page_title: Glossary of meteorology
section_title: B
hierarchical_section_title: Glossary of meteorology / B
caption_attribution_description: Radar image of the bow echo that crossed the Kansas City Metropolitan Area during the early hours of May 2, 2008. The shot was taken approximately 2 AM CDT on May 2 or at the same time the bow echo is crossing the Kansas-Missouri state line in Kansas City. Courtesy of NWS Kansas City
context_page_description: This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.
context_section_description: backscatter
  The diffuse reflection of waves, particles, or signals back to the same direction from which they originated. Backscattering is the principle underlying all weather radar systems, which can distinguish radar returns backscattered from target aerosols such as raindrops and snowflakes because the strength of the returns depends largely on the size and reflectivity of the targets.
  ball lightning
  banana belt
  Any segment of a larger geographic region that typically experiences warmer temperatures than the region as a whole, especially during the local winter season, which may prove favorable for agricultural production.
  barbs
  barograph
  A scientific instrument used to measure and record changes in atmospheric pressure over time.
  baroclinity
  A measure of the misalignment between a pressure gradient and a density gradient in a stratified fluid such as the atmosphere. In the context of meteorology, a baroclinic atmosphere is one in which atmospheric density depends on both temperature and pressure, in contrast to a barotropic atmosphere, in which density depends only on pressure. Areas of high atmospheric baroclinity are generally found in the temperate and polar latitudes and are characterized by the frequent formation of cyclones.
  barotropity
  The close alignment between a pressure gradient and a density gradient in a stratified fluid such as the atmosphere. In the context of meteorology, a barotropic atmosphere is one in which atmospheric density depends only on pressure and is more or less independent of temperature, in contrast to a baroclinic atmosphere. Unlike liquids, gaseous fluids such as the air in the atmosphere are generally not barotropic, but the assumption of barotropity can nonetheless be useful in modeling fluid behavior. Tropical latitudes are more nearly barotropic than the mid-latitudes because air temperature is more nearly horizontally uniform in the tropics.
  barometer
  A scientific instrument used to measure atmospheric pressure.
  Beaufort scale
  Bernoulli's principle
  A principle of fluid dynamics which states that an increase in the speed of a moving fluid occurs simultaneously with a decrease in the pressure exerted by the fluid or in the fluid's potential energy.
  Bishop's ring
  black ice
  A thin, nearly transparent coating of glaze ice on a solid surface, especially a road or walkway, which because of its transparency is often practically invisible and therefore presents a significant hazard to drivers and pedestrians.
  blizzard
  A severe snowstorm characterized by strong sustained winds of at least 35 mph (56 km/h) and typically lasting three hours or more. They can have an immense size, covering hundreds or thousands of square miles, and occur most often in temperate, polar, or mountainous regions during the winter.
  block
  A nearly stationary pattern in the atmospheric pressure field overlying a large geographic area, which effectively "blocks" or diverts the movements of cyclones and other convective systems. These blocks can remain in place for days or weeks, causing the areas affected by them to experience the same kind of weather for extended periods of time.
  blowing dust or sand
  blowing snow
  Snow blown about by wind, either from falling snow or snow lifted from the surface, to a height of at least 2 metres (6.6 ft), reducing visibility. It is a defining characteristic of blizzards.
  bounded weak echo region (BWER)
  bow echo
  A characteristic radar return from a mesoscale convective system that is shaped like an archer's bow and usually associated with squall lines or lines of convective thunderstorms. The distinct bow shape is a result of the focusing of a strong flow at the rear of the system. Especially strong bow echoes may develop into derechos.
  breeze
  brightband
  Bulk Richardson Number (BRN)
  A dimensionless ratio related to the consumption of turbulence divided by the shear production of turbulence (the generation of kinetic energy caused by wind shear). It is an approximation of the Gradient Richardson Number.
  bushfire
  See wildfire.
  Buys Ballot's law
caption: A radar image showing a distinct bow echo in a line of thunderstorms over Kansas City, Missouri
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