A320 FLT CREW ENCOUNTERS TURB JETSTREAM ACTIVITY AT ALT. AIRSPD DETERIORATES TO THE V ALPHA PROT RANGE (HIGH ANGLE OF ATTACK; STALL AREA). FLT CREW IS FORCED TO DSND TO GAIN AIRSPD BACK.

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AT FL370 WE WERE GIVEN A 070 DEG HDG FOR SPACING TO ORD. THERE WERE A LOT OF PIREPS FOR LIGHT TO MODERATE TURB ASSOCIATED WITH THE JETSTREAM AS WELL AS MOUNTAIN WAVE ACTIVITY. WE WERE ALSO ASSIGNED A SPD OF MACH .74; BUT THE CAPT TOLD CTR WE COULD ONLY GIVE THEM MACH .75. (MACH .74 WOULD HAVE BEEN TOO CLOSE TO V ALPHA PROT). I LOOKED AT MY PFD AND NOTICED A DROP OF 20 KTS OF AIRSPD WHICH PUT OUR SPD VERY CLOSE TO V ALPHA PROT. I DISCONNECTED THE AUTOPLT AND BEGAN A SHALLOW DSCNT TO BUILD UP SPD. I TOLD THE CAPT TO TELL CTR WE WERE DSNDING. WE WERE DOING 200-300 FPM DOWN. THE CAPT RESPONDED 'WAIT JUST A MIN.' I THEN LOOKED AT THE EPR ON THE UPPER ECAM DISPLAY AND THE AUTOTHRUST WAS ALREADY COMMANDING THE MAX EPR LIMIT. THE CAPT TOLD ME TO DISCONNECT THE AUTOTHROTTLES. AFTER DOING SO; I REALIZED THAT WE NEEDED MORE THRUST; SO I WENT TO TOGA; WHICH YIELDED NO FURTHER INCREASE. I THEN SET MCT AND HAD NO OTHER OPTION BUT TO CONTINUE TO SACRIFICE ALT FOR AIRSPD AT APPROX FL365 ATC SAID THAT WE WERE 500 FT LOW. THE CAPT SAID 'STAND BY.' WE WERE THEN GIVEN A DIRECT CLRNC. WE DECIDED TO STAY ON THE HDG BECAUSE IF WE TURNED; THAT WOULD HAVE DECREASED V ALPHA PROT ENOUGH TO BRING US CLOSER TO STALL. AFTER THE AIRSPD RECOVERED; I BEGAN A CLB BACK TO FL370. DURING THIS EVENT THERE WAS ONLY LIGHT CHOP. THE AIRSPD DECREASE WAS DUE TO WINDSHEAR ASSOCIATED WITH THE JETSTREAM. THE WIND VELOCITY DECREASED APPROX 30 KTS IN A SHORT DISTANCE. AFTER WE RPTED THE SHEAR TO ATC; AN ACR FLT RPTED THE SAME AND SAID THAT THEY HAD TO GO TO MCT AS WELL EARLIER. THEY DID NOT RPT A PIREP DURING THEIR OCCURRENCE; HOWEVER. WE ALSO MADE A RPT TO DISPATCH. WE DID NOT EXCEED ANY AIRSPD OR ENG LIMITS TO MY KNOWLEDGE AND DID NOT TRIGGER V ALPHA PROT.