The effects of topography on
convective storm environments in
the Eastern Region
Branden Katona & Paul Markowski
Department of Meteorology
Penn State University
Branden Katona
Severe weather reports are heterogeneous
It is unclear to what extent the
heterogeneity is due to a small sample
size, population bias, or real influences of
terrain on storms (all three probably
contribute to the heterogeneity of the
reports).
Tornado reports, 1950–2011.
Although most scientists and forecasters,
at least anecdotally, express little doubt
that terrain can affect convective storms,
there are few controlled studies of the
influence of terrain on convective storms
and their environments.
Prior work: limited to idealized convective systems
and idealized topography
Simulations of squall lines with idealized terrain (COMET Partners Project at PSU, 2002–2004)
a)
pink: w = 6 m/s isosurface
blue: q’ = -1.7 K isosurface
Frame & Markowski (2006)
The primary difficulty with purely observational studies is that it is never possible to
know how the convective storms would have evolved in the absence of terrain;
thus, observational research tends to remain fairly speculative about the impact of
terrain on the observed structure and evolution of convection.
b)
c)
Prior work: limited to idealized convective systems
and idealized topography
Simulations of supercells with idealized terrain
(Markowski sabbatical leave, summer & fall 2009)
The primary difficulty with purely observational studies is that it is never possible to
know how the convective storms would have evolved in the absence of terrain;
thus, observational research tends to remain fairly speculative about the impact of
terrain on the observed structure and evolution of convection.
Markowski & Dotzek (2011)
Markowski & Dotzek (2011)
Prior work: limited to idealized convective systems
and idealized topography
Our understanding to date largely remains confined to idealized
environments, idealized storms, and idealized terrain.
There is a clear need to extend the prior idealized studies of the
effects of terrain on convection to more realistic environments
and terrain configurations if there is to be an improvement in
warning skill from better anticipation of the effects of terrain on
storms.
Objective 1: Identify how the topography of the NWS Eastern
Region affects severe storm environments (CAPE, CIN, shear, etc.)
NCEP HRRR analyses of CAPE, CIN, vertical wind shear, SRH, and other convective storm forecasting
parameters (e.g., composite indices like the STP) are being used to develop a climatology of of
these parameters in the NWS Eastern Region.
Basic idea: the synoptic and mesoscale variability not
due to topographic influences ought to vanish in the
mean fields, such that the remaining variability
represents mostly standing patterns of topographically
generated variability (and a likely smaller contribution
from the hemispheric-scale mean meridional
temperature and pressure gradient)
Is there any pattern of systematic enhancement or
reduction of CAPE, CIN, shear, etc.?
How is the pattern related to the terrain configuration?
How do the amplitudes of the CAPE, CIN, shear, etc.
perturbations depend on the wind speed, and how
does the pattern of the perturbations change as the
wind direction changes?
Objective 1: Identify how the topography of the NWS Eastern
Region affects severe storm environments (CAPE, CIN, shear, etc.)
The terrain-induced modifications of
the convective storm environment are
unlikely to be resolved by the popular
SPC mesoanalysis products given that
these are derived from coarser
background fields from the NCEP Rapid
Refresh (RAP) and considerably coarser
hourly observations, which are
objectively analyzed with the RAP
background fields via a Barnes analysis.
Objective 2: Determine how the topographically generated
perturbations in CAPE, CIN, shear, etc., affect convective storms in
the NWS Eastern Region using high-resolution numerical simulations
Step 1:
Use idealized, horizontally homogeneous environments, similar to the
approach of Frame & Markowski (2006) and Markowski & Dotzek (2011),
but with the actual terrain of the NWS Eastern Region.
Experiment with a variety of low-level wind directions and initiate both
isolated storms and convective systems (prior studies have shown that the
effects of terrain on convective storms are dependent on the convective
mode and low-level terrain-relative winds). For each set of initial
conditions and subregion, a flat-surface “control simulation” will be
compared with a simulation containing terrain.
Step 2:
Simulate actual historic severe weather events in the NWS Eastern Region.
31 May 1985
This builds upon the idealized-environment simulations by including the
vertical motions and horizontal heterogeneity present on a range of scales
within convective storm environments (such heterogeneity is virtually
ubiquitous owing to the fact that migrating extratropical cyclones typically
play a major role in the development of severe storm environments in the
eastern U.S.).
29 June 2012
Katona’s “Hello World” WRF simulations
Branden Katona
smooth terrain
realistic terrain
Katona’s “Hello World” WRF simulations
Branden Katona
smooth terrain
realistic terrain