Potential Vorticity (PV) Thinking in Operations: The Utility of Nonconservation Michael J. Brennan*, Gary M. Lackmann, and Kelly M. Mahoney Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

Introduction PV can potentially be used by operational forecasters as a tool in the forecast processPV can potentially be used by operational forecasters as a tool in the forecast process PV hasn’t gained widespread acceptance in the operational forecasting communityPV hasn’t gained widespread acceptance in the operational forecasting community Goals of the paperGoals of the paper Provide examples of situations where PV diagnosis adds value to traditional forecast methods Provide examples of situations where PV diagnosis adds value to traditional forecast methods Provide specific suggestions for diagnostic PV tools for use in forecasting Provide specific suggestions for diagnostic PV tools for use in forecasting

Overview of PV Concepts PV principles PV principles PV is proportional to the product of absolute vorticity and static stabilityPV is proportional to the product of absolute vorticity and static stability PV = (1/ρ)η ∙ ▼ θ PV = (1/ρ)η ∙ ▼ θ In the Northern Hemisphere positive PV anomalies are associated with positive relative vorticity and high values of static stabilityIn the Northern Hemisphere positive PV anomalies are associated with positive relative vorticity and high values of static stability PV is conserved in frictionless, adiabatic flowPV is conserved in frictionless, adiabatic flow PV is not conserved in diabatic processesPV is not conserved in diabatic processes

Overview of PV Concepts PV is invertiblePV is invertible Piecewise inversions can be used to quantify effects of heating and friction influenced developments of specific anomalies by solving a boundary value problem Piecewise inversions can be used to quantify effects of heating and friction influenced developments of specific anomalies by solving a boundary value problem Davis, C.A., and K.A. Emanuel, 1991: Potential vorticity diagnostics of cyclogenesis. Mon. Wea. Rev., 119, Davis, C.A., and K.A. Emanuel, 1991: Potential vorticity diagnostics of cyclogenesis. Mon. Wea. Rev., 119, Not practical for operational forecasters Not practical for operational forecasters Cyclogenesis can occur when a cyclonic circulation associated with an upper-level +PV anomaly extends to the surface creating a surface warm anomaly through advectionCyclogenesis can occur when a cyclonic circulation associated with an upper-level +PV anomaly extends to the surface creating a surface warm anomaly through advection Diabatic PV anomalies can play a large role in moisture transport and precipitation distributionDiabatic PV anomalies can play a large role in moisture transport and precipitation distribution

Case Study Examples Moisture transport in ETC Moisture transport in ETC East coast cyclone of January 24-25, 2000 was poorly forecast by NWP modelsEast coast cyclone of January 24-25, 2000 was poorly forecast by NWP models A piecewise Ertel PV inversion was used to show that a lower-tropospheric PV maximum, generated by LH in an “incipient precipitation” (IP) area, was critical in moisture transport for the heavy precipitation areaA piecewise Ertel PV inversion was used to show that a lower-tropospheric PV maximum, generated by LH in an “incipient precipitation” (IP) area, was critical in moisture transport for the heavy precipitation area Models did not forecast the IP and therefore were unable to generate the PV maximum responsible for the moisture transportModels did not forecast the IP and therefore were unable to generate the PV maximum responsible for the moisture transport

A)RUC analysis 0000UTC Jan. 25, 2000 SLP (solid), 800mb wind barbs, mb PV (shaded PVU). B) 24 hr ETA forecast model. C) RUC SLP (solid), 800mb wind barbs, 800mb moisture flux (shaded g/kg m/s). D) 24 hr ETA forecast

Case Study Examples Moisture Transport in ETC cont… Moisture Transport in ETC cont… ETA model did not forecast the PV maximum and showed little moisture transport compared to RUC analysisETA model did not forecast the PV maximum and showed little moisture transport compared to RUC analysis The PV inversion showed that the PV maximum was responsible for 20-25kt of the onshore flow, enhancing the moisture fluxThe PV inversion showed that the PV maximum was responsible for 20-25kt of the onshore flow, enhancing the moisture flux How can this be used?How can this be used? Overlay lower-tropospheric PV from high-frequency analyses with radar imagery to model QPF and PV forecasts Overlay lower-tropospheric PV from high-frequency analyses with radar imagery to model QPF and PV forecasts Evaluate PV forecasts in NWP to diagnose errors Evaluate PV forecasts in NWP to diagnose errors This example shows that a low level PV max can increase the onshore flow poleward of its location causing precipitation to spread farther inland than predicted in NWP models This example shows that a low level PV max can increase the onshore flow poleward of its location causing precipitation to spread farther inland than predicted in NWP models

Case Study Examples Coastal extratropical cyclogenesis Coastal extratropical cyclogenesis PV provides a conceptual tool for diagnosing extratropical coastal cyclogenesisPV provides a conceptual tool for diagnosing extratropical coastal cyclogenesis Mahoney and Lackmann found that the model predicted cyclones and fronts were associated with the Betts- Miller-Janjic (BMJ) CP schemeMahoney and Lackmann found that the model predicted cyclones and fronts were associated with the Betts- Miller-Janjic (BMJ) CP scheme In this case PV was a useful tracer for monitoring the influence of CP scheme-driven diabatic processes in model forecastsIn this case PV was a useful tracer for monitoring the influence of CP scheme-driven diabatic processes in model forecasts Workstation version ETA model forecasts using the BMJ CP scheme and the Kain-Fritsch (KP) CP scheme were performedWorkstation version ETA model forecasts using the BMJ CP scheme and the Kain-Fritsch (KP) CP scheme were performed

a)30 hr forecast BMJ, mb PV (shaded, PVU), SLP (dashed), 3-h convective precip (solid, mm). b) as in a except 36 hr c,d) as in a,b except for KP scheme

