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METEOROLOGICAL MEASUREMENTS C H A P T E R 2

SEVERE AND HAZARDOUS WEATHER

METEOROLOGICAL MEASUREMENTS

•  Synoptic Meteorology •  Viewing a variety of measurements at one time

METEOROLOGICAL MEASUREMENTS

•  Meteorologists use Universal Coordinated Time (UTC) •  Otherwise known as •  Greenwich Mean Time •  Zulu Time

•  Word used to represent Z in radio transmission

2.1

METEOROLOGICAL MEASUREMENTS

•  To convert Eastern Standard Time to UTC just add 5 (and switch to 24-hour time) •  Convert the EST to UTC •  3 AM •  0800 UTC

•  9 AM •  1400 UTC

•  1 PM (1300) •  1800 UTC

•  10 PM (2200) •  0300 UTC

METEOROLOGICAL MEASUREMENTS

•  During Daylight Savings Time add 4 (and switch to 24-hour time)

•  Convert the EST to UTC •  1 AM •  0500 UTC

•  5 AM •  0900 UTC

•  3 PM (1500) •  1900 UTC

•  7 PM (1900) •  2300 UTC

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METEOROLOGICAL MEASUREMENTS

•  Convert UTC to EST - Subtract 5 (switch to 12-hour time) •  Convert the UTC to EST •  0500 UTC •  12 AM

•  1000 UTC •  5 AM

•  1600 UTC •  11 AM

•  2000 UTC •  3 PM

METEOROLOGICAL MEASUREMENTS

•  Surface measurements are continuously recorded (automated) •  U.S. National Weather Service •  Automated Surface Observing Systems (ASOS)

•  Federal Aviation Administration and Department of Defense •  Automated Weather Observing Systems (AWOS)

2.2

WEATHER STATIONS METEOROLOGICAL MEASUREMENTS

•  Meteorological Aviation Report (METAR) •  Weather information written in code

KHFD 161833Z 03005KT 3SM BR OVC006 00/M01 A2985 RMK AO2 BR = Mist

OVC = Overcast 006 = 600 ft 00 = 0oC (Temp.) M01 = -1oC (dew point) A = Altimeter 2985 = 29.85 inches of mercury

(pressure)

K = North American Station HFD = Hartford 16 = January 16th 1833Z = 1833 UTC 030 = Winds from the Northeast 05KT = Winds at 5 knots 3SM = 3 statute miles

METEOROLOGICAL MEASUREMENTS

•  Meteorological Aviation Report (METAR) •  Plotted on Meteograms

2.3

-When is the wind blowing from the west?

-When is the pressure the lowest?

-When was the cloud cover the highest?

0100 UTC

1800 - 2000 UTC

0700 UTC

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2.3

-When is the relative humidity the highest?

-When is the relative humidity the lowest?

-When was the snowfall the greatest?

1300 UTC

2100 UTC

1300 - 1700 UTC

METEOROLOGICAL MEASUREMENTS

•  Rawinsondes •  Instrumentation system

attached to weather balloons

•  Temp., dew point, wind direction, wind speed

•  Launched worldwide twice a day 0000 UTC and 1200 UTC

•  Rise 20 km before bursting •  Parachute back down

DAILY LAUNCHES METEOROLOGICAL MEASUREMENTS

•  Soundings •  Depiction of

the vertical structure of the atmosphere

•  Plotted on Stuve diagram

•  Note: pressure decrease logarithmically (every 5.5km – cut in half)

•  What happens at the boxes?

