Variations Associated with Cores and Gaps of a Pacific Narrow Cold Frontal Rainband

Jorgensen, David P.; Pu, Zhaoxia; Persson, P.Ola G.; Tao, Wet-Kuo
November 2003
Monthly Weather Review;Nov2003, Vol. 131 Issue 11, p2705
Academic Journal
A NOAA P-3 instrumented aircraft observed an intense, fast-moving narrow cold frontal rainband (NCFR) as it approached the California coast on 19 February 2001 during the Pacific Coastal Jets Experiment. Airborne Doppler radar data obtained while the frontal system was well offshore indicated that a narrow ribbon of very high radar reflectivity convective cores characterized the rainband at low levels with echo tops to ∼4–5 km, and pseudo-dual-Doppler analyses showed the low-level convergence of the prefrontal air. The NCFR consisted of gaps of weaker reflectivity and cores of stronger reflectivity along its length, perhaps as a result of hydrodynamic instability along its advancing leading edge. In contrast to some earlier studies of cold frontal rainbands, density-current theory described well the motion of the overall front. The character of the updraft structure along the NCFR varied systematically along the length of the precipitation cores and in the gap regions. The vertical shear of the cross-frontal low-level ambient flow exerted a strong influence on the updraft character, consistent with theoretical arguments developed for squall lines describing the balance of vorticity at the leading edge. In short segments at the northern ends of the cores, the vertical wind shear was strongest with the updrafts and rain shafts more intense, narrower, and more erect or even downshear tilted. At the southern ends of the cores and just north of the gaps, the wind shear weakened with less intense updrafts that tilted upshear and contained a broader band of rainfall. Simulations using the nonhydrostatic nested grid version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) are used to investigate the core and gap regions, focusing on the relationship between the character of the modeled updrafts and the balance between the cold-air-induced vorticity and the prefrontal ambient shear vorticity. The cold air behind the NCFR, which forces new convection along its leading edge, is probably maintained by large-scale advection of cold air plus evaporative cooling processes within the heavy rain region of the NCFR. Observations confirm the model results; that is, that the updraft character depends on the balance of vorticity at the leading edge. Downshear-tilted updrafts imply that convection at the northern ends of cores may weaken with time relative to the frontal segments at the southern ends, because inflow air would be affected by passage through the heavy rain region before ascent. A mechanism for line modification is thus implied.


Related Articles

  • A Numerical Study on the Effects of Taiwan Topography on a Convective Line during the Mei-Yu Season. Chung-Chieh Wang; George Tai-Jen Chen; Tzu-Chin Chen; Tsuboki, Kazuhisa // Monthly Weather Review;Nov2005, Vol. 133 Issue 11, p3217 

    During the morning hours on 23 May 2002, a convective line associated with a mei-yu front brought heavy rainfall along the coast of central Taiwan under favorable synoptic conditions of warm air advection and large convective available potential energy (CAPE) of over 3000 m2 s-2. Doppler radar...

  • Spaceborne Doppler Radar Measurements of Rainfall: Correction of Errors Induced by Pointing Uncertainties. Tanelli, Simone; Im, Eastwood; Kobayashi, Satoru; Mascelloni, Roberto; Facheris, Luca // Journal of Atmospheric & Oceanic Technology;Nov2005, Vol. 22 Issue 11, p1676 

    In this paper a sea surface radar echo spectral analysis technique to correct for the rainfall velocity error caused by radar-pointing uncertainty is presented. The correction procedure is quite straightforward when the radar is observing a homogeneous rainfall field. When nonuniform beam...

  • Continental Passive Microwave-Based Rainfall Estimation Algorithm: Application to the Amazon Basin. Biscaro, Thiago S.; Morales, Carlos A. // Journal of Applied Meteorology & Climatology;Jul2008, Vol. 47 Issue 7, p1962 

    This paper presents a new statistical algorithm to estimate rainfall over the Amazon Basin region using the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The algorithm relies on empirical relationships derived for different raining-type systems between coincident...

  • Vertical Structure of Hurricane Eyewalls as Seen by the TRMM Precipitation Radar. Hence, Deanna A.; Houze, Robert A. // Journal of the Atmospheric Sciences;Aug2011, Vol. 68 Issue 8, p1637 

    Statistical analysis of the vertical structure of radar echoes in the eyewalls of tropical cyclones, shown by the Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR), shows that the eyewall contains high reflectivities and high echo tops, with deeper and more intense but highly...

  • A Real-Time Four-Dimensional Doppler Dealiasing Scheme. James, Curtis N.; Houze Jr., Robert A. // Journal of Atmospheric & Oceanic Technology;Oct2001, Vol. 18 Issue 10, p1674 

    Presents a study which proposed a real-time four-dimensional Doppler dealising scheme. How the scheme examines tilt angles; Data dimensions used to interpret and dealias each tilt; Description of four-dimensional dealising.

  • Doppler Velocity from Sea Surface on the Spaceborne and Airborne Weather Radars. Kobayashi, Satoru; Kumagai, Hiroshi // Journal of Atmospheric & Oceanic Technology;Mar2003, Vol. 20 Issue 3, p372 

    The Doppler operation applied to the sea surface is studied for the spaceborne and airborne weather radars. In the space mission, a small amount of beam misalignment can cause large contamination of a platform velocity into a measured Doppler velocity. In this paper, theoretical bases for...

  • Effects of Vertical Wind Shear and Storm Motion on Tropical Cyclone Rainfall Asymmetries Deduced from TRMM. Chen, Shuyi S.; Knaff, John A.; Marks Jr., Frank D. // Monthly Weather Review;Nov2006, Vol. 134 Issue 11, p3190 

    Vertical wind shear and storm motion are two of the most important factors contributing to rainfall asymmetries in tropical cyclones (TCs). Global TC rainfall structure, in terms of azimuthal distribution and asymmetries relative to storm motion, has been previously described using the Tropical...

  • Profiles of Raindrop Size Distributions as Retrieved by Microrain Radars. Peters, Gerhard; Fischer, Bernd; Münster, Hans; Clemens, Marco; Wagner, Andreas // Journal of Applied Meteorology;Dec2005, Vol. 44 Issue 12, p1930 

    Data of vertically pointing microrain radars (MRRs), located at various sites around the Baltic Sea, were analyzed for a period of several years. From the Doppler spectra profiles of drop size distributions (DSDs) are obtained. A significant height dependence of the shape of the DSDs—and...

  • Misocyclone Characteristics along Florida Gust Fronts during CaPE. Friedrich, Katja; Kingsmill, David E.; Young, Carl R. // Monthly Weather Review;Nov2005, Vol. 133 Issue 11, p3345 

    Multiple-Doppler radar and rawinsonde data are used to examine misocyclone characteristics along gust fronts observed during the Convection and Precipitation/Electrification (CaPE) project in Florida. The objective of this study is to investigate the observational representativeness of previous...


Read the Article


Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics