real time mesoscale analysis
DESCRIPTION
Real Time Mesoscale Analysis. RTMA Temperature 1500 UTC 14 March 2008. John Horel Department of Meteorology University of Utah [email protected]. Acknowledgements Dan Tyndall (Univ . of Utah) Dave Myrick (WRH/SSD ) Manuel Pondeca (NCEP/EMC) References - PowerPoint PPT PresentationTRANSCRIPT
Real Time Mesoscale Analysis
John HorelDepartment of Meteorology
University of [email protected]
RTMA Temperature 1500 UTC 14 March 2008
• Acknowledgements– Dan Tyndall (Univ. of Utah)– Dave Myrick (WRH/SSD)– Manuel Pondeca (NCEP/EMC)
• References– Benjamin, S., J. M. Brown, G. Manikin, and G. Mann, 2007: The RTMA
background – hourly downscaling of RUC data to 5-km detail. Preprints, 22nd Conf. on WAF/18th Conf. on NWP, Park City, UT, Amer. Meteor. Soc., 4A.6.
– De Pondeca, M., and Coauthors, 2007: The status of the Real Time Mesoscale Analysis at NCEP. Preprints, 22nd Conf. on WAF/18th Conf. on NWP, Park City, UT, Amer. Meteor. Soc., 4A.5.
– Horel, J., and B. Colman, 2005: Real-time and retrospective mesoscale objective analyses. Bull. Amer. Meteor. Soc., 86, 1477-1480.
– Tyndall, D., 2008: Sensitivity of Surface Temperature Analyses to Specification of Background and Observation Error Covariances. M.S. Thesis. U/Utah
An Analysis of Record• Forecasters have needs for higher resolution
analyses than currently available– Localized weather forecasting– Gridded forecast verification– Climatological applications
• AOR program established in 2004– Three phases
1. Real Time Mesoscale Analysis2. Delayed analysis: Phase II3. Retrospective reanalysis: Phase III
Real-Time Mesoscale Analysis (RTMA)
• Fast-track, proof-of-concept intended to:– Enhance existing analysis capabilities at the NWS and generate
near real-time hourly analyses of surface observations on domains matching the NDFD grids.
– Background errors can be defined using characteristics of background fields (terrain, potential temperature, wind, etc.)
– Provide estimates of analysis uncertainty
• Developed at NCEP, ESRL, and NESDIS– Implemented in August 2006 for CONUS (and southernmost
Canada) & recently for Alaska, Guam, Puerto Rico– Analyzed parameters: 2-m T, 2-m q, 2-m Td, sfc pressure, 10-m
winds, precipitation, and effective cloud amount– 5 km resolution for CONUS with plans for 2.5 km resolution
More Info… www.meted.ucar.edu
The Real-Time Mesoscale Analysis
• Several layers of quality control for surface observations
• Two dimensional variational surface analysis (2D-Var) using recursive filters
• Utilizes NCEP’s Gridpoint Statistical Interpolation software (GSI)
• Uses various surface observations and satellite winds– METAR, PUBLIC, RAWS, other mesonets– SSM/I and QuikSCAT satellite winds
• Analysis became available in 2006, and is being evaluated by WFOs and several universities
The actual ABCs…• The RTMA analysis equation looks like:
• Covariances are error correlation measures between all pairs of gridpoints
• Background error covariance matrix can be extremely large– 2,900 GB memory requirement for continental scale– Recursive filters significantly reduce this demand
1 1T T T T Tb b o b b o o b
a b b
P P H P HP v P H P y H x
x x P v
The Real-Time Mesoscale Analysis
RTMA Domains
CONUS Alaska Hawaii Puerto Rico Guam
Resolution 5-km ~6-km 2.5-km 2.5-km 2.5-km
Background (downscaled) RUC NAM NAM NAM GFS
Precip NCEP Stage II analysis No No No No
Effective Cloud
Amount
GOES sounder No No No No
RTMA Vancouver Area
CVOC &CVOI
CVOD
Background DownscalingBenjamin et al. (2007)
• CONUS RTMA background = 1-h forecast from the NCEP-operational 13-km RUC downscaled to the 5-km NDFD terrain
