FAA Sport Pilot Airplane (SPA)WeatherMedium
On a surface analysis chart, a pilot notices that isobars over a region are spaced very closely together. What does this indicate about surface wind conditions in that area?
- ALight and variable winds due to a weak pressure gradient
- BNo reliable relationship exists between isobar spacing and wind speed
- CCalm winds because closely spaced isobars indicate stable air
- DStrong winds due to a steep pressure gradient
Show answer & explanationAnswer & explanation
Correct answer: D. Strong winds due to a steep pressure gradient
Closely spaced isobars indicate a steep pressure gradient, meaning pressure changes rapidly over a short distance. This produces strong winds as air accelerates from high to low pressure; widely spaced isobars indicate a weak gradient and lighter winds.
Why the other options are wrong
- A. Closely spaced isobars indicate a strong, not weak, gradient.
- B. Isobar spacing is a standard, reliable indicator of wind speed on weather charts.
- C. Isobar spacing relates to wind speed, not atmospheric stability.
Pressure Gradient and Isobar Spacing
The distance between isobars on a chart indicates the strength of the pressure gradient force; closely spaced isobars mean stronger winds.
- Tight isobar spacing = steep gradient = strong wind
- Wide isobar spacing = weak gradient = light wind
- Wind flows roughly parallel to isobars aloft due to Coriolis balance
- Near the surface, friction causes wind to cross isobars at an angle toward low pressure
Memory trick: Tight lines, Tight squeeze, strong breeze!