Votex Initialization in HWRF/HMON Models HWRF Tutoial Januay 018 Pesented by Qingfu Liu NOAA/NCEP/EMC 1
Outline 1. Oveview. HWRF cycling syste 3. Bogus sto 4. Sto elocation 5. Sto size coection 6. Sto intensity coection 7. Suay and discussions 1/14/018
HWRF Initial Fields: 1. Oveview Votex Initialization + GSI data assiilation o The votex initialization is to ceate a bette backgound field using TcVital infoation, and includes thee pats: sto elocation (data: sto cente position) sto size coection (data: adius of axiu suface wind speed, and adius of the outeost closed isoba o aveage adius of 34 knots wind speed) sto intensity coection (data: axiu suface wind speed, to soe extent, iniu suface pessue). o Ipotant fo odel consistent foulation in votex initialization: if votex location, size and intensity in backgound ae close to obsevations: all coections ae sall. 1/14/018 3
Ceating HWRF initial fields: 1) No bogus data in data assiilation Reasons: a) bogus data ay conflict with obsevation data b) we will get the sto stuctue we specified ) No conflict between votex initialization and data assiilation a) if we have no data assiilation, we can use the esults fo votex initialization + envionental field fo GFS analysis fo huicane odel initialization (cuently used in HMON) b) If we have data assiilation, we can add inne coe data (such as the aibone ada data) though data assiilation, votex initialization + data assiilation to futhe ipove the votex stuctue and the envionent fields though GSI data assiilation 1/14/018 4
3) Model-consistent Geneally speaking, the diffeences ae lage between the odel and the obsevation in huicane aea. We have two choices: a) Sall coection po: con: odel-consistent sall adjustent duing odel foecast votex stuctue ay be bad HWRF votex initialization can be consideed as sall coection (coection is lage in soe cases): Sto size coection is liited to 15% wind speed coection < 15% (geneally speaking) As odel physics ipove, the votex stuctue will becoe bette, and the final analysis eventually will convege to obsevation. 1/14/018 5
Model-consistent (continue) b) Lage coection po: con: bette votex stuctue ost likely not odel-consistent Lage adjustent duing odel foecast Once odel foecast stats, the good votex stuctue can be lost in seveal hous foecast tie. Exaple: 005 Wila has an 8-k eyewall size at 140 knots wind. Model foecast gives ~ 0k eyewall size in the backgound fields. If we foce the initial votex to be 8-k eyewall size in HWRF initial fields, the eyewall will collapse, and significant spin-down will occu in odel foecast. The cuent HWRF odel does not have the capability to aintain this kind of huicane stuctue. 1/14/018 6
. HWRF Cycling Syste In HWRF analysis syste, only the HWRF votex is cycled, and the envionent guess field coes fo GDAS foecast (global odel). HDAS guess field = GDAS envionent field + coected votex fo HWRF 6h foecast Afte the guess field is ceated, HDAS analysis will be pefoed to ceate HWRF analysis field. If thee ae no data assiilation, the initial field will be, Final analysis = envionent field fo GFS analysis + coected 6h HWRF votex 1/14/018 7
3. Bogus votex Cold stat: If vobs < 0 /s, backgound votex coes fo GFS analysis if vobs > 0 /s, backgound votex will be bogused Wa stat: Bogus sto only be used to incease sto intensity if backgound votex is weake copaed to obsevation Bogus sto has the sae sto size as the obsevation Bogus sto is ceated fo a D axi-syetic coposite votex. The D axi-syetic coposite votex is pe-geneated. The D votex has huicane petubations U, V, T, (wate vapo ixing atio) and Ps 1/14/018 8
Bogus votex (continue) Ceation of the bogus votex Hoizontally sooth the D sto pofiles (U, V, T, and Ps, note: Ps is 1D) until the adius of axiu wind o the axiu wind speed of the D votex is close to the obsevation. Afte sooth, the sto size is coected to atch the obsevation Intepolate the D votex onto 3D odel gid The D coposite votex should be eceated wheneve the changes of odel physics stongly affect the sto stuctues 1/14/018 9
