Bulk Richardson number

Bulk Richardson number


The Bulk Richardson Number (BRN) is a dimensionless number in meteorology relating vertical stability and vertical shear (generally, stability divided by shear). It represents the ratio of thermally produced turbulence and turbulence generated by vertical shear.

Practically, its value determines whether convection is free or forced. High values indicate unstable and/or weakly-sheared environments; low values indicate weak instability and/or strong vertical shear. Generally, values in the range of around 10 to 45 suggest environmental conditions favorable for supercell development. See also: Monin-Obukhov Length.

For mesoscale forecasting purposes, the Bulk Richardson Number (BRN) relates buoyancy through convective available potential energy (CAPE) to vertical wind shear for a 5.5km thickness and is simply is defined as:

BRN = CAPE / (0.5 * (u6km - u500m)2)

Here, u6km is the wind speed at 6km above ground level (AGL) and u500 is the wind speed at 500m AGL.

Critical values and interpretation

There is no exact interpretation of BRN values but, in general, for a BRN less than 10, vertical shear dominates over buoyancy and the storm will likely be eviscerated by the shear. For BRN values between 10 and 45, the shear tends to balance the buoyancy favoring strong convective supercells. A BRN larger than 45 supports ordinary cell or multicell convective storms but due to updraft tilt stemming from the lack of shear, supercells are not likely to be observed.

Difficulties in interpretation

Different combinations of CAPE and shear can lead to identical BRN values so the same BRN can represent a myriad of convective situations. Another source of difficulty in forecasting convective storm potential with BRN is that the BRN does not include important assessment parameters like wind direction or air moisture. Insignificant levels of CAPE and shear can also produce significant BRN so it is important that CAPE or the lifted index (LI) are used as a primary measure of atmospheric instability first. Since CAPE is difficult to compute by hand, a computer program is often used to calculate and report BRN given a vertical temperature profile.



External links


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Nombre global de Richardson — Le Nombre global de Richardson (BRN) est un nombre sans dimension qui combine l énergie potentielle de convection disponible (EPCD) et le cisaillement vertical du vent. Cet indice mesure l importance relative des deux paramètres en établissant le …   Wikipédia en Français

  • Natasha Richardson — Richardson at the UK premiere of The Chronicles of Narnia: Prince Caspian in 2008. Born Natasha Jane Richardson 11 May 1963(1963 05 11) London, Englan …   Wikipedia

  • Nusselt number — In heat transfer at a boundary (surface) within a fluid, the Nusselt number is the ratio of convective to conductive heat transfer across (normal to) the boundary. Named after Wilhelm Nusselt, it is a dimensionless number. The conductive… …   Wikipedia

  • Convection — This figure shows a calculation for thermal convection in the Earth s mantle. Colors closer to red are hot areas and colors closer to blue are cold areas. A hot, less dense lower boundary layer sends plumes of hot material upwards, and likewise,… …   Wikipedia

  • Temperature — This article is about the thermodynamic property. For other uses, see Temperature (disambiguation). A map of global long term monthly average surface air temperatures i …   Wikipedia

  • Meteorology — For other uses of the root word meteor , see Meteor (disambiguation). For the work by Aristotle, see Meteorology (Aristotle). Not to be confused with Metrology. Part of the Nature series on Weather   …   Wikipedia

  • Fog — For other uses, see Fog (disambiguation). Part of the Nature series on Weather   Calendar seasons Spring  …   Wikipedia

  • Weather forecasting — weather forecaster redirects here. For other uses, see Weatherman (disambiguation). Forecast of surface pressures five days into the future for the north Pacific, North America, and north Atlantic ocean. Weather forecasting is the application of… …   Wikipedia

  • Sea surface temperature — Weekly average sea surface temperature for the World Ocean during the first week of February 2011, during a period of La Niña …   Wikipedia

  • Lightning — This article is about the atmospheric electrical phenomenon. For other uses, see Lightning (disambiguation). See also: Lightning strike Lightning striking Atlanta, United States Lightning is an atmospheric electrostatic discharge (spar …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.