10/31/14 What is PV Thinking? PV Thinking and the Dynamic Tropopause The use of poten@al vor@city conserva@on and “invertability” for understanding large-­‐scale atmospheric dynamics and the evolu@on of synop@c weather systems Atmos 5110/6110 Synop@c–Dynamic Meteorology I Jim Steenburgh University of Utah [email protected] Supplemental Reading: Lackmann (2011) Chapter 4 Poten@al Vor@city Poten@al Vor@city •  Conserved following fluid mo@on for adiaba@c, fric@onless flow ! = −! ! + !
•  Units of K kg-­‐1 m2 s-­‐1 •  Define 1 PVU = 10-­‐6 K kg-­‐1 m2 s-­‐1 !"
!"
!!!!!!!!!!!!!!
= !!
!"
!"
•  PV is typically higher in the stratosphere (>2 PVU) and lower in the troposphere (< 2 PVU) •  Components –  Absolute vor@city θ+Δθ
! + !!
Stratosphere ( > 2 PVU)
–  Sta@c Stability !"
− !!
!"
Dynamic
Tropopause
p
θ
Example 2 PVU
Troposphere ( < 2 PVU)
Key Features •  Dynamic tropopause – tropopause defined using poten@al vor@city (i.e., 1.5 or 2.0 PV surface) Stratospheric Reservoir
Dynamic
Tropopause
PV “Wall”
•  Dynamic Tropopause – Tropopause defined using PV (I use 2 PVU, others 1.5) •  Stratospheric reservoir – region of high PV in the stratosphere Tropopause Undulation
•  Tropopause undula@on – wave-­‐like undula@on in the tropopause Not quite a fold
Troposphere
•  Tropopause fold – area where stratospheric air folds under tropospheric air 1 10/31/14 Mean Distribu@on of PV Dynamic Tropopause (DT) Analysis •  DT height is high in tropics, low in high la@tudes •  An analysis of variables (e.g., wind, pressure) on the dynamic tropopause •  DT pressure is low in tropics, high in high la@tudes •  Advantages •  DT poten@al temperature is high in tropics, low in high la@tudes •  On an isentropic surface (e.g., 320 K) PV increases toward the poles –  Jets (subtropical and polar) are frequently at differing pressure levels, but are typically near the dynamic tropopause –  Tropopause pressure or poten@al temperature can be used to iden@fy PV “anomalies” & upper-­‐level troughs and ridges –  Contain a huge amount of informa@on about the upper-­‐
levels on a single map Bluestein (1993) The Dynamic
Tropopause
Dynamic Tropopause Pressure 500-­‐mb height and PV Note how jet cores all intersect
same PV isosurface: Dynamic
tropopause
GFS 144-­‐h forecast valid 12 UTC 10 Feb 2010 From Lackmann (2011) Lecture Notes Correspondence with 500 mb Conceptually straighkorward, but not conserved Dynamic Tropopause Theta Conserved for adiaba@c, fric@onless flow (can use advec@on to explain/an@cipate changes) 2 10/31/14 PV on an Isentropic Surface (315 K) PV Thinking •  Under adiaba@c condi@ons, the evolu@on of PV is controlled by advec@on –  Changes in DT poten@al temperature (or PV on an isentropic surface) can be an@cipated based on advec@on •  PV can be “inverted” to deduce the the wind and thermodynamic fields –  Changes in the large-­‐scale flow can be an@cipated based on these advec@ve changes in DT poten@al temperature •  Non-­‐conserva@on of PV (i.e., changes in DT poten@al temperature not explained by advec@on) can be used to understand how diaba@c processes influence large-­‐scale systems •  Phenomena that can be diagnosed in this manner include cyclogenesis, trough and ridge amplifica@on, trough fracture, trough merger, downstream development, etc. Conserved for adiaba@c, fric@onless flow (can use advec@on to explain/an@cipate changes) PV Inversion -
PV Inversion •  PV can be inverted assuming a suitable balance condi@on +
-
•  The induced cyclonic circula@on and temperature anomalies are strongest near the PV anomaly and spread horizontally and ver@cally +
•  Cyclonic PV anomalies (i.e., locally high PV) induce a cyclonic circula@on +
-
•  An@cyclonic PV anomalies (i.e., locally low PV) induce an an@cyclonic circula@on Hoskins et al. (1985) +
-
•  Ver@cal penetra@on is inversely propor@onal to stability –  High stability = weak penetra@on –  Low stability = strong penetra@on Hoskins et al. (1985) Synop@c Applica@on •  Regions of low DT poten@al temperature (high DT pressure) are cyclonic PV anomalies and accompanied by upper-­‐level troughs/cyclones •  Regions of high DT poten@al temperature (low DT pressure) are an@cyclonic PV anomalies and accompanied by upper-­‐level ridges/
an@cyclones •  Amplifica@on (weakening) of a cyclonic PV anomaly is an indica@on of a developing (decaying) trof Class Ac@vity: Real-­‐Time Examples •  weather.utah.edu graphics •  IDV •  Amplifica@on (weakening) of an an@cyclonic PV anomaly is an indica@on of a developing (decaying) ridge •  Strong jets are usually found in regions of large tropopause pressure gradients (a.k.a. the PV Wall) Displays -­‐> Favorite Bundles -­‐> Diagnos@cs -­‐> PV-­‐Thinking 3