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4. Sto elocation Sto elocation to initialize huicanes was ipleented in GFS in yea 000. The elocation pocedue takes the guess field and oves the huicane votex to the coect location befoe the GSI updates the analysis. The steps can be biefly suaized as follows: 1) locate the huicane votex cente in the guess field, ) sepaate huicane odel's votex fo its envionental field, 3) ove the huicane votex to the NHC's official position, and 4) if the votex is too weak in the guess field, add a bogus votex in the GSI analysis Sto elocation is done in HWRF in a slightly diffeent way 1/14/018 13
5. Sto Size Coection Obsevation data used fo TC vitals fo the eyewall and sto size coections ae: adius of axiu wind speed adius of outost closed isoba adius of 34 knots wind (fo stong stos) We use this infoation to coect the size of the coposite sto, as well as the sto poduced fo the 6-h odel foecast by stetching o copessing the odel gid. 1/14/018 14
Sto Size Coection (continue) Stetch/copess the odel gid i i i a b i (1.4.1.1) Integate equation (4.1.1), we have f 1 ( ) a b (1.4.1.) Whee a and b ae constants, and ae the distances fo the sto cente befoe and afte the odel gid is stetched 1/14/018 15
Sto Size Coection (continue) Data used: Radius of the axiu wind speed ( and ) Radius of the outost closed isoba (R and R ) Model data:, R Obsevation data:, R 0 R R We copess/stetch the odel gids such that f ( ) At, (1.4.1.3) f R ) R R ( At, (1.4.1.4) 1/14/018 16
1/14/018 Sto Size Coection (continue) Substituting (1.4.1.3) and (1.4.1.4) into (1.4.1.), (1.4.1.5) (1.4.1.6) Solve equations (1.4.1.5) and (1.4.1.6), we have (1.4.1.7) ) ( R R R R a ) ( R R R R b 1 b a 1 R br ar 17
Sto Size Coection (continue) Define the adius of outost closed isoba fo odel output As discussed in HWRF Scientific Docuent, the iniu suface pessue need to be scaled to obsevation value (fo votex #1 and votex #) befoe calculating the adius of outost closed isoba Define the adius of 34 knots wind fo output Siila to the calculation of the adius of the outost closed isoba, we need to scale the ax wind speed to obsevation value fo votex #1 and votex # befoe calculating the adius of 34 knot wind. votex #1: votex fo HWRF 6h foecast (o GFS analysis) votex #: bogus votex (axi-syetic votex) 1/14/018 18
Sto Size Coection (continue) Sea-level pessue adjustent p p p (1.4.1.1.9) whee, v ( f 0 v) d (1.4.1.1.6) And 1 v f ( ) v( ) d ( ) ( ) f0 (1.4.1.1.4) 1/14/018 19
Sto Size Coection (continue) Tepeatue adjustent Tepeatue adjustent is popotional to the agnitude of the votex tepeatue petubation, T Te T T ( 1) T (1.4.1..9) 1/14/018 0
Sto Size Coection (continue) Wate vapo adjustent Assuption: elative huidity is unchanged befoe and afte the tepeatue coection, we have and q e e q e e s s q q e ( e s s 1) q (1.4.1.3.4) e e s s 17.67 43.5( T exp[ ( T 9.66)( T T) ] 9.66) (1.4.1.3.6) 1/14/018 1
Sto Size Coection (continue) Convegence If =1.0, no sto size coection, we have ( ) / 1.0 fo equations (1.4.1.1.9), (1.4.1..9) and (1.4.1.3.6), thee will be no adjustents in D sea-level pessue, 3D tepeatue and 3D wate vapo fields in the backgound 1/14/018
6. Sto Intensity Coection Wind speed coection Denotes u 1 and v 1 as the backgound hoizontal velocity, and u and v as the votex hoizontal velocity Define two functions F F 1 ( u1 u) ( v1 v) ( u1 bu) ( v1 bv) (1.4..1.1) (1.4..1.) F 1 is the 3D wind speed if we siply add a votex to the backgound fields, and F is the new wind speed afte intensity coection. To find b, assue that the axiu wind speed fo F 1 and F ae at the sae odel gid point. Fist find the odel gid point whee F 1 is at its axiu (denotes the wind coponents as u 1, v 1, u, and v ). At odel gid, let F =v obs, then solve the equation to obtain b. 1/14/018 3
1/14/018 Sto Intensity Coection (continue) New initial 3D wind fields And (1.4..1.4) whee v obs is the axiu 10 obseved wind conveted to the fist odel level. ),, ( ),, ( ),, ( 1 z y x u z y x u z y x u b ),, ( ),, ( ),, ( 1 z y x v z y x v z y x v b ) ( ) ( ) ( ( 1 1 1 1 obs v u u v v u v u v v v u u b 4
Sto Intensity Coection (continue) We conside two cases in the following discussion Case I: wind speed in backgound is stonge than obs. The backgound fields ae the sae as the HWRF (o GFS) envionent fields (no votex). We coect the intensity of votex #1 (6h HWRF odel votex) befoe adding it to the backgound fields Case II: wind speed in backgound is weake than obs. Fist, we add back the 6-h HWRF odel votex to the GFS envionent fields (afte elocation and sto size coection) Coect the intensity of votex # (axi-syetic votex) befoe adding it to the new backgound fields. Note: Votex # has the obseved adius of the axiu wind speed and adius of outost closed isoba (o adius of 34 knot wind) as votex #1 1/14/018 5
