scholarly journals On the Signatures of Equatorial and Extratropical Wave Forcing in Tropical Tropopause Layer Temperatures

2013 ◽  
Vol 70 (4) ◽  
pp. 1084-1102 ◽  
Author(s):  
Kevin M. Grise ◽  
David W. J. Thompson
Keyword(s):  
Reanalysis Data ◽  
Planetary Waves ◽  
Large Temperature ◽  
Equatorial Waves ◽  
Vertical Resolution ◽  
Tropical Tropopause Layer ◽  
Temperature Anomalies ◽  
Tropical Tropopause ◽  
Asymmetric Component ◽  
High Vertical Resolution

Abstract Temperatures in the tropical tropopause layer (TTL) play an important role in stratosphere–troposphere exchange and in the formation and maintenance of thin cirrus clouds. Many previous studies have examined the contributions of extratropical and equatorial waves to the TTL using coarse-vertical-resolution satellite and reanalysis data. In this study, the authors provide new insight into the role of extratropical and equatorial waves in the TTL using high-vertical-resolution GPS radio occultation data. The results examine the influence of four different wave forcings on the TTL: extratropical waves that propagate vertically into the stratosphere, extratropical waves that propagate meridionally into the subtropical stratosphere, extratropical waves that propagate meridionally into the subtropical troposphere, and the equatorial planetary waves. The vertically and meridionally propagating extratropical stratospheric waves are associated with deep, zonally symmetric temperature anomalies that extend and amplify with height throughout the lower-to-middle tropical stratosphere. In contrast, the extratropical tropospheric waves and the equatorial planetary waves are associated with tropical temperature anomalies that are confined below 20-km altitude. The equatorial planetary waves dominate the zonally asymmetric component of the TTL temperature field, and both the equatorial planetary waves and the extratropical tropospheric waves are linked to large temperature variability in a 1–2-km-deep layer near the tropical tropopause. The fine vertical scale of the TTL temperature features associated with the equatorial planetary waves and the extratropical tropospheric waves is only readily apparent in high-vertical-resolution data.

scholarly journals In situ observation of new particle formation (NPF) in the tropical tropopause layer of the 2017 Asian monsoon anticyclone – Part 1: Summary of StratoClim results

2021 ◽  
Vol 21 (15) ◽  
pp. 11689-11722
Author(s):  
Ralf Weigel ◽  
Christoph Mahnke ◽  
Manuel Baumgartner ◽  
Antonis Dragoneas ◽  
Bärbel Vogel ◽  
...  
Keyword(s):  
Asian Monsoon ◽  
Particle Formation ◽  
In Situ Observation ◽  
Aerosol Layer ◽  
New Particle Formation ◽  
Tropical Tropopause Layer ◽  
Temperature Anomalies ◽  
Nucleation Mode ◽  
Tropical Tropopause

Abstract. During the monsoon season of the year 2017 the airborne StratoClim mission took place in Kathmandu, Nepal, with eight mission flights of the M-55 Geophysica in the upper troposphere–lower stratosphere (UTLS) of the Asian monsoon anticyclone (AMA) over northern India, Nepal, and Bangladesh. More than 100 events of new particle formation (NPF) were observed. In total, more than 2 h of flight time was spent under NPF conditions as indicated by the abundant presence of nucleation-mode aerosols, i.e. with particle diameters dp smaller than 15 nm, which were detected in situ by means of condensation nuclei counting techniques. Mixing ratios of nucleation-mode particles (nnm) of up to ∼ 50 000 mg−1 were measured at heights of 15–16 km (θ ≈ 370 K). NPF was most frequently observed at ∼ 12–16 km altitude (θ ≈ 355–380 K) and mainly below the tropopause. Resulting nnm remained elevated (∼ 300–2000 mg−1) up to altitudes of ∼ 17.5 km (θ ≈ 400 K), while under NPF conditions the fraction (f) of sub-micrometre-sized non-volatile residues (dp > 10 nm) remained below 50 %. At ∼ 12–14 km (θ ≈ 355–365 K) the minimum of f (< 15 %) was found, and underneath, the median f generally remains below 25 %. The persistence of particles at nucleation-mode sizes is limited to a few hours, mainly due to coagulation, as demonstrated by a numerical simulation. The frequency of NPF events observed during StratoClim 2017 underlines the importance of the AMA as a source region for UTLS aerosols and for the formation and maintenance of the Asian tropopause aerosol layer (ATAL). The observed abundance of NPF-produced nucleation-mode particles within the AMA is not unambiguously attributable to (a) specific source regions in the boundary layer (according to backward trajectory analyses), or (b) the direct supply with precursor material by convective updraught (from correlations of NPF with carbon monoxide), or (c) the recent release of NPF-capable material from the convective outflow (according to air mass transport times in the tropical tropopause layer, TTL). Temperature anomalies with ΔT of 2 K (peak-to-peak amplitude), as observed at a horizontal wavelength of ∼ 70–100 km during a level flight of several hours, match with NPF detections and represent an additional mechanism for local increases in supersaturation of the NPF precursors. Effective precursor supply and widely distributed temperature anomalies within the AMA can explain the higher frequency of intense NPF observed during StratoClim 2017 than all previous NPF detections with COPAS (COndensation PArticle counting System) at TTL levels over Brazil, northern Australia, or West Africa.

