A Multiscale Examination of a Mesoscale Cyclogenesis Event in a Polar Air Stream Tom Galarneau, Dan Keyser, and Lance Bosart Department of Earth and Atmospheric Sciences University at Albany, SUNY 8th Northeast Regional Operational Workshop, Albany, NY 1 November 2006

Motivation Heavy snow with thunder reported across eastern PA, NJ, and LI on 5 April 2006 Heavy snow with thunder reported across eastern PA, NJ, and LI on 5 April 2006 Review during “Friday Map Discussion” revealed two comma-cloud structures and led to arguments on whether these were true polar lows Review during “Friday Map Discussion” revealed two comma-cloud structures and led to arguments on whether these were true polar lows Investigation in graduate “Extratropical Cyclones” class (spring 2006) indicated the involvement of a coherent tropopause disturbance (CTD) in the evolution of the polar lows Investigation in graduate “Extratropical Cyclones” class (spring 2006) indicated the involvement of a coherent tropopause disturbance (CTD) in the evolution of the polar lows

X CTD Polar Low 1 Polar Low 2 Storm Tracks 00Z/25 06Z/05

CTD Structure Fig. 11a from Hakim (2000)Fig. 10c from Hakim (2000) DT  (K) DT  anomaly (K) Ertel PV (PVU)  (K)

CTD Example Hakim (2000) 300 hPa Height, Temp,  DT , Wind, 850 hPa 

The Polar Low Spectrum Rasmussen and Turner (2003) Reed (1979) Adapted from Rasmussen and Turner (2003); originally suggested by Emanuel in 1986 Cold low Orographic Boundary-layer front Comma cloud Reverse shear Forward shear Trough system

Polar Low Timeline High latitude TC-like lows Instability lows near Norway Instability lows obtain fronts Cold air depressions near British Isles Lows occur in cold unstable air mass over warm ocean 1st comprehensive observational study using sfc/upper air Baroclinic instability suggested mechanism Conditional Instability of Second Kind (CISK) suggested mechanism Norwegian Polar Lows Project 1983–85 -Aircraft obs; climo; modeling Satellite studies of comma clouds Comma clouds vs. ‘real’ polar lows Polar lows in NPAC, Sea of Japan, SH Studies using Scatterometer data Polar low Classification (1985–96) Idealized simulations Aircraft obs of Antarctic polar low CTDsWISHE processes Intense polar lows dubbed “Arctic hurricanes”

Polar Low Timeline High latitude TC-like lows Instability lows near Norway Instability lows obtain fronts Cold air depressions near British Isles Lows occur in cold unstable air mass over warm ocean 1st comprehensive observational study using sfc/upper air Baroclinic instability suggested mechanism Conditional Instability of Second Kind (CISK) suggested mechanism Norwegian Polar Lows Project 1983–85 -Aircraft obs; climo; modeling Satellite studies of comma clouds Comma clouds vs. ‘real’ polar lows Polar lows in NPAC, Sea of Japan, SH Studies using Scatterometer data Polar low Classification (1985–96) Idealized simulations Aircraft obs of Antarctic polar low CTDsWISHE processes Intense polar lows dubbed “Arctic hurricanes” Pre-CTD

Businger and Reed (1989) Classification Short-wave/jet streak type (baroclinic) Short-wave/jet streak type (baroclinic) Form in polar air mass in wake of synoptic-scale cyclone in region of cyclonic vorticity advection Form in polar air mass in wake of synoptic-scale cyclone in region of cyclonic vorticity advection Comma-cloud structure Comma-cloud structure Arctic front type (baroclinic) Arctic front type (baroclinic) Form along continental arctic-maritime polar air mass boundaries Form along continental arctic-maritime polar air mass boundaries Comma-cloud structure Comma-cloud structure Cold low type (warm core) Cold low type (warm core) Form in arctic air masses over warm oceans Form in arctic air masses over warm oceans Spiral-cloud structure Spiral-cloud structure

Goals Examine large-scale environment Examine large-scale environment Document evolution of CTD and two polar lows Document evolution of CTD and two polar lows Relate to classification scheme in polar low spectrum Relate to classification scheme in polar low spectrum

