Severe and Unusual Weather ESAS 1115 Spotter Training and Radar Meteorology Part 2 – Introduction to Radar Meteorology Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Meteorological Sensors Two types of two types of sensors: Remote vs. In-situ Active vs. Passive Our passive eyes can only see features of the storm In order to see the inner workings of a thunderstorm, and to understand it better, we need an active remote sensor – weather radar Radar will allow us to interrogate information about the storm by detecting precipitation and wind information within Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Radio Detection and Ranging NEXRAD – Next Generation Radar WSR-88D – Weather Surveillance Radar, 1988 Doppler Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Important Angles The azimuth angle is the compass angle from north (360°) Targets are indicated by A/R (Azimuth/Range) Birds eye view is displayed on a PPI (Planned Position Indicator) A cross sectional display is an RHI (Range Height Indicator) Volume scan Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Gate Size Reflectivity Information is displayed in pixel-like units of area called “gates” Gate size is determined by pulse length and angular beam width Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Reflectivity dBm = 10log(power returned/1milliwatt) Z is reflectivity dBZ is a logarithmic scale similar to dBm 1dBZ is the power returned by a sphere of 1mm6/m3 Doubling of power results in a linear increase of 3dBZ Z is proportional to D6 Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Clear Air Mode Range from -28 to 28 dBZ 16 4dBz increments Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Precipitation Mode Range from 5 to 75 dBZ 16 5dBz increments Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

The Significance of Clear Air Mode During Snowfall Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

NIDS - Nexrad Information Dissemination Service Base Reflectivity – Various Elevation Angles Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

NIDS - Nexrad Information Dissemination Service Base (or Storm Relative) Velocity – Various Elevation Angles Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

NIDS - Nexrad Information Dissemination Service 1 Hour Precipitation Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

NIDS - Nexrad Information Dissemination Service Storm Total Precipitation Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

NIDS - Nexrad Information Dissemination Service VIL – Vertically Integrated Liquid Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

NIDS - Nexrad Information Dissemination Service Echo Tops Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

NIDS - Nexrad Information Dissemination Service VAD – Velocity Azimuth Display VWP – VAD Wind Profile Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

NIDS - Nexrad Information Dissemination Service Composite Reflectivity Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Interpreting Doppler Radar Radial Velocity is the velocity toward or away from a radar Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Using the Zero Isodop When the radial is perpendicular to the the wind, the radar displays zero velocity - This “zero zone” is called the “Zero Isodop”. What percentage of actual wind will the radar detect? 00 = 100% - Parallel 150 = 97% 300 = 87% 450 = 71% 600 = 50% 750 = 26% 900 = 0% - Perpendicular When the wind velocity is parallel to the radial, the full component of the wind is measured Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Interpreting Doppler Radar Winds will flow perpendicular to the zero isodop from green to red Veering wind profile is denoted by an “S” on the overall winds display Veering winds with height indicate warm air advection and hence rising air Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Interpreting Doppler Radar Backing wind profile is denoted by a backwards “S” on the overall winds display Backing winds with height indicate cold air advection and hence sinking air (subsidence) Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

What Does this Represent? Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Veering Winds on VWP Velocity Azimuth Display (VAD) Wind Profile Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Hurricane Katrina Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Divergence Divergence is indicated by radial shear (along the radius) Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Rotation Cyclonic rotation is indicated by azimuthal shear (from one azimuth to another) Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Low-level Rotation and Storm Top Divergence Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Rotation or Convergence? Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Automated Detection of Meteorological Phenomena Algorithms help detect significant features MDA – Mesocyclone Detection Algorithm Meso - “donut” Persistent, strong and detected over a large depth of the storm TDA – Tornado Detection Algorithm TVS – Tornado Vortex Signature Strong gate to gate shear HDA – Hail Detection Algorithm SCIT - Storm Cell Identification and Tracking Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Composite Reflectivity with Storm Attribute Table Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Composite Reflectivity with Symbols Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Gate to Gate Shear (TVS) Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather TVS Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather TVS Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Azimuth Resolution Considerations Rotational couplet identification can be affected by azimuth resolution. As the diagram shows, the closer a rotation is to the radar the more likely it will be identified correctly. If the rotation is smaller than the 10 beam width (possible at long ranges) then the rotation will be diluted or averaged by all the velocities in that sample volume. This may cause the couplet to go unidentified until it gets closer to the radar. Azimuth 3 Weak inbound, weak outbound Rotation too small to be resolved Azimuth 2 Strong inbound, strong outbound Azimuth 1 Stronger inbound than outbound Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Strong TVS Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

SRV vs. Base Velocity with Subtle Rotation Storm Relative When diagnosing straight line winds use base velocity. The strength of an advancing line of storms producing straight line winds is the sum of the winds produced by the storms, plus the movement of the storms. When diagnosing rotation, use storm relative velocity. SRV subtracts out the motion of a storm to display pure rotational characteristics of that storm. Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather FAR vs. POD FAR (False Alarm Ratio) – An event is warned for but does not occur results in a false alarm POD (Probability of Detection) – An event that occurs and has been warned for results in a 100% POD A high POD is achieved at the expense of an increased FAR Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Doppler Dilemma Radial velocity and range is limited by PRF High PRF’s result in short unambiguous ranges and vice versa Low PRF’s result in velocity aliasing and vice versa Given a PRF, the radar can determine the radial velocity within some range, + or – some velocity, called the velocity interval Any velocity beyond that range will “fold over” into the incorrect value Bad data must be “dealiased” The Doppler Dilemma: There is no single PRF that maximizes both Rmax and Vmax Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Velocity Aliasing and Dealiasing Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Three-Body Scatter Spike (TBSS) The “flare” appears further than the main core along the same radial as the highest core The added distance the beam makes from stone to ground to stone (3 bodies) results in a display further than reality Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather TBSS Examples Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Same Storm, Different Radar Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather TBSS in Velocity Data Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Anomalous Propagation (AP) In the wake of this line of thunderstorms, a low-level inversion created by the cold pool results in superrefraction and thus AP Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

AP and Ground Clutter AP is enhanced by strong returns from buildings (ground clutter) Cooling in the evening hours results in a low-level nocturnal inversion and AP Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Sunset Spike Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Sunset Spikes Sunset spikes Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Sunset Spike Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather What the Heck Is This? Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather