Regionally Varying Assessments of Upper-Level Tropical Width in Reanalyses and CMIP5 Models Using a Tropopause Break Metric

Martin, Elinor R.; Homeyer, Cameron R.; McKinzie, R.; McCarthy, Kevin M.; Xian, Tao

doi:10.1175/jcli-d-19-0629.1

Cited by 6 publications

(18 citation statements)

References 64 publications

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“…in the remaining reanalyses. Moreover, the dipole is consistent with significant narrowing of the tropics over the eastern Pacific that has been identified in the reanalyses via subtropical jet and tropopause break analysis (Manney and Hegglin, 2018;Martin et al, 2018).…”

Section: Eulerian Mean Tropopause Altitude Trendssupporting

confidence: 80%

Global Tropopause Altitudes in Radiosondes and Reanalyses

Tang¹,

Homeyer²

2018

Preprint

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<p><strong>Abstract.</strong> Accurate depictions of the tropopause and its changes are important for studies such as stratosphere-troposphere exchange and climate change.Here, the fidelity of primary lapse-rate tropopause altitudes and double tropopause frequencies in four modern reanalyses (ERA-Interim, JRA-55, MERRA-2, and CFSR) is examined using global radiosonde observations. In addition, long-term trends (1981&#8211;2015) in these tropopause properties are diagnosed in both the reanalyses and radiosondes. It is found that ERA-Interim, JRA-55, and CFSR reproduce observed tropopause altitudes with little bias and error comparable to the model vertical resolution, while MERRA-2 tropopause altitudes are biased 500&#8211;600&#8201;m high. All reanalyses underestimate the double tropopause frequency (up to 30&#8201;% lower than observed), with the largest biases found in JRA-55 and the smallest in CFSR. The underestimates in double tropopause frequency are primarily attributed to the coarse vertical resolution of the reanalyses. Significant increasing trends in both tropopause altitude (40&#8211;120&#8201;m per decade) and double tropopause frequency (&#8805;&#8201;3&#8201;% per decade) were found in both the radiosonde observations and reanalyses over the 35-year analysis period. ERA-Interim, JRA-55, and MERRA-2 broadly reproduce the patterns and signs of observed significant trends, while CFSR is inconsistent with the remaining datasets. These trends were diagnosed in both the native Eulerian coordinate system of the reanalyses and in a relative latitude coordinate system where the tropopause break (the discontinuity in tropopause altitude between the tropics and extratropics) was used as the reference latitude in each hemisphere. The tropopause break-relative coordinate facilitates the evaluation of tropopause behavior within the tropical and extratropical reservoirs and revealed significant differences in trend estimates compared to the traditional Eulerian analysis. Notably, increasing tropopause altitude trends were found to be of greater magnitude in tropopause break-relative coordinates and increasing double tropopause frequency trends were found to occur primarily poleward of the tropopause break in each hemisphere.</p>

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Section: Eulerian Mean Tropopause Altitude Trendssupporting

confidence: 80%

Global Tropopause Altitudes in Radiosondes and Reanalyses

Tang¹,

Homeyer²

2018

Preprint

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“…The subtropical tropopause altitudes increase as the STJ shifts poleward, resulting in a broader Hadley Cell according to Held [10]. Longitudinal variability in the amount of Hadley Cell expansion was also noted with this methodology [54]. Fu and Lin [56] found a significant cooling in the lower stratosphere due to the subtropical jet poleward shifting, and thus the maximum cooling (LST) can be adopted to represent the Hadley Cell edge.…”

Section: Thermal Metricsmentioning

confidence: 95%

“…In the subtropical upper troposphere, there is a sharp discontinuity of lapse rate tropopause [51] near the STJ known as the "tropopause break" TPB; [52][53][54], where the tropopause altitudes change from the tropical one to the extratropical one well below abruptly. For simplicity, the latitude where the tropopause altitudes have a given threshold (e.g., Z 15 ) is used to locate the Hadley Cell edge [55].…”

Section: Thermal Metricsmentioning

confidence: 99%

“…In addition, the latitude of subtropical minimum in the probability density function (PDF) of tracer concentration is employed to define the Hadley Cell edge [60,61]. More recently, the PDF method is also employed to locate the tropopause break latitude [54]. The 1σ method's edge generally lies polewards of the GWL metrics, while the PDF method locations are on the equatorwards of the GWL metrics.…”