Case Study Examples Coastal extratropical cyclogenesis cont… Coastal extratropical cyclogenesis cont… Results of the forecasts show that the character of the cyclone was very sensitive to the CP scheme usedResults of the forecasts show that the character of the cyclone was very sensitive to the CP scheme used The differences in model runs can lead to changes in moisture transport and thermal advectionThe differences in model runs can lead to changes in moisture transport and thermal advection Both are important to forecasters. Both are important to forecasters. How can this be used?How can this be used? PV can be used as an indicator of intense CP scheme activity PV can be used as an indicator of intense CP scheme activity PV maxima can continue after convective precipitation has ended and serve as a tracer of the influence of earlier latent heating PV maxima can continue after convective precipitation has ended and serve as a tracer of the influence of earlier latent heating Forecasters should be aware of possible intense CP scheme influence when heavy convective precipitation is collocated with new lower-tropospheric PV maxima Forecasters should be aware of possible intense CP scheme influence when heavy convective precipitation is collocated with new lower-tropospheric PV maxima

Case study Examples Low-level jet enhancement Low-level jet enhancement January 13-14, 2005: a slow cold front moved across central and eastern U.S. producing precipitation totals over 25mm, high winds, hail, and tornadoesJanuary 13-14, 2005: a slow cold front moved across central and eastern U.S. producing precipitation totals over 25mm, high winds, hail, and tornadoes At 0600Z a PV maximum developed along a cold frontal rain band, and an LLJ was East of the PV maximumAt 0600Z a PV maximum developed along a cold frontal rain band, and an LLJ was East of the PV maximum By 1200Z the PV maximum increased to 1.5 PVU in the heaviest precipitation area and the LLJ increased to 80kt over southern MaineBy 1200Z the PV maximum increased to 1.5 PVU in the heaviest precipitation area and the LLJ increased to 80kt over southern Maine

0600 Jan mb PV (solid, PVU) and 2km radar mosaic reflectivity

1200 Jan mb PV (solid, PVU) and 2km radar mosaic reflectivity

0600 Jan. 14, mb PV (shaded, PVU), 850mb wind barbs, and 850mb isotachs (dashed)

1200 Jan. 14, mb PV (shaded, PVU), 850mb wind barbs, and 850mb isotachs (dashed)

Case Study Examples Low-level jet enhancement cont… Low-level jet enhancement cont… A PV budget showed that latent heating associated with the precipitation aided the LL PV maximum developmentA PV budget showed that latent heating associated with the precipitation aided the LL PV maximum development A quasigeostrophic PV inversion indicated that over 40% of the LLJ was due to the presence of the LL PV anomalyA quasigeostrophic PV inversion indicated that over 40% of the LLJ was due to the presence of the LL PV anomaly How can this be used?How can this be used? Overlaying LL PV, winds, and radar imagery can identify situations when a PV maximum associated with LHR is enhancing a LLJ Overlaying LL PV, winds, and radar imagery can identify situations when a PV maximum associated with LHR is enhancing a LLJ Comparing model QPF to short term observations and examining PV distribution can help forecasters determine if models are over or under-estimating LLJ intensity Comparing model QPF to short term observations and examining PV distribution can help forecasters determine if models are over or under-estimating LLJ intensity

Operational Tools New “procedure” for the National Weather Service’s Advanced Weather Interactive Processing System (AWIPS) New “procedure” for the National Weather Service’s Advanced Weather Interactive Processing System (AWIPS) Introduced to promote the use of PV in identifying impacts of latent heating in model forecastsIntroduced to promote the use of PV in identifying impacts of latent heating in model forecasts Allows forecasters to examine model forecasts of SLP, LL PV and winds, and total and convective precipitationAllows forecasters to examine model forecasts of SLP, LL PV and winds, and total and convective precipitation Allows users to identify the impact of latent heating on atmospheric dynamicsAllows users to identify the impact of latent heating on atmospheric dynamics Met Office developments Met Office developments Forecasters directly alter model generated PV fields, then use PV inversion to obtain other fieldsForecasters directly alter model generated PV fields, then use PV inversion to obtain other fields Forecasters can use PV framework to adjust NWP model guidance which can improve lead times for short and medium-range forecastsForecasters can use PV framework to adjust NWP model guidance which can improve lead times for short and medium-range forecasts

AWIPS: mb PV (Shaded, PVU), total precip. (blue contours), convective precip. (red contours), 850mb wind barbs, and SLP (white contours)

Conclusions Using PV to identify and diagnose diabatically produced LL cyclonic PV anomalies gives forecasters a new motive to incorporate PV framework into their forecast methodsUsing PV to identify and diagnose diabatically produced LL cyclonic PV anomalies gives forecasters a new motive to incorporate PV framework into their forecast methods PV can be used as a tool along with ensemble forecasts to give more confidence in forecasts of fields with high uncertainties (i.e. QPF)PV can be used as a tool along with ensemble forecasts to give more confidence in forecasts of fields with high uncertainties (i.e. QPF) This forecasting method may gain more acceptance in operational meteorology with further research, enhanced graphical displays, and training modulesThis forecasting method may gain more acceptance in operational meteorology with further research, enhanced graphical displays, and training modules