day, lee waves are often present all day, as long as the winds  aloft continue. The daytime dissipation of lee waves is not as  notable for large mountains. For instance, during the 1950s  Sierra Wave Project (see www.soaringmuseum.org), it was  found that the wave amplitude reached a maximum in mid  to late afternoon, when convective heating was a maximum.  Rotor turbulence also increased dramatically at that time. Topography upwind of the wave-producing range can also  create problems, as illustrated in  Figure 9-27 . In the first case  [Figure 9-27A] , referred to as destructive interference, the  wavelength of the wave from the first range is out of phase  with the distance between the ranges. Lee waves do not form  downwind of the second range, despite winds and stability  aloft being favorable. In the second case  [Figure 9-27B] ,  referred to as constructive interference, the ranges are in  phase, and the lee wave from the second range has a larger  amplitude than it might otherwise. Convergence lift is most easily imagined when easterly and  westerly winds meet. When two opposing air masses meet,  air is pushed aloft by the two opposing winds. Air does not  need to meet head on to go up, however. Wherever air piles  up, it leads to convergence and rising air. One type of convergence line commonly found near coastal  areas is the so-called sea-breeze front. Inland areas heat  during the day, while the adjacent sea maintains about the  same temperature. Inland heating leads to lower pressure,  drawing in cooler sea air. As the cooler air moves inland, it  behaves like a miniature shallow cold front, and lift forms  along a convergence line. Sometimes consistent lift can be  found along the sea-breeze front while at other times it acts  as a focus for a line of thermals. If the inland air is quite  unstable, the sea-breeze front can act as a focus for a line of  thunderstorms. Additionally, since the air on the coast side  of the sea-breeze front is rather cool, passage of the front can  spell the end of thermal soaring for the day.  Wave flight is a unique soaring experience and requires  planning, equipment and Federal Aviation Administration  (FAA) notification for the flight. The Soaring Society of  America (SSA) Awards and Badges offers soaring pilots  Lennie Awards for completing and documenting a wave  flight.  [Figure 9-28] Isolated small hills or conical mountains do not form classic  lee waves. In some cases, they do form waves emanating at  an angle to the wind flow similar to water waves created by  the wake of a ship. A single peak may require only a mile  or two in the dimension perpendicular to the wind for high- amplitude lee waves to form, though the wave lift is confined  to a relatively small area in these cases. 9-19 Figure 9-28.  Lennie Awards are given for completing and  documenting a wave flight. Figure 9-27.  Constructive and destructive interference. Lift Due to Convergence While working out of the Bishop, California, airport in the late 1940s, mountain pilot and wave pilot pioneer Robert F.  Symons created a new and unique system of awards for wave  flying, which he called “Iennie” pins. Pilots who soared to great  heights in the Sierra Wave received a one-lennie pin for  attaining an altitude of 25,000 to 35,000 feet, a two-lennie pin  for reaching 35,000 to 40,000 feet, and a three-lennie pin for  exceeding 40,000 feet. Very early, Symons recognized the excellent soaring  conditions in the Owens Valley and helped organize a soaring  group in 1938. As a professional pilot engaged in cloud  seeding, he learned first hand of the power generated in the  Sierra Wave and became well known for his studies and  lectures on mountain wave phenomena. Although his lists are incomplete, it is believed that he issued some 35 one-lennie,  16 two-lennie, and 10 three-lennie pins. The awarding of  these pins ceased in 1958, when Symons lost his life in a  glider accident. In 1962 Carl Burson, Jr., saw one of these pins and upon learning of its history, became interested in reestablishing  their issuance as a memorial to Bob Symons. In 1963, the  program was reestablished under the official auspices of the SSA, with each new pin holder also receiving a handsome  wall plaque. The pin itself is 7mm in diameter (the same as the  FAI Gold Badge) and has one, two, or three white lenticular  clouds against a blue background with a silver rim. Each pin  is consecutively numbered. A B Wavelength Wavelength