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 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 Global temperature estimates in the troposphere and stratosphere: a validation study of COSMIC/FORMOSAT-3 measurements

2009 ◽  
Vol 9 (3) ◽  
pp. 897-908 ◽  
Author(s):  
P. Kishore ◽  
S. P. Namboothiri ◽  
J. H. Jiang ◽  
V. Sivakumar ◽  
K. Igarashi
Keyword(s):  
Validation Study ◽  
Radio Occultation ◽  
Reanalysis Data ◽  
First Year ◽  
Data Sets ◽  
Tropical Tropopause ◽  
The United Kingdom ◽  
Tropopause Region ◽  
Environmental Prediction ◽  
Good Agreement

Abstract. This paper mainly focuses on the validation of temperature estimates derived with the newly launched Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC)/Formosa Satellite 3 (FORMOSAT-3) system. The analysis is based on the radio occultation (RO) data samples collected during the first year observation from April 2006 to April 2007. For the validation, we have used the operational stratospheric analyses including the National Centers for Environmental Prediction - Reanalysis (NCEP), the Japanese 25-year Reanalysis (JRA-25), and the United Kingdom Met Office (MetO) data sets. Comparisons done in different formats reveal good agreement between the COSMIC and reanalysis outputs. Spatially, the largest deviations are noted in the polar latitudes, and height-wise, the tropical tropopause region noted the maximum differences (2–4 K). We found that among the three reanalysis data sets the NCEP data sets have the best resemblance with the COSMIC measurements.

scholarly journals Cold trap dehydration in the Tropical Tropopause Layer characterized by SOWER chilled-mirror hygrometer network data in the Tropical Pacific

2012 ◽  
Vol 12 (9) ◽  
pp. 25833-25885 ◽  
Author(s):  
F. Hasebe ◽  
Y. Inai ◽  
M. Shiotani ◽  
M. Fujiwara ◽  
H. Vömel ◽  
...  
Keyword(s):  
Ice Nucleation ◽  
Tropical Pacific ◽  
Cold Trap ◽  
Mixing Ratio ◽  
Back Trajectories ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Scatter Plots ◽  
Cold Point ◽  
The Tropical Pacific

Abstract. A network of balloon-born radiosonde observations employing chilled-mirror hygrometers for water and electrochemical concentration cells for ozone has been operated since late 1990s in the Tropical Pacific trying to capture the progress of dehydration for the air parcels advected horizontally in the Tropical Tropopause Layer (TTL). The analyses of this dataset are made on isentropes taking advantage of the conservative properties of tracers in adiabatic motion. The existence of ice particles is diagnosed by lidars simultaneously operated with sonde flights. Characteristics of the TTL dehydration are presented on the basis of individual soundings and statistical features. Supersaturations close to 80% in the relative humidity with respect to ice (RHice) have been observed in subvisible cirrus clouds located near the cold point tropopause at extremely low temperatures around 180 K. Further observational evidence is needed to confirm the credibility of such high values of RHice. The progress of TTL dehydration is reflected in isentropic scatter plots between the sonde-observed mixing ratio (OMR) and the minimum saturation mixing ratio (SMRmin) along the back trajectories associated with the observed air mass. The supersaturation exceeding the critical value of the homogeneous ice nucleation (OMR > 1.6 × SMRmin) is frequently observed on 360 and 365 K surfaces indicating that the cold trap dehydration is under progress in the TTL. The near correspondence between the two (OMR ~ SMRmin) on 380 K on the other hand implies that this surface is not significantly cold for the advected air parcels to be dehydrated. Above 380 K, the cold trap dehydration would scarcely function while some moistening in turn occurs before the air parcels reach the lowermost stratosphere at around 400 K where OMR is generally smaller than SMRmin.

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.

Moisture fluxes in the tropics dominated by deep convection up to near tropical tropopause levels

2021 ◽  
Author(s):  
Maximilien Bolot ◽  
Stephan Fueglistaler
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Convective Scale ◽  
Moisture Fluxes ◽  
Global Impacts ◽  
Observational Estimate ◽  
Cold Point ◽  
Open Question

<p>The role played by tropical storms in the tropical tropopause layer (TTL), the transitional layer regulating the flux into the stratosphere of trace gases affecting radiation and the ozone layer, has been a long-standing open question. Progress has been slow because of computational limitations and challenging conditions for measurements and most numerical studies have used simulations over limited domains whose results must be upscaled to the tropical surface to infer global impacts. We compute the first global observational estimate of the convective ice flux at near tropical tropopause levels by using spaceborne lidar measurements from CALIOP. The calculation uses a method to convert from lidar extinction to sedimenting ice flux and uses error propagation to provide margins of uncertainty. We show that, at any given level in the TTL, the sedimenting ice flux exceeds the inflow of vapor computed from ERA5 reanalysis, revealing additional ice transport and allowing to deduce the advective ice flux as a function of altitude. The contribution to this flux of large-scale motions (resolved by ERA5) is computed and the residual is hypothesized to represent the flux of ice on the convective scale. Results show without ambiguity that the upward ice flux in deep convection dominates moisture transport up to close to the level of the cold point tropopause.</p>

scholarly journals Asian water tower evinced in total column water vapor: a comparison among multiple satellite and reanalysis data sets

2019 ◽  
Vol 54 (1-2) ◽  
pp. 231-245 ◽  
Author(s):  
Yin Zhao ◽  
Tianjun Zhou
Keyword(s):  
Water Vapor ◽  
Satellite Data ◽  
Annual Cycle ◽  
Reanalysis Data ◽  
Radiosonde Data ◽  
Data Sets ◽  
Important Indicator ◽  
Ensemble Mean ◽  
Asian Water ◽  
Total Column

Abstract The total column water vapor (TCWV) over the Tibetan Plateau (TP) is one important indicator of the Asian water tower, and the changes in the TCWV are vital to the climate and ecosystem in downstream regions. However, the observational data is insufficient to understand the changes in the TCWV due to the high elevation of the TP. Satellite and reanalysis data can be used as substitutes, but their quality needs to be evaluated. In this study, based on a homogenized radiosonde data set, a comprehensive evaluation of the TCWV over the TP derived from two satellite data sets (AIRS-only and AIRS/AMSU) and seven existing reanalysis data sets (MERRA, MERRA2, NCEP1, NCEP2, CFSR, ERA-I, JRA55) is performed in the context of the climatology, annual cycle and interannual variability. Both satellite data sets reasonably reproduce the characteristics of the TCWV over the TP. All reanalysis data sets perform well in reproducing the annual mean climatology of the TCWV over the TP (R = 0.99), except for NCEP1 (R = 0.96) and NCEP2 (R = 0.92). ERA-I is more reliable in capturing the spatial pattern of the annual cycle (R = 0.94), while NCEP1 shows the lowest skill (R = 0.72). JRA55 performs best in capturing the features of the interannual coherent variation (EOF1, R = 0.97). The skill-weighted ensemble mean of the reanalysis data performs better than the unweighted ensemble mean and most of the single reanalysis data sets. The evaluation provides essential information on both the strengths and weaknesses of the major satellite and reanalysis data sets in measuring the total column water vapor over the TP.

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