Trimodal distribution of ozone and water vapor in the UT/LS during boreal summer

Timothy J Dunkerton

NorthWest Research Associates WARM SEASON

Tropical Tropopause Layer (TTL)

• Contains critical questions for atmospheric chemistry and climate

• Represents the gateway for constituents entering the middle atmosphere

• Composition and motion of air are influenced by a combination of tropospheric and stratospheric processes

• Extends vertically from the level of maximum convective outflow (200-250 hPa) to the cold point tropopause or, alternatively, to the highest altitude of convective clouds, which sometimes overshoot the tropopause

• Extends meridionally to the subtropical jet and tropopause break

• BOREAL SUMMER: jet and tropopause break are displaced well to the north, near 45°N, and thermodynamic characteristics of tropical air extend into midlatitudes

• BOREAL WINTER: rotational circulations more symmetric about equator, tropical tropopause temperatures attain their coldest values

Ping Chen (1995 JGR) studied isentropic mixing in the middle world using ECMWF analyses

overworldmiddle world

upper & lowermiddle world

PVU=2

DJF

Randel et al, 2001

Depletion byconvection

TransportInto tropics

High O3Wet

Low O3Wet

Low O3Dry

Randel et al, 2001

Low O3Wet

High O3Wet

Low O3Dry

Randel et al, 2001

Cross-isentropic transport associated with deep convection and cirrus in active monsoon regionscauses a provocative upward bulge of water vapor isopleths to isentropic surfaces lying above thetropical cold point. There are some interesting implications for the water-vapor tape recorder.

Randel et al, 2001

Summer hydration is contiguous tomoist phase of tape recorder head.

Randel et al, 2001

Gettelman et al, 2002

*coldest cloud top

“hot” spots*

Cold season convection near equator

Image courtesy Mark BaldwinImage courtesy Mark Baldwin

(used w/o permission)(used w/o permission)

solid: 30-90 E 20-40 Nopen: 30-105 E 15-45 N

HALOE levels 32-34

Preliminary conclusions from HALOE

• Warm-season hydration of UT/LS is observed in a shallow layer about the tropopause

• Visible after 1993, not due to Pinatubo aerosol contamination

• N American and S Asian monsoons contribute

• Asian summer monsoon is stronger and deeper

• Extreme events are more likely over Asia

• HALOE ozone agrees with SAGE: low ozone within Tibetan anticyclone, arm of higher O3 air drawn equatorward & westward over E China & Ind O

• Orbital pattern of data in midlatitudes suggests interannual variation, especially in local winter

• Spotty pattern of data in tropics and subtropical monsoon regions suggests local and episodic sources

• Origin of local anomalies unknown, possibly deep convection upstream