Tropopause altitude determination from temperature profile measurements of reduced vertical resolution

König, Nils; Braesicke, Peter; Clarmann, T. von

doi:10.5194/amt-12-4113-2019

Cited by 5 publications

(5 citation statements)

References 24 publications

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“…However, the magnitude of the warm bias is roughly 2-3 times smaller compared to Bland et al (2021). This difference may be related to vertical smoothing of the radiosonde profiles in Bland et al (2021), which could lead to a higher tropopause temperature (König et al, 2019). Large N² biases (-2 to 3x10 -4 s -2 ) in the analysis are found in the ±0.5 km layer around the tropopause.…”

Section: Discussionmentioning

confidence: 77%

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Influence of radiosonde observations on the sharpness and altitude of the midlatitude tropopause in the ECMWF IFS

Krüger,

Schäfler,

Weissmann

et al. 2023

Preprint

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Abstract. Initial conditions of current numerical weather prediction systems insufficiently represent the sharp vertical gradients across the midlatitude tropopause. Data assimilation may provide a means to improve the tropopause structure by correcting the erroneous background forecast towards the observations. In this paper, the influence of assimilating radiosonde observations on the tropopause structure, i.e., the sharpness and altitude, is investigated in the ECMWF IFS. We evaluate 9729 midlatitude radiosondes launched during one month in autumn 2016. About 500 of these radiosondes, launched on request during the North Atlantic Waveguide Downstream impact Experiment (NAWDEX) field campaign, were used to set up an observing system experiment (OSE). The OSE comprises two cycled assimilation forecast experiments, one with and one without the non-operational soundings. The influence on the tropopause is assessed in a statistical, tropopause–relative evaluation of observation departures of temperature, static stability (N2), wind speed and wind shear from the background forecast and the analysis. The background temperature is overestimated at the tropopause (warm bias, ~1 K) and underestimated in the lower stratosphere (cold bias, −0.3 K) leading to an underestimation of the abrupt vertical increase of N2 at the tropopause. We show that the increments (differences of analysis and background) reduce background biases and improve the tropopause sharpness. Profiles with sharper tropopause exhibit stronger background biases and, in turn, an increased positive influence of the observations on temperature and N2 in the analysis. Wind speed is underestimated in the background, especially in the upper troposphere (~1 m s−1), but the assimilation improves the wind profile. For the strongest winds the background bias is roughly halved. The positive influence on the analysis wind distribution is associated with an increase of vertical wind speed shear, which is underestimated above the tropopause. In addition to the tropopause sharpening, we detect a shift of the analysis tropopause altitude towards the observations. The comparison of the OSE runs highlights that the main contribution to the tropopause sharpening can be attributed to the radiosondes. This study shows that data assimilation improves wind and temperature gradients across the tropopause, but the sharpening is small compared to the model biases. Hence, the analysis still systematically underestimates the tropopause sharpness which may negatively impact weather and climate forecasts.

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Section: Discussionmentioning

confidence: 77%

“…Bland et al (2021) showed a higher tropopause altitude of about 200 m in IFS analyses using a previous model cycle (Cy41r2) and 3204 radiosondes that are a subset of the data set analysed in this study. Again, the differing results may be related to the vertical smoothing of the radiosonde profiles (König et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

Influence of radiosonde observations on the sharpness and altitude of the midlatitude tropopause in the ECMWF IFS

Krüger,

Schäfler,

Weissmann

et al. 2023

Preprint

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“…Of course, the new method can also assist the researches on tropopause inversion layer characteristics. o N], which may be related to the different vertical resolution of temperature profiles provided by various data sources (König et al, 2019;Hoffmann and Spang, 2022;Pan et al, 2004;Wang et al, 2019). Moreover, tropopause structures over the Tibetan Plateau differ from those in the same latitudinal zone, likely due to unique atmospheric circulation structures such as the Asian summer monsoon anticyclone, planetary wave breaking and uploading, orographic gravity waves, and atmospheric temperature disturbances in the UTLS.…”

