Transcript Recent progress in the development of Upper air Systems Catherine Gaffard Met Office Upper Air Team, University of Reading With contributions from J.Nash, T.Hewison, Richard.

Recent progress in the development of
Upper air Systems
Catherine Gaffard
Met Office Upper Air Team, University of Reading
With contributions from
J.Nash, T.Hewison, Richard Smout and T Oakley
© Crown copyright 2004
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Introduction
 Upper air observations are required to improve
climate and weather prediction
 Climate observations require “reference” quality , and
improved reliability in new generation measurements
 Observations need to be provided at higher temporal
and spatial resolution than in earlier networks
 for understanding processes
 for improved data assimilation
- (1km grid, update every 15 minutes)
 Achievable by a mix of in situ measurements
(Radiosondes, aircraft) and ground based remote
sensing stations to complement satellite observations.
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Outline of talk
 Progress in radiosonde technology
 Progress in ground base remote sensing for
operational use.
 Expected results from integration
 Conclusion
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Progress in radiosonde technology
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Temperature sensors
Thermistor or thermocapacitor devices
now have fast response, small radiation error.
time response = Function of (density, speed of
the flow, specific heat, size of sensor, shape of
sensor) small and thin sensor will be fast
radiation error = Function of (infrared and
visible emissivity, total incoming flux in infrared
and visible, surface of the sensor, sensor
temperature) compensation by radiation
correction scheme, however small aluminised
coated sensor will have small radiation error
thus small error in the correction .
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thermistor
white paint coating,
fine for short wave.
but 0.8 emissivity in IR
Modem radiosonde
in Brazil,WMO test 2001
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Modem radiosonde
2006
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capacitor
RS80 Vaisala temperature
Sensor, 1.2mm diameter
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RS92 Vaisala temperature
Sensor, 0.1mm diameter
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Mauritius comparison Temperature sensor
evaluation.
Systematic differences in nighttime temperature
referenced to the average of Graw, Meisei, Sippican, SRS-adjusted and Vaisala
WMO High Quality Radiosonde Comparison Test, Mauritius 2005
35
The reference is obtained by
a careful editing of each flight
rejecting data when contamination is identified. Night time
-0.5
30
Height [km]
25
20
15
10
5
0
-2.50
Vaisala RS92
SRS
Meisei
Modem
Sippican
Graw
3 Therm
SRS-adj
-2.00
-1.50
-1.00
-0.50
Temperature difference [K]
nearly all RS fall within
±0.20K bias (sip and 3 therm are <0.1K)
Graw and Srs had a calibration problem
Modem white coating induced strong
radiative cooling (replaced now by
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aluminized coating)
0.00
0.5
0.50
1.00
1.50
10 years ago bias >1k were
commonly observed in the
stratosphere (above 25km)
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Estimated random errors in nighttime temperature measurements,
WMO High Quality Radiosonde Comparison, Mauritius 2005,
assuming Vaisala random errors were as shown
35
30
Height [km]
25
20
15
Vaisala RS92
SRS
Meisei
Modem
Sippican
Graw
3 Therm
10
5
0
0.00
0.0
0.20
0.2
0.40
0.4
0.60
0.80
1.00
1.20
Random Error in Temperature [K]
std less than 0.1K for RS92 and 3 therm up to 35km,
in general very good reproducibility for all sensors
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cloud
top
Evaporative cooling,
well prevented by RS92 hydrophobic coating
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Geopotential height comparison
GPS heights are very consistent with themselves. This seems to
indicate that GPS heights are reliable.
At 10hPa (31 km) in the tropics an error of 0.1hPa introduces an error of
70m in height
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Progress in humidity sensor
 The majority of modern radiosondes use thin film capacitors e.g.
Vaisala(Finland), Meisei (Japan) Modem (France) and Graw
(Germany), Sippican (USA), Intermet (USA)
 Carbon hygristor sensors are much larger than the thin film
capacitors. These were distributed widely in the past by
Sippican/VIZ [USA], being used by many national radiosonde
designs. Sensors also now developed in China and India
 Gold-beater’s skin sensors have much slower response than the
capacitors and hygristors but are still used in Russia and China [
to a limited extent].
