If a quick descent is needed or desired, the sink downwind of  the wave crest can be used. Sink can easily be twice as strong  as lift encountered upwind of the crest. Eventual descent into  downwind rotor is also likely. Sometimes the space between  a rotor cloud and overlying lenticulars is inadequate and  a transition downwind cannot be accomplished safely. In  this case, a crosswind detour may be possible if the wave  is produced by a relatively short ridge or mountain range.  If clouds negate a downwind or crosswind departure from  the wave, a descent on the upwind side of the wave crest  is needed. Spoilers or dive brakes may be used to descend  through the updraft, followed by a transition under the rotor  cloud and through the rotor. A descent can be achieved by  moving upwind of a very strong wave lift if spoilers or dive  brakes alone do not allow an adequately fast descent. A trip  back through the rotor is at best unpleasant. At worst, it can  be dangerous if the transition back into the rotor is done with  too much speed. In addition, strong wave lift and lift on the  upwind side of the rotor may make it difficult to stay out of  the rotor cloud. This wave descent requires a good deal of  caution and emphasizes the importance of an exit strategy  before climbing too high in the wave, keeping in mind that  conditions and clouds can rapidly evolve during the climb. In the discussion thus far, a climb in the primary wave has been  assumed. It is also possible to climb in the secondary or tertiary  lee wave (if existing on a given day) and then penetrate into  the next wave upwind. The success of this depends on wind  strength, clouds, the intensity of sink downwind of wave crests,  and the performance of the glider. Depending on the height  attained in the secondary or tertiary lee wave, a trip through the  rotor of the next wave upwind is a distinct possibility. Caution  is needed if penetrating upwind at high speed. The transition  into the downwind side of the rotor can be as abrupt as on the  upwind side, so speed should be reduced at the first hint of  turbulence. In any case, expect to lose a surprising amount of  altitude while penetrating upwind through the sinking side of  the next upwind wave.  [Figure 10-40] Some of the dangers and precautions associated with wave  soaring have already been mentioned. Those and others are  summarized below. •  If any signs of hypoxia appear, check the oxygen system  and immediately begin a descent to lower altitudes  below which oxygen is not needed. Do not delay! •  Eventually, a pilot becomes cold at altitude regardless  of how warmly the pilot is dressed. Descend well  before it becomes uncomfortably cold. 10-22 Figure 10-39.  Techniques for working lift near the top of the wave in weak winds. Weak Wind S-turns with slight drift to stay in weak lift Series of circles with an upwind leg Upwind leg with a 360° turn Band of wave lift Lift weakens—Turn back into wind Downwind turn leads to strong sink or rotor Wind Figure 10-38.  Proper crabbing to stay in lift and effects of upwind  turn (correct) or downwind turn (incorrect).