Transcript The Powerpoint used for my talk on the response time of radiosondes at low temperatures

RADIOSONDE TEMPERATURE,
HUMIDITY, AND PRESSURE
RESPONSE AT LOW TEMPERATURES
Stephen R. Hudson, Michael S. Town,
Von P. Walden, and Stephen G. Warren
24 June 2003
Introduction
• Vaisala RS80 and AIR 4A and 5A radiosondes
were tested during summer and winter at South
Pole.
• Their response to sudden, large changes in
temperature and humidity was characterized.
• Some data were collected with the RS80s to
characterize their response to smaller, more
gradual changes in temperature, humidity and
pressure.
Large, Sudden Changes
• Moved sondes from inside to
outside and recorded response of
reported temperature (T), humidity
(RH) and pressure (P).
• Usually building was heated, with
an indoor T of –5° to +25°C.
• A couple tests were done with an
unheated building, with indoor T
between –43° and –56°C.
• Outside T ranged from -24° to
–71°C.
• Range of T differences was 11 to
94 K.
RS80 Temperature Response
RS80 Temperature Response 2001/09/20
Reported Temperature
Exponential Decay Fit
20
10
0
Temperature (C)
 = 4.7 s
-10
-20
-30
-40
-50
-60
-70
0
10
20
30
40
Elapsed time (seconds)
50
60
70
RS80 Temperature Response
• Reported temperature responded with a simple
exponential decay.
Minimum
2.6 s
Median
5.4 s
Mean
5.9 s
Maximum
10.9 s
• Exponential-decay time
constants ranged from 2.6
to 10.9 seconds, with a
mean of 5.9 seconds.
• There was no apparent difference in the
character or time of the response between
summer and winter.
RS80 Humidity Response
RS80 Humidity Response 2001/09/20
55
Relative Humidity (%)
50
45
40
 = 321.8 seconds = 5.4 minutes
35
Reported Humidity
Exponential Decay Fit
30
0
5
10
15
Elapsed time (minutes)
20
RS80 Humidity Response
• When moved outside, reported RH initially decreased, then
increased with an exponential decay towards the outside value.
• The exponential decay began between 5 and 120 seconds after
being moved outside.
• E-folding time constants were between 13 and 420 seconds.
• Response was significantly slower in winter (T<-40°C) than in
summer (T near –25°C).
• Response in unheated winter cases (DT = 17 K) was similar to
winter cases using a heated building.
Summer
Winter
Unheated
winter
# of Tests
5
24
2
Outside T (°C)
-24 to -25
-45 to -71
-60
t1 (sec)
5-30 (30)
5-120 (33)
60-90
 (sec)
13-20 (15) 30-420 (146)
50-120
RS80 Pressure Response
RS80 Pressure Response 2001/09/20
681
Reported Pressure
Exponential Decay Fit
680
679
 = 328.2 seconds = 5.5 minutes
Pressure (mb)
678
677
676
675
674
673
672
671
0
5
10
15
Elapsed time (minutes)
20
25
30
RS80 Pressure Response
• When moved outside, the sonde initially reported increasing P,
followed by a slow exponential decay back to the correct P.
• Reported P increased by 0.4 to 10.0 mb over a period of 175 to
450 seconds.
• E-folding time constants were between 230 and 600 seconds.
• Magnitude of maximum error increased with increasing thermal
shock.
Summer
Winter
Unheated Winter
# of Tests
1
24
2
Outside T (°C)
-25
-45 to -71
-60
t1 (sec)
450
175 to 450 (300)
275 to 400
dP (mb)
3.3
3.5 to 10.0 (6.0)
0.4 to 1.6
 (sec)
N/A
230 to 600 (380) N/A, ~1500 to recover
Small, Gradual Changes
• After equilibrating to
conditions outside, sonde
was raised and lowered on
a 22 m tower at speeds of
0.4 to 1.0 ms-1.
• At the top of the tower, the temperature was 3 to
5 K warmer, the relative humidity was 3 to 5%
higher, and the pressure was about 2 mb lower
than at the surface.
(a)
Pressure (mb)
692
Tower Tests
691
690
689
0
50
100
150
Time (seconds)
-58
200
(b)
• Pressure responded to within the noise
level by the time descent was completed.
Change (about 2.2 mb) is approximately
correct, according to hypsometric eqn.
Temperature (C)
-59
• Temperature responded fully within 8 to
15 seconds of completion of descent.
-60
-61
-62
-63
-64
Relative humidity w.r.t. ice (%)
0
50
100
150
Time (seconds)
106
200
(c)
105
104
103
102
101
0
50
100
150
Time (seconds)
200
•Relative Humidity took 15 to 20 seconds
after descent to fully equilibrate. The
sonde was able to correctly report the
supersaturation with respect to ice.
Conclusions
• Radiosondes should be stored and prepared
at ambient temperatures
• If sondes must be prepared inside, they
should be given at least 30 minutes to
equilibrate to cold environments before
launching
• Problems can arise even from small
temperature differences, so unheated
buildings should be avoided unless well
ventilated
Conclusions (continued)
• Tests on the tower indicate that the sondes
are capable of providing better data in cold
conditions when given time to equilibrate to
shock of being moved outside
• Further work should be done in more
controlled environments, and with proper
ventilation
• Radiosonde instrumentation still remains
sluggish at low temperatures