Air Masses, Fronts and Synoptic Systems
This domain tests air-mass classification, the weather sequence at each frontal type, and the synoptic patterns that produce them.
Air masses
Source regions give continental Arctic or Polar (cold, dry), maritime Polar (cold, moist), maritime Tropical (warm, moist) and continental Tropical (hot, dry) air. Pakistan receives cT air over Sindh and Balochistan in summer, mT monsoon air from the Arabian Sea, and cP air from Central Asia in winter.
Fronts
A cold front has a steep slope near 1:50, a narrow belt of heavy showery rain, squall-line gusts, cumulonimbus, a wind veer, a pressure fall then rise, and good visibility behind. A warm front has a shallow slope of 1:100 to 1:150, a wide belt of stratiform cloud (cirrus, cirrostratus, altostratus, nimbostratus), steady rain, poor visibility and a temperature rise after passage. An occluded front forms when the cold front catches the warm front and brings complex weather. A stationary front gives prolonged cloud and rain.
Worked example
A station reports south-east wind force 3, steadily falling pressure, and cirrus thickening into cirrostratus. Twelve hours later altostratus appears, then nimbostratus with continuous rain: this is the classic warm-front approach. After passage the wind veers to south-west, temperature rises 3°C, pressure steadies and rain turns to drizzle.
Traps
Wind veers at both cold and warm front passage in the Northern Hemisphere; the cold front has the steeper slope and narrower rain belt; the warm-front cloud sequence runs cirrus to cirrostratus to altostratus to nimbostratus, never the reverse.