Comparison of the extratropical transition of Hurricane Gloria (1985) and a rapidly deepening east coast winter storm from an energetics perspective Molly.

Comparison of the extratropical transition of Hurricane Gloria (1985) and a rapidly deepening east coast winter storm from an energetics perspective Molly Smith ATM 621 10 May 2017

Extratropical Transition
When tropical cyclones (TCs) move poleward from low to middle latitudes, they can undergo extratropical transition (ET).

When tropical cyclones (TCs) move poleward from low to middle latitudes, they can undergo extratropical transition (ET). During ET, a TC interacts with a preexisting midlatitude baroclinic zone.

When tropical cyclones (TCs) move poleward from low to middle latitudes, they can undergo extratropical transition (ET). During ET, a TC interacts with a preexisting midlatitude baroclinic zone. Eventually merges with it and acquires a core of cold, dense air (Klein et al ).

When tropical cyclones (TCs) move poleward from low to middle latitudes, they can undergo extratropical transition (ET). During ET, a TC interacts with a preexisting midlatitude baroclinic zone. Eventually merges with it and acquires a core of cold, dense air (Klein et al ). ET also results in a substantial increase in the kinetic energy of the midlatitude jet (Palmén 1958).

When tropical cyclones (TCs) move poleward from low to middle latitudes, they can undergo extratropical transition (ET). During ET, a TC interacts with a preexisting midlatitude baroclinic zone. Eventually merges with it and acquires a core of cold, dense air (Klein et al ). ET also results in a substantial increase in the kinetic energy of the midlatitude jet (Palmén 1958). This is achieved through advection of low-PV air by the TC’s divergent outflow (Archambault et al. 2013).

Archambault et al. (2013)

Kinetic Energy During ET
Harr et al. (2000) computed an Eulerian kinetic energy budget for extratropically-transitioning Typhoon David (September 1997).

Harr et al. (2000) computed a Eulerian kinetic energy budget for extratropically-transitioning Typhoon David (September 1997). Determined the respective roles that particular mechanisms played in the jet’s increase of kinetic energy.

Harr et al. (2000) computed a Eulerian kinetic energy budget for extratropically-transitioning Typhoon David (September 1997). Determined the respective roles that particular mechanisms played in the jet’s increase of kinetic energy. How much KE is:

Harr et al. (2000) computed a Eulerian kinetic energy budget for extratropically-transitioning Typhoon David (September 1997). Determined the respective roles that particular mechanisms played in the jet’s increase of kinetic energy. How much KE is: generated by the TC’s outflow crossing the baroclinic zone associated with the jet?

Harr et al. (2000) computed a Eulerian kinetic energy budget for extratropically-transitioning Typhoon David (September 1997). Determined the respective roles that particular mechanisms played in the jet’s increase of kinetic energy. How much KE is: generated by the TC’s outflow crossing the baroclinic zone associated with the jet? horizontally and vertically imported/exported by the TC’s outflow and vertical motion?

Harr et al. (2000) computed a Eulerian kinetic energy budget for extratropically-transitioning Typhoon David (September 1997). Determined the respective roles that particular mechanisms played in the jet’s increase of kinetic energy. How much KE is: generated by the TC’s outflow crossing the baroclinic zone associated with the jet? horizontally and vertically imported/exported by the TC’s outflow and vertical motion? dissipated through friction?

𝜕𝐾 𝜕𝑡 = −𝑉∙𝛻𝜙 −𝛻∙𝑘𝑉 − 𝜕𝜔𝑘 𝜕𝑝 𝑘 0 𝜕 𝑝 0 𝜕𝑡 𝑉∙𝐹 ∫ = 1 𝑔 𝑝 𝑑𝑝

𝜕𝐾 𝜕𝑡 = −𝑉∙𝛻𝜙 −𝛻∙𝑘𝑉 − 𝜕𝜔𝑘 𝜕𝑝 𝑘 0 𝜕 𝑝 0 𝜕𝑡 𝑉∙𝐹 Change in KE with time ∫ = 1 𝑔 𝑝 𝑑𝑝

𝜕𝐾 𝜕𝑡 = −𝑉∙𝛻𝜙 −𝛻∙𝑘𝑉 − 𝜕𝜔𝑘 𝜕𝑝 𝑘 0 𝜕 𝑝 0 𝜕𝑡 𝑉∙𝐹 GKE HFC VFC Bd D Generation of KE ∫ = 1 𝑔 𝑝 𝑑𝑝

𝜕𝐾 𝜕𝑡 = −𝑉∙𝛻𝜙 −𝛻∙𝑘𝑉 − 𝜕𝜔𝑘 𝜕𝑝 𝑘 0 𝜕 𝑝 0 𝜕𝑡 𝑉∙𝐹 GKE HFC VFC Bd D Horizontal flux convergence ∫ = 1 𝑔 𝑝 𝑑𝑝

