Ozone Conservation and Entrainment in Cumulus Congestus

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  • 1 Department of Atmospheric Science, Colorado State University, Ft. Collins, Colorado
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Abstract

This study demonstrates that ozone mixing ratio (O3) is conserved during moist convection and can be used as a tracer for cloud entrainment studies. The approach used is to apply mixing line analysis to pairs of liquid water potential temperature (θl), total water mixing ratio (Q), O3 and pseudo-equivalent potential temperature (θe) derived from aircraft penetrations of growing cumulus congestus. Conclusions about entrainment from the mixing diagrams employing O3 agree with those using thermodynamic quantities. Any disagreement uncovered deficiencies in the water substance measurement technique. Strong updrafts, thought to be diluted adiabatic cores, entrained laterally from the environment at the observation level. In contrast, the downshear region of the cloud entrained air from above the observation level as well as laterally. Lastly, two strong reasons are found for preferring θl over θe in mixing line analyses with Q. First, the propagated error in calculating θl is normally less than that for θe, particularly for the majority of points outside adiabatic cores where cloud liquid water is low. Second, θe, and Q are shown to be mathematically dependent to a degree that may lead to erroneous conclusions about entrainment.

Abstract

This study demonstrates that ozone mixing ratio (O3) is conserved during moist convection and can be used as a tracer for cloud entrainment studies. The approach used is to apply mixing line analysis to pairs of liquid water potential temperature (θl), total water mixing ratio (Q), O3 and pseudo-equivalent potential temperature (θe) derived from aircraft penetrations of growing cumulus congestus. Conclusions about entrainment from the mixing diagrams employing O3 agree with those using thermodynamic quantities. Any disagreement uncovered deficiencies in the water substance measurement technique. Strong updrafts, thought to be diluted adiabatic cores, entrained laterally from the environment at the observation level. In contrast, the downshear region of the cloud entrained air from above the observation level as well as laterally. Lastly, two strong reasons are found for preferring θl over θe in mixing line analyses with Q. First, the propagated error in calculating θl is normally less than that for θe, particularly for the majority of points outside adiabatic cores where cloud liquid water is low. Second, θe, and Q are shown to be mathematically dependent to a degree that may lead to erroneous conclusions about entrainment.

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