Mesoscale Meteorology Exam 2 Study Guide

Front

List and describe the defining visual characteristics of a supercell storm with particular emphasis on the mesocyclone.

Back

Discrete, uni-cellular appearance

Multicell looks more "lumpy" or continuous

Flanking line

Wall cloud

Hook echo

Bounded Weak Echo Region (BWER)

May be rain wrapped (visually hard to see)

Front

List and describe the defining radar characteristics and signatures of a supercell storm with particular emphasis on the mesocyclone.

Back

Discrete, uni-cellular appearance

May be rain wrapped (clear radar circulation)

Hook echo (radar reflectivity signature of rotating updraft; kidney bean shaped)

Meso (updraft) associated with minimum in radar reflectivity called BWER (nearly vertical channel of weak radar echo, surrounded on the sides and top by significantly stronger echo

Downward extension of rear side of (forward) echo overhang that caps the BWER forms the pendant shaped hook echo in radar imagery at low-levels

Front

Define and describe in words and graphically the primary 3-D kinematic (i.e., airflow) patterns in a supercell including the updraft, mesocyclone, forward flank downdraft (FFD) and rear flank downdraft (RFD) of supercells, including the physical processes responsible for them. Identify likely locations of tornadoes relative to supercell structure.

UPDRAFT

Back

Quasi-steady rotating updraft = mesocyclone

Broad, intense updraft enters the SE flank of a storm

Updraft rises vertically and then curves outward to the anvil outflow region

Vertical velocities in main updraft can exceed 50 m s^-1

Updraft interacts with vertical shear of environment

Wall clouds indicate an area of updraft and inflow

BWER - signature of a strong updraft (carries newly formed hydrometeors to high levels before they can grow to radar-detectable sizes)

New updraft - a change in the pressure field will cause a non-hydrostatic force and acceleration

Updraft gradient tilts horizontal vorticity into the vertical (stretching by updraft would then intensify the vorticity now in the vertical)

Physical processes responsible: surface heating, moisture and condensation, convergence of air masses, orographic lifting, vertical wind shear

Front

Define and describe in words and graphically the primary 3-D kinematic (i.e., airflow) patterns in a supercell including the updraft, mesocyclone, forward flank downdraft (FFD) and rear flank downdraft (RFD) of supercells, including the physical processes responsible for them. Identify likely locations of tornadoes relative to supercell structure.

MESOCYCLONE

Back

Quasi-steady rotating updraft

Dynamical criterion for a supercell

Region of (positive) vertical velocity (cyclonic rotation) with characteristic width 3-8 km and magnitude on order of >= 10^-2 s^-1 (refers specifically to region of rotation within convective storms)

Should extend through at least 1/2 depth of updraft

Should persist through convective time scale

Can be seen with Doppler velocity from radar (azimuthal shear in velocity; Vr couplet)

Precipitation in mesocyclone is not heavy

Any precipitation is displaced far from updraft/mesocyclone

Updraft/Mesocyclone may be rain wrapped (visually hard to see, but clear radar circulation)

Physical processes responsible: vertical wind shear, buoyant updrafts, baroclinic boundaries, stretching and conservation of angular momentum, dynamic pressure gradients

Front

Define and describe in words and graphically the primary 3-D kinematic (i.e., airflow) patterns in a supercell including the updraft, mesocyclone, forward flank downdraft (FFD) and rear flank downdraft (RFD) of supercells, including the physical processes responsible for them. Identify likely locations of tornadoes relative to supercell structure.

FFD

Back

Downdraft consists of FFD and RFD

Result of deep layer wind shear and strong upper-level winds advecting hydrometeors to forward flank

Evaporation and melting lead to development of negative buoyancy and the downdraft in this region

Most of precipitation production in FFD

Classic supercell - If hook echo is present, then Z (dBZ) < FFD

Front

Define and describe in words and graphically the primary 3-D kinematic (i.e., airflow) patterns in a supercell including the updraft, mesocyclone, forward flank downdraft (FFD) and rear flank downdraft (RFD) of supercells, including the physical processes responsible for them. Identify likely locations of tornadoes relative to supercell structure.

RFD

Back

Downdraft consists of FFD and RFD

Associated with hook echo

Forms when dry mid- and upper-level air impinge on backside of updraft - leads to evaporative cooling and negative buoyancy; downward acceleration)

Downward vertical PGF on upshear flank also likely plays a role

Classic supercell: Downdrafts are weak and RFD often entirely absent

Front

Define and describe in words and graphically the primary 3-D kinematic (i.e., airflow) patterns in a supercell including the updraft, mesocyclone, forward flank downdraft (FFD) and rear flank downdraft (RFD) of supercells, including the physical processes responsible for them. Identify likely locations of tornadoes relative to supercell structure.

Back

RFD

Wall cloud

Hook echo

Tornadoes are not as common in HP (High-Precipitation) supercells as in classic supercells

Front

List and describe in words and graphically the key structures and properties inferred primarily visually and from radar for the three (3) archetypes in the supercell spectrum, namely the classic (CL), low-precipitation (LP) and high precipitation (HP) supercells. Identify the primary defining environmental characteristics of each archetype.

CLASSIC (CL) SUPERCELL

Back

Classic supercells occur within the middle range of upper-level winds (18-28 m s^-1)

Classic supercells have most of their precipitation on the FF (forward flank), with only a small amount within the hook echo at the rear of the updraft

Front

List and describe in words and graphically the key structures and properties inferred primarily visually and from radar for the three (3) archetypes in the supercell spectrum, namely the classic (CL), low-precipitation (LP) and high precipitation (HP) supercells. Identify the primary defining environmental characteristics of each archetype.

LOW-PRECIPITATION (LP) SUPERCELL

Back

Strong upper-level winds (>28 m s^-1), hydrometeors are deposited far downstream of the updraft (favors LP)

Tornadoes can/often do occur during a transition from LP to CL

Front

List and describe in words and graphically the key structures and properties inferred primarily visually and from radar for the three (3) archetypes in the supercell spectrum, namely the classic (CL), low-precipitation (LP) and high precipitation (HP) supercells. Identify the primary defining environmental characteristics of each archetype.

HIGH PRECIPITATION (HP) SUPERCELL

Back

HP supercells have a large amount of precipitation within the hook echo region and on the backside of the storm

Visually, the updraft may be difficult to see if it is engulfed in rain, and on radar HP storms can take on a kidney-bean appearance

Downdrafts can be intense

Tornadoes are not as common (perhaps because the downdrafts are so strong that they repeatedly undercut the updraft with cold outflow

Large hail and damaging downburst winds

Lightning, straight line winds, flooding

Some scientists consider cells associated with classic tornado producing radar echoes like bow echoes, comma echo, LEWP (line echo wave pattern) to be HP supercells