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| Titel |
Are Atmospheric Rivers Lagrangian Coherent Structures? |
| VerfasserIn |
Daniel Garaboa, Jorge Eiras, Florian Huhn, Gonzalo Míguez-Macho, Vicente Pérez-Muñuzuri |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096884
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| Publikation (Nr.) |
 EGU/EGU2014-12414.pdf |
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| Zusammenfassung |
| Most of the advective moisture transport from the tropics (main planetary precipitable water
source) to mid-latitudes is not smooth and uniform. More than 90% of poleward water vapor
transport is accomplished by narrow and elongated (longer than 2000km and narrower than
1000km) structures within the pre-cold frontal Warm Conveyor Belt (WCB) and
Low Level Jet (LLJ) of extratropical cyclones, mostly associated to the polar front.
These structures, labeled as Tropospheric or Atmospheric Rivers (ARs), are defined
as areas of Integrated Water Vapor (IWV) column over 2cm and strong winds,
transporting water vapor whitin the lower troposphere (close to 1km above the sea
level).
Due to their nature, we analyzed these structures in terms of Lagrangian Coherent
Structures (LCS), using the Finite-Time Lyapunov Exponents (FTLE).
In order to develop such analysis, we extract 2D-velocity field from vector flux fields over
the North Atlantic Ocean, using vertical integrals of water vapor (Q) and eastward/northward
water vapor flux (Φλ,ΦÏ), retrieved from the ECMWF Reanalysis (ERA-Interim) at a
0.7°x 0.7° horizontal resolution. Such 2D-velocity fields are dominated by those layers with
high water vapor flux content.
We carry out an Atmospheric River analysis in terms of the FTLE for a set of 10 strong
events whit different shape (7 of them have a clear water transport filament shape and the
rest have a scattered one) over the North Atlantic Ocean. To that end, we compare
the LCS extracted from the FTLE fields computed backward and forward for 5
days with the ridge extracted from the vertical integral Q. We find that repelling
LCS derived from the forward FTLE do not show any connection with the ARs.
However, for the well defined AR there is a strong correlation between AR ridges and
the attracting LCS and both present similar structures, whereas for the other ARs
with scattered shape we do not find a principal LCS derived from the AR event. |
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