scholarly journals Comparison of equatorial wave activity in the tropical tropopause layer and stratosphere represented in reanalyses

2019 ◽  
Author(s):  
Young-Ha Kim ◽  
George N. Kiladis ◽  
John R. Albers ◽  
Juliana Dias ◽  
Masatomo Fujiwara ◽  
...  
Keyword(s):  
Satellite Data ◽  
Wave Activity ◽  
Spatial Structures ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Equatorial Wave ◽  
Biennial Oscillation ◽  
Considerable Spread

Abstract. Equatorial Kelvin and mixed Rossby-gravity (MRG) waves in the tropical tropopause layer and stratosphere represented in recent reanalyses for the period of 1981–2010 are compared in terms of spectral characteristics, spatial structures, long-term variations and their forcing of the quasi-biennial oscillation. For both wave types, the spectral distributions are broadly similar among most of the reanalyses, while the peak amplitudes exhibit considerable spread. The longitudinal distributions and spatial patterns of wave perturbations show reasonable agreement between the reanalyses. A few exceptions to the similarity of the spectral shapes and spatial structures among them are also noted. While the interannual variations of wave activity appear to be coherent for both the Kelvin and MRG waves, there is substantial variability in long-term trends among the reanalyses. Most of the reanalyses which assimilate satellite data exhibit large increasing trends in wave variance (~ 15–50 % increase in the 30 years at 100–10 hPa), whereas one reanalysis (JRA-55C) produced without satellite data does not. Several discontinuities are found around 1998 in the time series of the Kelvin and MRG wave variances, which manifest in different ways depending on the reanalysis, and are indicative of impacts of the transition of satellite measurements during that year. The equatorial wave forcing of the quasi-biennial oscillation, estimated by the Eliassen–Palm flux divergence, occurs in similar phase-speed ranges among the reanalyses, while the forcing magnitudes show considerable spread. The forcing maxima of the Kelvin waves exhibit slightly different altitudes between the reanalyses (by ~ 3 km at around 15 hPa). In addition, at around 20 hPa, a wave signal which appears only in easterly mean winds with westward phase speeds is found and discussed.

scholarly journals Comparison of equatorial wave activity in the tropical tropopause layer and stratosphere represented in reanalyses

2019 ◽  
Vol 19 (15) ◽  
pp. 10027-10050 ◽  
Author(s):  
Young-Ha Kim ◽  
George N. Kiladis ◽  
John R. Albers ◽  
Juliana Dias ◽  
Masatomo Fujiwara ◽  
...  
Keyword(s):  
Satellite Data ◽  
Phase Speed ◽  
Wave Activity ◽  
Spatial Structures ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause Layer ◽  
Wave Forcing ◽  
Tropical Tropopause ◽  
Equatorial Wave

Abstract. Equatorial Kelvin and mixed Rossby–gravity (MRG) waves in the tropical tropopause layer and stratosphere represented in recent reanalyses for the period of 1981–2010 are compared in terms of spectral characteristics, spatial structures, long-term variations, and their forcing of the quasi-biennial oscillation (QBO). For both wave types, the spectral distributions are broadly similar among most of the reanalyses, while the peak amplitudes exhibit considerable spread. The longitudinal distributions and spatial patterns of wave perturbations show reasonable agreement between the reanalyses. A few exceptions to the similarity of the spectral shapes and spatial structures among them are also noted. While the interannual variations of wave activity appear to be coherent for both the Kelvin and MRG waves, there is substantial variability in long-term trends among the reanalyses. Most of the reanalyses which assimilate satellite data exhibit large increasing trends in wave variance (∼15 %–50 % increase in 30 years at 100–10 hPa), whereas one reanalysis (Japanese 55-year Reanalysis assimilating conventional observations only; JRA-55C) produced without satellite data does not. Several discontinuities are found around 1998 in the time series of the Kelvin and MRG wave variances, which manifest in different ways depending on the reanalysis, and are indicative of impacts of the transition of satellite measurements during that year. The equatorial wave forcing of the QBO, estimated by the Eliassen–Palm (EP) flux divergence, occurs in similar phase-speed ranges in the lower stratosphere among the reanalyses. However, the EP flux and its divergence are found to be dependent on the zonal-mean winds represented in reanalyses, exhibiting different magnitudes, altitudes, and phase-speed ranges of the Kelvin wave forcing between the reanalyses, especially at 20–10 hPa. In addition, at around 20 hPa, a wave signal which appears only in easterly mean winds with westward phase speeds is found and discussed.

