1. Lecture 12 Rossby waves, propagation, breaking, climatic effects
Marine stratocumulus regime
The ocean, its role in the climate system

2. Rossby wave mechanism

3. “Rossby wave” conceptual model
Even though the term “wave” conjures up linear wave propagation, this concept can be extended to apply to nonlinear waves or breaking waves.
The largest scales in the extratropics can be described as quasi-linear and quasi-stationary.
Define linear, stationary

4. Rossby waves (continued)
Planetary scale is quasi-stationary, quasi-linear
Synoptic scale can range from linear waves to strongly nonlinear breaking waves
Storm tracks are manifestations of these. In the entrance region have developing systems (or waves) at the exit occluding low pressure systems or breaking waves

5. Midlatitude Stormtracks
From lecture 11
Midlatitude Stormtracks
In the NH they are concentrated over the two ocean basins, Pacific and Atlantic, guided by the jet maxima over the two ocean basins
In the SH form an almost continuous band in midlatitudes
Collection of storms in various stages of development, usually cyclogenesis at the entrance and mature storms further on

6. From lecture 11
Rossby Waves

7. Meridional and Zonal Flow
From lecture 11
Meridional and Zonal Flow

8. Linear, dissipative and time dependent theory
 absorption.
Linear theory appears to work well in explaining observed longitudinal asymmetries, however……….

9. PV on 350K surface on 4, 5 and 6 July 1979
PV on 350K surface on 16, 17 and 18 Dec 1993

10. Nonlinear theory
Linear propagation from midlatitudes to lower latitudes
Waves break as they approach their critical latitude (u=0 stationary waves)
Rearrangement of PV field in the critical layer (advection around closed streamlines)
Wave
propagation
Wave
breaking

11. Linear vs nonlinear behavior near critical line
Linear absorption
Undulating PV contours
Once wave breaking takes place, wave activity can pile up in the wave breaking region
Wave activity may still be absorbed in the wave breaking region given enough dissipation -- or else, given suitable background flow…..

12. Wave breaking can result in reflection
Nonlinear reflection. Wave activity is flushed out of the wave breaking region
Once wave breaking takes place there is the possibility of nonlinear reflection

13. Planetary Wave Breaking (PWB) : rapid and irreversible large-scale overturning of PV.
Example of a PWB event, 4 Feb Animation of Daily PV on 340K surface (2-8 Feb).

14. Criteria for detecting PWB
Reversal in the latitudinal PV gradient in the tropopause region.
Localized eastward PV gradient about the break (anticyclonic breaking).
High (low) PV must be part of a tongue of PV originating in the extratropics (tropics).
Identify “breaking point” – the point farthest west & equatorward that satisfies the above criteria the earliest.

15. Both cyclonic and anticyclonic breaking
Have extended the work to look cyclonic as well as anticyclonic breaking
Have found forcing of climate patterns from breaking:
NAO (direct)
NAO (due to breaking over E Pacific a few days earlier)
PDO (direct)

16. NCEP / NCAR Reanalysis

40. The marine stratocumulus
In the area of the subtropical high (descending branch of the Hadley cell)
Cold underlying ocean (east ocean basins)
Sets up a temperature inversion at the top of the planetary boundary layer (PBL)
The cloud layer exists at the top of PBL

41. Stratus/stratocumulus regime as seen in a visible satellite image

42. Effects of subsidence on lapse rate
Upper region descends over greater distance than lower region. Therefore, warms more.

43. Remember flow over mountain
Remember flow over mountain. On the way up latent heat release mitigates some of the cooling. On the way down, warms at the dry adiabatic lapse rate. Very hot and dry.

44. Oceanography – the study of oceans
They are a source of atmospheric water vapor
They exchange energy and trace gases with the atmosphere
They transport heat poleward
It takes approximately two weeks for all the water in the atmosphere to recycle. The oceans provide the majority of water for precipitation.

45. Net energy gains/losses at the surface of the ocean --- Surface heat flux

46. Surface fluxes of energy and trace gases
The rate of heat and moisture transfer depends on temperature/moisture difference as well as wind speed.
Warm SST and high wind are favorable to large heat exchanges between atmosphere and ocean
US west coast vs. coast of N. Europe, cool SST vs. warm SST: Affects climate profoundly

47. Annual mean poleward transport of energy by atmosphere and ocean

48. More on poleward heat transport
There is a certain compensation between heat transport in the atmosphere and ocean. If the atmosphere transports less, the ocean will step in and transport more and vice versa.

49. Ocean: typical vertical temperature structure Upside version of the atmosphere
Thermocline is the transition zone between mixed and deep layer

50. Just like tropopause height in the atmosphere, the depth of the mixed layer depends on latitude

51. Sea surface temperature (SST)

52. Things to note about distribution of SSTs
SSTs off west coasts in subtropics (to midlatitudes) are cool
SSTs off east coasts in midlatitudes are warm
SSTs off east coasts in high latitudes are cold

53. The major surface ocean currents (wind driven so they resemble the atmospheric wind patterns)