Three body scatter spike
Encyclopedia
A hail spike or three body scatter spike (TBSS) is an artifact
on a weather radar
display indicative of large hail
. They are identified by a spike of weak reflectivity
echoes that extend out from a thunderstorm
, and away from the radar site.
Generally known as hail spikes, these are the result of energy from the radar hitting hail, or very heavy rain, and being deflected to the ground, where they deflect back to the hail and then to the radar as in the image on the left. This results in the radar picking up the energy from the multiple path at a later time than the energy that came back directly from the hail to the radar. Both are however on the same radial angle from the radar as the antenna did not have the time to turn significantly.
The multipath echoes are then analyzed on the radar display as echoes extending in a triangular shape further away than the actual location of the hail/heavy rain core. The loss of energy by hitting the ground at least once and the hail multiple times, means weaker return echoes. The hail spike region has thus comparatively quite weaker echoes than the echoes directly from the hail or heavy rain core.
Since hail cores are most intense at higher elevations, hail spikes only appear at the levels aloft that accompany the most intense hail. Because of this, hail spikes are usually not seen at lower elevations. Another restriction to detection is that the signal of the radar beam has to do multiple reflections, each time weakening it. So hail spikes are usually noticeable only in extremely large hailstone cases.
to identify thunderstorms that could likely produce large, severe hail. This would warrant the issuance of a severe thunderstorm warning or mention of large hail in a tornado
warning.
Artifact (error)
In natural science and signal processing, an artifact is any error in the perception or representation of any visual or aural information introduced by the involved equipment or technique....
on a weather radar
Weather radar
Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...
display indicative of large hail
Hail
Hail is a form of solid precipitation. It consists of balls or irregular lumps of ice, each of which is referred to as a hail stone. Hail stones on Earth consist mostly of water ice and measure between and in diameter, with the larger stones coming from severe thunderstorms...
. They are identified by a spike of weak reflectivity
Reflectivity
In optics and photometry, reflectivity is the fraction of incident radiation reflected by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength...
echoes that extend out from a thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
, and away from the radar site.
Cause
The multipath echoes are then analyzed on the radar display as echoes extending in a triangular shape further away than the actual location of the hail/heavy rain core. The loss of energy by hitting the ground at least once and the hail multiple times, means weaker return echoes. The hail spike region has thus comparatively quite weaker echoes than the echoes directly from the hail or heavy rain core.
Since hail cores are most intense at higher elevations, hail spikes only appear at the levels aloft that accompany the most intense hail. Because of this, hail spikes are usually not seen at lower elevations. Another restriction to detection is that the signal of the radar beam has to do multiple reflections, each time weakening it. So hail spikes are usually noticeable only in extremely large hailstone cases.
Use in forecasting
Because of their observed accuracy in indicating large hail aloft, TBSS's are used operationally by the National Weather ServiceNational Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...
to identify thunderstorms that could likely produce large, severe hail. This would warrant the issuance of a severe thunderstorm warning or mention of large hail in a tornado
Tornado
A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...
warning.
Related link
- Convective storm detectionConvective storm detectionConvective storm detection is the meteorological observation of deep, moist convection and consists of detection, monitoring, and short-term prediction. This term includes the minority of storms which do not produce lightning and thunder. Convective storms can produce tornadoes as well as large...
- Severe weather terminology (United States)Severe weather terminology (United States)This article describes the United States National Weather Service severe weather terminology. The NWS defines precise meanings for nearly all its weather terms. This article describes NWS terminology and related NWS weather scales...
- Severe weather terminology (Canada)Severe weather terminology (Canada)This article describes Severe weather Terminology used by the Environment Canada's Meteorological Service of Canada. This article primarily describes various weather warnings, and their criteria. Related weather scales and general weather terms are also addressed in this article...
External links
- Three-Body Scatter Spike course by the National Weather Service