scholarly journals Long-term behavior of the Kelvin waves revealed by CHAMP/GPS RO measurements and their effects on the tropopause structure

2006 ◽  
Vol 24 (5) ◽  
pp. 1355-1366 ◽  
Author(s):  
M. Venkat Ratnam ◽  
T. Tsuda ◽  
T. Kozu ◽  
S. Mori
Keyword(s):  
Wave Activity ◽  
Kelvin Waves ◽  
Tropopause Height ◽  
Kelvin Wave ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause ◽  
Hemisphere Winter ◽  
Biennial Oscillation ◽  
Northern Hemisphere Winter

Abstract. The vertical and temporal variations of Kelvin waves and the associated effects on the tropical tropopause were studied using long-term (from May 2001 to October 2005) CHAMP/GPS (CHAllenging Mini satellite Payload/Global Positioning System) radio occultation (RO) measurements. The periods of these waves were found to be varying in between 10 and 15 days, with vertical wavelengths 5–8 km. These variations clearly show eastward phase propagation in the time-longitude section and eastward phase tilts with height in altitude-longitude, displaying the characteristics of Kelvin waves. The peak variance in the temperature is found over the Indian Ocean and into the western Pacific within the broad region of the equator. Kelvin wave amplitudes were found significantly enhanced in the eastward shear of the quasi-biennial oscillation (QBO) and are confined in and around the tropopause during westward phase of QBO, where it extends between 17 and 25 km during the eastward phase of QBO and is damped away above, consistent with earlier reported results. The amplitudes are increasing during the months of Northern Hemisphere winter and sometimes they are highly sporadic in nature. Seasonal and inter-annual variations in the Kelvin wave amplitudes near the tropical tropopause coincide exactly with the tropopause height and temperature, with a sharp tropopause during maximum Kelvin wave activity. A clear annual oscillation, along with a month-to-month coincidence is evident most of the time in both the tropopause height and Kelvin wave activity, with maximum and minimum Kelvin wave amplitudes during the Northern Hemisphere winter and summer, respectively. In addition, a signature of quasi-biennial oscillation (QBO) in the tropopause structure is also seen in long-term tropopause variations, although the amplitudes are less when compared to the annual oscillation. In the westward phase of QBO (during strong Kelvin wave activity) at 20km (in 2001–2002 winter and 2003–2004 winter), the tropopause height was slightly larger with a sharp tropopause and low temperature. The process behind these observed features has been discussed.

scholarly journals Contribution of different processes to changes in tropical lower-stratospheric water vapor in chemistry–climate models

2017 ◽  
Vol 17 (13) ◽  
pp. 8031-8044 ◽  
Author(s):  
Kevin M. Smalley ◽  
Andrew E. Dessler ◽  
Slimane Bekki ◽  
Makoto Deushi ◽  
Marion Marchand ◽  
...  
Keyword(s):  
Water Vapor ◽  
Regression Model ◽  
21St Century ◽  
Climate Models ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause Layer ◽  
Stratospheric Water Vapor ◽  
Tropical Tropopause ◽  
The Impact

Abstract. Variations in tropical lower-stratospheric humidity influence both the chemistry and climate of the atmosphere. We analyze tropical lower-stratospheric water vapor in 21st century simulations from 12 state-of-the-art chemistry–climate models (CCMs), using a linear regression model to determine the factors driving the trends and variability. Within CCMs, warming of the troposphere primarily drives the long-term trend in stratospheric humidity. This is partially offset in most CCMs by an increase in the strength of the Brewer–Dobson circulation, which tends to cool the tropical tropopause layer (TTL). We also apply the regression model to individual decades from the 21st century CCM runs and compare them to a regression of a decade of observations. Many of the CCMs, but not all, compare well with these observations, lending credibility to their predictions. One notable deficiency is that most CCMs underestimate the impact of the quasi-biennial oscillation on lower-stratospheric water vapor. Our analysis provides a new and potentially superior way to evaluate model trends in lower-stratospheric humidity.

