Wind speed limitation in athletics goes back a long way. In the beginning of the 30s an experimental study showed that the (tail) wind velocity should be below 1 m/s so as not to offer a performance gain greater than 0.1 second. What was the rationale behind this? At that time the races were hand-timed and a new record could be homologated only if it improved upon the previous by 0.1 s. Hence the 1 m/s limit. However in the 1936 decision of the IAAF the maximum acceptable assisting wind velocity was fixed at 2 m/s. Going from 1 m/s to 2 m/s was a compromise decided by the IAAF congress so as not to have to invalidate too many performances. (A glance at the list of the all-time best performances over 100 m shows that roughly half of them were realised with a wind velocity in excess of 1 m/s, but still below the 2 m/s limit).
Speaking of compromises there is one that I find ridiculous. For combined events it is specified that the wind velocity in any individual event should not exceed 4 m/s. Moreover the average wind velocity (based on the algebraic sum of the wind velocities, as measured for each individual event, divided by the number of such events) must not exceed 2 m/s. Why on earth did they decide to use a different rule for combined events? Clearly that was a decision taken under pressure from influence groups i.e. elite athletes, their coaches and their federation officials. A most pathetic decision.
Before going back to to the 2 m/s limit let us summarise the rules for wind velocity measurement. According to the IAAF/WA rules
-All wind gauge equipment shall be manufactured and calibrated according to international standards. The accuracy of the measuring equipment used in the competition shall have been verified by an appropriate organisation accredited by the national measurement authority.
-Non-mechanical wind gauges shall be used at all major International Competitions and for any performance submitted for ratification as a World Record.
A mechanical wind gauge should have appropriate protection to reduce the impact of any crosswind. Where tubes are used, their length on either side of the measuring device should be at least twice the diameter of the tube.
-The Track Referee shall ensure that the wind gauge for Track Events is placed beside the straight, adjacent to lane 1, 50m from the finish line. The measuring plane shall be positioned 1.22 m ± 0.05 m high and not more than 2 m away from the track.
-The wind gauge may be started and stopped automatically and/or remotely, and the information conveyed directly to the competition computer.
-The periods for which the wind velocity shall be measured from the flash/smoke of the Starter’s gun are as follows:
Seconds 100 m 10, 100 m hurdles 13, 110 m hurdles 13
In the 200 m event, the wind velocity shall normally be measured for a period of 10 seconds commencing when the first athlete enters the straight.
-The wind gauge shall be read in metres per second, rounded to the next higher tenth of a metre per second, unless the second decimal is zero, in the positive direction (that is, a reading of +2.03 metres per second shall be recorded as +2.1; a reading of -2.03 metres per second shall be recorded as -2.0). Gauges that produce digital readings expressed in tenths of metres per second shall be constructed so as to comply with this Rule.
-For horizontal jumps the relevant Field Events Referee shall ensure that the wind gauge is placed 20 m from the take-off line. The measuring plane shall be positioned 1.22 m ± 0.05 m high and not more than 2 m away from the runway.
-The wind velocity shall be measured for a period of 5 seconds from
the time an athlete passes a mark placed alongside the runway, for the Long Jump 4 0m from the take-off line and for the Triple Jump 35 m. If an athlete runs less than 40 m or 35 m, as appropriate, the wind velocity shall be measured from the time he commences his run.
So, there you have it. The wind velocity is measured by one anemometer (wind gauge) and is recorded with a 0.1 m/s precision. All this was OK in the olden times when performances were recorded at 0.1 s. But how about today when records are homologated at a precision of 0.01 s? One can superficially conclude that if the wind velocity is measured with a 0.1 m/s precision the possible uncertainty on the final time is of the order of 5 milliseconds and thus should not have a "visible" effect. (Incidentally this calculation is one more argument against the use of milliseconds in track events). And if you wonder about horizontal jumps a 0.1 m/s uncertainty of the wind velocity would correspond to 0.5 cm for a 7-8 m long jump but already a full cm for triple jump. And as we know one cm suffices in order to improve an existing record.
