Mesoscale Ensemble-Based Data Assimilation Fuqing Zhang Texas A&M University, College Station, Texas Collaborators: Ellie Meng, Altug Aksoy, Chris Snyder, David Dowell, Jenny Sun and John Nielsen-Gammon • Regional scale [O(1 day) & O(1000km)]: assimilating sounding and surface observations using a mesoscale model (MM5) • Storm-scale [O(1 hour) & O(100km)]: assimilating radar observations using a cloud-resolving model • Thermally-forced circulation: assimilating only surface observations for simultaneous state and parameter estimation using a 2D sea-breeze model
Mesoscale Ensemble-Based Data Assimilation Fuqing Zhang Texas A&M University, College Station, Texas Collaborators: Ellie Meng, Altug Aksoy, Chris Snyder, David Dowell, Jenny Sun and John Nielsen-Gammon. - PowerPoint PPT Presentation
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Mesoscale Ensemble-Based Data Assimilation
Fuqing Zhang Texas A&M University, College Station, Texas
Collaborators: Ellie Meng, Altug Aksoy, Chris Snyder, David Dowell, Jenny Sun and John Nielsen-Gammon
• Storm-scale [O(1 hour) & O(100km)]: assimilating radar observations using
a cloud-resolving model
• Thermally-forced circulation: assimilating only surface observations for
simultaneous state and parameter estimation using a 2D sea-breeze model
Ensemble-Kalman Filter (Evensen 1994)
Use ensemble forecast to estimate flow-dependent background error covariance
t=t0-t t=t0
ensemble forecast
x1a
xNa
obs y x1a
EnKF
xNa
x1f
xNf
xa = xf + BHT(HBHT+R) -1(y-Hxf)
Kalman Filter (Kalman 1960)
Uses all available information in order to produce the most accurate possible description of the state of the flow. Also
provides the uncertainty in the state of the flow resulting from the uncertainties in the various sources of information.
ensemble forecast
x1f
xNf
t=t0+t
Vertical velocity at 5km(colored) and surface cold pool (black lines, every 2K)
Storm-scale EnKF with Simulated Radar OBS (Snyder and Zhang 2003; Zhang, Snyder and Sun 2004)
Assimilating Vr if dBZ>12 every 5 minutes; no storm in initial ensemble
Truth
EnKF
Black curves: EnKF analyses at the tower location Gray curves: Independent observations from the instrumented tower Open circles: Samples from the dual-Doppler analysis.
Storm-Scale EnKF with Real Radar OBS (Dowell, Zhang, Wicker, Snyder and Crook 2004)
Assimilating Vr from one radar verify against dual-doppler analysis and tower data
Experimental Design: Regional-scale EnKF(Zhang, Meng and Aksoy 2004; Meng and Zhang 2004)