Section: Chemical Metricsmentioning

confidence: 99%

“…Modern reanalyses are not free from these shortcomings. Considerable variability is presented in the strength and width of the Hadley Cell within the different products [54,70,71]. Simpler metrics, such as changes to the mean jet stream position, are better-captured by the reanalyses and have less scatter in the estimates.…”

Section: Reanalysismentioning

confidence: 99%

See 2 more Smart Citations

Is Hadley Cell Expanding?

et al. 2021

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This review provides a comprehensive coverage of changes of the Hadley Cell extent and their impacts on the weather, climate, and society. The theories predicting the Hadley Cell width are introduced as a background for the understanding of the circulation changes and the metrics used for detection. A variety of metrics derived from various data sources have been used to quantify the Hadley Cell width. These metrics can be classified as dynamical, hydrological, thermal, and chemical metrics, based on the properties of the variables used. The dynamical metrics have faster trends than those based on thermal or hydrological metrics, with the values exceeding 1 degree per decade. The hydrological metric edge poleward trends were found a slightly faster expansion in the Northern Hemisphere than its southern counterpart. The chemical metrics show a poleward trend of more than 1 degree per decade in both hemispheres. We also suggest a few reasons for the discrepancy among trends in Hadley Cell expansion found in previous studies. Multiple forcings have been found responsible for the expansion, which seems to be more attributed to the natural variability than anthropogenic forcing. Validation of the scaling theories by the trends in Hadley Cell width suggests that theories considering the extratropical factor would be better models for predicting the Hadley Cell width changes. The Hadley Cell has an impact on different atmospheric processes on varying spatio-temporal scales, ranging from weather to climate, and finally on society. The remaining questions regarding Hadley Cell climate are briefly summarized at the end.

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Variability and trends of the tropical tropopause derived from a 1980–2021 multi-reanalysis assessment

Zou,

Hoffmann,

Müller

et al. 2023

Front. Earth Sci.

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As the tropopause plays a key role in regulating the entry of air from the troposphere into the stratosphere and in controlling stratosphere-troposphere exchange, variation of the tropopause impacts the atmospheric dynamics, circulation patterns, and the distribution of greenhouse gases in the upper troposphere and lower stratosphere (UTLS). Therefore, it is of particular interest to investigate the climatological characteristics and trends of the tropopause. Previous studies have investigated the tropopause characteristics using reanalyses and multi-source observations. This study extends the analysis of long-term variability and trends of tropical tropopause characteristics in earlier studies from 1980 up to 2021 using the modern ERA5 reanalysis and compares the results with those of other reanalyses, including ERA-Interim, MERRA-2, and NCEP1/2. Our analysis reveals a general rise and cooling of the tropical tropopause between 1980 and 2021. The geopotential height has increased by approximately 0.06 ± 0.01 km/decade (at a 95% confidence level), while the temperature has decreased by −0.09 ± 0.03 K/decade (at a 95% confidence level) for both the lapse rate tropopause and the cold point tropopause in ERA5. However, from 2006 to 2021, ERA5 shows a warming tropical tropopause (0.10 ± 0.11 K/decade) along with a slower rise in tropopause height (0.05 ± 0.02 km/decade) (at a 95% confidence level). Furthermore, our analysis demonstrates a decline in the rise and cooling of the tropical tropopause since the late 1990s, based on moving 20-year window trends in ERA5. Similar trends are observed in other investigated reanalyses. In addition, this study evaluated the variability of the width of the tropical belt based on tropopause height data from the reanalyses. The ERA5 data show a narrowing tropical belt (−0.16 ± 0.11°/decade) for the time period 1980–2021 according to the relative threshold method. It reveals a tropical widening (0.05 ± 0.22°/decade) for the period between 1980 and 2005, followed by a tropical narrowing (−0.17 ± 0.42°/decade) after 2006. However, the large uncertainties pose a challenge in drawing definitive conclusions on the change of tropical belt width. Despite the many challenges involved in deriving the characteristics and trends of the tropopause from reanalysis data, this study and the open reanalysistropopause data sets provided to the community will help to better inform future assessments of stratosphere-troposphere exchange and studies of chemistry and dynamics of the upper troposphere and lower stratosphere region.

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Regionally Varying Assessments of Upper-Level Tropical Width in Reanalyses and CMIP5 Models Using a Tropopause Break Metric

Cited by 6 publications

References 64 publications

Global Tropopause Altitudes in Radiosondes and Reanalyses

Global Tropopause Altitudes in Radiosondes and Reanalyses

Is Hadley Cell Expanding?

Variability and trends of the tropical tropopause derived from a 1980–2021 multi-reanalysis assessment

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