Refinement of the vertical diffusion scheme in the ARPÈGE/ALADIN model
Item
Title (Dublin Core)
eng
Refinement of the vertical diffusion scheme in the ARPÈGE/ALADIN model
hrv
Poboljšanje sheme vertikalne difuzije u ARPÈGE/ALADIN modelu
Description (Dublin Core)
eng
In atmospheric numerical weather prediction (NWP) models, the use of
long time-steps as allowed by efficient numerical/dynamical schemes can
lead to spurious oscillations due to the parameterized physical part. Typical
examples of this are the oscillations associated with simplified parameterization
schemes for vertical diffusion or shallow-convection, such as usually
used for NWP.
The oscillations generated by K-type vertical-diffusion schemes are well
documented, and being called fibrillations; they are characterized by high
temporal and vertical frequencies. Since they are linked to high vertical
resolution, these spurious oscillations are generally found in the low-levels
of model’s domain.
In ARPÈGE, the MÉTÉO-FRANCE NWP global model, and in ALADIN,
its limited-area model (LAM) version developed in cooperation with
Eastern European countries, and also used for operational NWP purpose,
some oscillations still remained in the evolution of the forecast fields, despite
the fact that a first anti-fibrillation scheme (AFS) had been included.
This study was made to examine the possible sources of these oscillations,
through the 1-D (vertical) version of these models.
First, the parameterization of shallow-convection (which is in fact part
of the vertical diffusion scheme) was found to be an important source of oscillations,
and some solutions for eliminating this problem are proposed.
Second, the original AFS is shown not to completely prevent the generation
of fibrillations, and a more efficient formulation is derived.
All AFSs basically consist in a temporal first-order decentering of the
diffusion equation, keeping an explicit form for the exchange coefficient itself.
The AFS correction thus always improves the stability at the expense of
the accuracy in some way. In the new AFS proposed here, the number of
grid-points which need a correction is lessen from almost 90% to some 5%,
resulting in a more accurate scheme. Unlike AFSs proposed in the literature,
the correction has now to be applied not only for grid points of atmospheric
stable conditions (i.e. Richardson number, Ri > 0) but also for atmospheric
slightly unstable conditions (Ri < 0).
long time-steps as allowed by efficient numerical/dynamical schemes can
lead to spurious oscillations due to the parameterized physical part. Typical
examples of this are the oscillations associated with simplified parameterization
schemes for vertical diffusion or shallow-convection, such as usually
used for NWP.
The oscillations generated by K-type vertical-diffusion schemes are well
documented, and being called fibrillations; they are characterized by high
temporal and vertical frequencies. Since they are linked to high vertical
resolution, these spurious oscillations are generally found in the low-levels
of model’s domain.
In ARPÈGE, the MÉTÉO-FRANCE NWP global model, and in ALADIN,
its limited-area model (LAM) version developed in cooperation with
Eastern European countries, and also used for operational NWP purpose,
some oscillations still remained in the evolution of the forecast fields, despite
the fact that a first anti-fibrillation scheme (AFS) had been included.
This study was made to examine the possible sources of these oscillations,
through the 1-D (vertical) version of these models.
First, the parameterization of shallow-convection (which is in fact part
of the vertical diffusion scheme) was found to be an important source of oscillations,
and some solutions for eliminating this problem are proposed.
Second, the original AFS is shown not to completely prevent the generation
of fibrillations, and a more efficient formulation is derived.
All AFSs basically consist in a temporal first-order decentering of the
diffusion equation, keeping an explicit form for the exchange coefficient itself.
The AFS correction thus always improves the stability at the expense of
the accuracy in some way. In the new AFS proposed here, the number of
grid-points which need a correction is lessen from almost 90% to some 5%,
resulting in a more accurate scheme. Unlike AFSs proposed in the literature,
the correction has now to be applied not only for grid points of atmospheric
stable conditions (i.e. Richardson number, Ri > 0) but also for atmospheric
slightly unstable conditions (Ri < 0).
hrv
Učinkovite numeričko-dinamičke sheme u atmosferskim numeričkim prognostičkim modelima dozvoljavaju uporabu duljeg vremenskog koraka prilikom numeričke integracije, ali često dolazi do neželjenih oscilacija uzrokovanih parametrizacijom fizikalnog dijela. Tipičan primjer je pojava oscilacija povezanih s pojednostavljenim parametrizacijskim shemama za vertikalnu difuziju ili plitku konvekciju, koje se uobičajeno koriste u numeričkoj prognozi vremena.
Oscilacije koje se generiraju shemama vertikalne difuzije K-tipa do sada su detaljno razmatrane, i nazvane su fibrilacijama. Visoke prostorne i vremenske frekvencije karakteristike su fibrilacija. Zbog njihove povezanosti s velikom vertikalnom rezolucijom,
ove lažne oscilacije se općenito uočavaju na nižim nivoima domene modela.
