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(Jason Andrew for Wall Street Journal: photo of Park Slope, Brooklyn)

The Evolution of Quasi-Linear Convective Systems Encountering the Northeastern US Coastal Marine Environment Kelly Lombardo & Brian Colle Stony Brook University. (Jason Andrew for Wall Street Journal: photo of Park Slope, Brooklyn). Let’s compare the evolution of 2 different QLCS events….

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(Jason Andrew for Wall Street Journal: photo of Park Slope, Brooklyn)

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  1. The Evolution of Quasi-Linear Convective Systems Encountering the Northeastern US Coastal Marine Environment Kelly Lombardo & Brian Colle Stony Brook University (Jason Andrew for Wall Street Journal: photo of Park Slope, Brooklyn)

  2. Let’s compare the evolution of 2 different QLCS events… 23 JUL 2002 1600 UTC – 24 JUL 2002 0400 UTC 31 MAY 2002 1700 UTC – 01 JUN 2002 1000 UTC

  3. Let’s compare the evolution of 2 different QLCS events… 23 JUL 2002 1600 UTC – 24 JUL 2002 0400 UTC 31 MAY 2002 1700 UTC – 01 JUN 2002 1000 UTC Why does one event survive over the Atlantic while the other decays upon reaching the coastline?

  4. Data & Methods: Composites • Manually examined 2-km NOWrad radar reflectivity for 6 warms seasons (May-Aug) 2002-2007; Identified 73 QLCS that encountered the Atlantic coast. • 65 QLCS events were classified into 4 different categories based on their evolution encountering the coastline. • 32 decaying events: Decay at the coastline. • 18 slowly decaying events: Show no signs of decay at the coast, but decay over the water within 100 km of the coast. • 9 sustaining events: Maintain their intensity more than 100 km from coastline. • 6 organize events: Organize along the • coastline (not addressed in this study). • Feature-based composites for decaying, • slowly decaying, and sustaining • events using 32-km NARR data. • Centered on the point where the • QLCS crosses the coast at the • closest 3-hr NARR time prior • to the crossing. QLCS >100 km 0-100 km

  5. Geography for reference only: Star center point for feature based composites. Decaying Sustaining MUCAPE (J kg-1), MSLP (hPa), 1000 theta (2 K), 10 m wnd (kts) Decaying: MUCAPE 1250 J kg-1; collocated with a surface pressure trough & 1000 hPa thermal ridge. Sustaining: MUCAPE 1000 J kg-1; surface pressure trough 300 km to west; QLCS collocated with 1000 hPa baroclinic zone.

  6. Geography for reference only: Star center point for feature based composites. Decaying MUCIN (shaded, J kg-1), 1000 hPa RH (red, %), 0-3 km wind shear (kts) Sustaining 80 80 70 70 Decaying: MUCIN 15 J kg-1 and increases rapidly offshore; RH of 68% (lowest 100 hPa); potential for evaporative cooling; Shear 15 kts. Sustaining: MUCIN 35 J kg-1 with a weak offshore gradient; RH 77%; less of a chance for evaporative cooling; shear 25 kts.

  7. Geography for reference only: Star center point for feature based composites. Decaying 900:800 frontogenesis (10-2 K (100 km)-1 (3 hr)-1), 900 tmp (black, oC), 900 tmp adv (10-5oC s-1), 900 winds (kts) Sustaining Decaying: QLCS on the warm side of a fronotogenesis maximum; strengthening baroclinic zone/front. Sustaining: QLCS within a region of WAA with little frontogenesis.

  8. Motivational Questions • What is the role of warm air advection during sustaining events? • What is the role of the stable layer and convective inhibition? • How is the enhanced vertical wind shear important to the maintenance of a QLCS? • What role does low-level diabatic cooling play in the evolution of QLCSs?

  9. 2 Case Studies • Better understand the processes that govern the maintenance and decay of a QLCS • Simulations: WRF ARW core • Initial & Boundary Conditions: 32-km NARR • Explicit convection • Morrison double-moment microphysics • MYNN2.5 PBL • Thermal LSM 2002 Sustaining: 31 MAY 1200 UTC – 01 JUN 0600 UTC 2 km 2002 Decaying: 23 JUL 0600 UTC – 24 JUL 0300 UTC 500 m

  10. 31 May 2002 Sustaining Event 0100 UTC 01 JUN 2002

  11. 2100 UTC 31 May 2002 NARR: 300 wnd (shaded, m s-1), 500 hght (solid, dam), 500 Q-vect conv (dashed, 10-15 K m-2 s-1), 500 wnd (m s-1) 2km WRF: mslp (solid, hPa), 2 m tmp (dashed, oC), 2 m dwpt (shaded, oC), 10 m winds (m s-1) • Cold front and prefrontal trough • Cold front & prefrontal trough • Convection ahead of cold front, consistent with composites. • Thermal ridge in the Appalachian lee • Coastal baroclinic zone • Relatively moist air along coast (dew points 17-18oC) • 300 hPa jet extending into base of an upper level trough • 500 hPa trough axis over eastern NY • 500 hPa Q-vector convergence over the Northeast coastal region