1.Horizontal - bilinear interpolation2.Vertical interpolation – varies by variable, for temperature it is
based on near-surface stability and moisture from the RUC native data used to adjust to the RTMA 5-km terrain
– If RTMA terrain lower than RUC, then local RUC lapse rate used (between dry adiabatic and isothermal)
– If RTMA terrain higher than RUC, interpolated between native RUC vertical levels, but shallow, surface-based inversions maintained
3.Coastline sharpening
• Real-time RTMA analysis begins ~30 min past the hour• Getting the data in time is a challenge
– RTMA uses obs taken (+/-12 min from top of hour)• RAWS and Quickscat winds (-30 min to +12 min)
• Many remote obs still don’t make it in time, as well as some obs with longer latencies (Snotel = every 3 hrs)
Surface Data Issues
Observation Network MADIS NCEP
RTMA CONUS Temperature Analysis
Subjective Evaluation of the RTMA Temperature
• Development of web based graphics for many analyses over selected subdomains– Wasatch Valley, UT– Puget Sound, WA– Norman, OK– Shenandoah Valley, VA
• Analysis problems based on subjective evaluation– Non-physical treatment of temperature inversions– Smoothed features– Bull's-eye features around observations– Overfitting issues
• Case study– 0900 UTC 22 October 2007– Shenandoah Valley, VA
Case Study Orientation0900 UTC 22 October 2007RTMA
RTMA Topography vs. Actual Topography
0 100 200 300 400 500 600 700 800 900 1000
Sterling, VA Atmospheric Sounding
1200 UTC 22 October 2007KIAD
RUC 1-hr Forecast
Valid 0900 UTC 22 October 2007RUC 1-hr Forecast
RTMA Temperature Analysis
0900 UTC 22 October 2007RTMA
RTMA Temperature Analysis Increments
0900 UTC 22 October 2007
RTMA Temperature Analysis Increments
Observations
• Surface observations: METAR, RAWS, PUBLIC, OTHER
• Observations must fall in ±12 min time window (−30/+12 min for RAWS)
• Observations undergo quality control by MADIS and internal checks by RTMA
• Approximately 11,000 observations for almost 900,000 gridpoints for CONUS
Observation Density
METAR
16/59/1,744
PUBLIC
215/575/6,486
OTHER
10/75/1,961
RAWS
3/11/1,301
Observation Density
Observation and Background Error Variances
• Ratio of σo2/σb
2 estimated by accumulating statistics over a time period for entire CONUS– 8 May 2008 – 7 June 2008
• RTMA used σo2/σb
2 = 1 for METAR observations and σo
2/σb2 = 1.2 for mesonet observations
• Statistics computed in our research suggest σo
2/σb2 between 2 and 3
– Background should be “trusted” more than observations
Estimation of Observation and Background Error Covariances
• Temperature errors at two gridpoints may be correlated with each other
• Error covariances specify over what distance an observation increment should be “spread”
• RTMA used decorrelation lengths of:– Horizontal (R): 40 km– Vertical (Z): 100 m
Error Correlation Example – KOKV
R = 40 km, Z = 100 mError Correlation- KOKV
Error Correlation Example – KOKV
R = 80 km, Z = 200 mError Correlation- KOKV
Local Surface Analysis• RTMA experiments run on NCEP’s Haze supercomputer
but limited computer time available• Development of a local surface analysis (LSA)
– Same background field– Same observation dataset, but without internal quality
control– Similar 2D-Var method, but doesn’t use recursive filters– Smaller domain– Control run uses same characteristics of RTMA
(decorrelation length scales; observation to background error ratio) at time of study
LSA Temperature Analysis
R = 40 km, Z = 100 m, σo2/σb
2 = 1LSA
RTMA Temperature Analysis
0900 UTC 22 October 2007RTMA
