Abstract
An automated method for segmenting digital images of orographic cumulus and a simple metric for characterizing the transition from shallow to deep convection are presented. The analysis is motivated by the hypothesis that shallow convection conditions the atmosphere for further deep convection by moistening it and preventing the evaporation of convective turrets through the entrainment of dry air. Time series of convective development are compared with sounding and surface data for 6 days during the summer of 2003. The observations suggest the existence of a threshold for the initiation of shallow convection based on the surface equivalent potential temperature and the saturated equivalent potential temperature above the cloud base. This criterion is similar to that controlling deep convection over the tropical oceans. The subsequent evolution of the convection depends on details of the environment. Surface fluxes of sensible and latent heat, along with the transport of boundary layer air by upslope flow, increase the surface equivalent potential temperature and once the threshold value is exceeded, shallow convection begins. The duration of the shallow convection period and growth rate of the deep convection are determined by the kinematic and thermodynamic structure of the mid- and upper troposphere.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 2527-2546 |
| Number of pages | 20 |
| Journal | Monthly Weather Review |
| Volume | 134 |
| Issue number | 9 |
| DOIs | |
| State | Published - Sep 1 2006 |
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ASJC Scopus subject areas
- Atmospheric Science
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Using digital cloud photogrammetry to characterize the onset and transition from shallow to deep convection over orography. / Zehnder, Joseph A.; Zhang, Liyan; Hansford, Dianne; Radzan, Anshuman; Selover, Nancy; Brown, Constance M.
In: Monthly Weather Review, Vol. 134, No. 9, 01.09.2006, p. 2527-2546.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Using digital cloud photogrammetry to characterize the onset and transition from shallow to deep convection over orography
AU - Zehnder, Joseph A.
AU - Zhang, Liyan
AU - Hansford, Dianne
AU - Radzan, Anshuman
AU - Selover, Nancy
AU - Brown, Constance M.
PY - 2006/9/1
Y1 - 2006/9/1
N2 - An automated method for segmenting digital images of orographic cumulus and a simple metric for characterizing the transition from shallow to deep convection are presented. The analysis is motivated by the hypothesis that shallow convection conditions the atmosphere for further deep convection by moistening it and preventing the evaporation of convective turrets through the entrainment of dry air. Time series of convective development are compared with sounding and surface data for 6 days during the summer of 2003. The observations suggest the existence of a threshold for the initiation of shallow convection based on the surface equivalent potential temperature and the saturated equivalent potential temperature above the cloud base. This criterion is similar to that controlling deep convection over the tropical oceans. The subsequent evolution of the convection depends on details of the environment. Surface fluxes of sensible and latent heat, along with the transport of boundary layer air by upslope flow, increase the surface equivalent potential temperature and once the threshold value is exceeded, shallow convection begins. The duration of the shallow convection period and growth rate of the deep convection are determined by the kinematic and thermodynamic structure of the mid- and upper troposphere.
AB - An automated method for segmenting digital images of orographic cumulus and a simple metric for characterizing the transition from shallow to deep convection are presented. The analysis is motivated by the hypothesis that shallow convection conditions the atmosphere for further deep convection by moistening it and preventing the evaporation of convective turrets through the entrainment of dry air. Time series of convective development are compared with sounding and surface data for 6 days during the summer of 2003. The observations suggest the existence of a threshold for the initiation of shallow convection based on the surface equivalent potential temperature and the saturated equivalent potential temperature above the cloud base. This criterion is similar to that controlling deep convection over the tropical oceans. The subsequent evolution of the convection depends on details of the environment. Surface fluxes of sensible and latent heat, along with the transport of boundary layer air by upslope flow, increase the surface equivalent potential temperature and once the threshold value is exceeded, shallow convection begins. The duration of the shallow convection period and growth rate of the deep convection are determined by the kinematic and thermodynamic structure of the mid- and upper troposphere.
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UR - http://www.scopus.com/inward/citedby.url?scp=33749001459&partnerID=8YFLogxK
U2 - 10.1175/MWR3194.1
DO - 10.1175/MWR3194.1
M3 - Article
AN - SCOPUS:33749001459
VL - 134
SP - 2527
EP - 2546
JO - Monthly Weather Review
JF - Monthly Weather Review
SN - 0027-0644
IS - 9
ER -