progress in using doppler radar for three-dimensional wind...

PProgress in using Doppler radar for rogress in using Doppler radar for threethree--dimensional wind retrieval and dimensional wind retrieval and

shortshort--term QPF term QPF

廖宇慶廖宇慶Department of Atmospheric SciencesDepartment of Atmospheric Sciences

National Central UniversityNational Central UniversityJhongliJhongli City, TaiwanCity, Taiwan

Collaborators:Collaborators:陳台琦陳台琦蔡宜君蔡宜君唐玉霜唐玉霜楊靜伃楊靜伃林林沛練沛練李永安李永安黃沛瑜黃沛瑜

CAA

RCGI

RCWF

RCHL

RCKT

RCCG

NCU(C-POL)

CWB(S) (4)AF(C) (3)

CAA(C) (1) NCU C-POL (1) --------------------------------------

Total (9)

3 dual-Pol radars(RCCK, RCMK, NCU)

Taiwan Ground-Based Radar Network

RCCK

RCMK

NSC-NCU Taiwan Experimental Atmospheric Mobile-Radar

TEAM-R (X-band, dual-pol)

TEAM-R and S-POL(SoWMEX, 2008)

Future radar deployment in Taiwan

(1)Taiwan Typhoon and Flood Research Institute (TTFRI): 1 C-POL (2013); Cloud radar (2015~2016); wind profiler..

(2) Water Resource Agency (WRA): 3 C-band dual-Pol for QPE.Proposal for 2 more has been approved.

Major research and applicationMajor research and application• Real-time monitoring and warning.• Structure and evolution of severe

weathers (typhoon, MCS, frontal system..).• Topographic effect.• Wind/thermodynamic field retrieval.• Cloud physics, and QPE.• Radar data assimilation and model QPF. • Hydrology and disaster prevention and

reduction.

Recovery of the3-dimensional wind fields

using Doppler radars

Doppler radar Doppler radar radial windradial wind

(unknown)

(unknown)

(observed)

zVtwvyuxVr r )(

Positive/negativeVr means thereceding/approaching flow w.r.t. the radar.

Doppler Radial wind signature (Doviak and Zrnic, 1992)

Limitations of traditional method:

(1) Need over-lapped data coverage (analysis domain is limited).

(2) Cannot obtain winds along radar base line.

• Radar Baseline

1313

A B

Single-Doppler Velocity Retrieval(SDVR)

Recovering 3D wind using only one Dopplerradar, without sacrificing data resolution.

Optimal Moving Frame(Liou 1999 (a),(b); Liou and Luo 2001; Liou 2002; Liou 2007)

Full adjoint:(Sun et al. 1991；Sun and Crook 1994 )

Simple adjoint: (Qiu and Xu 1992；Xu et al. 1995；Xu et al. 2001)

Two scalar conserved method: (Shapiro et al. 1995; Weygandt et al. 2002)

Single-Doppler Velocity Retrieval (SDVR)4DDA:(Liou 1989; Liou 1991)

Dual-Doppler Radial wind by CP-4

SDVR by CP-4Dual-Doppler

Storm-relative winds (left:Dual-Doppler; right: SDVR)

SDVR by CP-4 to cover a larger area

Limitations of SDVR(1)Need fast scan radar data(< 3.0 min, operational radars ~ 7.5 min)

(2) Accuracy depends on radar position. An index is designed to show the retrieval’s reliability.(Liou and Luo 2001)

(3) Wind speed under-estimation is inevitable. An explanation is given.(Liou 2002; Liou 2007)

Purpose of this research:

Re-design a new method for retrieving the 3-D wind field by fully using the Doppler radars in Taiwan.

DData ata from from NN radars, radars, 22 volume scansvolume scans

Use Use variationalvariational method method to get to get 33--DD wind wind fields at fields at 22 time levelstime levels((LiouLiou and Chang 2009, MWR)and Chang 2009, MWR)

Use Use immersed boundary method immersed boundary method totoiinclude nclude topographic effectstopographic effects..((LiouLiou et al., 2012 MWR)et al., 2012 MWR)

•IBM: First introduced by Peskin (1972) for cardiac mechanics

•Simulate the forcing from topography, without the need to use terrain-

following coordinate.