𝜕𝐾 𝜕𝑡 = −𝑉∙𝛻𝜙 −𝛻∙𝑘𝑉 − 𝜕𝜔𝑘 𝜕𝑝 𝑘 0 𝜕 𝑝 0 𝜕𝑡 𝑉∙𝐹 GKE HFC VFC Bd D Vertical flux convergence ∫ = 1 𝑔 𝑝 𝑑𝑝

𝜕𝐾 𝜕𝑡 = −𝑉∙𝛻𝜙 −𝛻∙𝑘𝑉 − 𝜕𝜔𝑘 𝜕𝑝 𝑘 0 𝜕 𝑝 0 𝜕𝑡 𝑉∙𝐹 GKE HFC VFC Bd D Related to change in column mass (Ignore in isobaric framework) ∫ = 1 𝑔 𝑝 𝑑𝑝

𝜕𝐾 𝜕𝑡 = −𝑉∙𝛻𝜙 −𝛻∙𝑘𝑉 − 𝜕𝜔𝑘 𝜕𝑝 𝑘 0 𝜕 𝑝 0 𝜕𝑡 𝑉∙𝐹 GKE HFC VFC Bd D Dissipation of KE through friction (calculated as residual) ∫ = 1 𝑔 𝑝 𝑑𝑝

𝜕𝐾 𝜕𝑡 = −𝑉∙𝛻𝜙 −𝛻∙𝑘𝑉 − 𝜕𝜔𝑘 𝜕𝑝 𝑘 0 𝜕 𝑝 0 𝜕𝑡 𝑉∙𝐹 GKE HFC VFC Bd D ∫ = 1 𝑔 𝑝 𝑑𝑝

Harr et al. (2000)

This matches the results from Palmén (1958), and many other ET energetics studies since!
Generation by flow down a pressure gradient Horizontal flux convergence

Rapidly deepening winter cyclones can produce a similar effect on the midlatitude jet.
However, whereas an intense jet streak is a result of extratropical transition, it is a necessary precursor to bombogenesis.

However, whereas an intense jet streak is a result of extratropical transition, it is a necessary precursor to bombogenesis. Uccellini and Kocin (1987) suggests that an existent upper-level jet allows boundary layer processes such as the low-level diabatic heating that occurs when very cold air moves off the continent into the much warmer environment of the Atlantic, as well as latent heat release within the cyclone itself, to rapidly deepen a coastal low.

However, whereas an intense jet streak is a result of extratropical transition, it is a necessary precursor to bombogenesis. Uccellini and Kocin (1987) suggests that an existent upper-level jet allows boundary layer processes such as the low-level diabatic heating that occurs when very cold air moves off the continent into the much warmer environment of the Atlantic, as well as latent heat release within the cyclone itself, to rapidly deepen a coastal low. Because of this difference, kinetic energy in an intense winter cyclone primarily increases through boundary flux convergence (Smith and Dare 1986), rather than by negative PV advection in the outflow layer.

Smith and Dare (1986) Computed a KE budget for winter cyclones.
Found that KE in an intense winter cyclone primarily increases through flux convergence, rather than by generation. This is different than what is seen in transitioning TCs.

Objectives Perform a case study comparing and contrasting the kinetic energy budgets of a TC undergoing ET and a winter cyclone undergoing bombogensis. Ideally, the two systems should have similar tracks. I have selected Hurricane Gloria (1985) and a rapidly deepening east coast winter storm from 29 December 1997 to 01 January 1998 for this analysis. How much KE is: generated by the storms’ outflow crossing the baroclinic zone associated with the jet? horizontally and vertically imported/exported by the storms’ circulation? dissipated through friction?

Gloria and the 1998 Cyclone Date Time MSLP (hPa) 24-hr Bergerons
29 Dec 0600 UTC 1009.7 1200 UTC 1002.6 1800 UTC 995.6 30 Dec 0000 UTC 987.7 982.3 1.83 976.1 1.68 972.7 1.38 31 Dec 969.9 1.02 968.1 0.79 962.3 0.74 957.7 0.78 01 Jan 956.1 0.70 Source: Alicia Bentley

Methods ERA-Interim data were obtained for the 42-hour overlap period in each storm. Hurricane Gloria: 18Z 26 September 1985 to 12Z 28 September 1985. 1997 Extratropical Cyclone: 12Z 29 December 1997 to 06Z 31 December 1997. The kinetic energy and budget components from Harr et al. (2000) were calculated and compared for the two storms. Following the methods of Harr et al. (2000), area averages of each component were taken for a 25° box centered on each storm, and then used to create time series and vertical profiles.

Kinetic Energy Hurricane Gloria EC1997

GKE Hurricane Gloria EC1997

HFC Hurricane Gloria EC1997

Time Series Hurricane Gloria EC1997

Vertical Profiles Hurricane Gloria EC1997

In summary… Comparing two storms in similar positions with similar synoptic setups appears to produce similar kinetic energy budgets.

Questions?

Comparison of the extratropical transition of Hurricane Gloria (1985) and a rapidly deepening east coast winter storm from an energetics perspective Molly.

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Comparison of the extratropical transition of Hurricane Gloria (1985) and a rapidly deepening east coast winter storm from an energetics perspective Molly.

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