It was feet per minute.
If you depart into a headwind, you benefit from the wind shear which produces a higher rate of climb, for a short time during which the aircraft inertia disipates.
Say the reported surface wind is a head-on 20kt. That is on a 10m (32ft) pole. The wind at say 1m (3ft) might be 10kt. The wind at say 200ft might be 30kt. So during the climb from the runway to 200ft (which takes something like 15-20 seconds) you have gained 20kt of airspeed, which given the trim remains essential unchanged will translate into a big temporary rise in VS.
During this time the ground speed drops off, because you are flying in an increasing headwind, so what happened is that you have traded kinetic energy for potential energy.
Has none of you looked at the VSI during takeoff?
That effect you describe is the same one you have with a windshear on approach, when the wind suddenly comes from behind and you have a higher sink rate for some moments. But I doubt it has much to do with this take-off
I knew what you intended when you posted that in the first place. 
However, a slight boost in headwind cannot increase the rate of climb from 1200 to 2500 fpm. If that happens, it is due to an updraft, but not (at least not entirely) due to a 20 knot increase in wind. Also, it would be very momentary thing. In a steady state, an aircraft will obviously have the same ROC irrespective of wind.
Peter, if I may, once you’re in the air, if the headwind increases your IAS won’t increase…
It will, momentatily. If the increase is sudden enough and you maintain the same pitch angle. It’s is then like a gust.
if the headwind increases your IAS won’t increase…
It does increase a bit but what happens is that if you fly into a wind shear (into an airflow which is speeding up) the aircraft gets a lot more lift (because the AoA is not being changed – the aircraft remains trimmed for the previous lower IAS) so it goes up (resulting in the increased VS).
I routinely see +2500fpm on a departure into a strong wind, and you feel it too.
Obviously in any steady state condition an aircraft is completely unaware of any wind, which is merely a movement between the airmass and the earth’s surface.
In theory it shouldn’t happen. In practice it does. I once took off from Cork with wind at 40G55Kt straight down the runway, a gust hit just as I became airborne and the VSI hit the top peg until passing 1500’. The forecast 2000’ wind was 80 kts. so the windshear was considerable. Normal ROC would be 1200fpm. However usually the effect is a lot less noticeable.
Slight thread drift but why does stalling speed reduce with the gear lowered?
In theory if the gear extends forward, this would result in a more forward CofG, resulting in more downforce from the tailplane, resulting in more lift required, resulting in a higher stall speed as you reach critical AoA sooner.
So my suggestion maybe a change in CAS with gear extended? Although no obvious reason as the pitot head shouldn’t be affected.
Some aircraft the main gear extends backwards, eg PA23, so there may be a small reduction of stall speed due to the CoG moving a bit further aft.
See the beechtalk thread and the reference to the famous J. Eckelbar book. On Bonanzas, gear down does seem to sensibly reduce stall speed.
Bosco correct, but he is not sure whether it is a calibration error, or a slight improvement in lift due to the main gear wells – in any event he indicates it is only around 4 knots.
