My 10cents worth.
Wind speed as measured by an anemometer (hand held or meteorological) is simply the number and speed of molecules of air hitting the paddles or cups of the instrument. The more molecules or the faster they are, the faster it spins and the higher the reading.
Hotter air is less dense so less molecules will hit the paddles for a given speed of wind. Thus reducing the reading slightly in less dense air and increasing it in more dense air. IE the anemometer measures exactly the same factors that affect the kite. 20 knots measured whether hot or cold, dense or thin means X number of molecules hitting the kite at a certain speed. Thus 20 knots is 20 knots hot or cold for both the anemomenter AND the kite.
However! There does seem to be a difference in summer and winter in the pull of the kite in 20kts of wind. A possible explanation is the point at which the wind is measured. The only wind that matters to us is the breeze at kite level. This can be quite a bit stronger than the wind at sea level. For example the wind at the airport is measured at 50 feet above mean sea level.
Your hend held instrument measures the breeze at sea level. This is why the breeze at Dolls never seems as strong as the graph indicates for the airport.
Colder air is less "sticky" than hot air, so there is a grater gradient or difference in wind speed as height changes. This means that in cold air your hand held might show 20kt but at kite level there might be 25kt. In hot "sticky" air you might show 20kt and at kite level have 21kt.
Cofused? I am!
