A rainband is a cloud and precipitation structure associated with an area of rainfall which is significantly elongated. Rainbands in can be either stratiform or convective and are curved in shape. They consist of showers and thunderstorms, and along with the eyewall and the eye, they make up a tropical cyclone. The extent of rainbands around a tropical cyclone can help determine the cyclone's intensity.
Rainbands spawned near and ahead of can be which are able to produce . Rainbands associated with cold fronts can be warped by mountain barriers perpendicular to the front's orientation due to the formation of a low-level barrier jet. Bands of thunderstorms can form with sea breeze and land breeze boundaries, if enough moisture is present. If sea breeze rainbands become active enough just ahead of a cold front, they can mask the location of the cold front itself. Banding within the comma head precipitation pattern of an extratropical cyclone can yield significant amounts of rain or snow. Behind extratropical cyclones, rainbands can form downwind of relative warm bodies of water such as the Great Lakes. If the atmosphere is cold enough, these rainbands can yield heavy snow.
Extratropical cyclones
Rainbands in advance of warm
and
are associated with weak upward motion,
[Owen Hertzman (1988). Three-Dimensional Kinematics of Rainbands in Midlatitude Cyclones. Retrieved on 2008-12-24] and tend to be wide and stratiform in nature.
[Yuh-Lang Lin (2007). Mesoscale Dynamics. Retrieved on 2008-12-25.] In an atmosphere with rich low level moisture and vertical
wind shear,
[Richard H. Grumm (2006). 16 November Narrow Frontal Rain band Floods and severe weather. Retrieved on 2008-12-26.] narrow, convective rainbands known as
form generally in the
cyclone's warm sector, ahead of strong cold fronts associated with extratropical cyclones.
[Glossary of Meteorology (2009). Prefrontal squall line. Retrieved on 2008-12-24.] Wider rain bands can occur behind cold fronts, which tend to have more stratiform, and less convective, precipitation.
[K. A. Browning and Robert J. Gurney (1999). Global Energy and Water Cycles. Retrieved on 2008-12-26.] Within the cold sector north to northwest of a cyclone center, in colder cyclones, small scale, or mesoscale, bands of heavy snow can occur within a cyclone's comma head precipitation pattern with a width of to .
[KELLY HEIDBREDER (2007). Mesoscale snow banding. Retrieved on 2008-12-24.] These bands in the comma head are associated with areas of frontogensis, or zones of strengthening temperature contrast.
[David R. Novak, Lance F. Bosart, Daniel Keyser, and Jeff S. Waldstreicher (2002). A CLIMATOLOGICAL AND COMPOSITE STUDY OF COLD SEASON BANDED PRECIPITATION IN THE NORTHEAST UNITED STATES. Retrieved on 2008-12-26.] Southwest of extratropical cyclones, curved flow bringing cold air across the relatively warm
Great Lakes can lead to narrow
lake-effect snow bands which bring significant localized snowfall.
Narrow cold-frontal rainband
A narrow cold-frontal rainband (NCFR) is a characteristic of particularly sharp cold frontal boundaries. These can usually be seen very easily on satellite photos. NCFRs are typically accompanied by strong gusty winds and brief but intense rainfall. Convection may or may not occur depending on the stability of the air mass being lifted by the front. Such fronts usually are also marked by a sharp wind shift and temperature drop.
Tropical cyclones
Rainbands exist in the periphery of tropical cyclones, which point towards the cyclone's center of low pressure.
[Glossary of Meteorology (2009). Tropical cyclone. Retrieved on 2008-12-24.] Rainbands within tropical cyclones require ample moisture and a low level pool of cooler air.
[A. Murata, K. Saito and M. Ueno (1999). A Numerical Study of Typhoon Flo (1990) using the MRI Mesoscale Nonhydrostatic Model. Retrieved on 2008-12-25.] Bands located to from a cyclone's center migrate outward.
[Yuqing Wang (2007). How Do Outer Spiral Rainbands Affect Tropical Cyclone Structure and Intensity? Retrieved on 2008-12-26.] They are capable of producing heavy
Rain and
of wind, as well as
,
[NWS JetStream – Online School for Weather (2008). Tropical Cyclone Structure.| National Weather Service. Retrieved on 2008-12-24.] particularly in the storm's right-front quadrant.
[National Oceanic and Atmospheric Administration (1999). Hurricane Basics. Retrieved on 2008-12-24]
Some rainbands move closer to the center, forming a secondary, or outer, eyewall within intense hurricanes.[Jasmine Cetrone (2006). Secondary eyewall structure in Hurricane Rita: Results from RAINEX. Retrieved on 2009-01-09.] Spiral rainbands are such a basic structure to a tropical cyclone that in most tropical cyclone basins, use of the satellite-based Dvorak technique is the primary method used to determine a tropical cyclone's maximum sustained winds.[University of Wisconsin–Madison (1998). Objective Dvorak Technique. Retrieved on 2006-05-29.] Within this method, the extent of spiral banding and difference in temperature between the eye and eyewall is used to assign a maximum sustained wind and a central pressure.[Atlantic Oceanographic and Meteorological Laboratory (2007). Subject: H1) What is the Dvorak technique and how is it used? Retrieved on 2006-12-08.] Central pressure values for their centers of low pressure derived from this technique are approximate.
Different programs have been studying these rainbands, including the Hurricane Rainband and Intensity Change Experiment.
Forced by geography
Convective rainbands can form parallel to terrain on its
windward side, due to
triggered by hills just upstream of the cloud's formation.
[Daniel J. Kirshbaum, George H. Bryan, Richard Rotunno, and Dale R. Durran (2006). The Triggering of Orographic Rainbands by Small-Scale Topography. Retrieved on 2008-12-25.] Their spacing is normally to apart.
[Daniel J. Kirshbaum, Richard Rotunno, and George H. Bryan (2007). The Spacing of Orographic Rainbands Triggered by Small-Scale Topography. Retrieved on 2008-12-25.] When bands of precipitation near frontal zones approach steep topography, a low-level barrier
jet stream forms parallel to and just prior to the mountain ridge, which slows down the frontal rainband just prior to the mountain barrier.
[J. D. Doyle (1997). The influence of mesoscale orography on a coastal jet and rainband. Retrieved on 2008-12-25.] If enough moisture is present,
sea breeze and
land breeze fronts can form convective rainbands. Sea breeze front
thunderstorm lines can become strong enough to mask the location of an approaching cold front by evening.
[A. Rodin (1995). Interaction of a cold front with a sea-breeze front numerical simulations. Retrieved on 2008-12-25.] The edge of
ocean currents can lead to the development of thunderstorm bands due to heat differential at this interface.
[Eric D. Conway (1997). An Introduction to Satellite Image Interpretation. Retrieved on 2008-12-26.] Downwind of islands, bands of showers and thunderstorms can develop due to low level wind convergence downwind of the island edges. Offshore
California, this has been noted in the wake of cold fronts.
[Ivory J. Small (1999). AN OBSERVATIONAL STUDY OF ISLAND EFFECT BANDS: PRECIPITATION PRODUCERS IN SOUTHERN CALIFORNIA. Retrieved on 2008-12-26.]
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