U prognostičkim poljima ARPÈGE-a (numeričkom prognostičkom globalom modelu u MÉTÉO-FRANCE) i ALADIN-a (njegovoj verziji modela za ograničeno područje razvijenom u suradnji sa zemljama istočne Europe) neke oscilacije su se i dalje zadržale unatoč činjenici da je uključena prva anti-fibrilacijska shema (AFS). Ovaj rad prikazuje provedena ispitivanja mogućih izvora fibrilacija pomoću 1-D (vertikalne) verzije ovih modela.
Ispitivanja su dala sljedeće rezultate: 1. znatan izvor oscilacija je pronađen u parametrizaciji plitke konvekcije (što je u stvari dio sheme vertikalne difuzije) te su predložena neka riješenja za njihovo uklanjanje, 2. pokazalo se da početna AFS ne može u potpunosti spriječiti generiranje fibrilacija te je izvedena uspješnija formulacija.
Jednadžbe vertikalne difuzije prikazane u numeričkom vremenskom raspisu prvog reda, zadržavajući eksplicitnu formu samog koeficijenta izmjene, u osnovi sadrže AFS. Stoga, korekcija AFS-om uvijek poboljšava stabilnost na račun točnosti.
S novom anti-fibrilacijskom shemom, broj točaka mreže u kojima je potrebno izvršiti korekciju smanjen je s gotovo 90% na približno 5%, čime je shema dobila na točnosti.
Za razliku od predloženih AFS iz literature, korekcija se mora primjenjivati ne samo na točke mreže sa stabilnim atmosferskim uvijetima (Richardsonov broj, Ri > 0) već i na one točke u kojima je atmosfera blago nestabilna (Ri < 0).
Oscilacije koje se generiraju shemama vertikalne difuzije K-tipa do sada su detaljno razmatrane, i nazvane su fibrilacijama. Visoke prostorne i vremenske frekvencije karakteristike su fibrilacija. Zbog njihove povezanosti s velikom vertikalnom rezolucijom,
ove lažne oscilacije se općenito uočavaju na nižim nivoima domene modela.
U prognostičkim poljima ARPÈGE-a (numeričkom prognostičkom globalom modelu u MÉTÉO-FRANCE) i ALADIN-a (njegovoj verziji modela za ograničeno područje razvijenom u suradnji sa zemljama istočne Europe) neke oscilacije su se i dalje zadržale unatoč činjenici da je uključena prva anti-fibrilacijska shema (AFS). Ovaj rad prikazuje provedena ispitivanja mogućih izvora fibrilacija pomoću 1-D (vertikalne) verzije ovih modela.
Ispitivanja su dala sljedeće rezultate: 1. znatan izvor oscilacija je pronađen u parametrizaciji plitke konvekcije (što je u stvari dio sheme vertikalne difuzije) te su predložena neka riješenja za njihovo uklanjanje, 2. pokazalo se da početna AFS ne može u potpunosti spriječiti generiranje fibrilacija te je izvedena uspješnija formulacija.
Jednadžbe vertikalne difuzije prikazane u numeričkom vremenskom raspisu prvog reda, zadržavajući eksplicitnu formu samog koeficijenta izmjene, u osnovi sadrže AFS. Stoga, korekcija AFS-om uvijek poboljšava stabilnost na račun točnosti.
S novom anti-fibrilacijskom shemom, broj točaka mreže u kojima je potrebno izvršiti korekciju smanjen je s gotovo 90% na približno 5%, čime je shema dobila na točnosti.
Za razliku od predloženih AFS iz literature, korekcija se mora primjenjivati ne samo na točke mreže sa stabilnim atmosferskim uvijetima (Richardsonov broj, Ri > 0) već i na one točke u kojima je atmosfera blago nestabilna (Ri < 0).
Creator (Dublin Core)
Telišman Prtenjak, Maja
Marki, Antun
Benard, Pierre
Subject (Dublin Core)
eng
NWP model; ARPÈGE/ALADIN model; shallow-convection; Richardson number; fibrillation; anti-fibrillation scheme
hrv
numerički prognostički modeli; ARPÈGE/ALADIN model; plitka konvekcija; Richardson-ov broj; fibrilacije; anti-fibrilacijska shema
Publisher (Dublin Core)
Andrija Mohorovicic Geophysical Institute
Date (Dublin Core)
1998
Type (Dublin Core)
text
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Format (Dublin Core)
application/pdf
Identifier (Dublin Core)
https://hrcak.srce.hr/17703
eng
https://hrcak.srce.hr/file/27392
Source (Dublin Core)
Geofizika
ISSN 0352-3659 (Print)
ISSN 1846-6346 (Online)
Volume 15
Issue 1
Language (Dublin Core)
eng
Rights (Dublin Core)
info:eu-repo/semantics/openAccess
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