Section: Discussionmentioning

confidence: 99%

A novel method to detect the tropopause structure based on bi-Gaussian function

Zhang,

Luo,

et al. 2024

Preprint

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Abstract. The tropopause is important as a diagnostic of the upper troposphere and lower stratosphere structures, with unique atmospheric thermal, dynamic structures. A comprehensive understanding of the evolution of the fine tropopause structures is necessary and primary to further study the complex multi-scale atmospheric physicochemical coupling processes in the upper troposphere and lower stratosphere. Utilizing the bi-Gaussian function, a novel method is capable of identifying the characteristic parameters of tropopause vertical structures, as well as providing the information of double tropopauses (DT) structures. The new method improves the definition of cold point tropopause, and detects one (or two) most significant local coldest point(s) in mathematical statistics by fitting the temperature profiles to the bi-Gaussian function, which is (are) defined as the tropopause height(s). The bi-Gaussian function exhibits remarkable potential for explicating the variation trend of temperature profiles. The recognition results of the bi-Gaussian method and lapse rate tropopause, as defined by World Meteorological Organization, are compared in detail for different cases. Results indicate that the bi-Gaussian method possesses a lower missed detection rate and false detection rate than lapse rate tropopause, because it is not restricted by thresholds, even in the presence of multiple temperature inversion layers at higher elevations. Five-year (from 2012 to 2016) historical radiosondes in China revealed that the occurrence frequency and thickness of DT, as well as the single tropopause height, and the first and second DT height displayed significant meridional monotonic variations. The occurrence frequency (thickness) of DT increased from 2.93 % (2.61 km) to 72.45 % (6.84 km) in the latitude range [16° N, 50° N]. At mid-latitudes [30° N, 40° N], the meridional gradients of tropopause height were relatively large, essentially corresponding to the climatological location of the subtropical jet and Tibetan Plateau. The average DT thickness reported in this study is approximately 1–2 km thicker than that in previous studies, particularly in the mid-high latitudes [45° N, 50° N], which may be related to the different vertical resolution of temperature profiles provided by various data sources. DT structure occurs most frequently and has the largest meridional gradient in the mid-latitudes, formatted by a combination of poleward advection in the low-latitude upper troposphere and equatorward advection in the high-latitude lower stratosphere. In addition, although DT is thick in winter, the DT temperature difference is small, even the case of the first tropopause temperature is lower than the second tropopause temperature happens occasionally.

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“…Instead of only focusing on the average temperature lapse rates, we define the temperature‐based tropopause as the pressure above the boundary layer at which: dT/dh crosses from being negative to being positive. This effectively corresponds to the so‐called “cold‐point tropopause” which is often used instead of the WMO definition for tropical regions (Highwood & Hoskins, 1998; Kim & Son, 2012; Laura L. Pan et al., 2018; Mehta et al., 2008; Zhou et al., 2001), but can also be used for extratropical regions (König et al., 2019). dT/dh and dT/dP begin to oscillate wildly. …”

Section: Methodsmentioning

confidence: 99%

“…dT/dh crosses from being negative to being positive. This effectively corresponds to the so‐called “cold‐point tropopause” which is often used instead of the WMO definition for tropical regions (Highwood & Hoskins, 1998; Kim & Son, 2012; Laura L. Pan et al., 2018; Mehta et al., 2008; Zhou et al., 2001), but can also be used for extratropical regions (König et al., 2019).…”

Section: Methodsmentioning

confidence: 99%

Comparing Different Tropopause Estimates From High‐Resolution Ozonesondes

Connolly,

Dingley,

Connolly

et al. 2024

Earth and Space Science

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Since the tropopause was first identified, the quality and resolution of weather balloons has dramatically improved. NOAA Earth System Research Laboratories (ESRL) have provided high resolution and very high quality ozonesondes from eight locations: Fiji; American Samoa; Greenland; Antarctica; and several locations in USA (Hawai'i, Colorado, California and Alabama). These locations collectively cover polar regions, mid‐latitudes and tropics. Using this publicly archived data set, we studied the variability of the tropopause for all eight locations for one complete year (2016). Along with the standard estimates of the tropopause provided by NOAA ESRL, we developed four alternative tropopause definitions each based on changes in one of the following: (a) molar density; (b) temperature lapse rates; (c) water vapor content; (d) ozone content. These old and new tropopause definitions appear to hold over all eight locations—for all seasons and from the tropics to the poles. The cohesiveness between all five of these independent tropopause definitions is remarkable, although the NOAA ESRL estimates sometimes identify higher tropopause onsets than the other estimates. Therefore, each tropopause definition could potentially be used as proxies for other tropopause definitions. However, it also confirms that the troposphere/tropopause transition is a multi‐faceted physical and chemical phenomenon associated with more than just temperature changes. Finally, these high‐resolution results suggest that the original term “tropopause” might be a misnomer since they suggest increases in temperature lapse rate variability, rather than the “pausing” implied by lower resolution data or by lapse rates that are averaged over large distances.

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Tropopause altitude determination from temperature profile measurements of reduced vertical resolution

Cited by 5 publications

References 24 publications

Influence of radiosonde observations on the sharpness and altitude of the midlatitude tropopause in the ECMWF IFS

Influence of radiosonde observations on the sharpness and altitude of the midlatitude tropopause in the ECMWF IFS

A novel method to detect the tropopause structure based on bi-Gaussian function

Comparing Different Tropopause Estimates From High‐Resolution Ozonesondes

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