On the Structure and Formation of UTLS PV Dipole/Jetlets in Tropical Cyclones by Convective Momentum Surges

Abstract The structure and origin of mesoscale jets and associated potential vorticity (PV) dipoles in the upper troposphere and lower stratosphere (UTLS) in tropical cyclones (TCs) are investigated. UTLS PV dipole/jetlets, which occurred in Talas (2011), Edouard (2014), and Ita (2014), are simulated with the University of Wisconsin Nonhydrostatic Modeling System (UWNMS). PV dipoles are confined to the UTLS, where the jetlets oppose the ambient anticyclonic flow. They form ~100–250 km from the eye in convective asymmetries and are characterized by surges of air that accelerate in the updraft, overshoot, and extend radially outward. In these cases, the outflow jet merges with the subtropical westerly jet. Analysis of the structure of UTLS PV dipole/jetlets led to a new physical interpretation for their formation, based on the difference in momentum between the updraft and air in the UTLS: the convective momentum transport hypothesis. This view is complementary to the vorticity tilting hypothesis. A jetlet will form whenever an updraft carries horizontal winds to a level with different wind. Schematic diagrams show how to predict jetlet orientation based on horizontal speeds in the updraft and UTLS ambient air. In TCs, horizontal winds in the updraft are cyclonic, so a UTLS jetlet will be cyclonic and oppose the ambient flow. Each jetlet creates an anticyclonic, inertially unstable PV member, which lies radially outward. Estimates of terms in the PV conservation equation support the hypothesis that the dipoles arise from the curl of shear stress. Convective asymmetries associated with PV dipole/jetlets can significantly modify TC evolution by local thermodynamic acceleration.

Download Full-text

On the Similarity of Lower-Stratospheric Potential Vorticity Dipoles above Tropical and Midlatitude Deep Convection

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-16-0239.1 ◽

2017 ◽

Vol 74 (8) ◽

pp. 2593-2613 ◽

Cited By ~ 4

Author(s):

Matthew H. Hitchman ◽

Shellie M. Rowe

Keyword(s):

Potential Vorticity ◽

Deep Convection ◽

Potential Temperature ◽

Vertical Shear ◽

Ambient Flow ◽

Westerly Jet ◽

University Of Wisconsin ◽

Upward Deflection ◽

The University ◽

The Relationship

Abstract Simulations of the effects of deep convection on the structure of potential vorticity (PV) in the upper troposphere and lower stratosphere (UTLS) have shown that a common signature in the presence of ambient horizontal vorticity is a horizontal PV dipole. Here, the relationship between convection and PV structures in the UTLS in Tropical Cyclone Talas and the extratropical “Super Tuesday” cyclone is investigated with the University of Wisconsin Nonhydrostatic Modeling System (UWNMS). Dipoles of potential temperature in the UTLS are interpreted as an upward deflection of the ambient flow over the updraft (cold), followed by subsidence in its lee (warm), aligned with the wind direction. PV dipoles larger than ±20 PV units (1 PVU = 10−6 K kg−1 m2 s−1) are identified, with typical vertical and horizontal extents of ~3 and ~200 km, respectively, and lifetimes up to 12 h. Confirming the findings of Chagnon and Gray, it is found that horizontal PV dipoles are related to vortex tilting, where horizontally oriented vorticity associated with vertical shear of the ambient wind is bent into a horseshoe shape by the updraft, yielding a PV dipole. This suggests that theta dipoles are perpendicular to PV dipoles and that “low PV lies to the left of the wind shear,” or, in the case of tropical cyclones, “low PV lies radially outward.” Mesoscale jets occur between the dipoles, which oppose the ambient anticyclonic flow. During the extratropical transition of Talas, convective PV anomalies evolved under synoptic-scale deformation into a pair of PV streamers, which modified the midlatitude westerly jet.

Download Full-text

Rapid Destruction of a Stratospheric Potential Vorticity Anomaly by Convectively Induced Inertial Instability during the Southern Wisconsin Extreme Flooding Event of 20 August 2018

Monthly Weather Review ◽

10.1175/mwr-d-19-0213.1 ◽

2020 ◽

Vol 148 (11) ◽

pp. 4397-4414

Author(s):

Shellie M. Rowe ◽

Matthew H. Hitchman

Keyword(s):