scholarly journals Long-term climatology of air mass transport through the Tropical Tropopause Layer (TTL) during NH winter

2008 ◽  
Vol 8 (4) ◽  
pp. 813-823 ◽  
Author(s):  
K. Krüger ◽  
S. Tegtmeier ◽  
M. Rex
Keyword(s):  
Mass Transport ◽  
El Niño ◽  
El Nino ◽  
Volcanic Eruptions ◽  
Radiative Heating ◽  
Quasi Biennial Oscillation ◽  
Air Mass ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause

Abstract. A long-term climatology of air mass transport through the tropical tropopause layer (TTL) is presented, covering the period from 1962–2005. The transport through the TTL is calculated with a Lagrangian approach using radiative heating rates as vertical velocities in an isentropic trajectory model. We demonstrate the improved performance of such an approach compared to previous studies using vertical winds from meteorological analyses. Within the upper part of the TTL, the averaged diabatic ascent is 0.5 K/day during Northern Hemisphere (NH) winters 1992–2001. Climatological maps show a cooling and strengthening of this part of the residual circulation during the 1990s and early 2000s compared to the long-term mean. Lagrangian cold point (LCP) fields show systematic differences for varying time periods and natural forcing components. The interannual variability of LCP temperature and density fields is found to be influenced by volcanic eruptions, El Niño Southern Oscillation (ENSO), Quasi-Biennial Oscillation (QBO) and the solar cycle. The coldest and driest TTL is reached during QBO easterly phase and La Niña over the western Pacific, whereas during volcanic eruptions, El Niño and QBO westerly phase it is warmer and less dry.

scholarly journals Effects of tropical deep convection on interannual variability of tropical tropopause layer water vapor

2017 ◽  
Author(s):  
Hao Ye ◽  
Andrew E. Dessler ◽  
Wandi Yu
Keyword(s):  
Water Vapor ◽  
Interannual Variability ◽  
Deep Convection ◽  
Tropospheric Temperature ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Tropical Deep Convection ◽  
The Impact ◽  
Biennial Oscillation

Abstract. Water vapor interannual variability in the tropical tropopause layer (TTL) is investigated using satellite observations and model simulations. We breakdown the influences of the Brewer-Dobson circulation (BDC), the quasi-biennial oscillation (QBO), and the tropospheric temperature (ΔT) as a function of latitude and longitude using a 2-dimensional multivariable linear regression. This allows us to examine the spatial distribution of the impact on TTL water vapor from these physical processes. In agreement with expectation, we find that the impacts from the BDC and QBO act on TTL water vapor by changing TTL temperature. For ΔT, we find that TTL temperatures alone cannot explain the influence. We hypothesize a moistening role for the evaporation of convective ice from increased deep convection as troposphere warms. Tests with simulations from GEOSCCM and a corresponding trajectory model support this hypothesis.

Variability in QBO Temperature Anomalies on Annual and Decadal Time Scales

2021 ◽  
Vol 34 (2) ◽  
pp. 589-605
Author(s):  
Zane Martin ◽  
Adam Sobel ◽  
Amy Butler ◽  
Shuguang Wang
Keyword(s):  
Time Scales ◽  
Lower Stratosphere ◽  
Boreal Winter ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause Layer ◽  
Temperature Anomalies ◽  
Tropical Tropopause ◽  
Tropical Troposphere ◽  
The Relationship ◽  
Biennial Oscillation