scholarly journals Effect of tropical cyclones on the tropical tropopause parameters observed using COSMIC GPS RO data

2015 ◽  
Vol 15 (18) ◽  
pp. 10239-10249 ◽  
Author(s):  
S. Ravindra Babu ◽  
M. Venkat Ratnam ◽  
G. Basha ◽  
B. V. Krishnamurthy ◽  
B. Venkateswararao
Keyword(s):  
Tropical Cyclones ◽  
Lower Stratosphere ◽  
Thermal Structure ◽  
Radial Distance ◽  
Lapse Rate ◽  
Tropical Tropopause Layer ◽  
Water Vapour Transport ◽  
Tropical Tropopause ◽  
High Vertical Resolution ◽  
Cold Point

Abstract. Tropical cyclones (TCs) are deep convective synoptic-scale systems that play an important role in modifying the thermal structure, tropical tropopause parameters and hence also modify stratosphere–troposphere exchange (STE) processes. In the present study, high vertical resolution and high accuracy measurements from COSMIC Global Positioning System (GPS) radio occultation (RO) measurements are used to investigate and quantify the effect of tropical cyclones that occurred over Bay of Bengal and Arabian Sea in the last decade on the tropical tropopause parameters. The tropopause parameters include cold-point tropopause altitude (CPH) and temperature (CPT), lapse-rate tropopause altitude (LRH) and temperature (LRT) and the thickness of the tropical tropopause layer (TTL), that is defined as the layer between convective outflow level (COH) and CPH, obtained from GPS RO data. From all the TC events, we generate the mean cyclone-centred composite structure for the tropopause parameters and removed it from the climatological mean obtained from averaging the GPS RO data from 2002 to 2013. Since the TCs include eye, eye walls and deep convective bands, we obtained the tropopause parameters based on radial distance from the cyclone eye. In general, decrease in the CPH in the eye is noticed as expected. However, as the distance from the cyclone eye increases by 300, 400, and 500 km, an enhancement in CPH (CPT) and LRH (LRT) is observed. Lowering of CPH (0.6 km) and LRH (0.4 km) values with coldest CPT and LRT (2–3 K) within a 500 km radius of the TC centre is noticed. Higher (2 km) COH leading to the lowering of TTL thickness (2–3 km) is clearly observed. There are multiple tropopause structures in the profiles of temperature obtained within 100 km from the centre of the TC. These changes in the tropopause parameters are expected to influence the water vapour transport from the troposphere to the lower stratosphere, and ozone from the lower stratosphere to the upper troposphere, hence influencing STE processes.

scholarly journals Temperature and tropopause characteristics from reanalyses data in the tropical tropopause layer

2020 ◽  
Vol 20 (2) ◽  
pp. 753-770 ◽  
Author(s):  
Susann Tegtmeier ◽  
James Anstey ◽  
Sean Davis ◽  
Rossana Dragani ◽  
Yayoi Harada ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Reanalysis Data ◽  
Radiosonde Data ◽  
Data Sets ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Occultation Data ◽  
Cold Point ◽  
Good Agreement

