mpo 674 lecture 22 4/2/15. single observation example for 4d variants d. kleist et al. 4dvar...

MPO 674 Lecture 22

4/2/15

Single Observation Examplefor 4D Variants

D. Kleist et al.

4DVAR

H-4DVAR_ADbf-1=0.25

H-4DENVARbf-1=0.25

4DENVARTLMADJ

TLMADJ

ENSONLY

ENSONLY

Lorenz, E.N., and K.A. Emanuel, 1998: Optimal Sites for Supplementary Weather Observations: Simulation with a Small Model. J. Atmos. Sci., 55, 399–414.

Lorenz, E.N., and K.A. Emanuel, 1998: Optimal Sites for Supplementary Weather Observations: Simulation with a Small Model. J. Atmos. Sci., 55, 399–414.

UYonsei MM5SV NRL SV JMA SV

ECMWF SV UMiami-NCEP ETKF UKMO ETKF

Targeted observing guidance (Typhoon Sinlaku, 2008)

Sensitivity Methods

• Observation sensitivity– ETKF– Adjoint Observation Sensitivity / Impact

• Analysis sensitivity– Singular Vectors (done)– Adjoint Sensitivity (done)– Ensemble Sensitivity

Signals and Signal VarianceSquared NCEP MRF signal

1/2 (u’2+v’2) + (cp/Tr) T’2

valid at analysis time ta

Predicted ETKF signal variance Sq, using ensembles initiated 36h prior

to analysis time ta

tata

ETKF Summary map of Signal

Variance Sq, for many different q.

Summary bar chart

tv tv

GoodPoor

Aim: to improve a

24-hr forecast on the West Coast

Evolution of operational

signal over 84h

Evolution of predicted ETKF signal variance

over 84h

Signal realization versus forecast

error reduction, at verification time tv

0ld method: ETKF-based Pr

Heavy emphasis on TC (obvious target)

Secondary targets in areas of high ensemble variance over ocean, downstream of TC

New method: Ensemble transform based on operational analysis error variance

Less emphasis on TC

Secondary targets: often upstream, in subtropical jet and mid-latitude troughs

Suppose we wish to sample through 4 days of Typhoon Ewiniar (2006) as it recurves.

Can one identify spatio-temporal continuity of ETKF target regions?

Extension into medium-range (forecasts beyond 2 days)

-4 days

-3.5 days

-3 days

-2.5 days

-2 days

-1.5 days

-1 day

-0.5 days

0 days

Serial adaptive sampling

• Many combinations and permutations of adaptive observations are available.

• Suppose that two sets of observations can be deployed simultaneously.

• First, find the optimal first deployment. Next, calculate the best second deployment given that the first set of observations are to be assimilated by the ETKF at the same time.

• Reduces observational redundancy.

Flight track number Flight track number

Serial adaptive sampling during

Winter Storm Reconnaissance

Shortcomings of ETKF targeting strategy

• Inconsistency between imperfect error covariance in ETKF and operational data assimilation scheme

• Limited # ensemble members gives a rank-deficient P : leads to spurious correlations

• Ensemble mean and variance predictions must be reasonably accurate

• Theory is (quasi) linear

Dependence of SVs on the analysis-time norm: Hurricane Charley (2004)

Using NAVDAS analysis error variance as constraint pushes primary target northward into Canada. 2-day growth diminished from 54.4 to 36.4.

NOGAPS Total-Energy SV NOGAPS Variance SV

NAVDAS Analysis Error Variance

Reynolds

Ensemble Sensitivity (from Ryan

Torn)

Overview

• Want to understand how initial condition errors associated with vortex and environment regulate the predictability of TC genesis

• Focus on two forecasts initialized roughly 48 h prior to genesis, one for Karl and another for Danielle

R. Torn

Karl Forecast

R. Torn

Methods

• Use ensemble-based sensitivity analysis to compute the sensitivity of 48 h 850 hPa circulation associated with the pre-genesis system to the initial conditions

R. Torn

Sensitivity

R. Torn

Sensitivity of 48-h 850 hPa circ to 0-h 850 hPa circ

Sensitivity of 48-h 850 hPa circ to 0-h 400 hPa theta-e

Vortex Sensitivity

• Most of the sensitivity appears to be associated with the pre-genesis system itself

• Instead compute sensitivity of forecast to vortex-average quantities at each vertical level for different lead times.

R. Torn

Vortex Sensitivity

R. Torn

Upwind Moisture Sensitivity

• Interesting to see the sensitivity of upwind moisture to the initial moisture field

• Compute sensitivity as before, except metric is now 0-48 h upwind moisture in 400-600 hPa layer

R. Torn

Upwind Moisture Sensitivity

R. Torn

Danielle Forecast

R. Torn

Danielle Sensitivity

R. Torn

Sensitivity of 48-h 850 hPa circ to 0-h 850 hPa circ

Sensitivity of 48-h 850 hPa circ to 0-h 400 hPa theta-e

Increase theta-e to the south stronger circulation

Decrease theta-e to the north stronger circulation

Danielle Sensitivity

R. Torn

Forecast of pre-Danielle has less “memory” of the initial vortex than Karl. Lower-level sensitivity of q and theta-e.