Tropopause altitude determination from temperature profile measurements of reduced vertical resolution

• Published in: Atmospheric measurement techniques Vol. 12; no. 7; pp. 4113 - 4129
• Main Authors: König, Nils, Braesicke, Peter, von Clarmann, Thomas
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 29-07-2019; Copernicus Publications
• Subjects: Altitude; Analysis; Atmospheric sounding; Displacement; Interferometers; Kernels; Lapse rate; Measurement; Methods; Mixing ratio; Pricing policies; Profiles; Radiosondes; Resolution; Saturation; Temperature; Temperature effects; Temperature measurement; Temperature profile; Temperature profile measurements; Temperature profiles; Tropical climate; Tropopause; Water vapor; Water vapour
• ISSN: 1867-8548; 1867-1381; 1867-8548
• DOI: 10.5194/amt-12-4113-2019

Inference of the lapse rate tropopause or the cold point from temperature
profiles of finite vertical resolution entails an uncertainty of the
tropopause altitude. For tropical radiosonde profiles the tropopause altitude
inferred from coarse-grid profiles was found to be lower than that inferred
from the original profiles. The mean (median) displacements of the lapse rate
tropopause altitude when inferred from a temperature profile of 3 km vertical
resolution and a Gaussian kernel are −130, −400, −730, and −590 m
(−70, −230, −390, and −280 m) for Nairobi, Hilo, Munich, and Greifswald,
respectively. In the case of a Michelson Interferometer for Passive Atmospheric
Sounding (MIPAS) averaging kernel, the displacement of the lapse
rate tropopause altitude is −640 m. The mean (median) displacement of the
cold point tropopause inferred from a temperature profile of 3 km vertical
resolution (Gaussian kernels) was found to be −510, −610, −530, and
−390 m (−460, −510, −370, and −280 m) for the stations mentioned above.
Unsurprisingly, the tropopause altitude displacement is larger for coarser
resolutions. The effect of the tropopause displacement on the water vapor
saturation mixing ratio is roughly proportional to the vertical resolution.
In tropical latitudes the resulting error is about 1 to 2 ppmv per vertical resolution in kilometers. The spread of the tropopause
displacements within each sample of profiles seems too large as to recommend
a correction
scheme for tropical temperature profiles, while for midlatitudinal temperature
profiles of vertical resolutions of 1 to 5 km a lapse rate of −1.3 K km−1
reproduces tropopause altitudes determined from high-resolution temperature
profiles with the nominal lapse rate criterion of −2 K km−1 fairly well.