Title: Discussion of Observational Biases of Some Aircraft Types at NCEP Dr. Bradley Ballish NCEP/NCO/PMB 7 September 2006
1Discussion of Observational Biases of Some
Aircraft Types at NCEPDr. Bradley Ballish
NCEP/NCO/PMB7 September 2006
- Where Americas Climate and Weather Services
Begin -
2Overview
- Introduction
- Sonde/Aircraft temperature biases
- Monthly average temperature bias time series
plots
3Overview (Continued)
- Aircraft bias factors
- Aircraft biases by aircraft types
- Monthly average temperature increment plots
- Collocation results
- Monthly average plots of analysis minus guess
- Summary
4Introduction
- Observational data biases are serious in part as
they can cause errors in the analysis - Biases can be due to errors in the data or our
use that we would like to correct - Biases can be due to forecast model bias that is
best corrected in the model - It is helpful to know if the bias is due to
problems in the data or the guess - Bias correction looks encouraging but has issues
5Sonde/Aircraft Temperature Biases
- Data monitoring shows that aircraft temperatures
as a whole are warmer than the NCEP guess
especially around 250 hPa while radiosondes are
colder there - Aircraft and radiosonde data are very important
for NWP model analyses and forecasts - One objective of this study was to investigate
the key reasons for the bias discrepancies and
its potential impacts on model analyses and
forecasts
6Monthly Average Temperature Bias Time Series
Plots
- Biases are global for all data, passing QC from
300 to 200 hPa for GDAS runs - Note that on average, sondes are colder than the
guess, while all aircraft types are warmer than
guess - We investigated biases for ACARS, AMDAR, AIREPS
SONDES - For more details, see our paper from the AMS
annual meeting
7Monthly Average Temperature Biases 300 to 200
hPa 00Z
8Monthly Average Temperature Biases 300 to 200
hPa 12Z
9Aircraft Bias Factors
- Many factors affect aircraft biases
- These include aircraft type, influence of past
data on the guess, airlines, pressure level,
software, temperature sensors and Phase of Flight
(POF) - Specific aircraft type seems to be most important
such as 767-432 versus 767-322
10Aircraft Temperature Biases by Aircraft Types 300
hPa and up all Times of Day
11Aircraft Temperature Biases by Aircraft Types 300
hPa and up all Times of Day
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16Aircraft Temperature Biases 250 /- 25 hPa 00Zon
2.5 by 2.5 degree grid January 2005
17Radiosonde Temperature Biases 250 /- 25 hPa
00ZJanuary 2005
18Average Analysis minus Guess Temperature 250 hPa
January 2005
19Aircraft Temperature Biases 250 /- 25 hPa 00Zon
2.5 by 2.5 degree grid July 2005
20Radiosonde Temperature Biases 250 /- 25 hPa
00ZJuly 2005
21Average Analysis minus Guess Temperature 250 hPa
July 2005
22Discussion of Temperature Bias Impact
-
- The aircraft bias maps show mostly red dots
(warm) while the sonde plots show mostly blue
dots (cold) but not always - The analysis minus guess plots often show
patterns explainable by the data increments - For 00Z January 2005, huge warming over NE Canada
mixed changes over the CONUS, pattern bears
comparison with data increments - For 00Z July 2005, both data types show red dots
in the Southern US resulting in a large warming - Wherever both data types show blue dots, there is
often cooling in the analysis -
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25Summary
-
- The warm aircraft bias versus the cold sonde bias
can be explained in part by RADCOR and large
variance in aircraft biases for different types - There is evidence of systematic impact on NCEP
analyses due to these temperature biases -
26Summary (Continued)
-
- RADCOR needs fundamental improvement and more
frequent updates - Bias correction for aircraft biases needs to be
performed - Similar studies are planned for AMDAR data
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