meteorology m.sc. peter lynch meteorology & climate centre school of mathematical sciences
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Meteorology M.Sc. Peter Lynch Meteorology & Climate Centre School of Mathematical Sciences University College Dublin. Synoptic Meteorology MAPH 40410 Peter Lynch Meteorology & Climate Centre School of Mathematical Sciences University College Dublin. Forecasting Module Lecture 1. - PowerPoint PPT PresentationTRANSCRIPT
MAPH40410 Synoptic Meteorology
Meteorology M.Sc.
Peter LynchMeteorology & Climate Centre
School of Mathematical Sciences
University College Dublin
MAPH40410 Synoptic Meteorology
Synoptic MeteorologyMAPH 40410
Peter Lynch
Meteorology & Climate CentreSchool of Mathematical Sciences
University College Dublin
MAPH40410 Synoptic Meteorology
Forecasting Module Lecture 1
Refresher:Airmasses, Fronts &Frontal Depressions
MAPH40410 Synoptic Meteorology
PolarMaritime
ReturningPolar Maritime
TropicalMaritime
TropicalContinental
PolarContinental
Arctic Maritime
Air Masses
MAPH40410 Synoptic Meteorology
Norwegian Model
MAPH40410 Synoptic Meteorology
167 181
64
045
10
1/30
Mean sea level pressureLast 3 figures of the MSL Pressure
e.g... 181 = 1018.1hPa
Present weatherSymbols
Rain
DrizzleSnow
Showers
Thunderstorm
Fog
Phenomena occurred in past hour.
Visibility01 to 50 add 00 for visibility in metres56 to 89 subtract 50 for visibility in km
Cloud amount and height ( Low, Medium and High)Amount of cloud in eighths /height of cloud in feet
01 to 50 add 00 for height in feet56 to 89 subtract 50 for height in thousands of feet
Past weatherSymbols as Present weather
Period covered0000,0600,1200,1800 last 6hrs0300,0900,1500,2100 last 3hrs
All other hours last hour
Type of low cloud
Dew point in tenths of a degreee.g.... 045 = 4.5 C
Screen temperature in tenths of a degreee.g... 167 = 16.7 C
Type of medium and high cloud.
Decode over page
Change in pressure (tendency)Difference in pressure from 3 hours
in tenths of hPa and direction ofup or down. Decode over page
Windspeed and directionWind from direction of the shaft
Triangle = 50 ktsFull feather =10 ktsHalf feather = 5 kts
Just shaft < 3kts
The Station Circle
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Observations
012
65
9
724
11
11,4510
50 3500199711
11
30 159978
475
00706 20
,,9
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Tephigrams & Stability
Any point on an ascent
AbsolutelyUnstable
AbsolutelyStable
ConditionallyUnstable
The position of the ELR gives the stability of the ascent at that point
DALR > SALR > ELR
ELR > DALR > SALR
DALR > ELR > SALR
MAPH40410 Synoptic Meteorology
EXTRATROPICAL CYCLONES
They form along the line between the polar air mass and the maritime tropical air mass.
Shearing produces cyclonic motion.
Under suitable conditions frontal surface will assume a wave shape.
MAPH40410 Synoptic Meteorology
EVOLUTION OF A FRONTAL DISTURBANCE
initial stage open wave cyclone
occluding fully occluded (mature)
stationary polar front
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INITIAL DISTURBANCE
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OPEN WAVE DEPRESSION
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OCCLUSION BEGINNING
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FULLY OCCLUDED
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LIFE-CYCLE OF A AN EXTRATROPICAL CYCLONE
MAPH40410 Synoptic Meteorology
13
2 4
Lifecycle of frontal
disturbances
Surface isobars (solid) temperature (dashed)
MAPH40410 Synoptic Meteorology2
13
4
Upper-level Height
Contours
Note displacement of upper-level trough to west of surface low
MAPH40410 Synoptic Meteorology
RELATIONSHIP BETWEEN SURFACE RELATIONSHIP BETWEEN SURFACE CYCLONE AND UPPER LEVEL FLOWCYCLONE AND UPPER LEVEL FLOW
500 mb height (thick lines), SLP isobars (thin lines), and layer-mean
temperature (dashed). The deflection of the upper-level wave contributes to deepening of the surface low.
MAPH40410 Synoptic Meteorology
CYCLOGENESISCYCLOGENESIS
Formation of cyclones
Close relationship between surface disturbances and flow of air aloft.
For a mid-latitude cyclone to form: cyclonic flow must be established
Inward flow of air near surface must be supported by outflow aloft.