Abstract. The tropical tropopause layer (TTL) is the transition region between the well-mixed convective troposphere and the radiatively controlled stratosphere with air masses showing chemical and dynamical properties of both regions. The representation of the TTL in meteorological reanalysis data sets is important for studying the complex interactions of circulation, convection, trace gases, clouds, and radiation. In this paper, we present the evaluation of climatological and long-term TTL temperature and tropopause characteristics in the reanalysis data sets ERA-Interim, ERA5, JRA-25, JRA-55, MERRA, MERRA-2, NCEP-NCAR (R1), and CFSR. The evaluation has been performed as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The most recent atmospheric reanalysis data sets (ERA-Interim, ERA5, JRA-55, MERRA-2, and CFSR) all provide realistic representations of the major characteristics of the temperature structure within the TTL. There is good agreement between reanalysis estimates of tropical mean temperatures and radio occultation data, with relatively small cold biases for most data sets. Temperatures at the cold point and lapse rate tropopause levels, on the other hand, show warm biases in reanalyses when compared to observations. This tropopause-level warm bias is related to the vertical resolution of the reanalysis data, with the smallest bias found for data sets with the highest vertical resolution around the tropopause. Differences in the cold point temperature maximize over equatorial Africa, related to Kelvin wave activity and associated disturbances in TTL temperatures. Interannual variability in reanalysis temperatures is best constrained in the upper TTL, with larger differences at levels below the cold point. The reanalyses reproduce the temperature responses to major dynamical and radiative signals such as volcanic eruptions and the quasi-biennial oscillation (QBO). Long-term reanalysis trends in temperature in the upper TTL show good agreement with trends derived from adjusted radiosonde data sets indicating significant stratospheric cooling of around −0.5 to −1 K per decade. At 100 hPa and the cold point, most of the reanalyses suggest small but significant cooling trends of −0.3 to −0.6 K per decade that are statistically consistent with trends based on the adjusted radiosonde data sets. Advances of the reanalysis and observational systems over the last decades have led to a clear improvement in the TTL reanalysis products over time. Biases of the temperature profiles and differences in interannual variability clearly decreased in 2006, when densely sampled radio occultation data started being assimilated by the reanalyses. While there is an overall good agreement, different reanalyses offer different advantages in the TTL such as realistic profile and cold point temperature, continuous time series, or a realistic representation of signals of interannual variability. Their use in model simulations and in comparisons with climate model output should be tailored to their specific strengths and weaknesses.

scholarly journals The impact of temperature vertical structure on trajectory modeling of stratospheric water vapor

2015 ◽  
Vol 15 (6) ◽  
pp. 3517-3526 ◽  
Author(s):  
T. Wang ◽  
A. E. Dessler ◽  
M. R. Schoeberl ◽  
W. J. Randel ◽  
J.-E. Kim
Keyword(s):  
Water Vapor ◽  
Vertical Structure ◽  
Vertical Resolution ◽  
Tropical Tropopause Layer ◽  
Stratospheric Water Vapor ◽  
Dry Air ◽  
Tropical Tropopause ◽  
Cold Point ◽  
The Impact ◽  
Modern Era

Abstract. Lagrangian trajectories driven by reanalysis meteorological fields are frequently used to study water vapor (H2O) in the stratosphere, in which the tropical cold-point temperatures regulate the amount of H2O entering the stratosphere. Therefore, the accuracy of temperatures in the tropical tropopause layer (TTL) is of great importance for understanding stratospheric H2O abundances. Currently, most reanalyses, such as the NASA MERRA (Modern Era Retrospective – analysis for Research and Applications), only provide temperatures with ~ 1.2 km vertical resolution in the TTL, which has been argued to miss finer vertical structure in the tropopause and therefore introduce uncertainties in our understanding of stratospheric H2O. In this paper, we quantify this uncertainty by comparing the Lagrangian trajectory prediction of H2O using MERRA temperatures on standard model levels (traj.MER-T) to those using GPS temperatures at finer vertical resolution (traj.GPS-T), and those using adjusted MERRA temperatures with finer vertical structures induced by waves (traj.MER-Twave). It turns out that by using temperatures with finer vertical structure in the tropopause, the trajectory model more realistically simulates the dehydration of air entering the stratosphere. But the effect on H2O abundances is relatively minor: compared with traj.MER-T, traj.GPS-T tends to dry air by ~ 0.1 ppmv, while traj.MER-Twave tends to dry air by 0.2–0.3 ppmv. Despite these differences in absolute values of predicted H2O and vertical dehydration patterns, there is virtually no difference in the interannual variability in different runs. Overall, we find that a tropopause temperature with finer vertical structure has limited impact on predicted stratospheric H2O.

scholarly journals The tropical tropopause layer in reanalysis data sets

2019 ◽  
Author(s):  
Susann Tegtmeier ◽  
James Anstey ◽  
Sean Davis ◽  
Rossana Dragani ◽  
Yayoi Harada ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Radio Occultation ◽  
Reanalysis Data ◽  
Radiosonde Data ◽  
Data Sets ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Occultation Data ◽  
Cold Point ◽  
Good Agreement

