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 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 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 Representation of Vertical Atmospheric Structures by Radio Occultation Observations in the Upper Troposphere and Lower Stratosphere: Comparison to High-Resolution Radiosonde Profiles

2019 ◽  
Vol 36 (4) ◽  
pp. 655-670 ◽  
Author(s):  
Zhen Zeng ◽  
Sergey Sokolovskiy ◽  
William S. Schreiner ◽  
Doug Hunt
Keyword(s):  
High Resolution ◽  
Radio Occultation ◽  
Lower Stratosphere ◽  
Small Scale ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Low Latitudes ◽  
Observational Noise ◽  
Horizontal Inhomogeneity ◽  
Cold Point

AbstractGlobal positioning system (GPS) radio occultation (RO) is capable of retrieving vertical profiles of atmospheric parameters with high resolution (<100 m), which can be achieved in spherically symmetric atmosphere. Horizontal inhomogeneity of real atmosphere results in representativeness errors of retrieved profiles. In most cases these errors increase with a decrease of vertical scales of atmospheric structures and may not allow one to fully utilize the physical resolution of RO. Also, GPS RO–retrieved profiles are affected by observational noise of different types, which, in turn, affect the representation of small-scale atmospheric structures. This study investigates the effective resolution and optimal smoothing of GPS RO–retrieved temperature profiles using high-pass filtering and cross correlation with collocated high-resolution radiosondes. The effective resolution is a trade-off between representation of real atmospheric structures and suppression of observational noise, which varies for different latitudes (15°S–75°N) and altitudes (10–27 km). Our results indicate that at low latitudes the effective vertical resolution is about 0.2 km near the tropical tropopause layer and about 0.5 km in the lower stratosphere. The best resolution of 0.1 km is at the cold-point tropical tropopause. The effective resolutions at the midlatitudes are slightly worse than at low latitudes, varying from ~0.2 to 0.6 km. At high latitudes, the effective resolutions change notably with altitude from ~0.2 km at 10–15 km to ~1.4 km at 22–27 km. Our results suggest that the atmospheric inhomogeneity plays an important role in the representation of the vertical atmospheric structures by RO measurements.

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

2008 ◽  
Vol 8 (3) ◽  
pp. 8327-8355 ◽  
Author(s):  
P. Kishore ◽  
S. P. Namboothiri ◽  
J. H. Jiang ◽  
V. Sivakumar ◽  
K. Igarashi
Keyword(s):  
Radio Occultation ◽  
Specific Humidity ◽  
First Year ◽  
Data Sets ◽  
Tropical Tropopause ◽  
The United Kingdom ◽  
Tropopause Region ◽  
Environmental Prediction ◽  
Humidity Profiles ◽  
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 sample collected during the first year observation from April 2006 to April 2007. For the validation, we have used the operational stratospheric analyses (models) including the National Centers for Environmental Prediction-Reanalysis (NCEP-Reanalysis), the Japanese 25-year Reanalysis (JRA-25), and the United Kingdom Met Office (MetO) data sets. Comparisons done in different formats reveal excellent agreement between the COSMIC and model outputs. Spatially, the largest deviations are noted in the polar latitudes, and height-wise, the tropical tropopause region noted the maximum differences. However, these differences are only 2–4 K. We found that among the three models the NCEP data sets have the best resemblance with the COSMIC measurements. We also have done comparison of specific humidity and refractivity profiles with other measurements/models. Specific humidity profiles show comparatively large differences at altitudes below 5 km. Refractivity profiles derived by the COSMIC and other datasets show very good agreement.

scholarly journals Comparison of ECMWF analyses with GPS radio occultations from CHAMP

2008 ◽  
Vol 26 (11) ◽  
pp. 3225-3234 ◽  
Author(s):  
T. Schmidt ◽  
J. Wickert ◽  
S. Heise ◽  
F. Flechtner ◽  
E. Fagiolini ◽  
...  
Keyword(s):  
Radio Occultation ◽  
Polar Vortex ◽  
Data Sets ◽  
Mean Values ◽  
Tropical Tropopause ◽  
Before And After ◽  
Tropopause Region ◽  
Standard Deviations ◽  
Occultation Data ◽  
Radio Occultation Data

Abstract. A climatological validation of the 6-hourly operational ECMWF troposphere and lower stratosphere temperatures as well as geopotential heights between 1000 and 10 hPa is performed using the 2001–2007 (80 months from May 2001 to December 2007) CHAMP radio occultation data. Generally there is a good agreement between ECMWF and CHAMP temperatures averaged over 300–10 hPa for all years/seasons with global annual mean biases (standard deviations) less than 0.3 (1.7) K. Regional and temporal discrepancies occur within the polar vortex mainly on the Southern Hemisphere and the tropical tropopause region. Global annual mean biases (standard deviations) of geopotential heights between 300 and 10 hPa are in the range of −30 up to +5 (30–50) geopotential meter. Larger deviations from the mean values are also observed in the tropics and polar zones. Both, the biases and standard deviations between CHAMP and ECMWF temperatures and geopotential heights differ significantly before and after February and December 2006, i.e. the dates when ECMWF increased the number of model levels from L60 to L91 (1 February 2006) and where ECMWF became one of the first weather centers assimilating radio occultation data (since 12 December 2006), mainly from the COSMIC mission. At ECMWF the CHAMP data were only assimilated until 4 February 2007, e.g. both data sets are mostly independent from each other during the time period considered here.

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.

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