IPVfeb2002

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Published on January 16, 2008

Author: Stella

Source: authorstream.com

IPV and the Dynamic Tropopause:  IPV and the Dynamic Tropopause John W. Nielsen-Gammon Texas A&M University 979-862-2248 n-g@tamu.edu Outline:  Outline PV basics Seeing the world through PV Waves and vortices Nonconservation Forecasting applications Short-range forecasting Tracking disturbances over the Rockies Understanding the range of possibilities Mathematical Definitions of PV:  Mathematical Definitions of PV Rossby: Vorticity divided by theta surface spacing : Relative vorticity in isentropic coordinates Minus sign: makes PV positive since pressure decreases upward Mathematical Definitions of PV:  Mathematical Definitions of PV Rossby: Ertel: Vorticity times static stability Units of Potential Vorticity:  Units of Potential Vorticity 1 PVU equals…you don’t want to know Midlatitude Troposphere: -0.2 to 3.0 PVU Typical value: 0.6 PVU Midlatitude Stratosphere: 1.5 to 10.0 PVU Typical value: 5.0 PVU PV Cross Section Pole to Pole at 80W:  PV Cross Section Pole to Pole at 80W PV and Westerlies (m/s):  PV and Westerlies (m/s) PV and Absolute Vorticity (*10-5 s-1):  PV and Absolute Vorticity (*10-5 s-1) PV and Potential Temperature (K):  PV and Potential Temperature (K) 280 310 330 350 380 What do PV gradients imply?:  What do PV gradients imply? Steep PV gradients Jet streams High PV to left of jet Vorticity gradients Same sign as PV gradients Stratification gradients High stratification where PV is large Vertical tropopause Flat PV gradients Boring No wind or vorticity variations Stratification high where PV is large Flat tropopause Slide11:  PV Contours: 0, 0.25, 0.5, 1, 2, 4, 8 Slide14:  PV Contours: 0, 0.25, 0.5, 1, 2, 4, 8 Strong PV gradients matter; PV maxes and mins are inconsequential:  Strong PV gradients matter; PV maxes and mins are inconsequential Jet stream follows PV gradients Waves in the PV field correspond to waves in the jet stream PV extrema bounded by strong gradients could mean short waves or cutoffs High PV = trough; Low PV = ridge Forget PV! The Traditional Geopotential Height Maps Work Fine!:  Forget PV! The Traditional Geopotential Height Maps Work Fine! Advantages of Height Identification and assessment of features Inference of wind and vorticity Inference of vertical motion? Disadvantages of Height Gravity waves and topography Inference of evolution and intensification Role of diabatic processes is obscure Need 300 & 500 mb What’s PV Got that Traditional Maps Haven’t Got?:  What’s PV Got that Traditional Maps Haven’t Got? Advantages of PV PV is conserved PV unaffected by gravity waves and topography PV at one level gives you heights at many levels Easy to diagnose Dynamics Disadvantages of PV Unfamiliar Not as easily available Not easy to eyeball significant features Qualitative inference of wind and vorticity Hard to diagnose vertical motion? DYNAMICS?:  DYNAMICS? A given PV distribution implies a given wind and height distribution If the PV changes, the winds and heights change If you know how the PV is changing, you can infer everything else And PV changes only by advection! The PV Conundrum:  The PV Conundrum Maps of mean PV between pressure surfaces Encapsulates the PV distribution Cannot diagnose evolution or dynamics The PV Conundrum:  The PV Conundrum IPV (Isentropic Potential Vorticity) maps Many isentropic surfaces have dynamically significant PV gradients Hard to know which isentropic surfaces to look at The PV Solution: Tropopause Maps:  The PV Solution: Tropopause Maps Pick a PV contour that lies within the (critical) tropopause PV gradient Overlay this particular contour from all the different isentropic layers (or interpolate to that PV value) Result: one map showing the location of the important PV gradients at all levels Contours advected by horizontal wind The 1.5 PVU contour on the 320 K isentropic surface is…:  The 1.5 PVU contour on the 320 K isentropic surface is… …identical to the 320 K contour on the 1.5 PVU (tropopause) surface!:  …identical to the 320 K contour on the 1.5 PVU (tropopause) surface! Color Fill Version of Tropopause Map:  Color Fill Version of Tropopause Map Tropopause Map with Jet Streams:  Tropopause Map with Jet Streams Tropopause Map, hour 00:  Tropopause Map, hour 00 Tropopause Map, hour 06:  Tropopause Map, hour 06 Tropopause Map, hour 12:  Tropopause Map, hour 12 Tropopause Map, hour 18:  Tropopause Map, hour 18 Tropopause Map, hour 24:  Tropopause Map, hour 24 Tropopause Map, hour 30:  Tropopause Map, hour 30 Tropopause Map, hour 36:  Tropopause Map, hour 36 Tropopause Map, hour 42:  Tropopause Map, hour 42 Tropopause Map, hour 48:  Tropopause Map, hour 48 Tropopause Map, hour 48, with jets:  Tropopause Map, hour 48, with jets Midway Point:  Midway Point Play with some PV Watch a movie PV Dynamics: The Short Course:  PV Dynamics: The Short Course High PV / Stratosphere / Low Theta on Tropopause Low PV / Troposphere / High Theta on Tropopause Superposition:  Superposition PV field Basic state Anomalies Associated wind field Basic state wind Winds associated with each anomaly Add ‘em all up to get the total wind/PV PV Anomaly: A Wave on the Tropopause:  PV Anomaly: A Wave on the Tropopause + PV Anomaly: Anomalous Winds:  PV Anomaly: Anomalous Winds + Think of each PV anomaly as a cyclonic or anticyclonic vortex PV Wind Rules (for Northern Hemisphere):  PV Wind Rules (for Northern Hemisphere) Positive anomalies have cyclonic winds Negative anomalies have anticyclonic winds Winds strongest near anomaly Winds decrease with horizontal distance Winds decrease with vertical distance PV Anomaly: What will the total wind field be?:  PV Anomaly: What will the total wind field be? + + Short Wave Planetary Wave Wave Propagation:  Wave Propagation Individual waves propagate upstream Short waves move slower than jet Long waves actually retrogress + + The Making of a Rossby Wave Packet:  The Making of a Rossby Wave Packet + + Trough amplifies downstream ridge Ridge amplifies downstream trough, weakens upstream trough Wave packet propagates downstream - + - + Intensification: Two Ways:  Intensification: Two Ways Increase the size of the PV anomaly “Amplification” Increase the amount of PV (or number of PV anomalies) within a small area “Superposition” Tropopause, Feb. 10, 2001, 00Z:  Tropopause, Feb. 10, 2001, 00Z Superposition? Amplification Tropopause, Feb. 10, 2001, 06Z:  Tropopause, Feb. 10, 2001, 06Z Tropopause, Feb. 10, 2001, 12Z:  Tropopause, Feb. 10, 2001, 12Z Tropopause, Feb. 10, 2001, 18Z:  Tropopause, Feb. 10, 2001, 18Z Tropopause, Feb. 11, 2001, 00Z:  Tropopause, Feb. 11, 2001, 00Z 500 mb, Feb. 10, 2001, 00Z:  500 mb, Feb. 10, 2001, 00Z 500 mb, Feb. 10, 2001, 06Z:  500 mb, Feb. 10, 2001, 06Z 500 mb, Feb. 10, 2001, 12Z:  500 mb, Feb. 10, 2001, 12Z 500 mb, Feb. 10, 2001, 18Z:  500 mb, Feb. 10, 2001, 18Z 500 mb, Feb. 11, 2001, 00Z:  500 mb, Feb. 11, 2001, 00Z Low-Level Potential Temperature:  Low-Level Potential Temperature Acts like upper-level PV Locally high potential temperature = cyclonic circulation Locally low potential temperature = anticyclonic circulation But gradient is backwards Winds from north intensify upper-level PV Winds from south intensify low-level warm anomaly MSLP (mb), 950 mb theta-e (K), 700-950 mb PV, 300 K 1.5 PV contour:  MSLP (mb), 950 mb theta-e (K), 700-950 mb PV, 300 K 1.5 PV contour Surface, Feb. 10, 2001, 06Z:  Surface, Feb. 10, 2001, 06Z Surface, Feb. 10, 2001, 12Z:  Surface, Feb. 10, 2001, 12Z Surface, Feb. 10, 2001, 18Z:  Surface, Feb. 10, 2001, 18Z Surface, Feb. 11, 2001, 00Z:  Surface, Feb. 11, 2001, 00Z Cyclogenesis:  Cyclogenesis Mutual Amplification Southerlies assoc. w/ upper-level trough intensify surface frontal wave Northerlies assoc. w/ surface frontal wave intensify upper-level trough Superposition Trough and frontal wave approach and occlude Diabatic Processes:  Diabatic Processes Latent heating max in mid-troposphere PV increases below LH max PV decreases above LH max It’s as if PV is brought from aloft to low levels by latent heating Strengthens the surface low and the upper-level downstream ridge Diabatic Processes: Diagnosis:  Diabatic Processes: Diagnosis Low-level PV increases Upper-level PV decreases Tropopause potential temperature increases Diabatic Processes: Prediction:  Diabatic Processes: Prediction Plot low-level equivalent potential temperature instead of potential temperature Compare theta-e to the potential temperature of the tropopause If theta-e is higher: Deep tropospheric instability Moist convection likely, rapid cyclogenesis Forecasting Applications (1): Evolution:  Forecasting Applications (1): Evolution Can directly diagnose evolution Motion of upper-level systems Intensification and weakening Formation of new troughs and ridges downstream Forecasting Applications (2): Model Correction:  Forecasting Applications (2): Model Correction Can correct forecast for poor analyses or short-range deviation Where’s the real trough? How will it affect the things around it? How will its surroundings affect its evolution? Forecasting Applications (3): The Rockies:  Forecasting Applications (3): The Rockies Can track systems over topography Vorticity is altered by stretching and shrinking as parcels go over mountains Potential vorticity is conserved on isentropic surfaces PV shows you what the trough will look like once it leaves the mountains Better forecasts, better comparison with observations Forecasting Applications (4): Uncertainty:  Forecasting Applications (4): Uncertainty Can understand the range of possibilities Could this trough intensify? Could a downstream wave be triggered? How many “objects” must be simulated correctly for the forecast to be accurate? Summary:  Summary Definition of PV IPV maps and tropopause maps Diagnosis of evolution using PV Dynamics using PV Forecasting applications of PV

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