Tropopause Height Diagnostics

Motivation

• tropopause is important feature of the observed atmosphere

• determined by conditions in both tropo- and stratosphere

• position of tropopause is relevant for climate studies:

e.g. cross tropopause transport

indicator of climate change

Method

• apply same criterion as for determination from radiosondes:

a. lowest level at which lapse rate decreases to 2 K/km b. 2 km deep layer above must not exceed critical lapse rate

• problem of coarse vertical resolution > vertical interpolation

• limit for heights to be valid: 450-75 hPa failure rate: overall 0.1%, mostly over Antarctica during JJA

• rms: 30-40 hPa in extratropics, 10-20 hPa in tropics

Input Data

• 3D temperature field: daily or monthly data

• all comparisons on standard pressure levels

Tropopause pressure (hPa)daily reanalysis-1: CDC vs. TJR

DJF 1983-1998 JJA

CD

CT

JR

DJF 1983-1998 JJA

reanalysis-1 vs. reanalysis-2re

an.

2re

an.

1

DJF 1983-1998 JJA

reanalysis-1: daily vs. monthly datam

on

thly

dat

ad

aily

dat

a

DJF 1983-1998 JJA

p11/exp55danA

M2

mo

nth

lyr1

mo

nth

ly

DJF 1983-1998 JJA

exp42 vs. exp55danex

p42

- r

1ex

p55

dan

- r

1

DJF 1983-1998 JJA

p12L32_3 vs. exp55danp

12L

32_3

- r

1ex

p55

dan

- r

1

DJF 1983-1998 JJA

CAM 2.0.1C

AM

mo

nth

lyr1

mo

nth

ly

DJF 1983-1998 JJA

NSIPPN

SIP

P m

on

thly

r1 m

on

thly

DJF 1983-1998 JJA

NCEP SFMS

FM

mo

nth

lyr1

mo

nth

ly

Summary

rms exp55 exp42 p12L32 CAM2 NSIPP SFM

DJF 16 19 26 22 20 42

JJA 13 16 25 11 16 40

• AM2 tropopause height is generally too low (too high pressure), consistent with a too cold troposphere and too warm stratosphere

• biases over northern extratropics: +30 hPa in DJF (ca. -600 m) +10 hPa in JJA (ca. -200 m)

• tropical biases: +8 hPa in DJF (ca. -600 m) +3 hPa in JJA (ca. -200 m)

• biases over southern extratropics: -20 hPa in DJF +20 hPa in JJA

• global mean rms of tropopause pressure (hPa):