The Impact of Ice Microphysics on the Genesis of Hurricane Julia (2010)

Stefan Cecelski1 and Dr. Da-Lin ZhangDepartment of Atmospheric and Oceanic Science

University of Maryland College Park1: Research is funded by NASA’s Earth and Space Science Fellowship (NESSF)

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Motivation• A lack of focus on the impacts of ice microphysics for tropical

cyclogenesis (TCG) and related processes– Need to properly represent ice microphysical properties for tropical

cyclone (TC) structure and intensity (Ji et. al. 2014)• Our previous work investigating the TCG of Hurricane Julia (2010)

depicted:– Meaningful ensemble differences for upper tropospheric outflow,

warming, and cloud ice content– Warming in the upper troposphere was responsible for meso-α-scale

MSLP falls leading to TCG• Are the upper-tropospheric dynamical and thermodynamical

changes during TCG at all related to ice microphysical processes?

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Objectives

• Examine the role of ice microphysics and related heating during the TCG of Julia– Focus on depositional heating since our previous

work has shown thermodynamic changes to the upper troposphere during TCG

• Analyze the changes of deep convection and other parameters pertinent to TCG when ice microphysical processes are modified

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Hurricane Julia (2010) Background

• Declared a tropical depression (TD) 0600 UTC 12 Sep 2010 (hereafter 12/0600)– Tropical storm 12 h later at 1800 UTC 12 Sep

2010• Formed within a potent African easterly

wave (AEW)• Prominent features during TCG:

– Pronounced upper-tropospheric warming• Hydrostatically induced surface pressure falls on

the meso-α-scale

– Persistent deep convection within the AEW closed circulation • Created a storm-scale outflow in the upper

troposphere that expanded warming with time

• Growth of low-level cyclonic vorticity occurred from the bottom-up with mesovortex merging Right: METEOSAT-9 IR imagery at

1200 UTC 10, 1200 UTC 11, 0600, and 1800 UTC 12 Sep 2010.

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Methodology• Conduct 2 WRF high-resolution

sensitivity simulations– Modify the Thompson graupel 2-

moment microphysics scheme (Thompson 2004, 2008) used in the control

– Compare to the control simulation from Cecelski and Zhang (2013)

• WRF Details– 3 domains: 9 (D1), 3 (D2), and 1 km

(D3 is a moving domain; see right)– 66-h simulation from 0000 UTC 10 to

1800 UTC 12 Sep 2010– Genesis occurs 54 h into simulation

WRF simulation setup. D1, D2, and D3 represent 9, 3, and 1-km horizontal resolution domains,

respectively. D3 is a moving domain with initial and final positions drawn. NOAA OI SSTs are

shaded (°C).

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Sensitivity Simulations• Experiment 1: “No Fusion”

– Removes latent heat of fusion in deposition/sublimation– Thompson scheme definitions for various enthalpies (uses standard values at 0°C):

• Sublimation (Ls) = 2.834×106 J kg-1

• Vaporization (Lv) = 2.5×106 J kg-1

• Fusion (Lf) = 3.34×105 J kg-1

– Modification:• Ls = Lv = 2.5×106 J kg-1

• Still allows for portion of cloud water mass to become cloud ice; • Only reduces amount of heating released into the environment by that of Lf

• Experiment 2: “No HFRZ”– Removes any homogeneous freezing of cloud water

• Occurs with rapid transport of cloud water to upper troposphere via intense convective updrafts

– In Thompson scheme, the temperature at which all cloud water must be frozen to become cloud ice is 235.16K

– Modification:• Temperature at which cloud water must turn into cloud ice is changed to 100.00K• Effectively turns off any homogeneous freezing

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First-Order Simulation Results

Above: Comparison of track and MSLP intensity of experiments (blue and red) with the control (black);

Right: Comparison of WRF-derived brightness temperatures (gray shades; K) and composite radar reflectivity (color shades; dBZ)

1800 UTC 11 Sep – first differences

Also in extent and intensity of deep convection“No Fusion” has weaker

deep convection at time of TCG

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Upper-tropospheric differences

Above: 100 km × 100 km area-averaged temperature difference from 0600 UTC 11 Sep (shaded, °C), absolute vorticity (black contours every 2×10-5 s-1) and cloud ice mixing ratio (blue contours at 2, 5, 10, and 20 ×10 -4 g kg-1.

Above: 200 hPa temperatures (shaded, °C) and co-moving wind vectors (reference vector is 10 m s-1) with MSLP overlaid (contoured every 1 hPa).

Lack of fusion heating during deposition leads to:i) Minimal meso-α-scale upper-tropospheric thermodynamic

changesa) Results in no prominent meso-α-scale hydrostatic MSLP

fallsii) Weaker and less expansive storm-scale outflow

Less warming near storm center in comparison to

control

Lack of low-level cyclonic vorticity

growth versus control

Minimal differences

between HFRZ and control

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Convective differences

Above: Time-series of 200 km × 200 km area-averaged upper-level Brunt-Vaisala frequency (×10-3 s-1), Rossby radius for deformation (km), composite radar reflectivity (dBZ), and upper-level cloud ice divergence (×10-5 s-1).

Right: Count of convective updrafts exceeding various thresholds (m s-1) within a 100 km × 100 km area for No Fusion (blue), No HFRZ (right), and the control (black).

Weaker and less convective development near storm

center in “No Fusion” during TCG

Upper-troposphere has greater static stability in “No Fusion”

Results in less potent storm-scale upper-level outflow

Limits expansion of upper-level warming with time

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Conclusions

• The latent heat of fusion taking place during deposition impacts the TCG of Julia via:– Augmenting the warming of the upper troposphere– Limiting the growth of TD-scale MSLP disturbance– Modifying the strength and spatial extent of deep convection

• Research Implications– Could properly representing ice microphysics be a critical

factor for TCG?– Can we reproduce this characteristic using other microphysics

schemes and for other cases?– Are we able to obtain suitable observational data to observe

cloud ice and other upper-tropospheric changes?