ANALYSIS OF UPPER AIR CONSTANT

1
ANALYSIS OF UPPER AIR CONSTANT
PRESSURE SURFACES! REFERENCE INTRODUCTION TO
FORECASTING VOL. 2 ATMOSPERIC ANALYSIS AG
1(AW) M. BUTCHER
2
LEARNING OJBECTIVES
1. Recognize plotted data on standard upper
air charts 2. Stress concepts and rules o
n analysis of upper air parameters to help p
repare students for the ITF course and C-sch
ool.
3
Constant pressure charts are used in conjunction
with surface synoptic charts for the following
- Determine the movement of weather systems
- Determine cyclonic and anticyclonic wind
circulation - Help define air masses - Loc
ate moist and dry areas - Aid in forecasting f
ormation, intensity, and dissipation of
weather systems - Determine the slopes of
fronts - Determine the vertical extent of pres
sure systems
4
Plotted data on constant pressure charts
The meteorological data displayed in upper air
reports are generally obtained at 0000 and 1200 G
MT (or Zulu) from radiosonde and rawinsonde obser
vations. Other types of reports,
such as aircraft and satellite derived data are
included when available. Although constant pre
ssure charts can be prepared for any of
the mandatory levels, the most common charts
are 850mb (approx 5000ft) 700m
b (approx 10000ft) 500mb (approx 18000ft)
300mb (approx 30000ft)
200mb (approx 34000ft)
5
TYPICAL UPPER AIR STATION MODEL
ON A CONSTANT PRESSURE CHART
TT
hhh
DD
hchc
TT TEMPERATURE TO NEAREST WHOLE DEGREE CELSIUS
hhh HEIGHT OF CONSTANT PRESSURE SURFACE IN METE
RS ON 850MB AND 700MB CHARTS, TENS OF METERS ON 5
00MB, 300MB AND 200MB CHARTS. DD DEWPOINT DEP
RESSION TO NEAREST WHOLE DEGREE CELSIUS
hchc 12 HOUR HEIGHT CHANGE IN TENS OF METERS
6
WIND DIRECTION PLOTTED TO 36 COMPASS POINTS.
WHEN WIND IS MISSING, THE LETTER M IS PLOTTED. W
HEN WIND SPEED IS LESS THAN 3 KNOTS, LV (DENOTING
LIGHT AND VARIABLE) IS PLOTTED.
- TEMPERATURES OR HEIGHTS WHICH HAVE BEEN ESTI
MATED BY THE ANALYSIS PROGRAM (ESPECIALLY OVER MO
UNTAINOUS REGIONS AT THE 850MB AND 700MB LEVELS),
ARE MARKED WITH A BRACKET TO THE
RIGHT OF THE REPORT. - REPORTED VALUES WHICH AR
E JUDGED BY THE ANALYST TO BE ERRONEOUS ARE ALSO
MARKED WITH A BRACKET TO THE RIGHT
OF THE REPORT. - AIRCRAFT REPORTS ARE PLOTTED W
ITH A SQUARE AND SATELLITE DERIVED DATA WITH A ST
AR RATHER THAN A STATION CIRCLE.
- THE HEIGHT IN AIRCRAFT REPORTS MAY INDICATE PR
ESSURE ALTITUDE IN HUNDREDS OF FEET RATHER THAN T
HE METERS DISPLAYED IN RADIOSONDE REPORTS.
7
CONTOURING CONVENTIONS
Geopotential Height- Drawn as solid lines labeled
with 3 digit numbers. - 30 meter intervals o
n 850mb and 700mb charts - 60 meter intervals o
n 500mb chart - 120 meter intervals on 300mb an
d and 200mb - High and low height centers are m
arked with an encircled X together with a larg
e letter H or L.
8
Temperature- Isotherms are drawn with red long
dashed lines at 5C intervals- Wind Speed- Lin
es of constant wind speed (isotachs) are drawn
on the 300mb and 200mb charts with green short
dashed lines at 20 knot intervals. Regions of hi
gh wind speeds are enhanced by alternate bands of
shading and no-shading at 40 knot intervals
beginning at 70 knot.
9
RULES OF UPPER AIR ANALYSIS
- Note previous position of troughs and ridges
for history. - Select a starting contour and sk
etch lightly with pencil interpolate between
reports. - Attempt to draw contours parallel to
wind flow (due to lack of surface friction), e
specially in straight line flow. Some
variation will occur on 300mb and 200mb charts
due to strong winds, any curved flow, and areas
of light winds. - Throw out reports that are o
bviously in error (check reports
around and above and below the report in
question). - Use the geostrophic wind scale (l
ocated in ITF vol. 2) to smooth
contour spacing and fill in data void areas.
10
RULES OF UPPER AIR ANALYSIS
- Do not kink upper level trough contours this
would imply a front - Label contours (in dec
ameters) at the margins, and preferably
once down the center of the chart for long
contours. - Label high and low height centers w
ith H and L with their center values in decamet
ers. - At 500mb, ridges and highs have a warm i
sotherm finger or pocket while troughs are cold
. - Isotherms are drawn at 5C intervals, beginn
ing with a value divisible by 5. - Ensure
a higher value on one side of an isotherm and a
lower value on the other side.
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
7412s can go back to work, non-7412s get out
your ITF
chartbooks for the hands on portion.