Data Denial Experiments• Evaluation of analyses done by splitting up all observations
randomly into 10 groups• Two error measures:
– Root-mean-square error calculated using the withheld observations only vs. using the observations assimilated into the analysis
– To avoid overfitting, want RMSE at withheld locations to be similar to RMSE at locations used in the analysis
– Root-mean-square sensitivity computed at all gridpoints– Want analyses to be less sensitive to withheld observations
2
1 1
M Nij ij
j i
a oRMSE
MN
2
1 1
M Lij ij
j i
d cS
ML
Withholding Observations
Group 5 R = 40 km, Z = 100 m, σo2/σb
2 = 1
Withheld Data Groups 1-5
0 0.5 1-0.5-1 2.5 4.5 6.5 8.5 10.5 12.5 14.5 16.5
R = 40 km, Z = 100 m, σo2/σb
2 = 1
Withheld Data Groups 6-10
0 0.5 1-0.5-1 2.5 4.5 6.5 8.5 10.5 12.5 14.5 16.5
R = 40 km, Z = 100 m, σo2/σb
2 = 1
RTMA Temperature Analysis Sensitivity
Group 1 RTMA
LSA RMSE and Sensitivity Compared to RTMA
Experiment
RMSE at Withheld
Observations (°C)
RMSE at All Observations
(°C)
Sensitivity (°C)
Background 2.15 2.15 -R = 40 km, Z = 100 m, σo
2/σb2 = 1 1.93 1.62 0.26
R = 80 km, Z = 200 m, σo2/σb
2 = 2 1.89 1.83 0.22
RTMA (group 1 only) 2.12 1.64 0.47
RTMA Background (group 1 only) 2.32 - -
Suggests overfittingOverly sensitive to withheldobservations
How good does the RTMA have to be?
• Is the downscaled RUC background field good enough?– RUC RMSE approximately 2°C to all
observations in CONUS• How much does a 2D-Var analysis
improve RMSE?– 0.1-0.2°C based on LSA results
Verifying Forecasts with Analyses
• Motivating Question: Is there a way we can define what constitutes a “good enough” forecast?
• Problem: Concerns about grid-based verification
• Reality: Forecasters need feedback for entire forecast grids not just selected key observation locations
Forecaster Concerns
• Quality of the verifying analysis• Penalty for adding mesoscale detail to
grids in areas unresolved by analysis• Bad (mesonet) observations influencing
analysis• Analysis in remote areas – driven mostly
by the background model
Using RTMA Analyses and RTMA Uncertainty Estimates for Forecast Verification
• RTMA uncertainty estimate grids are experimental products under development for temperature, moisture, wind
• Goal:– Higher uncertainty in data sparse areas or areas with
larger representativeness errors– Lower uncertainty in data dense areas or areas with
smaller representativeness errors• Basic premise
– Forecasters not penalized as much where the analysis is more uncertain
6
Temperature (oC) Forecast Verification Example
Forecast RTMA RTMA Uncertainty
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Temperature (oC) Forecast Verification Example
Forecast RTMA RTMA Uncertainty
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No color= Differences between the forecast and analysis are less than analysis uncertainty
Red = abs(RTMA – Forecast) > Uncertainty
Summary• Improving current analyses such as RTMA requires improving
observations, background fields, and analysis techniques– Increase number of high-quality observations available to the
analysis – Improve background forecast/analysis from which the analyses
begin– Adjust assumptions regarding how background errors are
related from one location to another• Future approaches
– Treat analyses like forecasts: best solutions are ensemble ones rather than deterministic ones
– Depend on assimilation system to define error characteristics of modeling system including errors of the background fields
– Improve forward operators that translate how background values correspond to observations