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WRF-EnKF Lightning Assimilation Real-Observation Experiments Overview

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Presentation on theme: "WRF-EnKF Lightning Assimilation Real-Observation Experiments Overview"— Presentation transcript:

1 WRF-EnKF Lightning Assimilation Real-Observation Experiments Overview
Cliff Mass, Greg Hakim, Phil Regulski, Ryan Torn Department of Atmospheric Sciences University of Washington February 15, 2008

2 Overview WRF-EnKF Overview Lightning Assimilation Technique Review
Project Review Model Estimate Experiments Case Studies December 2002 October 2004 November 2006 Conclusions In-progress/Future work

3 The Use of EnKF for Lightning Assimilation
In this work the ensemble Kalman filter is applied using the WRF model (WRF-EnKF). The covariance statistics from EnKF that spread the impact of observations are flow-dependent Lightning observations are ideal to provide WRF-EnKF with more observational information in areas with few in situ observations (e.g. Pacific Ocean) Impact of lightning observations will propagate into areas of high forecast impact (West coast and beyond)

4 Lightning Assimilation Techniques
Original Lightning Experiment (LTNG2) NLDN/LR lightning strike is detected Lightning strike is converted into lightning rate from nearby LTNG observations Lightning rate converted into convective rainfall rate using Pessi/Businger convective rain rate/lightning rate relationship Convective rainfall (mm) is assimilated into WRF-EnKF Successful test on Dec case

5 Lightning Assimilation Techniques
Minimal Counting Technique Lightning Experiment (LTNG4) NLDN/LR lightning strike is detected Lightning strike is converted into lightning rate from nearby LTNG observations Once any nearby lightning strikes are used to calculate a lightning density they are no longer available as an assimilation point (although they are still used to calculate LTNG densities) Lightning rate converted into convective rainfall rate using Pessi/Businger convective rain rate/lightning rate relationship Convective rainfall (mm) is assimilated into WRF-EnKF Successful testing on Dec case

6 Project Review Research Completed In-progress
Dec Test Case - Analysis and 12-hr Forecasts Oct Test Case - Analysis Nov Test Case - Analysis Modifications to LTNG2 and LTNG4 models to improve analysis and forecasts In-progress Forecast analysis of Oct Test Case Forecast analysis of Nov Test Case 1-hr assimilation of cumulative convective rain rate data (previously using 6-hr cumulative totals) for LTNG2 and LTNG4 models

7 Recent Experiments Can we further improve Dec 2002 performance?
Model-estimate and observations of cumulative convective precipitation calculated by LTNG density occasionally have large innovations leading to large increments in the model’s dynamical fields, possibly leading to locally unbalanced states Set a upper bound on assimilated cumulative convective precipitation Minimal Counting Technique Lightning Experiment (LTNG4) w/ modifications (LTNG5) Same techniques as LTNG4 but with upper bound (18mm) Less improvement in analysis and forecasts Original LTNG4 still best performing model to test further on new regimes Original Lightning Experiment (LTNG2) w/ modifications (LTNG6) Same techniques as LTNG2 with upper bound (18mm) Original LTNG2 still best performing model to test further on new regimes Another solution Reduce cumulative value of convective rain assimilated from 6- to 1-hr block (In-progress)

8 Case Study #1 – December 2002 Minimum SLP recorded at extra-tropical cyclone’s center
Limiting upper bound of cumulative convective precipitation degrades analysis performance (LTNG5/6) NCEP (black dashed) is NCEP subjective analysis

9 Case Studies Case #1: December 16-21, 2002 Analysis 12-hr Forecasts
LTNG Analysis Impact of SLP, H500 fields 12-hr Forecasts GFS Analysis v. Fcst 12-hr Control GFS Analysis v. Fcst 12-hr LTNG2 GFS Analysis v. Fcst 12-hr LTNG4

10 Major Findings EnKF allows lightning to have a substantial influence on atmospheric analyses The influence can be widespread over the domain

