Characterization of the composition, structure, and seasonal variation of the mixing layer above the...

Characterization of the composition, structure, and seasonal variation of the

mixing layer above the extratropical tropopause as revealed by MOZAIC

measurements

Jerome Brioude,

J-P. Cammas, O.R. Cooper, P. Nedelec

JGR 2008

STT and TST in midlatitudes

No Zonal symmetry of STT and TSTSTT in storm tracks over Atlantic and Pacific ocean

Sprenger and Wernli, 2003

Deep TST at high latitude

Sprenger and Wernli, 2003

Deep TST at high latitude due to WCB

Why STEs in the storm track regions?

DA WCB

IR channel

Storm tracks associated with fronts and upper level troughs.WCB in front of the cold front.DA from the upper trough above can be associated with tropopause folds.

FLEXPART simulation

Particles are released at the surface in USAFollowing the emission pattern from a COInventory.

TST occurs at higher latitude, following the transport of WCB in fall, winter and spring

It is important to understand the STEIn baroclinic waves for short lived species Coming from midlatitude.Because in a baroclinic waves, the isentropesCross the tropopause in upper trough,It is important to understand the transport in Upper troughs.

Where do the TSTs of anthropogenic CO emission from USA occur?

probability density function of deep TST(over 10 days)

stohl et al., 2003

The tropopause is disturbed in midlatitudes. Visible in a latitudinal cross section, but invisible in an average latitudinal cross section.

In a longitudinal cross section at midlatitude, the tropopause is disturbed byRossby waves and baroclinic waves. Isentropic mixing occur when the tropopause height is low In upper troughs.

A longitudinal cross section at 60N in latitude

MOZAIC data

- Large temporal and geographic coverage of ozone and CO measurements.- Cross the tropopause through upper troughs.

- We used 1575 MOZAIC flights in 2003

1) 3D PV field is filtered2) In zonal cross sections, an

upper trough is a region with a positive second derivative of PV

In upper troughs, it is necessary to use PV to:- Define a continuous tropopause near jet streams-- relative position of the measurements into the mixing layer and lowermost stratosphere.

How to select upper troughs in the dataset ?

Results

• Observation of a mixing layer

• Differences between the East side and West side

• Regional differences

Mixing layer in the tropopause region (1)

CO

O3

Mixing line (linear correlation= -1)

Equilibrium state ( bad linear correlation)

Strong correlation associated with strong wind speed => recent mixing due to stirring from jet streams

Mixing layer in the tropopause region (2)

Mixing layer -Tropospheric and stratospheric seasonal cycles of ozone and CO-- strong ozone and CO anticorrelation are encountered often.

The seasonal cycle of ozone and CO insidethis mixing layer is a combination of both the troposphericand stratospheric seasonal cycles.

Differences between the East and the west side of upper troughs

 The ozone and CO differences between the east side and the west side seem to be the consequence of a predominantly troposphere to mixing layer transport on the east side, and a predominantly stratosphere to mixing layer transport on the west side, which is consistent with previous studies.

Positive values= higher on the east side than on the west side

In the presence of a cold front at the surface, the eastside of an upper level trough is associated with a warmconveyor belt

Regional differences

Regional differences of CO concentration in the mixing layer have been observed between 2 and 4 pvu, and up to 6 pvu insummertime. Asia is the most polluted region especiallyin spring (140 ppbv)

Ozone and CO concentration are constant with PV above the mixing layer in spring.

Conclusion

-Using MOZAIC in situ measurements, we identified a mixing layer associated with stirring and mixing in the tropopause region between 2 and 6 pvu (up to 8pvu in summer).

-Regional variations of the ozone and CO distributions are found within the mixing layer, up to 4pvu. Above the mixing layer, constant ozone and CO concentration with PV are found.

-Chemical differences are found between the east and west side of upper troughs. In the mixing layer, TST occur preferentially on the east side, and STT occur preferentially on the west side.