Why is it important to HS3 science to estimate convective

vertical velocity accurately?

Ed Zipser and Jon ZawislakDept. of Atmospheric Sciences

University of Utah

With appreciation to Ramesh Kakar, Scott Braun, and the entire HS-3 team for continuing support

A few important questions about the role of convection in genesisand intensity change of tropical cyclones:

Vertical Profile of Mass flux and Latent heating: How partitioned between eyewalls, rainbands, and stratiform precipitation regions?

HYPOTHESIS: THE ANSWER DEPENDS STRONGLY ON THE VERTICAL VELOCITY (more precisely, on the PDF of vertical velocity in the different regions of the system)

Vertical velocity is quite challenging to measure, and just as challenging to simulate…..especially in the most critical region….. the mixed phase region, between 0° and -15°C,or between about 5 – 7 km altitude. What happens there may determine what happens in the upper troposphere as well.

We need to know this to help refine the flight rules for safe operation of the GH

But for the fundamental goals of HS3: Understanding and modeling of the storm!

Motivation: Adam Varble’spapers comparingupdrafts in a large MCS in adeveloping TC near Darwin (became a“landphoon”)

Varble et al. JGR 2011 and JGR 2014a,b.

Cloud resolving models perform badly when simulating maritime convection – it’s too strong!Question: Is this also the case for most simulations of tropical cyclones???

Many more processes are important in weak-moderate maritime convection • warm rain, • entrainment,• lofting of DSD’s – Strong dependence on W and D, • mixed phase interactions such as H-M) than in strong,

30 dBZ at 10 km

11.5 m/s peak at 10 km

Observed and Simulated Max. W and dBZ in TWP-ICE Deep Updrafts

XX

8 m/s at 6 km X

X

X

(we now needto get data herefrom remotesensing!)

Effect of rain freezing on simulated buoyancy

Effect of rain freezing on simulated w

Varble et al. (2014)

There are fundamental unanswered questions that are required to improve

retrievals and validate and improve models.

For example,

Lofting of condensate impacts upper tropospheric vertical velocity (through latent heat of fusion), yet

we know little about the variability of lofted condensate that freezes, how it freezes, and how it

interacts with other hydrometeors in the mixed phase region.

When, where, how fast, and how much ice forms?

What are its properties?

Observed—Black profile Simulated-

With/withoutRain freezing

After G. Heymsfield et al., JAS 2010; relationship between STRONG updrafts and dBZ (z) profiles

X

X

Red X showsthat the Darwin MCSIs similar tothese profiles

Composite shear-relative distribution of the percent occurrence of PR reflectivity > 20 dBZ at orabove 10 km elevation (c) SI, (d) RI (Initial), and (e) RI (Continuing). The black arrow represents the orientation of the vertical wind shear vector. After Zagrodnik and Jiang, JAS 2014

(Implied message: Symmetry is more important than intensity; coverage of 20 dBZ echoes to 10 kmhardly ever exceeds 10%)

Contoured Frequency by Altitude Diagrams (CFADs) for the inner-75 km, upshearsemicircle (upshear-left and upshear-right combined) in the intensity change category(e) RI, continuing. Contours represent the frequency occurrence relative to the maximum frequency bin (1 dB in size, 250 m in height) in each CFAD. Panel (f) depicts the 50% (modal) and 20% contour for the PR 2A23 stratiform (black) and convective (blue) pixels from the full sample.

After Zagrodnik and Jiang, JAS 2014(Implied message: Median of 30 dBZ at 10 km for Darwin case, and for Gerry Heymsfield’s ER-2 pverflights of overshooting tops, are rare outliers in hurricanes undergoing RI)

X X

After Cheng Tao and Haiyan Jiang; AMS Tropical Conference 2014. (Implied message: Symmetry is more important than intensity; coverage of their moderately deep convection hardly ever exceeds 10%; BUT coverage of moderate convection often exceeds 50%.)

Hence and Houze, JAS 2011. Implied message: 30 dBZ at 10 km hardly ever observed by TRMM PR in eyewalls of strong hurricanes. (But that was common in the Darwin MCS)

X X

X X

CFAD of eyewall radar reflectivity binned every 1 dBZ. Contours every 5% beginning at 5% represent the frequency of occurrence relative to the maximum absolute frequency in the data sample represented in the CFAD. The 50% contour line has been colored black for reference.

CFAD of eyewall vertical velocity binned every 1 m/s. Contours every 5% beginning at 5% represent the frequency of occurrence relative to the maximum absolute frequency in the data sample represented in the CFAD. The 50% contour line has been colored black for reference.

From DeHart, Houze, and Rogers, JAS 2014(Implied message: 30 dBZ at 10 km, and 8 m/s in mixed phase region, the median in the Darwin case, and in Gerry Heymsfield’s dataset, are uncommon in hurricane eyewalls.)

X

X

From Rogers, JAS 2010. Implied message: For this case, model overpredicts convective intensity.

X

X

X

X

After Zawislak and Zipser, MWR 2014Implied message: Karl, pre-Karl, Matthew, and Pre-Matthew had very respectable ice water paths (proxy for convective intensity), and the Global Hawk overflew with no problems.

Main Messages:

• We recognize from the ER-2 Emily (2005) encounter, and a few others, that intense convection does occur in tropical cyclones, and the science team is committed to do our best to keep the GH safe.

• Intense convection such as in Emily is the exception, not the rule, and the huge statistical sample from TRMM and from NOAA/HRD flights demonstrates this clearly.

• Evidence is mounting that the rare, exceptionally intense convection is less important for rapid intensification than areal coverage and symmetry of ordinary, moderate convection.

• To meet the scientific objectives of HS3, on the role of convective bursts in genesis and intensity change, we need lots of good AV-1 missions over deep convection; even better if the NOAA aircraft can fly in the same storm. “Most of the time”, this can be done safely.