FAA Flight Instructor Airplane (FIA)Weather and Weather ServicesHard
A flight instructor is reviewing a surface analysis chart with a student and points out an area where the isobars are drawn very close together, in tight, parallel bands, over the route of flight. Based on this pattern, the student should expect which surface wind condition in that area?
- ACalm winds because closely spaced isobars indicate a stationary high
- BLight and variable winds due to a weak pressure gradient
- CStrong, gusty surface winds due to a steep pressure gradient
- DA land breeze forming from nighttime radiational cooling
Show answer & explanationAnswer & explanation
Correct answer: C. Strong, gusty surface winds due to a steep pressure gradient
The spacing of isobars on a surface chart indicates the pressure gradient force: closely spaced isobars represent a steep pressure gradient, which drives stronger winds as air accelerates from high to low pressure. Widely spaced isobars indicate a weak gradient and light winds.
Why the other options are wrong
- A. Isobar spacing does not indicate a stationary high; it indicates gradient strength regardless of pressure system type.
- B. Light and variable winds are associated with widely spaced isobars, the opposite condition.
- D. A land breeze is a local thermal circulation, unrelated to isobar spacing on a synoptic chart.
Pressure Gradient and Isobar Spacing
The pressure gradient force is the rate of pressure change over distance; it is depicted on charts by isobar spacing, with closer isobars indicating a steeper gradient and stronger winds.
- Closely spaced isobars = steep gradient = strong winds
- Widely spaced isobars = weak gradient = light winds
- Wind flows from high to low pressure, modified by Coriolis and friction
Memory trick: Isobars packed tight like fence pickets = wind whistling hard through the gaps