Potential Vorticity ◽

Upper Troposphere ◽

Weather Forecasts ◽

Low Wind Speed ◽

University Of Wisconsin ◽

Rapid Destruction ◽

Convective Momentum Transport ◽

Extreme Flooding ◽

Vorticity Anomaly ◽

The University

AbstractThe stalling and rapid destruction of a potential vorticity (PV) anomaly in the upper troposphere–lower stratosphere (UTLS) by convectively detrained inertially unstable air is described. On 20 August 2018, 10–15 in. (~0.3–0.4 m) of rain fell on western Dane County, Wisconsin, primarily during 0100–0300 UTC 21 August (1900–2100 CDT 20 August), leading to extreme local flooding. Dynamical aspects are investigated using the University of Wisconsin Nonhydrostratic Modeling System (UWNMS). Results are compared with available radiosonde, radar, total rainfall estimates, satellite infrared, and high-resolution European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. Using ECMWF analyses, the formation of the UTLS PV anomaly is traced to its origin a week earlier in a PV streamer over the west coast of North America. The rainfall maximum over southern Wisconsin was associated with this PV anomaly, whereby convection forming in the warm-upglide sector rotated cyclonically into the region. The quasi-stationarity of this rainfall feature was aided by a broad northeastward surge of inertially unstable convective outflow air into southeastern Wisconsin, which coincided with stalling of the eastward progression of the PV anomaly and its diversion into southern Wisconsin, extending heavy rainfall for several hours. Cessation of rainfall coincided with dilution of the PV maximum in less than an hour (2100–2200 CDT), associated with the arrival of negative PV in the upper troposphere. The region of negative PV was created when convection over Illinois transported air with low wind speed into northeastward shear. This feature is diagnosed using the convective momentum transport hypothesis.

Download Full-text

Some Biological Applications of High Voltage Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100051505 ◽

1974 ◽

Vol 32 ◽

pp. 298-299

Author(s):

Hans Ris

Keyword(s):

High Voltage ◽

Chromosome Structure ◽

Nerve Fibers ◽

Good Resolution ◽

High Voltage Electron Microscopy ◽

Voltage Electron ◽

University Of Wisconsin ◽

High Voltage Electron ◽

One Year ◽

The University

The High Voltage Electron Microscope Laboratory at the University of Wisconsin has been in operation a little over one year. I would like to give a progress report about our experience with this new technique. The achievement of good resolution with thick specimens has been mainly exploited so far. A cold stage which will allow us to look at frozen specimens and a hydration stage are now being installed in our microscope. This will soon make it possible to study undehydrated specimens, a particularly exciting application of the high voltage microscope.Some of the problems studied at the Madison facility are: Structure of kinetoplast and flagella in trypanosomes (J. Paulin, U. of Georgia); growth cones of nerve fibers (R. Hannah, U. of Georgia Medical School); spiny dendrites in cerebellum of mouse (Scott and Guillery, Anatomy, U. of Wis.); spindle of baker's yeast (Joan Peterson, Madison) spindle of Haemanthus (A. Bajer, U. of Oregon, Eugene) chromosome structure (Hans Ris, U. of Wisconsin, Madison). Dr. Paulin and Dr. Hanna are reporting their work separately at this meeting and I shall therefore not discuss it here.

Download Full-text

Ultrastructural characteristics of sporidia of Ustilago

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100155906 ◽

1989 ◽

Vol 47 ◽

pp. 786-787

Author(s):

Patricia N. Hackney

Keyword(s):

Electron Microscope ◽

Type System ◽

Tube Formation ◽

High Voltage Electron Microscopy ◽

Voltage Electron ◽

University Of Wisconsin ◽

Transmission Electron ◽

Ustilago Hordei ◽

Silene Alba ◽

The University

Ustilago hordei and Ustilago violacea are yeast-like basidiomycete pathogens ofHordeum vulgare and Silene alba respectively. The mating type system in both species of Ustilago is bipolar, with alleles, A,a, (U.hordei) and a1, a2 (U.violacea) at a single locus. Haploid sporidia maintain the asexual phase by budding, while the sexual phase is initiated by conjugation tube formation between the mating types during budding and conjugation.For observation of budding, sporidia were prepared by culturing the four types on YEG (yeast extract glucose) broth for 24 hours. After centrifugation at 5000g cells were either left unmated or mated in a1/a2,A/a combinations. The sporidia were then mixed 1:1 with 4% agar and the resulting 1mm cubes fixed in 8% gluteraldehyde and post fixed in osmium tetroxide. After dehydration and embedding cubes were thin sectioned with a LKB ultratome and photographed in a Zeiss 9s transmission electron microscope or in an AE1 electron microscope of MK11 1MEV at the High Voltage Electron Microscopy Center of the University of Wisconsin-Madison.

Download Full-text