Sto Intensity Coection (continue) Sea-level pessue adjustent afte wind speed coection Case I: wind speed in backgound is stonge than obs. If the backgound votex is close to obsevation, we have, b is close to 1 And the pessue adjustent is and new new p p v1 ( v1) d f 0 (1.4...5) (1.4...) new ( bv1 ) [ bv1 f 0 ] d (1.4...3) 1/14/018 6
Sto Intensity Coection (continue) Sea-level pessue adjustent afte wind speed coection Case II: wind speed in backgound is weake than obs. Since the backgound votex is aleady added back, we have, b is close to 0 odel consistent pessue adjustent And 1 new new new p p v1 ( v1) d f 0 ( v 1 bv ) [ ( v1 bv f 0 )] d (1.4...7) (1.4...5) (1.4...6) 1/14/018 7
Sto Intensity Coection (continue) Tepeatue and wate vapo adjustents afte wind speed coection Model consistent tepeatue adjustent: Case I: wind speed in backgound is stonge than obs. If the backgound votex is close to obsevation, we have, b is close to 1 Define new Then tepeatue fields can be coected using equation (1.4.1..9), and wate vapo fields can be coected following equations (1.4.1.3.4) and (1.4.1.3.6), which ae the sae as those in sto size coections. 1/14/018 8
Sto Intensity Coection (continue) Tepeatue and wate vapo adjustents afte wind speed coection Model consistent tepeatue adjustent: Case II: wind speed in backgound is weake than obs. If the backgound votex is close to obsevation, we have, b is close to 0 Define new Then tepeatue field and oistue fields can be siilaly coected as in Case I. Note: Intensity coection can be odeately lage, the nonlinea effect of the balance equation is included in the foulation. 1/14/018 9
Sto Intensity Coection (continue) Convegence fo intensity adjustent Case I: wind speed in backgound is stonge than obs. In this case b=1.0, no wind speed coection, fo equations (1.4.1..), (1.4...3) and (1.4.1..5), we have, ( ) 1.0 Case II: wind speed in backgound is weake than obs. In Case II, b=0, no wind speed coection, fo equations (1.4...5), (1.4.1..6), we have (1.4.1..7), ( ) 1.0 Fo equations (1.4.1.1.9), (1.4.1..9) and (1.4.1.3.6), thee will be no adjustents in D suface pessue, 3D tepeatue and 3D wate vapo fields in the backgound 1/14/018 30
7. Suay and discussions Votex initialization can be consideed as a ini data analysis fo sto votex using TcVital infoation, and includes thee pats: sto elocation (data used: sto cente position) sto size coection (data used: adius of axiu suface wind speed, and adius of the outeost closed isoba) sto intensity coection (data used: axiu suface wind speed, and to soe extent, the iniu sea level pessue) Note: Do sto size coection befoe sto intensity coection to avoid boad eyewall stuctue, o wose, two distinct eyewalls. If the backgound votex is close to the obsevation, all coections ae sall. Fo the convegence discussions, if the sto location, sto size and sto intensity in the backgound fields atch the obsevations, thee will be no changes to any of the backgound fields 1/14/018 31
Suay and discussions (continue) Liitations in cuent opeational HWRF votex initialization The pupose of the votex initialization is to ceate bette backgound fields using TCVitals. Then add 3D data on top of the new votex. The cuent GSI has the capability to add aibone ada data. Since the aibone ada data ae expensive to collect, only less than 10% of the foecast cycles have these data. So, fo ost of the stos, we only have the low level contol, uppe level stuctue (fo exaple, sto depth) ay be vey diffeent copaed to obsevation, paticulaly in shea envionent. Continue ipoveent in HWRF intensity foecast It is possible to add the satellite adiance data in the inne coe aea to coect the huicane stuctue though votex initialization. Howeve, adding satellite adiance data though data assiilation ight be a bette way. We ae hoping the huicane intensity foecast will continue to ipove as oe and oe inne coe data ae used in data assiilation. If thee is no data assiilation in huicane odel, inne coe data should be added though votex initialization even though it is a challenging task. 1/14/018 3
Thank you vey uch fo attending this tutoial!!! 1/14/018 33