Abstract. The tropical tropopause layer (TTL) is the transition region between the well mixed, convective troposphere and the radiatively controlled stratosphere with air masses showing chemical and dynamical properties of both regions. The representation of the TTL in meteorological reanalysis data sets is important for studying the complex interactions of circulation, convection, trace gases, clouds and radiation. In this paper, we present the evaluation of TTL characteristics in reanalysis data sets that has been performed as part of the SPARC (Stratosphere– troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The most recent atmospheric reanalysis data sets all provide realistic representations of the major characteristics of the temperature structure within the TTL. There is good agreement between reanalysis estimates of tropical mean temperatures and radio occultation data, with relatively small cold biases for most data sets. Temperatures at the cold point and lapse rate tropopause levels, on the other hand, show warm biases in reanalyses when compared to observations. This tropopause-level warm bias is related to the vertical resolution of the reanalysis data, with the smallest bias found for data sets with the highest vertical resolution around the tropopause. Differences of the cold point temperature maximise over equatorial Africa, related to Kelvin wave activity and associated disturbances in TTL temperatures. Model simulations of air mass transport into the stratosphere driven by reanalyses with a warm cold point bias can be expected to have too little dehydration. Interannual variability in reanalysis temperatures is best constrained in the upper TTL, with larger differences at levels below the cold point. The reanalyses reproduce the temperature responses to major dynamical and radiative signals such as volcanic eruptions and the QBO. Long-term reanalysis trends in temperature in the upper TTL show good agreement with trends derived from adjusted radiosonde data sets indicating significant stratospheric cooling of around −0.5 to −1 K/decade. At 100 hPa and the cold point, most of the reanalyses suggest small but significant cooling trends of −0.3 to −0.6 K/decade that are statistically consistent with trends based on the adjusted radiosonde data sets. Advances of the reanalysis and observational systems over the last decades have led to a clear improvement of the TTL reanalyses products over time. Biases of the temperature profiles and differences in interannual variability clearly decreased in 2006, when densely sampled radio occultation data started being assimilated by the reanalyses. While there is an overall good agreement, different reanalyses offer different advantages in the TTL such as realistic profile and cold point temperature, continuous time series or a realistic representation of signals of interannual variability. Their use in model simulations and in comparisons with climate model output should be tailored to their specific strengths and weaknesses.

scholarly journals The Residual-Mean Circulation in the Tropical Tropopause Layer Driven by Tropical Waves

2014 ◽  
Vol 71 (4) ◽  
pp. 1305-1322 ◽  
Author(s):  
David A. Ortland ◽  
M. Joan Alexander
Keyword(s):  
Seasonal Variations ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Minor Effect ◽  
Equatorial Waves ◽  
Latent Heating ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
The Mean

Abstract Latent heating estimates derived from rainfall observations are used to construct model experiments that isolate equatorial waves forced by tropical convection from midlatitude synoptic-scale waves. These experiments are used to demonstrate that quasi-stationary equatorial Rossby waves forced by latent heating drive most of the observed residual-mean upwelling across the tropopause transition layer within 15° of the equator. The seasonal variation of the equatorial waves and the mean meridional upwelling that they cause is examined for two full years from 2006 to 2007. Changes in equatorial Rossby wave propagation through seasonally varying mean winds are the primary mechanism for producing an annual variation in the residual-mean upwelling. In the tropical tropopause layer, averaged within 15° of the equator and between 90 and 190 hPa, the annual cycle varies between a maximum upwelling of 0.4 mm s−1 during boreal winter and spring and a minimum of 0.2 mm s−1 during boreal summer. This variability seems to be due to small changes in the mean wind speed in the tropics. Seasonal variations in latent heating have only a relatively minor effect on seasonal variations in tropical tropopause upwelling. In addition, Kelvin waves drive a small downward component of the total circulation over the equator that may be modulated by the quasi-biennial oscillation.

scholarly journals Correlation between equatorial Kelvin waves and the occurrence of extremely thin ice clouds at the tropical tropopause

2008 ◽  
Vol 8 (1) ◽  
pp. 2849-2862 ◽  
Author(s):  
F. Immler ◽  
K. Krüger ◽  
M. Fujiwara ◽  
G. Verver ◽  
M. Rex ◽  
...  
Keyword(s):  
Kelvin Waves ◽  
Clear Correlation ◽  
Kelvin Wave ◽  
Ice Clouds ◽  
Tropical Tropopause Layer ◽  
Temperature Anomalies ◽  
Tropical Tropopause ◽  
Water Vapour Concentration ◽  
Cold Point ◽  
The Tropics

Abstract. A number of field-campaigns in the tropics have been conducted in the recent years with two different LIDAR systems at Paramaribo in Suriname (5.8° N, 55.2° W). The lidars detect particles in the atmosphere with high vertical and temporal resolution and are capable of detecting extremely thin cloud layers which frequently occur in the tropical tropopause layer (TTL). Radiosonde as well as operational ECMWF analysis show that temperature anomalies caused by equatorial Kelvin waves propagate downward, well below the cold point tropopause (CPT). We find a clear correlation between the temperature anomalies introduced by these waves and the occurrence of thin cirrus in the TTL. In particular we found that extremely thin ice clouds form regularly where cold anomalies shift the tropopause to high altitudes. This finding suggests an influence of Kelvin wave activity on the dehydration in the TTL and thus on the global stratospheric water vapour concentration.

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