[strat_list] Paper on stratospheric impact on tropospheric winds
y.b.l.hinssen at uu.nl
Mon Feb 1 02:51:50 PST 2010
You might be interested in our recent article, which has been
published online in "Early View" in the Quarterly Journal:
Hinssen Y, van Delden A, Opsteegh T, de Geus W. 2010. Stratospheric
impact on tropospheric winds deduced from potential vorticity
inversion in relation to the Arctic Oscillation. Q. J. R. Meteorol. Soc.
The zonal mean state of the atmosphere in the Northern Hemisphere in
winter is determined by the temperature at the Earth's surface and by
two potential vorticity (PV) anomalies (defined as that part of the PV
field that induces a wind field) centred over the North Pole: one in
the upper troposphere/lower stratosphere (UTLS), extending to the
Subtropics, and the other over the polar cap in the lower to middle
stratosphere. Isentropic PV inversion demonstrates that the UTLS PV
anomaly induces the main part of the zonal mean wind in the
troposphere, including the subtropical jetstream, while the
stratospheric PV anomaly induces the polar night stratospheric jet.
The stratospheric PV anomaly has a greater amplitude and extends
further downwards if the Arctic Oscillation (AO) index is positive.
Also, the UTLS PV anomaly has a slightly larger amplitude if the AO
index is positive, but the meridional PV gradient in the Subtropics
that is associated with this anomaly is greatest when the AO index is
negative, resulting in a stronger subtropical jet when the AO index is
negative. PV inversion translates the UTLS PV anomaly into a wind
anomaly and a static stability anomaly. The resulting differences in
the vertical wind shear and in the Brunt-Vaisala frequency between the
two AO phases show a larger baroclinicity in the extratropics when the
AO index is positive. This explains why more extratropical cyclones
are observed when the AO index is positive.
The pdf is available at: http://www.phys.uu.nl/~nvdelden/PV_Inversion&Stratosphere.pdf
Institute for Marine and Atmospheric research Utrecht (IMAU)
P.O. Box 80000
3508 TA Utrecht
email: y.b.l.hinssen at uu.nl
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