radar,  a  wide  variety  of  weather  features  of  great importance can be identified. It is beyond the scope of this  manual  to  describe  the  interpretation  of  doppler velocity  patterns. For a detailed explanation of the interpretation  of  doppler  velocity  patterns  refer  to  the FMH-11 (part B). MESOCYCLONE  SIGNATURE  DETECTION Mesocyclones  have  been  found  to  be  precursors  to many tornadoes. They generally have a core diameter of 1.5 to 5 nmi, maximum tangential velocities of 40 kts or greater, and time and height continuity. Previous doppler  experiments  have  found  that  weak  mesocyclone signatures  generally  result  in  severe  thunderstorms. Stronger  signatures  generally  produce  tornadoes, especially if a tornadic vortex signature is present. If an alert is received that a mesocyclone exists, or if there is no alert, but a mesocyclone is suspected, there are several products that can be used to confirm its presence. These products and how they might be used are  discussed  in  the  following  paragraphs. Recognition of a Mesocyclone Signature A   mesocyclone   typically   will   develop   at   the midlevels of a tomadic storm and build down to lower levels  as  the  storm  matures.  It  may  be  possible  to monitor   development   of   storm   rotation   or   a mesocyclone  in  the  velocity  field.  The  time  lapse capability with continuous update may be useful in monitoring this development. In the velocity field, the feature will appear as two velocity peaks of opposite signs, separated azimuthally. Interrogation of different elevation scans of the Mean Radial Velocity product (at 2000 ft intervals between 15,000 and 19,000 ft) can aid in determining the height continuity of a mesocyclone. The Quarter Screen mode can be useful for this purpose. If  correctly  oriented  through  the  storm,  storm rotation  (cyclonic  or  anticyclonic)  or  a  well-developed mesocyclone  may  be  evident  in  the  Mean  Radial Velocity  Cross  Section  product.  The  cross  section should be generated perpendicular to the mean flow. If a  mesocyclone  is  not  evident  in  the  Mean  Radial Velocity product or the Severe Weather Analysis Mean Radial  Velocity  product,  the  Storm  Relative  Mean Radial Velocity Map or Region products may display this  feature  (part  C  of  the  FMH-11). Removing the storm motion may aid in the detection of  a  mesocyclone,  but  the  mesocyclone  circulation pattern will exist in the velocity field even if the storm motion is not removed. In the presence of a strong rotational signature, the Combined  Moment  product  can  be  very  useful  in determining the existence of a mesocyclone. In such a case,  rotational  phenomena  should  be  clearly  evident due to the relative position of the arrows in a given area. In addition, high reflectivity core and high spectrum width values may be evident in the area. In a tornadic supercell, doppler data have indicated that a separation of the mesocyclone core from the bounded weak echo region occurs prior to or during the collapse of the bounded weak echo region. With the development of severe weather possible at this stage, the separation  of  the  mesocyclone  core  from  the  bounded weak  echo  region  may  be  monitored  by  displaying  an appropriate  Reflectivity  product  on  one  graphic  screen and a Storm Relative Mean Radial Velocity Map product on the other. A time lapse of the Mean Radial Velocity or  Storm  Relative  Mean  Radial  Velocity  Map  product, magnified  on  the  storm  under  investigation,  may  prove very  useful  in  determining  the  separation  of  the mesocyclone  core  from  the  bounded  weak  echo  region. If a mesocyclone is evident in the Mean Radial Velocity product, this separation may be monitored using the time lapse capability with continuous update for the Mean Radial Velocity and Reflectivity products. Considerations The mesocyclone algorithm provides the position of the feature reflected onto the lowest elevation angle in which the feature was detected. This is due to the fact that  mesocyclones  are  often  tilted  and  are,  therefore, displaced  at  higher  elevations.  Mesocyclones  may  not always  be  identified  by  the  algorithm  for  high reflectivity  core  storms,  for  storms  that  produce downbursts, or for weak tornadoes produced as a result of  convergence  boundaries.  Since  there  is  no  tracking algorithm for mesocyclone features, time continuity must be established. In addition, the Storm Relative Mean  Radial  Velocity  Map  and  Region  products  display the  maximum  velocity  sampled  over  four  0.13  nmi range bins. The peak velocity values, and thus the peak shear associated with a mesocyclone feature, are more likely to be displayed on these products than on the Mean  Radial  Velocity  product,  which  simply  displays every fourth 0.13 nmi range bin at the same resolution. Depending  upon  selection  of  storm  motion  removal, the existence of a mesocyclone may be more evident in the Storm Relative Mean Radial Velocity Map and 12-9