# Presentation: 573924

## A synoptic dynamic model of subseasonal variability: Formulation and Application

- Three subseasonal time scales
- The BIG Picture: global AAM and the torques - a robust MJO signal
- The next biggest picture: time evolution of zonal AAM and stochastic momentum transports
- The synoptic picture: baroclinic life cycles, wave breaking and baroclinic wave packets
- The synoptic dynamic model
- Tropical diabatic heating
- Wave-mean flow interaction
- Waves and orographic drag
- Application to recent variations of the weather-climate

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## Dynamics of subseasonal AAM variability

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- Seasonal (Peixoto + Oort)

-       60s         30          EQ          30          60n

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- role of mountains

- +   --  +

**Notes:**
(edited 12/27/04) The figure at left shows the “flow” of AAM within the seasonal cycle (with dM(ht,lat)/dt = 0). There is no “pileup” of AAM allowed, i.e., zero momentum tendency in the free atmosphere. The AAM is merely cycled within the atmosphere thus leaving a direct connection between the transports and the source/sink of momentum. (For the seasonal mean the “flow” is statistical rather than physical or coherent?  The upward branch is produced by the covariance between vertical motion and latitude <wcos2> and the horizontal branch by stationary and transient eddy momentum transports. They are not necessarily connected at any instant in time.)  For the transient case the time tendency is not small. Experience and statistical composites tell us that a mountain torque anomaly in northern mid-latitudes (red thick line) will be linked with orographic waves that transport momentum and produce zonal mean zonal wind anomalies as shown schematically by the “+ - +”.  The response to these tendencies is a mass circulation that produces the frictional torque, which eventually brings AAM back into balance. The time scale for this behavior is ~6 days, equating to periods or a life cycle of 20-40 days. 

The simplest way is to reproduce the subseasonal mid-latitude “mode” is to regress on a 7-day running mean of the mountain torque.  By focusing on the frictional torque as in w2003 there is no filtering involved and the result is more tied up with a precursor index cycle, which just sharpens up and gets extended in time. Egger has been doing lots of innovative work to examine the three dimensional evolution of AAM anomalies. These should be applied in the real time monitoring effort.

Synoptic reasoning: Large positive (negative) mountain torque will give westerly (easterly) wind acceleration in subtropics, which will lead to progression (retrogression) of the existing large scale wave pattern.

## West Pacific/North American Wavetrain: Tropical-extratropical interaction

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- 250 hPa
- Strmfcn
- Diabatic
- Heating

-     Day 0                                Day 14

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**Notes:**
What LIM captures well.

Winkler, C.R., M. Newman, and P.D. Sardeshmukh, 2001: A linear model of wintertime low-frequency variability. Part I: Formulation and forecast skill. J. Climate, 14, 4474-4494.

Part of MJO circulation is “missing”, masked by the persistent ENSO forcing.

This masking only affects the singular vector and does not influence the prediction skill.  Skill is the same irrespective of the phase of ENSO. See scatter plots in Winkler et al.

This is a prototype for weekly averages of a tropical-extratropical interaction where a jet streak coming off of Asia couples with heating east of Indonesia.

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- 7.5N-7.5S

- 2.5S-15.0S

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## 150 hPa Streamfunction and OLR

## ZONAL MEAN 200 hPa zonal wind

**Notes:**
Wvbrk 1: 10/14/04 and 10/18/04
Wvbrk 2: 1109/04 and 11/11/04
Wvbrk 3: 12/12/04 and 12/15/04

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- 11-17 December 2004

- 25-31 December 2004

- 6-12 November 2004

- 28 Nov-4 Dec 2004

- 8-14October 2004

- 17-23 October 2004

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**Notes:**
Top left: 11-17 Dec 2004
Top right: 25-31 Dec 2004
Middle left: 6-12 November 2004
Middle right: 28 Nov-4 Dec 2004
Bottom right: 17-23 October 2004
Bottom left: 8-14 October 200411 

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