Data Sources 1.0  GFS analyses 1.0  GFS analyses 32 km North American Regional Reanalysis 32 km North American Regional Reanalysis UAlbany surface/upper-air archive UAlbany surface/upper-air archive GIBBS and RAL satellite archive GIBBS and RAL satellite archive NCDC WSR-88D Level-II radar archive NCDC WSR-88D Level-II radar archive National Lightning Detection Network National Lightning Detection Network Dynamic tropopause (DT) defined as 1.5 PVU Dynamic tropopause (DT) defined as 1.5 PVU

1445Z/05GOES-12 Visible 1 2

1745Z/05GOES-12 Visible 1 2

2045Z/05GOES-12 Visible 1 2

VIS1145Z

VIS1445Z

VIS1845Z

CTD Track Map DT  (K) and wind (kts) at 0000 UTC 5 April 2006 X X X X X X X X X X X 00Z/04 00Z/25 00Z/03 00Z/ K isotherm on DT

Large-Scale Summary CTD extracted from high latitudes via two ridging episodes CTD extracted from high latitudes via two ridging episodes Ridging near 160  W on 30 March Ridging near 160  W on 30 March Ridging over Intermountain West on 2-4 April Ridging over Intermountain West on 2-4 April Two polar lows developed in association with CTD on 5 April in wake of synoptic- scale surface cyclone Two polar lows developed in association with CTD on 5 April in wake of synoptic- scale surface cyclone

00Z/05 DT  (K), Wind (kts), 850 hPa  (10 -5 s -1 )

03Z/05 DT  (K), Wind (kts), 850 hPa  (10 -5 s -1 )

06Z/05 DT  (K), Wind (kts), 850 hPa  (10 -5 s -1 )

09Z/05 DT  (K), Wind (kts), 850 hPa  (10 -5 s -1 )

12Z/05 DT  (K), Wind (kts), 850 hPa  (10 -5 s -1 )

15Z/05 DT  (K), Wind (kts), 850 hPa  (10 -5 s -1 )

18Z/05 DT  (K), Wind (kts), 850 hPa  (10 -5 s -1 )

21Z/05 DT  (K), Wind (kts), 850 hPa  (10 -5 s -1 )

00Z/06 DT  (K), Wind (kts), 850 hPa  (10 -5 s -1 )

00Z/ hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1

03Z/ hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1

06Z/ hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1 2

09Z/ hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1 2

12Z/ hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1 2

ALB OKX 12Z/  GFS OBS 925 hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1 2

15Z/ hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1 2

18Z/ hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1 2

21Z/ hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1 2

00Z/ hPa  e (K), 925–500 hPa wind shear (kts), 850–500 hPa lapse rate (  C km -1 ), cloud-to-ground lightning 1 2

SLP (hPa)  (  C) 06Z/05 1 2

1 2

SLP (hPa)  (  C) 1145Z 12Z/05 1 2

1 1 2

SLP (hPa)  (  C) 1445Z 15Z/05 1 2

2 2

SLP (hPa)  (  C) 1845Z 18Z/05 1 2

2

SLP (hPa)  (  C) 21Z/05

Summary Two polar lows developed in wake of synoptic-scale surface cyclone Two polar lows developed in wake of synoptic-scale surface cyclone Formed downstream of CTD Formed downstream of CTD Formed in surface baroclinic region Formed in surface baroclinic region Formed in moist-adiabatic environment Formed in moist-adiabatic environment Surface frontal structure developed during polar low evolution Surface frontal structure developed during polar low evolution Surface pressure minima formed beneath comma heads during polar low evolution Surface pressure minima formed beneath comma heads during polar low evolution

Concluding Remarks The two polar lows exhibit characteristics of short- wave/jet streak type described in Businger and Reed (1989). The two polar lows exhibit characteristics of short- wave/jet streak type described in Businger and Reed (1989). Are short waves discussed in previous polar low literature possibly CTDs? Are short waves discussed in previous polar low literature possibly CTDs? Are moist-adiabatic environments associated with CTDs over land analogous to those resulting from flow of arctic air over warm ocean? Are moist-adiabatic environments associated with CTDs over land analogous to those resulting from flow of arctic air over warm ocean? Can strong CTDs induce low-level vertical motion maxima and thus contribute to robust surface cyclogenesis via enhanced vortex stretching? Can strong CTDs induce low-level vertical motion maxima and thus contribute to robust surface cyclogenesis via enhanced vortex stretching?