METEOROLOGICAL MEASUREMENTS

•  Soundings •  Same data

Skew-T/Log P diagram

•  Skew relates to how air cools as altitude increases

METEOROLOGICAL MEASUREMENTS

•  Radar •  Transmits pulses of microwave energy •  Microwaves encounter rain and hail •  Energy scattered back toward antenna (radar echo) •  Signal processed and displayed •  Repeats process

1/1000 second

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2.8

METEOROLOGICAL MEASUREMENTS

•  Radar •  Determines size of precipitation •  Type of precip •  Amount of precip. This is a modified version of radar for the public

METEOROLOGICAL MEASUREMENTS

•  Radar reflectivity •  Direct relationship between

the returned signal and rate of rain fall

•  dB = decibel scale •  Logarithmic •  Shows intensity

•  Z denotes radar reflectivity

2.9

DOPPLER RADAR

•  National Weather Service Doppler radars are called •  WSR-88D (Weather Service

Radar -1988)

•  Network established early-mid 90’s

METEOROLOGICAL MEASUREMENTS

•  Doppler Radar •  Radars transmit energy at specific frequencies •  Energy scattered back to radar is shifted •  Doppler radars measure the shift •  Only measures motions back and forth within in the beam not

across. Radial velocity – (like radius) •  Helps to determine winds

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DOPPLER RADAR

DOPPLER RADAR

•  Figure A – infrared image with radar echoes superimposed

•  Figure B – Radar reflectivity •  Showing precipitation

intensity and wind direction

DOPPLER RADAR

•  Wind Profiler - array of cables (phased array antenna) •  Transmits electromagnetic radiation with a slight time

delay across the array (points in specific direction) •  Senses small variations in atmospheric densities

(turbulence or winds) •  Uses three beams and trigonometry to create a

vertical profile of wind patterns

2.12

DOPPLER RADAR – WIND PROFILER

•  Radio Acoustic Sounding System (RASS) •  Measures temp. •  Transmits acoustic sound waves vertically •  Wind profiler pulse backscatters off of acoustic waves •  Measures Doppler shift •  Speed of sound corresponds to air temp.

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WIND PROFILE

•  Wind Profile •  Time moves

right to left •  (Left – most

recent) •  Creates a

cross section •  Note: shaded

area = cold front

SATELLITES

•  Geostationary •  Circular orbit around Earth’s equator (rotates with Earth) •  Monitors visible, infrared, and water vapor

•  Low-earth orbits •  100’s – 1000’s of km above surface •  Near-polar orbits (travel N-S, pole to pole) •  Pass by the same location at the same time each day (sun-

synchronous)

SATELLITES

•  Geostationary •  Visible light •  Difficult to distinguish snow from clouds (animation helps) •  Gray – incoming radiation mostly absorbed (oceans, forests) •  Black – no reflected radiation (ex. night time)

2.15A

Visible Light

SATELLITES

•  Geostationary •  Infrared (heat) •  Objects radiating energy (heat) •  Images day or night •  High clouds (white) – emit less energy (temp. decreases with height) •  Low clouds (gray) – emit more energy •  Difficult to distinguish (cold ground) snow from clouds (animation

helps)

2.15B

Infrared - heat

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SATELLITES

•  Geostationary •  Water-vapor •  Infrared that is sensitive to radiation emitted from water vapor •  Found everywhere (animation useful) •  Images day or night •  Dark areas – dry air •  White areas – moist air and clouds

2.15C

Water Vapor

Thunderstorms

Jetstream

SATELLITES

•  Geostationary •  Satellites from multiple countries provides us with a complete

picture (excluding polar regions)

2.16

AIRCRAFT

•  Commercial and cargo aircrafts transmit meteorological data •  AMDAR (Aircraft

Meteorological Data Reporting) systems

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LIGHTNING DETECTION

•  National Lightning Detection Network (NLDN) •  Ground based sensors determine the location of cloud-to-

ground strikes •  Black areas – strikes

2.18

LIGHTNING DETECTION NETWORK

CHAPTER 2

•  What is a rawinsonde? •  Weather instrument attached to a weather balloon •  Records: press., temp., dewpoint, wind

•  How does a radar determine rainfall rates? •  Transmits microwaves •  Energy bounces off precip. And back to receiver

•  What are two types of satellites used to monitor weather? •  Geostationary – orbit with earth •  Low-earth orbit – orbits N-S across poles (same location and

time each day)