AbstractThe stratospheric quasi-biennial oscillation (QBO) induces temperature anomalies in the lower stratosphere and tropical tropopause layer (TTL) that are cold when lower-stratospheric winds are easterly and warm when winds are westerly. Recent literature has indicated that these QBO temperature anomalies are potentially important in influencing the tropical troposphere, and particularly in explaining the relationship between the QBO and the Madden–Julian oscillation (MJO). The authors examine the variability of QBO temperature anomalies across several time scales using reanalysis and observational datasets. The authors find that, in boreal winter relative to other seasons, QBO temperature anomalies are significantly stronger (i.e., colder in the easterly phase of the QBO and warmer in the westerly phase of the QBO) on the equator, but weaker off the equator. The equatorial and subtropical changes compensate such that meridional temperature gradients and thus (by thermal wind balance) equatorial zonal wind anomalies do not vary in amplitude as the temperature anomalies do. The same pattern of stronger on-equatorial and weaker off-equatorial QBO temperature anomalies is found on decadal time scales: stronger anomalies are seen for 1999–2019 compared to 1979–99. The causes of these changes to QBO temperature anomalies, as well as their possible relevance to the MJO–QBO relationship, are not known.

scholarly journals Trends in stratospheric ozone derived from merged SAGE II and Odin-OSIRIS satellite observations

2014 ◽  
Vol 14 (6) ◽  
pp. 7113-7140 ◽  
Author(s):  
A. E. Bourassa ◽  
D. A. Degenstein ◽  
W. J. Randel ◽  
J. M. Zawodny ◽  
E. Kyrölä ◽  
...  
Keyword(s):  
Southern Oscillation ◽  
Stratospheric Ozone ◽  
Stratospheric Aerosol ◽  
Basis Functions ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause ◽  
Infrared Imager ◽  
Ozone Profile ◽  
Biennial Oscillation

Abstract. Stratospheric ozone profile measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) II satellite instrument (1984–2005) are combined with those from the Optical Spectrograph and InfraRed Imager System (OSIRIS) instrument on the Odin satellite (2001–Present) to quantify interannual variability and decadal trends in stratospheric ozone between 60° S and 60° N. These data are merged into a multi-instrument, long-term stratospheric ozone record (1984–present) by analyzing the measurements during the overlap period of 2002–2005 when both satellite instruments were operational. The variability in the deseasonalized time series is fit using multiple linear regression with predictor basis functions including the quasi-biennial oscillation, El Niño-Southern Oscillation index, solar activity proxy, and the pressure at the tropical tropopause, in addition to two linear trends (one before and one after 1997), from which the decadal trends in ozone are derived. From 1984–1997, there are statistically significant negative trends of 5–10% per decade throughout the stratosphere between approximately 30–50 km. From 1997–present, a statistically significant recovery of 3–8% per decade has taken place throughout most of the stratosphere with the notable exception between 40° S–40° N below approximately 22 km where the negative trend continues. The recovery is not significant between 25–35 km altitude when accounting for a conservative estimate of instrument drift.

scholarly journals Testing chemistry-climate models' regulation of tropical lower-stratospheric water vapor

2016 ◽  
Author(s):  
Kevin M. Smalley ◽  
Andrew E. Dessler ◽  
Slimane Bekki ◽  
Makoto Deushi ◽  
Marion Marchand ◽  
...  
Keyword(s):  
Regression Model ◽  
21St Century ◽  
Climate Models ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause Layer ◽  
Stratospheric Water Vapor ◽  
Tropical Tropopause ◽  
The Impact ◽  
Long Term Trend

Abstract. Climate models predict that tropical lower stratospheric humidity will increase as the climate warms, with important implications for the chemistry and climate of the atmosphere. We analyze the trend in 21st-century simulations from 12 state-of-the-art chemistry-climate models (CCMs) using a linear regression model to determine the factors driving the trends. Within CCMs, the long-term trend in humidity is primarily driven by warming of the troposphere. This is partially offset in most CCMs by an increase in the strength of the Brewer-Dobson circulation, which tends to cool the tropical tropopause layer (TTL). We also apply the regression model to individual decades from the 21st century CCM runs and compare them to observations. Many of the CCMs, but not all, compare well with observations, lending credibility to their predictions. One notable deficiency in most CCMs is that they underestimate the impact of the quasi-biennial oscillation on lower stratospheric humidity. Our analysis provides a new and potentially superior way to evaluate model trends in lower stratospheric humidity.

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