Environmental & Climate Sciences Department Seminar

"Deep convective outflow, level of neutral buoyancy, entrainment rate and convective core: new insights from space-borne cloud radar observations"

Presented by Zhengzhao (Johnny) Luo, CUNY

Thursday, March 8, 2018, 11:00 am — Conference Room Bldg 815E

Level of neutral buoyancy (LNB) is an important parameter for understanding convection because it sets the potential vertical extent for convective development. It can be estimated from the parcel theory using the ambient sounding without having to observe any actual convective cloud development. In reality, however, convection interacts with the environment in complicated ways; it will eventually find its own effective LNB and manifests it through detraining masses and developing cirrus anvils. In a series of recent papers, we investigated the relationship between the LNB and actual deep convective outflow using 5 years of CloudSat observations. Due to entrainment dilution, the actual outflow level is almost always lower than the LNB. The difference between the two can be interpreted as a proxy for entrainment rate. It was found that the entrainment rate as determined this way is larger over tropical ocean (e.g., TWP warm pool) than tropical land (e.g., Africa and Amazon). Analysis of radar reflectivity profiles further shows that land convection has wider and more intense cores than the oceanic counterpart. These findings lend observational support to a long-standing assumption in convection models concerning the negative relationship between entrainment rate and convective core size. Finally, we examined the environment conditions for the observed convection cases and found that convective outflow tends to occur at a higher level when the mid-troposphere is more humid and when convective system size is smaller. Application of similar analysis to ground-based radar observations (such as those from the DOE ARM program) will be discussed. ?

Hosted by: Mike Jensen

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