But what are we talking about when we talk about a 0.1 m/s precision? This is the required precision of the measurement. While this is not unimportant the essential question is "what is the relation of the measured wind velocity to the real one?". And in particular in track events "do all the athletes experience the same assisting wind?". P.N. Linthorne performed as series of measurements placing two anemometers one at the position specified by the rules (next to the track, at 50 m from the finish line) and one in at 10 m, 30 m, 50 m, 70 m, or 90 m from the 100m start line, and on the line between lanes 2 and 3, or on the line between lanes 6 and 7. Due to the configuration of the stadium the wind gauges at the 90 m line were more sheltered for headwinds, and the wind gauges at the 10 m line were more sheltered for tail winds and more exposed for head winds. The figure below shows the relation between the official wind reading and a simultaneous wind reading from a second wind gauge placed at the 30 m line.
Where the two measurements identical, they should lie along the continuous line. The dispersion observed is far larger than the required 0.1 m/s precision. And moreover it does depend on the configuration of the stadium. (The only encouraging point of Linthorne's study is that there does not appear to be a significant difference between the measurements in lanes 2/3 and those in lanes 6/7. Thus all athletes in a given race experience essentially the same wind).
So, what should be done? The only fair solution would be to install a whole battery of anemometers along the track. Linthorne's choice of 10, 30, 50 70 and 90 m is a reasonable one. Moreover, instead of averaging over 10 s it would be preferable to take an instantaneous wind measurement as the runners pass next to each wind gauge. (For horizontal jumps doubling the number of anemometers, positioned at 30 and 10 m from the take-off board, appears necessary). Also, for major championships, a series of measurements like those of Linthorne would be necessary in order to establish the "wind force profile" of the stadium so as to know exactly how precise are the wind velocity measurements.
This is what should be done, instead of pretending that the single anemometer reading provides enough precision for records to be homologated in fairness.
A few years back I published a post on wind effects. In that article i made one of my "crazy" proposals, crazy meaning that I am aware that it has 0 % chance to be officially adopted one day. What I proposed was a correction for the wind velocity. Namely, based on a detailed biomechanical model, estimate the corrections to be applied to times registered in the presence of wind (be it tail- or head-wind) so as to evaluate the equivalent performances at “zero wind”. This is the only sustainable solution. And, of course, the first step towards its implementation would be to have a most accurate measure of wind velocity.
Speaking of compromises there is one that I find ridiculous. For combined events it is specified that the wind velocity in any individual event should not exceed 4 m/s. Moreover the average wind velocity (based on the algebraic sum of the wind velocities, as measured for each individual event, divided by the number of such events) must not exceed 2 m/s. Why on earth did they decide to use a different rule for combined events? Clearly that was a decision taken under pressure from influence groups i.e. elite athletes, their coaches and their federation officials. A most pathetic decision.
King Carl's non-homologated world record
Before going back to to the 2 m/s limit let us summarise the rules for wind velocity measurement. According to the IAAF/WA rules
-All wind gauge equipment shall be manufactured and calibrated according to international standards. The accuracy of the measuring equipment used in the competition shall have been verified by an appropriate organisation accredited by the national measurement authority.
-Non-mechanical wind gauges shall be used at all major International Competitions and for any performance submitted for ratification as a World Record.
A mechanical wind gauge should have appropriate protection to reduce the impact of any crosswind. Where tubes are used, their length on either side of the measuring device should be at least twice the diameter of the tube.
-The Track Referee shall ensure that the wind gauge for Track Events is placed beside the straight, adjacent to lane 1, 50m from the finish line. The measuring plane shall be positioned 1.22 m ± 0.05 m high and not more than 2 m away from the track.
-The wind gauge may be started and stopped automatically and/or remotely, and the information conveyed directly to the competition computer.
-The periods for which the wind velocity shall be measured from the flash/smoke of the Starter’s gun are as follows:
Seconds 100 m 10, 100 m hurdles 13, 110 m hurdles 13
In the 200 m event, the wind velocity shall normally be measured for a period of 10 seconds commencing when the first athlete enters the straight.
