FAA Airline Transport Pilot (ATM)Meteorology and Weather ServicesMedium
A dispatcher examining a surface analysis chart notes that isobars over the northern portion of the route are packed very closely together, while over the southern portion they are widely spaced. Assuming similar latitude and no other factors, the tightly packed isobars indicate
- AAn area of stagnant, calm air with no significant weather
- BThat a stationary occluded front is centered in that area
- CA stronger pressure gradient and stronger surface winds
- DA weaker pressure gradient and lighter surface winds
Show answer & explanationAnswer & explanation
Correct answer: C. A stronger pressure gradient and stronger surface winds
Isobar spacing on a surface analysis chart represents the pressure gradient force; closely spaced isobars indicate a steep pressure gradient, which corresponds to stronger surface winds, while widely spaced isobars indicate a weaker gradient and lighter winds.
Why the other options are wrong
- A. Stagnant, calm air corresponds to widely spaced isobars, not tightly packed ones.
- B. Isobar spacing alone does not indicate a frontal type; fronts are shown with specific line symbols, not spacing.
- D. This describes widely spaced isobars, the opposite of what is shown in the tightly packed area.
Isobar Spacing and Pressure Gradient
The distance between isobars on a surface analysis chart indicates the strength of the pressure gradient force, which directly relates to wind speed.
- Closely spaced isobars = steep gradient = strong winds
- Widely spaced isobars = weak gradient = light winds
- Isobars connect points of equal sea-level pressure
Memory trick: Tight isobars = tight rubber bands stretched hard, snapping wind fast.