Air Masses of Asia

Asia’s vast size, varied topography, and strong seasonal contrasts make it a fascinating laboratory for studying air masses. The Himalayas, Siberian High, summer monsoons, and surrounding oceans all shape the behaviour of air masses here.

We’ll look at winter and summer separately.

A. Winter Air Masses

1. Continental Polar (cP)

Origin:

• Extensive cold regions of Siberia and Outer Mongolia.
• Extremely cold ground surface → very cold, dry, stable air.
• Lower ~1 km has temperature inversion (temperature increases with height) due to intense cooling.

Modification & Routes into China:

(i) Land Route:

• High pressure over Mongolia & North China.
• Air masses move directly over land → become warmer in China than in source region.
• Weather: Clear skies, dry, cold winds.
• Sometimes bring dust and sand from deserts → deposited as loess.
• Do not reach Indian subcontinent — Himalayas block them.

(ii) Sea Route:

• High pressure over Manchuria & Japan Sea.
• Air masses travel over Japan Sea & Yellow Sea → pick up moisture → warmer and more humid than land-route cP.
• Weather: Pleasant unless linked with fronts; unstable lower layers → precipitation when lifted over mountains.

Interaction:

• Land-route and sea-route cP masses converge along east coast → frontogenesis → cyclones → precipitation.

2. Maritime Polar (mP)

Origin:

• Sea of Okhotsk.

Winter Influence:

• Affects only coastal Siberia, Manchuria, and South Korea.
• Eastern Asia south of Korea is unaffected because:
  1. Winter winds blow offshore (west to east) — block westward spread.
  2. Sea-route cP air can acquire mP-like traits.

Special Case:

• Invade Japan in early summer; meet mT air → fronts → overcast, moist weather with light rain.

3. Maritime Tropical (mT)

Winter Influence:

• Limited to southern China.
• Warm, humid; but overshadowed by dominant cP air masses.
• More active in southwest Pacific & eastern Indonesia.

B. Summer Air Masses

1. Continental Polar (cP)

Source Shift:

• Warmer summer → source region shifts further north in central Asia.

Summer Behaviour:

• Enters China mainly via sea route from Japan Sea & Yellow Sea.
• Colder than mT air masses → associated with clear skies, little rain, and few thunderstorms.
• Can cause cyclonic conditions when converging with mT air.

2. Maritime Tropical (mT) — Dominant Summer Player

Origin & Path:

• Southern oceans; move north/northeast toward Asia.

Role in South & Southeast Asia:

• Known as summer monsoons.
• Warm, humid, unstable.
• Forced ascent over mountains (e.g., Western Ghats, Himalayas) → torrential rainfall.
• Heated from below after landfall → stronger convectional currents → thunderstorms.

Interactions:

• In central China (spring) and Manchuria (mid-summer), mT meets cP → cyclonic systems develop.

3. Maritime Polar (mP)

Origin:

• Sea of Okhotsk.

Summer Behaviour:

• More active in summer than winter.
• Influences eastern Asia north of 40°N — especially Manchuria & east Siberia.
• Extends to southern Japan in early summer, but later retreated northward by incoming mT monsoon air.

✅ In summary:

• Winter in Asia: Dominated by cP from Siberia/Mongolia — land-route ones are dry and dusty, sea-route ones are moist. mT air plays a minor role.
• Summer in Asia: Maritime Tropical (mT) becomes the weather king — driving the monsoon and heavy rains — while cP retreats north, and mP influences the far northeast.