm surge
o Tornadoes
- Most destructive side is the right (wind speed, storm surge tornadoes)
- WATCH issued 24-48hrs prior to landfall
- WARNING issued within 24hrs prior to landfall
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