11 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG2

12 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG4

13 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG2

14 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG4

15 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG2

16 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG4

17 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG2

18 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG4

19 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG2

20 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG4

21 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG2

22 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG4

23 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG2

24 Case Study #1 – December 2002 Impact of Lightning Assimilation: LTNG4

25 The Impact on Forecasts Were Mixed

26 Case Study #1 – December 2002 12-hr Forecast Comparison: Control

27 Case Study #1 – December 2002 12-hr Forecast Comparison: LTNG2

28 Case Study #1 – December 2002 12-hr Forecast Comparison: Control

29 Case Study #1 – December 2002 12-hr Forecast Comparison: LTNG4

30 Case Study #1 – December 2002 12-hr Forecast Comparison: Control

31 Case Study #1 – December 2002 12-hr Forecast Comparison: LTNG2

32 Case Study #1 – December 2002 12-hr Forecast Comparison: Control

33 Case Study #1 – December 2002 12-hr Forecast Comparison: LTNG4

34 Case Study #1 – December 2002 12-hr Forecast Comparison: Control

35 Case Study #1 – December 2002 12-hr Forecast Comparison: LTNG2

36 Case Study #1 – December 2002 12-hr Forecast Comparison: Control

37 Case Study #1 – December 2002 12-hr Forecast Comparison: LTNG4

38 Case Study #1 – December 2002 12-hr Forecast Comparison: Control

39 Case Study #1 – December 2002 12-hr Forecast Comparison: LTNG2

40 Case Study #1 – December 2002 12-hr Forecast Comparison: Control

41 Case Study #1 – December 2002 12-hr Forecast Comparison: LTNG4

42 Case Studies Case #2: October 4-7, 2004 Analysis
LTNG Analysis Impact of SLP, H500 fields Number of LTNG strikes during test case is much smaller than Dec case

43 Case Study #2 – October 2004 Impact of Lightning Assimilation: LTNG4

44 Case Study #2 – October 2004 Impact of Lightning Assimilation: LTNG4

45 Case Study #2 – October 2004 Impact of Lightning Assimilation: LTNG4

46 Case Study #2 – October 2004 Impact of Lightning Assimilation: LTNG4

47 Case Study #2 – October 2004 Impact of Lightning Assimilation: LTNG4

48 Case Study #2 – October 2004 Impact of Lightning Assimilation: LTNG4

49 Case Study #2 – October 2004 Impact of Lightning Assimilation: LTNG4

50 Case Study #2 – October 2004 Impact of Lightning Assimilation: LTNG4

51 Case Study #2 – October 2004 Impact of Lightning Assimilation: LTNG4

52 Case Studies Case #3: November 8-12, 2006 Analysis
LTNG Analysis Impact of SLP, H500 fields

53 Case Study #3 – November 2006 Impact of Lightning Assimilation: LTNG4

54 Case Study #3 – November 2006 Impact of Lightning Assimilation: LTNG4

55 Case Study #3 – November 2006 Impact of Lightning Assimilation: LTNG4

56 Case Study #3 – November 2006 Impact of Lightning Assimilation: LTNG4

57 Case Study #3 – November 2006 Impact of Lightning Assimilation: LTNG4

58 Case Study #3 – November 2006 Impact of Lightning Assimilation: LTNG4

59 Case Study #3 – November 2006 Impact of Lightning Assimilation: LTNG4

60 Case Study #3 – November 2006 Impact of Lightning Assimilation: LTNG4

61 Conclusions Assimilated lightning observations impact analyses
Case 1: Lightning observations improving location of front associated with extratropical cyclone Cases 2 & 3 forecasts will be impacted by lightning observations Mixed forecast improvements seen in 12 hr forecasts for Dec Test Case

62 In-progress/Future Work
Reduce WRF cumulative convective precipitation assimilation from 6- to 1-hr to avoid unbalanced states 24-hr Forecasts for Oct 2004 Case 24-hr Forecasts for Nov 2006 Case Future Work Test Case #4 – December 2006 Investigate robustness of Pessi/Businger lightning rate/convective rain rate relationship Implement UW-ATMS lightning rate/convective rain rate relationship Investigate lightning/graupel relationship Questions/Comments?

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