Mesoscale Convective Vortices (MCVs) Chris Davis (NCAR ESSL/MMM and RAL) Stan Trier (NCAR ESSL/MMM) Boulder, Colorado 60-h Radar Composite Animation (00 UTC 11 June – 12 UTC 13 June, 2003) 500 km Acknowledgements: Morris Weisman, EOL staff

X Background and Definitions Mesoscale Convective System (MCS): an isolated, nearly contiguous region of thunderstorms, sometimes surrounded by an extensive region of moderate rainfall. Total size is usually km across. Bow-echo: a bow-shaped line of thunderstorms often containing strong surface winds. Mesoscale Convective Vortex: a lower-mid- tropospheric horizontal wind circulation derived from an area of convection (often an MCS) UTC 10 June, June, UTC 10 June, km

Long-time Behavior of MCSs Convection develops (often in response to synoptic-scale of mesoscale features) Convection organizes (internally or externally) Convection leads to modified or new balanced features (vortices) Balanced features produce new convection

Long-time Behavior of MCSs (twice) L H H Warm Cool

Diabatic Heating Deep convection (heating) Mesoscale updraft (heating) Melting and evaporation (cooling) Radiation (cooling) Gradient along vorticity vector determines PV generation rate Dependencies in models –Cumulus parameterization –Cloud physics (and radiative interaction) –Surface-atmosphere coupling (heating versus moistening)

MCV Induced Lifting and Destabilization Fritcsh et al. 1994, MWR

Raymond and Jiang (JAS 1990) Conceptual Model of Isentropic Lifting within a Steady Balanced Vortex (e.g., MCV)

Mature MCVs from the Bow Echo and MCV Experiment (BAMEX) 20 May – 6 July 2003 May 24: remnant of severe bow echo June 2: hybrid with cyclone wave June 5: remnant of large MCS June 11: Multi-day MCS/MCV system, late became frontal cyclone June 24: MCV from multi-MCS complex Data: dropsondes, MGLASS, profilers (storm relative and time-space corrected)

Precursor Conditions 500 hPa  850 hPa wind IOP 1: 00 UTC 24 May IOP 4: 00 UTC 2 JuneIOP 5: 00 UTC 5 June IOP 8: 00 UTC 11 June IOP 15: 00 UTC 29 June MCSMCV

MCS Precursors to MCVs IOP 1, 24 May IOP 4, 2 JuneIOP 15, 29 June 1500 UTC 0600 UTC IOP 5, 5 June 1100 UTC IOP 8, 11 June 0600 UTC 0500 UTC 150 km = Primary Vortex

IOP 1 IOP 5 IOP 8 IOP 15 Reflectivity, Temperature, and System-relative Winds IOP 4 = new convection triggered No CAPE Localized CAPEWidespread CAPE

Analysis Method Dropsonde, profiler and MGLASS Composited to common reference time (const MCV motion assumed) Divergence and vorticity analyzed assuming linear variation along sides Restrictions on minimum angle, area; maximum side length and area Overlapping triangles used to assess “confidence” (  ) 25-km analysis grid

MCV Vertical Structure Shading=low confidence Red line=vortex axis Contour: 5x10 -5 s -1

MCV Vertical Structure v’v’ v’v’

Wind Profiles ( averages of quadrant means)

Balance within MCVs Procedure:   via nonlinear balance    T v (hydrostatic)  T v profile at sounding locations  Quadrant averages (r<R max ; r≥R max )  Subtract mean outer profile from inner profile: T' v Pressure (hPa) T' v (K) Obs Bal IOPs 1 and 8 have best data coverage

00 UTC 6 July 12 UTC 6 July Eta 500 mb , wind analysis Airborne Doppler Domain 06 UTC 6 July Radar Composite Evolution of Mid-tropospheric Vortex 12 UTC 6 July 00 UTC 7 July 18 UTC 6 July

Diabatic Rossby Vortices Conzemius et al (2007, JAS) – idealized MM5 simulations in weakly sheared flow: shown are relative vorticity and potential temperature T=120 h (just prior to deep convection)T=173.6 h (after 2 days of convection) Observed MCV centers

Summary  4-8 km deep, centered between 500 and 600 mb  V~10 m/s  Nearly in gradient balance (Ro~1)  Tilts of vortices consistent with vertical shear  Temperature anomalies weak, even below MCV center  Deep vortices may require cyclonic precursor  Implications for rainfall organization, see S. Trier’s talk on Friday