Immersed Boundary Method (IBM)

FromLundquist et al.(MWR, 2010)

Constraints used in our new method

2) Anelastic continuity equation.

3) Simplified vertical vorticity equation.

1) Geometric relation between Vr and u, v, w.

4) Background wind field.

5) Top/bottom boundary conditions for winds.

6) Laplacian smoothing term.

Some of the advantages of this new method

2) Can synthesize wind fields along radar base line.

3) Retrieved 3D wind can be used directly for vorticity budget analysis.

1) Easily add any number of radars.

4) Can retrieve winds over complex terrain.

2008 SoWMEX

簡報者簡報註解真實個案測試

簡報者簡報註解虛線為RCCG與S-POL之baseline

From CEDRIC (a traditional method)

zu

yw

zv

xw

yv

xuf

zw

yv

xu

t

)(

The retrieved 3D wind satisfies the vertical vorticityequation, which allows us to do vorticity budgetanalysis. (no residual term !)

Advection Divergence(Stretching)

Tilting

)(yu

xv

Typhoon Morakot (2009)

Max. total rainfall ~ 3,000 mm / 4 days

Analysis domain

• RCCG and RCMK• Analysis domain

with good dual- Doppler coverage (pink box).

• Traditional method (CEDRIC) vs. new method

RCCG

RCMK

dbz andHorizontal windsat Z=2km(CEDRIC)

dbz andHorizontal windsat Z=2 km(new method)

w at z=3km(CEDRIC)

w at z=3km(New method)

Hor. Convergenceat Z=2 km(CEDRIC)

Hor. Convergenceat Z=2km(new method)

Vorticity at Z=3 km(CEDRIC)

Vorticity at Z=3 km(New method)

Larger analysis domain

• RCCG and RCMK• CEDRIC domain

marked by pink lines (much smaller).

• New method covers entire domain

RCCG

RCMK

A strong jet (~ 40 m/s )from Taiwan Strait to land.Impinges the mountains,Co-exists with strong dBZ.

Winds obtained from new method. Cannot be done with traditional method !

3-D Wind field at Z=1.25km

4343

• NW flow from the Morakot’s circulation converges with the SW flow, strengthen the rainband.

• Strong updraft (~ 4 m/s) and positive vertical vorticity in the rain band and near the terrain.

• Strong wind speed• (> 36 m/s) in the

rainband, but drops 50% over land.

reflectivity/wind field w

Wind speed

簡報者簡報註解In height of 1.25km, the north-west wind and south-west flow converged, and the convergence strengthen the rain band, and

3-D Wind field at Z=3.25km

4444

• Dominant wind is• NW flow from Morakot

circulation.

• Even stronger updraft• (~ 8 m/s) and vorticity• in rainband and near• CMR.

Vorticity produced mainly by advection, but tilting is alsosignificant.

• Wind speed dropsat coast, increasesrapidly to 40 m/s near

• the foothill

Reflectivity/wind field w

Wind speed

3-D Wind field at Z=5.75km ( > CMR)

4545

• Dominated by typhoon circulation.

• Strong updraft (~ 6 m/s) and vorticity still exist in the rainband over ocean.

• A belt of strong wind above mountain crest

Reflectivity/wind field w

Wind speed

Y = -40 km

The u-w wind, radar reflectivity, and w.

Retrieved winds Retrieved winds along along Y = Y = --40 km40 km

Wind increases along upslope. A wind speed maximum above the mountain. Why ?

Updraft (downdraft) in the windward/lee side of CMR.

No BB. Reflectivity starts to intensify when touching thefirst small hill.

