USE OF HS3 DATA TO UNDERSTAND THE TROPICAL CYCLONE OUTFLOW LAYER John Molinari, Kristen Corbosiero, Stephanie Stevenson, and Patrick Duran University at Albany, SUNY

The cirrus canopy is the major visible representation of the outflow layer.

Radial velocityTangential velocity Radial (left) and tangential (right) velocity from G-IV sondes, averaged over all tropical cyclones. Radial and vertical spacing are 250 km and 100 m, respectively.

Wind at the 12-km level (near 200 hPa), averaged over all tropical cyclones sampled by the NOAA G-IV. Long barb = 10 kt. Radial rings every 250 km out to r = 1500 km.

1. Fluxes of angular momentum by azimuthal eddies contribute to the tropical cyclone momentum budget. Because mean fluxes at outer radii are negligible, eddy momentum fluxes provide by far the primary source of angular momentum to balance the loss to friction. Change in mean tangential velocity (m s -1 d -1 ) produced by the convergence of flux of angular momentum by azimuthal eddies, averaged over all tropical cyclones. Peak “environmental interaction” FOUR INFLUENCES OF THE OUTFLOW LAYER ON TROPICAL CYCLONES

2. Emanuel and Rotunno (2011): theory of tropical cyclones closed by assuming the existence of a critical Ri in the outflow. The Ri closure ties directly to inner core structure and intensity. Percentage of rawinsondes having R B < 1 (blue) and < 0.25 (red), calculated from the surface to the 20 km elevation from all rawinsondes within 500 km of a major hurricane. Low Richardson numbers occur at the same levels as the cirrus canopy. They likely relate in part to radiative heating within the canopy and cooling near the top (Bu et al. 2014; Melhauser and Zhang 2014).

3. Diurnal cycle of deep cloud in tropical cyclones occurs within the outflow layer (Dunion et al. 2014). What drives this? Diurnal variation of infrared brightness temperature anomaly, averaged over 31 mature hurricanes. Show are the 400, 500, and 600 km radii (green, blue, and dark blue contours) over a 48-hour period spanning the time of maximum intensity. The horizontal axis shows local standard time.

4. Temperature differences between the cirrus canopy and the clear air beyond can create symmetric instability. This instability, which is found near the canopy edge, might have an influence of the length of tropical cyclone intensification periods. Radial-vertical cross-section of azimuthal and time-averaged absolute angular momentum (heavy dark contours) and θ e (shading and light dashed contours). Blue stippled region is moist symmetrically unstable. From Hurricane Ivan (2004) (Molinari and Vollaro 2014).

Location of all dropsondes released by the Global Hawk with respect to the tropical cyclone centers (from Alan Brammer). The cirrus canopy is well sampled, as is the region of maximum outflow. The radii with the strongest outflow anticyclone and the largest eddy momentum flux convergence are not well sampled. R = 500 km

How can we best use Global Hawk sondes to study the upper troposphere in tropical cyclones? Examine physical processes within the cirrus canopy, which are coupled to the existence of turbulence, the diurnal cycle, and inertial instability. Previous studies with G-IV sondes could not see the tropopause. Previous studies with rawinsondes could see the tropopause, but had no spatial resolution. GH sondes have high spatial resolution and see the tropopause, which has been terra incognita in tropical cyclones.

Nearly dry adiabatic layer Tropopause Low stability layer Strong inversion; huge shear Cold point tropopause Rawinsonde profile released within the cloud shield of Typhoon Mekkhala (January 2015). Provided to the Tropical Storms List by Scott Bachmeier. Base of cirrus overcast (again large shear)

Another Typhoon Mekkhala sounding showing similar structure.

Questions raised by the Mekkhala soundings Why is there a double inversion in the upper troposphere? How do we determine cloud top height? Why is there such strong shear at cloud top? Could the diurnal pulse represent a gravity wave ducted within this layer? Are numerical models reproducing these structures?

Figures from poster of Duran and Molinari from yesterday: CPL cloud top appears to be associated with the lower inversion. What produces the inversion above cloud top?

Summary: the physics and dynamics of the outflow layer plays many potential roles in tropical cyclones Turbulence associated with low stability produced by radiative processes and by sublimation of precipitation (Molinari et al. 2014) Cloud radiative interactions: influence intensity and track of TCs (Bu et al. 2014; Jin et al. 2014), and likely play a role in the diurnal cycle and the creation of symmetric instability. All of these can be studied using Global Hawk sondes, especially when the CPL is also available.