-The wind gauge shall be read in metres per second, rounded to the next higher tenth of a metre per second, unless the second decimal is zero, in the positive direction (that is, a reading of +2.03 metres per second shall be recorded as +2.1; a reading of -2.03 metres per second shall be recorded as -2.0). Gauges that produce digital readings expressed in tenths of metres per second shall be constructed so as to comply with this Rule.
-For horizontal jumps the relevant Field Events Referee shall ensure that the wind gauge is placed 20 m from the take-off line. The measuring plane shall be positioned 1.22 m ± 0.05 m high and not more than 2 m away from the runway.
-The wind velocity shall be measured for a period of 5 seconds from
the time an athlete passes a mark placed alongside the runway, for the Long Jump 4 0m from the take-off line and for the Triple Jump 35 m. If an athlete runs less than 40 m or 35 m, as appropriate, the wind velocity shall be measured from the time he commences his run.
So, there you have it. The wind velocity is measured by one anemometer (wind gauge) and is recorded with a 0.1 m/s precision. All this was OK in the olden times when performances were recorded at 0.1 s. But how about today when records are homologated at a precision of 0.01 s? One can superficially conclude that if the wind velocity is measured with a 0.1 m/s precision the possible uncertainty on the final time is of the order of 5 milliseconds and thus should not have a "visible" effect. (Incidentally this calculation is one more argument against the use of milliseconds in track events). And if you wonder about horizontal jumps a 0.1 m/s uncertainty of the wind velocity would correspond to 0.5 cm for a 7-8 m long jump but already a full cm for triple jump. And as we know one cm suffices in order to improve an existing record.
But what are we talking about when we talk about a 0.1 m/s precision? This is the required precision of the measurement. While this is not unimportant the essential question is "what is the relation of the measured wind velocity to the real one?". And in particular in track events "do all the athletes experience the same assisting wind?". P.N. Linthorne performed as series of measurements placing two anemometers one at the position specified by the rules (next to the track, at 50 m from the finish line) and one in at 10 m, 30 m, 50 m, 70 m, or 90 m from the 100m start line, and on the line between lanes 2 and 3, or on the line between lanes 6 and 7. Due to the configuration of the stadium the wind gauges at the 90 m line were more sheltered for headwinds, and the wind gauges at the 10 m line were more sheltered for tail winds and more exposed for head winds. The figure below shows the relation between the official wind reading and a simultaneous wind reading from a second wind gauge placed at the 30 m line.
Relation between the two wind readings
Where the two measurements identical, they should lie along the continuous line. The dispersion observed is far larger than the required 0.1 m/s precision. And moreover it does depend on the configuration of the stadium. (The only encouraging point of Linthorne's study is that there does not appear to be a significant difference between the measurements in lanes 2/3 and those in lanes 6/7. Thus all athletes in a given race experience essentially the same wind).
So, what should be done? The only fair solution would be to install a whole battery of anemometers along the track. Linthorne's choice of 10, 30, 50 70 and 90 m is a reasonable one. Moreover, instead of averaging over 10 s it would be preferable to take an instantaneous wind measurement as the runners pass next to each wind gauge. (For horizontal jumps doubling the number of anemometers, positioned at 30 and 10 m from the take-off board, appears necessary). Also, for major championships, a series of measurements like those of Linthorne would be necessary in order to establish the "wind force profile" of the stadium so as to know exactly how precise are the wind velocity measurements.
This is what should be done, instead of pretending that the single anemometer reading provides enough precision for records to be homologated in fairness.
A few years back I published a post on wind effects. In that article i made one of my "crazy" proposals, crazy meaning that I am aware that it has 0 % chance to be officially adopted one day. What I proposed was a correction for the wind velocity. Namely, based on a detailed biomechanical model, estimate the corrections to be applied to times registered in the presence of wind (be it tail- or head-wind) so as to evaluate the equivalent performances at “zero wind”. This is the only sustainable solution. And, of course, the first step towards its implementation would be to have a most accurate measure of wind velocity.
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