 Snow white is a chilled mirror hygrometer which measures dew
and frost point.
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Vaisala RS80 - H Humicap, main UK sensor, 1996 thin film polymer, capacitance changes with relative humidity
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Sippican Carbon Hygristor,
resistance very high at high relative humidity,
low at low relative humidity
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Vaisala RS90 in 2000,
No cover, heating pulses applied alternately to sensors to drive off
contamination
Sensors
In Mauritius in 2005 , bare circuit board near sensors aluminised
to reduce heating of sensor surrounds, but may not yet be available
In operational radiosondes
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Vertical structures are very similar in the
middle troposphere
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Mauritius Intercomparison
when temperature <-60C agreement
between sensor often diverges
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RS 92 against reference very good agreement.
Still some discrepancies at very low temperature
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Bias for day time larger than at night time (underestimation)
Day night difference ~5% for RS92 in the lower troposphere
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World wide radiosonde network
China is developing new generation of RS
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Progress in remote sensing technology
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Remote sensing technology may provide :-
 high time and space resolution data for model
validation and initialisation (assimilation)
automated unattended system for operational
use
complement to radiosonde (time evolution),
AMDAR (aircraft), and satellite data
Instruments considered here
 Microwave radiometer
 wind profiler
 GPS
 cloud radar, ceilometer
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Microwave radiometer : example of
radiometer retrieved profile temperature better than
1.5K (std) up to 3km
(against rs)
12 channels
around water
vapour line
and oxygen
complex
+IR channel
•automated
•unattended
•high time
resolution
•low vertical
resolution
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relative humidity
accuracy 20% std
(against rs)
Integrated water vapour with
optimum accuracy of
~0.7kg/m^2 (against rs)
Integrated liquid water with
optimum accuracy ~20g/m^2
(estimated error)
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Wind profiler and VAD winds
are assimilated in most of NWP centres
wind profiler network mixture of
operational
and research instruments
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weather radar VAD wind
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Wind profiler used for AMMA
(African Monsoon Multidisciplinary Analysis)
4 UHF ( 2 are permanently installed for airport security)
1 VHF
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example of diurnal cycle during dry season
Bamako (march 2005)
south easterly
MLJ
north easterly LLJ
shear,friction
turbulence
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convective
turbulence
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FMCW radar ( affordable technology)
Example of low stratus/fog evolution captured by the 78 GHZ cloud radar.
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GPS water vapour plot for Europe, showing current sites
supplying data to E-GVAP hub in near real-time
17
37
12
18
32
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Actual GPS sensor site used to measure
IWV in Africa
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Integrated ground base remote sensing
station- expected results
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Integrated profiling systems
RH retrieved by radiometer
RH measured by hourly RS
SNR measured by WP
Refractive (potential) index
gradient computed from RS
wind profiler SNR+ ceilometer could be used with radiometer
to get better vertical structure in the humidity profile
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convective scale: radiometer+ wind profiler
SNR (range corrected)
from WP
unstable before the updraft
stable and lower RH in the updraft
event last ~10min
in the future it will be possible
to assimilate such structure.
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vertical speed
updraft seen by WP
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cloud radar and ceilometer integration
liquid content=Function (size and concentration)
Cloud radar Zdb function of size( D^6)and concentration
Ceilometer return, function of size(D^2) and concentration,
The combination of the 2 allows an estimate of the water liquid profile
for thin water cloud.
Cloud base
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conclusion (radiosondes)
 Radiosondes are the only instrument that can give
detailed profiler of humidity, temperature collocated
with wind.
 It’s essential for climate reference that radiosonde
biases are minimised and kept stable.
 New generation of radiosondes have much better
design which minimise radiation error for temperature
sensor. In the night, the absolute accuracy of the
temperature sensor is reaching 0.1K with a very good
reproducibility 0.1K . Climate monitoring with selected
type of radiosonde could be envisaged using night
temperature.
 China is developing new generation radiosondes .
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conclusion (radiosonde)
 There is no discrepancy between GPS height.
 Pressure sensor might become obsolete unless
accuracy in both sensor can become such that their
information could be used for non-hydrostatic model.
