A LEAR 45 FLT CREW EXPERIENCE CLR AIR TURB AT FL430.

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WHILE ESTABLISHED IN LEVEL FLT AT FL430 OVER GEZ AT ABOUT XA00Z; WE EXPERIENCED A SUDDEN HIGH ALT SHEAR ASSOCIATED WITH THE JETSTREAM THAT RESULTED IN A HIGH SPD EXCURSION LASTING ABOUT 30-45 SECONDS. THE EVENT BEGAN WITHOUT MUCH ADVANCED WARNING AS THE FLT HAD EXPERIENCED NOTHING MORE THAN LIGHT TURB UP TO THAT POINT. THE AIRPLANE SUDDENLY ENCOUNTERED A STRONG HORIZ SHEAR THAT RESULTED IN THE AIRPLANE VERY QUICKLY EXCEEDING MACH .81. AS THE AIRSPD EXCEEDED MACH .81 AND THE OVERSPD WARNING SOUNDED; I PULLED BACK THE PWR. THIS HAD NO EFFECT ON REDUCING THE SPD. I THEN DEPLOYED THE SPOILERS. IT TOOK ABOUT ANOTHER 15-20 SECONDS TO SLOW THE AIRPLANE BACK TO BELOW MACH .81. THIS EVENT BEGAN SO SUDDENLY THAT; WITH THE AUTOPLT ON AND WITH ALT HOLD ENGAGED; THE ACFT ACHIEVED A NOSE LOW ATTITUDE OF ABOUT 3-4 DEGS WHICH RESULTED IN AN ALT LOSS OF ABOUT 300 FT. DISCONNECTING THE AUTOPLT AND HAND FLYING THE AIRPLANE IMMEDIATELY ARRESTED THIS TREND. IT WAS VERY DIFFICULT TO CTL THE AIRPLANE AT THIS POINT AS I WAS CONTENDING WITH INDICATED AIRSPD FLUCTUATIONS OF ABOUT 40-45 KTS WITH THE AIRSPD TREND BAR FLUCTUATING WILDLY. I ALSO OBSERVED THE WIND VELOCITY ON THE PFD FLUCTUATE FROM BTWN 40-85 KTS. THE AIRPLANE WAS ALSO EXPERIENCING MODERATE TURB WHICH ADDED TO THE HANDLING DIFFICULTIES. THE TURB WAS NOT A CRITICAL FACTOR IN TERMS OF STRUCTURAL INTEGRITY AS THE DYNAMICS OF THIS EVENT WERE MORE OF A HORIZ NATURE. THE FO MADE AN IMMEDIATE REQUEST FOR A LOWER ALT. THE SPD OF THE ACFT WAS EVENTUALLY SLOWED AND A DSCNT TO FL410 WAS INITIATED. ALTHOUGH I CANNOT BE CERTAIN; IT IS MY BELIEF THAT SUDDENNESS IN WHICH THIS EVENT OCCURRED RESULTED IN INCIPIENT MACH TUCK CAUSING THE NOSE TO LOWER AND ALT TO BE LOST WITH ALT HOLD ON THE AUTOPLT STILL ON. IT SHOULD ALSO BE RPTED THAT THERE WAS NO CONVECTIVE ACTIVITY PRESENT IN THE AREA.