~40 m/s

xH

Cug

x)F-(1 2

2r

u

H)-g(hC2

2

22r

uFC

Strong mixing makes the atmosphere more barotropic, suitable to apply a simplified 2-D shallow-water model.

u: cross barrier wind speedH: terrain heighth: depth of the underlying

barotropic atmosphere.C: Shallow water gravity wave

phase speed.Fr: shallow water Froud number

H)-g(hC2

2

22r

uFC

u ~ 20 m/s H ~ 2,000 mh > H C > uFr < 1.0 subcritical condition(Durran 1986)

> 0> 0

Typhoon Typhoon FanapiFanapi (2010)(2010)TTFRITTFRI--NCU joint missionNCU joint mission

RCMK+RCCG (upper)RCMK+RCCG (upper)RCMK+RCCG+RCKT+TEAMRCMK+RCCG+RCKT+TEAM--R R (lower)(lower)

Improve highImprove high--resolution resolution shortshort--term QPF using term QPF using Doppler radar dataDoppler radar data

•• VariationalVariational Doppler Radar Analysis System Doppler Radar Analysis System (VDRAS)(VDRAS): Developed at NCAR, a cloud: Developed at NCAR, a cloud--resolving resolving model, can assimilate Doppler radar data using model, can assimilate Doppler radar data using 4DVAR (4DVAR (Sun and Crook 1997, 1998).

• Applied in 2000 Sydney and 2008 Beijing Olympic game for real-time wind analysis (Crook and Sun 2002, 2004; Sun et al. 2010).

• Applied in prediction of a flood in Colorado (Warner et al. 2000), in IHOP_2002 for QPF of a squall line over US continent (Sun and Zhang, 2008).

Apply VDRAS in Taiwan & vicinity area to test its QPF skill (Tai et al., WAF, 2011)

Challenges:

(a) Complex topography: VDRAS does not resolve terrain.

(b) Surrounding oceans: limits in-situ observations. Radar data become crucial.

Case studyCase study

• 2008 SoWMEX/TiMREX• IOP8: 6/14 00 UTC to 6/17 00 UTC• Pre-frontal rainbands• Assimilation/forecast experiment:

6/14 1022 UTC to 1500 UTC

Background：

Real observation

or Reanalysis

Time1022 1039 1045 1102

RCKT

RCCG

SPOL Forecast cycle

Background：

Last Forecast field

Forecast 4hr

Initialize at 0600UTC

Reinitialize by VDRAS analysis at 1100 UTCWRF

VDRAS

VDWRF

Design of VDRAS assimilationDesign of VDRAS assimilation

WRFWRF

OBSOBS

VDRASVDRAS

VDWRFVDWRF

11-1411-1311-12 11-15

ETS for accumulated rainfallETS for accumulated rainfall

Statistics for Statistics for accumulated accumulated

rainfallrainfall

Summary and future work

(2) Encouraging results from using radar data to improve high-resolution short-term QPF in Taiwan (mountainous island surrounded by oceans).

(1) A new multiple-Doppler radar wind analysis method for retrieving 3-D wind field over complex terrain is developed. Radar base line is no longer a blind zone.

Summary and future work (cont.)

(3) Need more case studies and independent data sources for verification (e.g. wind profiler), especially for w.

(4) Use data from all radars in Taiwan. Build an integrated island-wide multiple-Doppler radar network.

(5) Need to solve radar data QC problem if real-time operation is desired.

Thank you !Thank you !

Progress in using Doppler radar for three-dimensional wind retrieval and short-term QPF �投影片編號 2投影片編號 3投影片編號 4Major research and application投影片編號 6Doppler radar radial wind投影片編號 8投影片編號 9投影片編號 10投影片編號 11投影片編號 12投影片編號 13投影片編號 14投影片編號 15投影片編號 16投影片編號 17投影片編號 18投影片編號 19投影片編號 20投影片編號 21投影片編號 22投影片編號 23投影片編號 24投影片編號 25Constraints used in our new methodSome of the advantages of this new methodSome of the advantages of this new method2008 SoWMEX投影片編號 30投影片編號 31Some of the advantages of this new method投影片編號 33Some of the advantages of this new method投影片編號 35Analysis domain投影片編號 37投影片編號 38投影片編號 39投影片編號 40Larger analysis domain投影片編號 423-D Wind field at Z=1.25km3-D Wind field at Z=3.25km3-D Wind field at Z=5.75km ( > CMR)Retrieved winds along Y = -40 km投影片編號 47投影片編號 48投影片編號 49投影片編號 50投影片編號 51投影片編號 52Case studyDesign of VDRAS assimilation投影片編號 55ETS for accumulated rainfall投影片編號 57Summary and future workSummary and future work (cont.)投影片編號 60

progress in using doppler radar for three-dimensional wind...

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