An Analysis of Clouds Produced by the Undular Bore of April 2, 2010

   Philip Lutzak April 2010

 

 

Introduction   The close-up visible satellite image at right in figure 1 shows the cloud patterns produced by an undular bore over northeastern Mexico during the morning of April 2nd, 2010. The banded appearance of the clouds near the center of the image indicates the existence of gravity waves, and when the waves are smooth and undular in shape, as these are, it is an indication that these clouds may have been created by an undular bore. These clouds occur in varying strengths almost every year during the early spring over the western Gulf of Mexico and adjacent coastal plains. While the clouds from this event are not as impressive in size or scope as some previous ones, the evidence (not shown here) did indeed prove that they were formed by an undular bore.  

  The following is a set of cloud analyses which may help give us a better idea of the typical characteristics of clouds produced by an undular bore. All cloud analyses images are courtesy of NASA Langley Cloud and Radiation Research and are from 2010-04-02 1445 UTC, the same time as the visible satellite image in figure 1.  Ive included in the captions my estimates of the cloud parameters based on the color keys.

 

  Figure 1. Close-up visible satellite image from 2010-04-02 1445. Courtesy NASA/GOES-12. Full Image.
Figure 2a. Cloud Base Height in km. ~ 0-1000 meters.          Wide image. Figure 2b. Cloud Top Height in km. ~ 1000-2000 meters. Wide Image. Figure 2c. Cloud Thickness in km. ~ 1000-2000 meters.       Wide Image.
 
Figure 3a. Cloud Base Pressure in millibars. ~ 900-950mb. Wide Image. Figure 3b. Cloud Top Pressure in millibars. ~ 800-900mb. Wide Image.  
Figure 4a. Cloud Phase. Liquid, with temp >273K.                   Wide Image. Figure 4b. Cloud Albedo. ~ 60-70%.                                           Wide Image. Figure 4c. Cloud Optical Depth. ~ 16 - 20 Tau.                        Wide Image.

 

Analysis

  The data in Figures 2a-c indicate that the bases of the clouds produced by the bore ranged from 0 to 1000 meters, the tops from 1,000 to 2,000 meters and average thickness was about 1,000 to 2,000 meters. The cloud pressure level analyses from 3a-c corroborate this well, with indications that these clouds extended from 900 or 950mb up to as high as 800mb.

  The NASA LARC data from the charts in Figure 4 show that these clouds were composed of liquid hydrometeors and had a high albedo, indicating that these are optically thick clouds that should show up quite well on visible satellite images (given few or no higher clouds above them). 

 

Conclusion

  These data are consistent with the initial studies I've conducted on nine other springtime bore events over the western Gulf region in March and April, using NASA cloud data, satellite images, model-derived skewT diagrams and actual soundings. While the other studies are very preliminary, this more detailed study agrees with the others in that it indicates clouds that are optically thick and low level in height, with an upper limit of about 1,500 to 2,000 meters and only about 50100 mb thick. Although it needs more study, the average cloud top height could be as low as 1,000 meters. I will update this report with a more comprehensive analysis after I analyze the rest of the selected cases.