The impact of vertical wind shear on hail growth in simulated supercells

Eli J. Dennis, Matthew R. Kumjian

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

Severe hailstorms produce over $1 billion in insured losses annually in the United States, yet details of a given storm's hail threat (e.g., maximum hailstone size and total hailfall) remain challenging to forecast. Previous research suggests that, in addition to maximum updraft speed, the storm-relative airflow could be equally important for hail formation and growth. This study is a first step toward determining how changes in environmental wind shear and subsequent changes in simulated supercell storm structure affect hail growth. Using Cloud Model 1 (CM1) with 500-m horizontal and 250-m vertical grid spacing, 20 idealized simulations are performed in which the thermodynamic profile remains fixed but the environmental hodograph is systematically altered. Hail growth is quantified using the hail mass mixing ratio from composites of storms over the last hour of simulation time. Hailstone growth "pseudotrajectories" are computed from these storm composites to determine favorable embryo source regions. Results indicate that increased deep-layer east-west shear elongates the storm's updraft in that direction, providing 1) increased volumes over which microphysically relevant hail processes can act, 2) increased hailstone residence times within the updraft, and 3) a larger potential embryo source region; together, these lead to increased hail mass. Increased low-level north-south shear, which results in hodographs with increased 0-3-km storm-relative helicity, also elongates the updraft in the north-south direction. However, hail mass is reduced owing to a separation of favorable embryo source regions (which shift southward) and available hydrometeors to serve as embryos (which shift northward).

Original languageEnglish (US)
Pages (from-to)641-663
Number of pages23
JournalJournal of the Atmospheric Sciences
Volume74
Issue number3
DOIs
StatePublished - Jan 1 2017

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supercell
hail
wind shear
updraft
embryo
mixing ratio
airflow
simulation
residence time
spacing
thermodynamics

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

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abstract = "Severe hailstorms produce over $1 billion in insured losses annually in the United States, yet details of a given storm's hail threat (e.g., maximum hailstone size and total hailfall) remain challenging to forecast. Previous research suggests that, in addition to maximum updraft speed, the storm-relative airflow could be equally important for hail formation and growth. This study is a first step toward determining how changes in environmental wind shear and subsequent changes in simulated supercell storm structure affect hail growth. Using Cloud Model 1 (CM1) with 500-m horizontal and 250-m vertical grid spacing, 20 idealized simulations are performed in which the thermodynamic profile remains fixed but the environmental hodograph is systematically altered. Hail growth is quantified using the hail mass mixing ratio from composites of storms over the last hour of simulation time. Hailstone growth {"}pseudotrajectories{"} are computed from these storm composites to determine favorable embryo source regions. Results indicate that increased deep-layer east-west shear elongates the storm's updraft in that direction, providing 1) increased volumes over which microphysically relevant hail processes can act, 2) increased hailstone residence times within the updraft, and 3) a larger potential embryo source region; together, these lead to increased hail mass. Increased low-level north-south shear, which results in hodographs with increased 0-3-km storm-relative helicity, also elongates the updraft in the north-south direction. However, hail mass is reduced owing to a separation of favorable embryo source regions (which shift southward) and available hydrometeors to serve as embryos (which shift northward).",
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The impact of vertical wind shear on hail growth in simulated supercells. / Dennis, Eli J.; Kumjian, Matthew R.

In: Journal of the Atmospheric Sciences, Vol. 74, No. 3, 01.01.2017, p. 641-663.

Research output: Contribution to journalArticle

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AB - Severe hailstorms produce over $1 billion in insured losses annually in the United States, yet details of a given storm's hail threat (e.g., maximum hailstone size and total hailfall) remain challenging to forecast. Previous research suggests that, in addition to maximum updraft speed, the storm-relative airflow could be equally important for hail formation and growth. This study is a first step toward determining how changes in environmental wind shear and subsequent changes in simulated supercell storm structure affect hail growth. Using Cloud Model 1 (CM1) with 500-m horizontal and 250-m vertical grid spacing, 20 idealized simulations are performed in which the thermodynamic profile remains fixed but the environmental hodograph is systematically altered. Hail growth is quantified using the hail mass mixing ratio from composites of storms over the last hour of simulation time. Hailstone growth "pseudotrajectories" are computed from these storm composites to determine favorable embryo source regions. Results indicate that increased deep-layer east-west shear elongates the storm's updraft in that direction, providing 1) increased volumes over which microphysically relevant hail processes can act, 2) increased hailstone residence times within the updraft, and 3) a larger potential embryo source region; together, these lead to increased hail mass. Increased low-level north-south shear, which results in hodographs with increased 0-3-km storm-relative helicity, also elongates the updraft in the north-south direction. However, hail mass is reduced owing to a separation of favorable embryo source regions (which shift southward) and available hydrometeors to serve as embryos (which shift northward).

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