Total spin / cyclonic height = constant
MAPH40410 Synoptic Meteorology
The jet stream wind is subgeostrophic in troughs, and supergeostrophic in ridges
slow
fast
fast
slow
MAPH40410 Synoptic Meteorology
slow
fast fast
MAPH40410 Synoptic Meteorology
slow
fast fast
MAPH40410 Synoptic Meteorology
MAPH40410 Synoptic Meteorology
Mid-latitude Frontal Disturbances:Mid-latitude Frontal Disturbances:interaction between low-level and jet-level interaction between low-level and jet-level
flowflow SL pressure and precipitation 300 mb height and wind speed
cold
warm
MAPH40410 Synoptic Meteorologysurface lowupper-level trough
Developing frontal lows tilt westward with height
MAPH40410 Synoptic Meteorology
slow
fast fast
Note the advection of cold and warm airmasses
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Satellite Views of Wave Cyclones
Open stage, with clouds over warm and coldfronts, with clear warmsector
Occluding stage
Mature stage
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mature stage
occluding stage
MAPH40410 Synoptic Meteorology
Locate the fronts and surface low
MAPH40410 Synoptic Meteorology
MAPH40410 Synoptic Meteorology
IR image
MAPH40410 Synoptic MeteorologyWater vapour image
Finding Surface Fronts
Using plotted surface charts
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Finding Surface Fronts What is a front? A boundary between different
types of air If we can define what those
differences typically are, or what we expect them to be …
… we can define the things that we should look for in order to find a front
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FrontsFronts
warm aircold air cool air
MAPH40410 Synoptic MeteorologyASXX MSLP Analysis 1200 UTC 20 Apr 2000
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Fronts on a Pressure Chart
992
988
984
980
976
972
996
1
23
4
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Station Circles
By studying different elements on a station circle, the position of the surface front can be found
So, what’s available on a station circle? temperature and dew point wind speed and direction, gusts present and past weather, visibility, cloud
amount, cloud type, cloud base pressure tendency
What happens to the weather as a front
passes?
Using the information from station circles
MAPH40410 Synoptic Meteorology
Fronts on a Pressure Chart
992
988
984
980
976
972
996
1
23
4
MAPH40410 Synoptic Meteorology
>200km ahead of the warm >200km ahead of the warm frontfront
12
07
965
07
251
75
4 75
1
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In the warm sector, 20km ahead of the cold front
G3211
09
752
31
1886 08
502
MAPH40410 Synoptic Meteorology
20km behind the cold front
08
06
814
18
2571 12
653
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>100km behind the cold front
08
04
840
12
3 28
72 4
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Positioning a Surface Front
Temperature and Dewpoint Windspeed and Direction, Gusts Present Weather and Past Weather Visibility Cloud Amount, Type and Lowest
Cloud Base Pressure Tendency
MAPH40410 Synoptic Meteorology
Temperature and Temperature and DewpointDewpoint Temperature isn’t such a good
guide as dewpoint The dewpoint within an airmass
tends to remain the same The dewpoint in the warm sector
will be constant and fairly high The dewpoint behind the cold
front may fall gradually
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Wind speed and direction
The wind will veer on the passage of a front
Veer = turn clockwise Back = turn anticlockwise Gusts are likely to be strongest on the cold
front
MAPH40410 Synoptic Meteorology
Present and Past Weather
The heaviest rain is often at the front
It is likely to rain ahead of a warm front
Drizzle is most likely in the warm sector
Showers develop behind a cold front
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Visibility
Visibility decreases when it is raining Drizzle will decrease the visibility
more than rain (the smaller drop size is more effective at scattering light)
Visibility in the warm sector will generally be poorer
Visibility in the cold air will be very good, up to 30km or more
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Clouds
Amount and type High clouds >200km ahead of the
warm front Lowest cloud is associated with
the heaviest rain, often on the front
Cloud base can be affected by orography
MAPH40410 Synoptic Meteorology
Pressure Tendency
The pressure falls just ahead of a front and rises just behind it, giving a pressure ‘kick’
Pressure
MAPH40410 Synoptic Meteorology
Positioning a Surface FrontPositioning a Surface Front
Dewpoint - constant in the warm sector Winds veer as a front passes Drizzle in the warm sector Moderate or heavy rain on the cold front Showers behind the cold front Overcast in the warm sector Broken cumulus behind the cold front Pressure ‘kick’ as a front passes
MAPH40410 Synoptic Meteorology
Conclusion.
Questions welcome