  12. 2km WRF: MUCAPE (J kg-1), 925 hPa hght (solid, dam), 925 tmc (dashed, oC), 925 wnd( m s-1) WAA similar to composites 1600-2000 J kg-1 CAPE in lee LI CAPE 400-1600 J kg-1 1500 UTC 31 May 2002 2100 UTC 31 May 2002 MUCAPE ~700 J kg-1 MUCIN ~25-100J kg-1 MUCAPE ~200 J kg-1 MUCIN ~25-75 J kg-1 700 hPa 700 hPa 900 hPa 900 hPa T925hPa ~18oC T925hPa ~22oC 500 m JFK: 1500 UTC 31 May 500 m JFK: 2100 UTC 1 Jun

  13. Observed radar reflectivity (dBZ) 2258 UTC 31 May 0145 UTC 1 Jun 0200 UTC 1 Jun 2 km WRF precip mixr (shaded, g kg-1), 100 m omega (contour, 10-2 m s-1), 100 m wnds 2215 UTC 31 May 0300 UTC 1 Jun 0145 UTC 1 Jun

  14. 23 July 2002 Decaying Event 2200 UTC 23 JUL 2002

  15. 2100 UTC 23 July 2002 2km WRF: mslp (solid, hPa), 2 m tmp (dashed, oC), 2 m dwpt (shaded, oC), 10 m winds (m s-1) NARR: 300 wnd (shaded, m s-1), 500 hght (solid, dam), 500 Q-vect conv (dashed, 10-15 K m-2 s-1), 500 wnd (m s-1) • 300 hPa jet core U.S.-Canada border • Broad 500 hPa trough • Little 500 hPa Q-vector convergence over coastal region • Limited mid- and upper-level forcing • Convection collocated with surface cold front, consistent with composites

  16. 2km WRF: MUCAPE (J kg-1), 925 hPa hght (solid, dam), 925 tmc (dashed, oC), 925 wnd( m s-1) Little temperature advection similar to composites 1600-2000 J kg-1 MUCAPE over coast Still 1200-1600 J kg-1 instability along coast and offshore 1800 UTC 23 Jul 2002 2100 UTC 23 Jul 2002 MUCIN ~25-150 J kg-1 MUCIN ~25-150 J kg-1 Inversion becoming reestablished 700 hPa 700 hPa 900 hPa 900 hPa 500 m JFK: 1800 UTC 500 m JFK: 2100 UTC

  17. Observed radar reflectivity (dBZ) 2016 UTC 23 Jul 2115 UTC 23 Jul 0005 UTC 24 Jul 2 km WRF precip mixr (shaded, g kg-1), 100 m omega (contour, 10-2 m s-1), 100 m wnds 2015 UTC 23 Jul 2115 UTC 23 Jul 0000 UTC 24 Jul

  18. vorticity generated by ambient low-level shear in along line direction vorticity generated by buoyancy gradients along leading edge of the cold pool Low-level Balance Theory for Long Lived Squall Lines = (Rotunno et al. 1988) QLCS experiences variations in low-level winds and thermodynamics (Weisman & Rotunno 2004)

  19. vorticity generated by ambient low-level shear in along line direction vorticity generated by buoyancy gradients along leading edge of the cold pool Low-level Balance Theory for Long Lived Squall Lines = (Rotunno et al. 1988) QLCS experiences variations in low-level winds and thermodynamics (Weisman & Rotunno 2004)

  20. vorticity generated by ambient low-level shear in along line direction vorticity generated by buoyancy gradients along leading edge of the cold pool Low-level Balance Theory for Long Lived Squall Lines = (Rotunno et al. 1988) QLCS experiences variations in low-level winds and thermodynamics (Weisman & Rotunno 2004)

  21. 0030 UTC 1 JUN (12.5h) 2130 UTC 23 JUL (15.5h) 500 m 500 m θ’ = 3.75 K hc = 1.2 km C = 19.3 m s-1 θ’ = 4 K hc = 1.3 km C = 18.3 m s-1 ΔU2.5km= 15.0 m s-1 ΔU2.5km= 7.5 m s-1 C/ΔU=1.3 C/ΔU=2.5 C C precip mixr (shaded, g kg-1), potential temp (solid, K), storm relative circulation vectors

  22. 2230 UTC 23 JUL (16.5h) 0100 UTC 1 JUN (13h) 500 m 500 m precip mixr (shaded, g kg-1), potential temp (solid, K), storm relative circulation vectors

