Overview: The relative importance of intense vs. moderate convection to rapid intensification

Transcription

1 Overview: The relative importance of intense vs. moderate convection to rapid intensification Edward Zipser Department of Atmospheric Sciences University of Utah, Salt Lake City, UT, USA Workshop: Prediction of Tropical Cyclone Rapid Intensity Change (RIC) Tuesday November 18, 2014

2 Hot Towers: Of vital importance for the Hadley Cell and for hurricanes, but how, exactly, are they defined? We postulated that all, or nearly all the mass reaching great heights in the core ascends rapidly in a few nearly undilute convective hot towers, rather than by a uniform and gradual mass circulation.. The Daisy data have in fact confirmed the importance of the hot tower mechanism and the concentration of the storm s heat release into individual buoyant elements. (Riehl and Malkus, 1961) In Simpson et al. (1998), On the role of hot towers in tropical cyclone formation, strong, deep convective towers were documented during the formation of Cyclone Oliver during TOGA COARE, which were extremely deep (17-18 km) and electrified, but only a few of them produced lightning. (EZ: Indicating moderate updrafts) It has become part of the lexicon that hot towers are common in tropical cyclones, and it is often assumed that they are necessary for genesis and for intensification. However, if the term hot tower is defined at all in the literature, that definition varies a great deal from paper to paper. More clarity is needed!

3 Hot Tower : The time has come to distinguish between CBs with different specific properties We argue here that high IR tops and intense W are not the same thing.

4 Higher echo tops are correlated with intensification in some datasets Kelley et al. (GRL 2004)

5 But CBs with 17 km echo tops over oceans, and in TCs, are much less intense than CBs with 17 dbz tops over continents \ Kelley et al. MWR 2010

6 Dan Cecil s MS Thesis research was a big surprise (to EJZ), because future intensity was far better correlated with area of passive microwave proxies for moderate convection than for those of intense convection. Why (he asked)? From Cecil and Zipser, MWR 1999

7 It is true that colder IR tops, higher radar echoes, and more ice scattering all are more favorable for RI, but. Jiang, MWR2012

8 BUT USING THIS TRUTH AS A PREDICTOR IS NOT THE ANSWER. Jiang, MWR2012

9 Hot Towers as RI predictors: Conclusions RI is more likely than not if extremely tall convection is in the eyewall or inside the radius of max. winds but It is far from necessary or sufficient, and it is not at all clear that the convection need be intense or deep. For large datasets, large, quasi-symmetric coverage of moderate convection seems to be the most reliable indicator of RI. (See Haiyan s presentation to follow)

10 Time to revisit the role of hot towers? What if Kerry Emanuel was correct? Many years ago, he (+ Schubert, Hack, Willoughby, Shapiro) constructed axisymmetric models that always intensified. In 2003, K.E. wrote numerically simulated storms invariably spin up to their maximum potential intensity (MPI), while few real storms achieve this limit. Ann. Rev. Earth Planet. Sci. Another way to put it: All storms want to reach their PI, and other things just get in the way (Jim Kossin , TC list, 14 Nov 2014)

11 Time to revisit the role of hot towers? What if Kerry Emanuel was correct? Many years ago, he (+ Schubert, Hack, Willoughby, Shapiro) constructed axisymmetric models that always intensified. In 2003, K.E. wrote numerically simulated storms invariably spin up to their maximum potential intensity (MPI), while few real storms achieve this limit. Ann. Rev. Earth Planet. Sci. Another way to put it: All storms want to reach their PI, and other things just get in the way (Jim Kossin , TC list, 14 Nov 2014) Consider the possibility that extremely intense hot towers or convective bursts could get in the way, and if so, how?

12 Time to revisit the role of hot towers? Modest Proposal: GIVEN a Tropical Cyclone that has attained near-symmetric surface winds, strong enough for substantial sea-air enthalpy flux, near-symmetric rainfall distribution and latent heat release sufficient for intensification... THEN, in the absence of disruptive factors, which may include not only unfavorable large scale environments, but also asymmetrical intense convection, the storm will proceed toward its maximum potential intensity (MPI).

13 Time to revisit the role of hot towers? Modest Proposal: GIVEN a Tropical Cyclone that has attained near-symmetric surface winds, strong enough for substantial sea-air enthalpy flux, near-symmetric rainfall distribution and latent heat release is sufficient for intensification. THEN, in the absence of disruptive factors, which may include not only unfavorable large scale environments, but also asymmetrical intense convection, the storm will proceed toward its maximum potential intensity (MPI). IN OTHER WORDS, instead of seeking factors for storm strengthening, seek factors that would interfere with strengthening. Might one of those factors be strong asymmetrical up/downdrafts in convective bursts???

14 Thank you! Questions, and contrary opinions, are always welcome in science, so let s hear from you!