 For the humidity, in the middle troposphere,at night,
the performance of sensors in Mauritius test was
rather similar within ±5%. At higher level above 11km
or when the temperature start to be lower than -60C,
the agreement between all the radiosonde diverge.
The best agreement with the snow white is obtained
with RS92.
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conclusion ( remote sensing)
 The need for weather forecasting and understanding
physical processes for climate prediction, requires
data at high temporal and spatial resolution. This can
only be achieved by a mixture of in situ and remote
sensing.
 With the help of European funding, the development of
a European network of wind profiler has facilitated the
use of wind profiler and VAD wind.
 During AMMA, the deployment of wind profiler in Africa
was successful, demonstrating the maturity of this
remote sensing technique. Help from international
funding will lead to sustainable development of wind
profiler network, including training for technicians
supporting the systems.
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conclusion ( remote sensing)
 With the evolution in the software and network
architecture, GPS integrated water quantities are now
available within 15 min. Integrated water quantities are
now assimilated operational into NWP. This
information is cheap and funding to help various
regions to expand their actual networks is desirable.
 While having a limited vertical resolution, radiometers
have the potential to be useful for high time resolution
description of physical processes.
 FMCW cloud radars are becoming affordable as
operational instruments.
 An integrated approach has the prospective to deliver
better products than independently retrieved
quantities.
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Conclusion : Future work
 The Met office is currently working on costed option of
a new upper air network which can deliver the user
needs for new generation of NWP.
 Several country in Europe including operational and
research centre have expressed their interest for
collaborative work to deliver an improved cost-effective
European ground-based observing system design,
providing essential atmospheric observations for both
climate and weather from one integrated operational
network for the decade 2010-2020.
© Crown copyright 2004
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Questions & Answers
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1
c
Estimated random errors in nighttime temperature measurements,
WMO High Quality Radiosonde Comparison, Mauritius 2005,
assuming Vaisala random errors were as shown
35
30
Height [km]
25
20
15
Vaisala RS92
SRS
Meisei
Modem
Sippican
Graw
3 Therm
10
5
0
0.00
0.20
0.40
0.60
0.80
1.00
1.20
Random Error in Temperature [K]
std less than 0.1K for rs92 and 3 therm up to
35km, in general very good reproducibility for all
sensors
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Page 41
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Page 42
Estimated random errors in daytime temperature measurements,
WMO High Quality Radiosonde Comparison, Mauritius, 2005
assuming Vaisala errors were as shown
35
30
Height [km]
25
20
Vaisala RS90
15
SRS
Meisei
10
Modem
Sippican
5
Graw
3 Therm
0
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
Random Error in Temperature [K]
std larger at day time than at night time
above 15km for all the sensors due to
solar heating
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Wind Profiler UK Model Assimilation
Wind Profiler Sites Assimilated in UK Met Office Model
35
30
25
20
Sites Assimilated
Total sites Reporting
15
Other NWP Centres
10
DWD – 20 Sites
Meteo France – 26 Sites
(with restrictions)
5
ECMWF – 13 Sites
-0
3
M
ay
-0
3
Ju
l-0
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Se
p03
N
ov
-0
3
Ja
n04
M
ar
-0
4
M
ay
-0
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M
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5
M
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Ju
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Se
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n06
M
ar
-0
6
M
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-0
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Ju
l-0
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Se
p06
M
ar
n03
0
Ja
Total number of sites
7 sites
Month
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Weather Radar UK Model Assimilation
Weather Radar Wind sites being Assimilated in UK Met Office Model
90
80
70
27 sites
50
Sites Assimilated
Total sites
40
Other NWP Centres
30
Only SMHI (local)
20
10
-0
3
M
ay
-0
3
Ju
l-0
3
Se
p03
N
ov
-0
3
Ja
n04
M
ar
-0
4
M
ay
-0
4
Ju
l-0
4
Se
p04
N
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-0
4
Ja
n05
M
ar
-0
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M
ay
-0
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Ju
l-0
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p05
N
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-0
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Ja
n06
M
ar
-0
6
M
ay
-0
6
Ju
l-0
6
Se
p06
M
ar
n03
0
Ja
Total Sites
60
Month
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