Title: Bow Echo Sensitivity to Ambient Moisture and Cold Pool Strength
1Bow Echo Sensitivity to Ambient Moisture and Cold
Pool Strength
- Richard P. James, Paul M. Markowski, and J.
Michael Fritsch, - 2006 Mon. Wea. Rev., 134, 950964.
Image source http//www.hpc.ncep.noaa.gov/researc
h/roth/072120031203zrad.gif
2Introduction
- Bow echoes are a common form of convective
organization often associated with severe wind
damage (Klimowski et al. 2003). - Previous studies (Johns and Hirt 1987) examined
warm-season derecho environments. - Numerical modeling results have previously
focused on sensitivity of bow echoes to CAPE and
low-level shear. - This paper attempts to address the role of
ambient moisture even when CAPE is held constant.
3Methodology
- Numerical model (James et al. 2005)
- 360 x 120 km domain
- 500 m horizontal resolution
- 200 m vertical resolution below 5 km, increasing
to 500 m above 8.5 km - The model was initialized with warm bubbles
spaced 20 km apart. - Ice physics were included in all simulations.
4Methodology (cont.)
- Three different mixing ratio lapse rates were
used (1 g kg-1 km-1, 3 g kg-1 km-1, and 4 g kg-1
km-1) - CAPE was held constant (4600 J kg-1) with a fixed
temperature, pressure, and relative humidity at
the top of the mixed layer. - Simulations used 02.5-km shear magnitudes of 16,
20, and 24 m s-1. - All simulations had an integration length of 6 h.
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6Results
7 4 g kg-1 km-1
8 3 g kg-1 km-1
9 1 g kg-1 km-1
10Cold Pool Strength (C) and C/?U Ratio
t 4 h
t 6 h
CAPE 4600 J kg-1 02.5-km shear 24 m s-1
Low level mixing ratio lapse rate 4 g kg-1
km-1 (Most Moist)
11Cold Pool Strength (C) and C/?U Ratio
t 4 h
t 6 h
CAPE 4600 J kg-1 02.5-km shear 24 m s-1
Low level mixing ratio lapse rate 3 g kg-1 km-1
12Cold Pool Strength (C) and C/?U Ratio
t 4 h
t 6 h
CAPE 4600 J kg-1 02.5-km shear 24 m s-1
Low level mixing ratio lapse rate 1 g kg-1
km-1 (Least Moist)
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14Conclusions
- Stronger cold pools are associated with larger
scale three-dimensional features. - An intermediate amount of ambient moisture
results in the most robust bow echo formation. - The cold pool strength balances the shear only
locally allowing bowing segments to develop. - Large CAPE and strong low-level shear constitute
may represent necessary, but not sufficient,
conditions for bow echo formation.