  23. Response of QLCS to Low Level (Nocturnal) Cooling Limited cooling: t=6h30m • Surface-based phase: Lifting by the surface cold pool. Unimited cooling: t=6h30m • Stalling phase: Mechanism for surface lifting disappears as the relative strength of the cold pool approaches zero. Unimited cooling: t=8h30m • Elevated phase: Convection forced by a bore atop the stable layer. (Parker 2008)

  24. Sustaining Event • Forcing similar to a bore, though not purely bore driven. • Stronger, deeper (up to 925 hPa; 750 m) temperature inversion (WAA) • Moist Brunt-Vaisala Frequency 0.04 s-1 • Decaying Event • More dominantly forced by a surface based density current. • More shallow inversion (975 hPa; 300 m) • Moist Brunt-Vaisala Frequency 0.36 s-1 precip mixr (shaded, g kg-1), potential temp (solid, K), storm relative circulation vectors

  25. Sensitivity Experiments

  26. t = 16 h t = 17 h t = 24 h 2 km 15%EVAP • 23 JULY 2002: Decrease Diabatic Cooling • At t = 13h, reduced the evaporative cooling to 15% of the original value • Convection more intense and moves over the coastal waters 2km CTRL t=15h

  27. 23 JULY 2002: ‘Remove’ Atlantic Ocean • Ocean replaced with land surface representative of the northeastern U.S. • A few stronger convective cores, but decay similar to CTRL • Drier, warmer, deeper boundary layer in LAND run. • Increase ‘offshore’ CAPE for LAND run. • Increase chance for evaporative cooling. • Reduced vertical wind shear for LAND run. t=16h t=17h CTRL-LAND RH (%) at t=16h LAND precip mixr (g kg-1) and CTRL-LAND line-perpendicular wind (m s-1) at t=16h

  28. Summary • In the mean, QLCSs that decay upon encountering the northeastern U.S. coastline are collocated with frontal boundaries and regions of 900:800 hPa frontogenesis, with little temperature advection over the QLCS. • Events that survive over the ocean waters are associated with warm air advection (destabilize atmosphere and strengthen low level temperature inversion: 31 May 2002 case) with little 900:800 hPa frontogenesis associated with the QLCS. • 31 May 2002 event • Stronger vertical wind shear helps to balance the cold pool, extending the longevity of the QLCS. • Forcing transitions from a surface-based cold pool to more of a bore type feature (perhaps due to a stronger stable layer compared to 23 July?). • 23 July 2002 event • Reducing the diabatic cooling to 15% of the CTRL simulation extended the longevity of the QLCS. • Shows that diabatic processes can be as important as the marine layer in influencing the evolution of QLCS (though this may not always be the case).

  29. extra slides

  30. 2km WRF: mslp (solid, hPa), 2 m tmp (dashed, oC), 2 m dwpt (shaded, oC), 10 m winds (m s-1) • Cold front and prefrontal trough • Convection ahead of cold front, consistent with composites. • Thermal ridge in Appalachian lee • Coastal baroclinic zone • Relatively moist air along coast Surface observations, mslp (black, dam), surface temp (blue, oC) WRF ~1oC cooler compared to surface obs within thermal ridge WRF and obs same at buoy 44025 WRF 0.5oC too cool at Ambrose Light Tower 2100 UTC 31 May 2002

  31. 2km WRF: MUCAPE (J kg-1), 925 hPa hght (dam), 925 tmc (oC), 925 wnd( m s-1) WAA similar to composites NARR MUCAPE is ~400 J kg-1 greater 2100 UTC 31 May 2002 1500 UTC 31 May 2002 WRF 2-3oC cooler than obs T925hPa increases ~5oC 700 hPa 700 hPa 900 hPa 900 hPa 1200 UTC 500 m OKX: 0000 UTC 31 May KOKX: 0000 UTC 1 Jun

  32. 2km WRF: mslp (solid, hPa), 2 m tmp (dashed, oC), 2 m dwpt (shaded, oC), 10 m winds (m s-1) • Convection collocated with surface cold front, consistent with composites • WRF does not capture mesoscale details of surface pressure features Surface observations, mslp (black, dam), surface temp (blue, oC) WRF ~2 oC too warm in cold sector and ~2 oC too cool in warm sector WRF 1oC too cool at buoy 44025 WRF 100 m winds 2.5 m s-1 too weak at Ambrose Light Tower H L 2100 UTC 23 Jul 2002

  33. Let’s compare the evolution of 2 different QLCS events… 23 JUL 2002 1600 UTC – 24 JUL 2002 0400 UTC 31 MAY 2002 1700 UTC – 01 JUN 2002 1000 UTC

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