scholarly journals Untangling the Annual Cycle of the Tropical Tropopause Layer with an Idealized Moist Model

2017 ◽  
Vol 30 (18) ◽  
pp. 7339-7358 ◽  
Author(s):  
M. Jucker ◽  
E. P. Gerber
Keyword(s):  
Annual Cycle ◽  
Lower Boundary ◽  
Boreal Summer ◽  
Simple Modification ◽  
Tropical Tropopause Layer ◽  
Planetary Scale ◽  
Tropical Tropopause ◽  
Westerly Winds ◽  
Cold Point ◽  
The Impact

Abstract The processes regulating the climatology and annual cycle of the tropical tropopause layer (TTL) and cold point are not fully understood. Three main drivers have been identified: planetary-scale equatorial waves excited by tropical convection, planetary-scale extratropical waves associated with the deep Brewer–Dobson circulation, and synoptic-scale waves associated with the midlatitude storm tracks. In both observations and comprehensive atmospheric models, all three coexist, making it difficult to separate their contributions. Here, a new intermediate-complexity atmospheric model is developed. Simple modification of the model’s lower boundary allows detailed study of the three processes key to the TTL, both in isolation and together. The model shows that tropical planetary waves are most critical for regulating the mean TTL, setting the depth and temperature of the cold point. The annual cycle of the TTL, which is coldest (warmest) in boreal winter (summer), however, depends critically on the strong annual variation in baroclinicity of the Northern Hemisphere relative to that of the Southern Hemisphere. Planetary-scale waves excited from either the tropics or extratropics then double the impact of baroclinicity on the TTL annual cycle. The remarkably generic response of TTL temperatures over a range of configurations suggests that the details of the wave forcing are unimportant, provided there is sufficient variation in the upward extent of westerly winds over the annual cycle. Westerly winds enable the propagation of stationary Rossby waves, and weakening of the subtropical jet in boreal summer inhibits their propagation into the lower stratosphere, warming the TTL.

scholarly journals The radiative role of ozone and water vapour in the temperature annual cycle in the tropical tropopause layer

2016 ◽  
Author(s):  
Alison Ming ◽  
Amanda C. Maycock ◽  
Peter Hitchcock ◽  
Peter Haynes
Keyword(s):  
Water Vapour ◽  
Annual Cycle ◽  
Temperature Response ◽  
Radiative Heating ◽  
Latitudinal Gradients ◽  
Peak Amplitude ◽  
Tropical Tropopause Layer ◽  
Enhanced Absorption ◽  
Tropical Tropopause ◽  
Cold Point

Abstract. The prominent annual cycle in temperatures (with maximum peak to peak amplitude of ~ 8 K around 70 hPa and ~ 6 K at 90 hPa) is a key feature of the tropical tropopause layer (TTL). There is also a strong annual cycle observed in both ozone and water vapour in the TTL, with the latter understood as a consequence of the temperature annual cycle. The radiative contributions of the annual cycle in ozone and water vapour to the temperature annual cycle are studied, first with a seasonally evolving fixed dynamical heating calculation (SEFDH) where the dynamical heating is assumed to be unaffected by the radiative heating. In this framework, the variations in ozone and water vapour derived from satellite data lead to variations in temperature that are respectively in phase and out of phase with the observed annual cycle. The ozone contribution is at the upper range of previous calculations. This difference in phasing can be understood from the fact that an increase in water vapour cools the TTL, predominantly through enhanced local emission, whereas an increase in ozone warms the TTL, mostly through enhanced absorption of upwelling longwave radiation from the troposphere. The relative phasing of the water vapour and ozone effects on temperature is further influenced by the fact that for water vapour there is a strong non-local effect on temperatures from variations in concentrations occurring in lower layers of the TTL. In contrast, for ozone it is the local variations in concentration that have the strongest impact on local temperature variations. The factors that determine the vertical structure of the annual cycle in temperature are also examined. Radiative damping time scales are shown to maximize over a broad layer centred on the cold point. Non-radiative processes in the upper troposphere are inferred to impose a strong constraint on temperature perturbations below 130 hPa. These effects, combined with the annual cycles in dynamical and radiative heating, which both peak above the cold point, result in a maximum amplitude of temperature response that is relatively localized around 70 hPa. Finally, the SEFDH assumption is relaxed by considering the temperature responses to ozone and water vapour variations in a zonally symmetric dynamical model. While the magnitude of the tropical averaged temperature annual cycle in this framework is found to be consistent with the SEFDH results, the effects of the dynamical adjustment act to reduce the strong latitudinal gradients and inter-hemispheric asymmetry in the temperature response. This results in a temperature response that shows a considerably smoother structure than inferred from the SEFDH model. Whilst precise numerical values are likely to be sensitive to changes in the details of radiation code and of ozone and water vapour concentrations, the net contribution to the annual cycle in temperature from both ozone and water vapour averaged between 20° N–S, calculated in this work, is substantial and around 35 % of the observed peak to peak amplitude at both 70 hPa and 90 hPa.

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 Annual cycle of ozone at and above the tropical tropopause: observations versus simulations with the Chemical Model of the Stratosphere (CLaMS)

2009 ◽  
Vol 9 (5) ◽  
pp. 17937-17962
Author(s):  
P. Konopka ◽  
J.-U. Grooß ◽  
G. Günther ◽  
F. Plöger ◽  
R. Pommrich ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Potential Temperature ◽  
Early Spring ◽  
Chemical Model ◽  
Boreal Summer ◽  
Meridional Transport ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
The Mean

Abstract. Multi-annual simulations with the Chemical Model of the Stratosphere (CLaMS) are used to study the seasonality of O3 and of the mean age within the stratospheric part of the tropical tropopause layer (TTL) In agreement with satellite (HALOE) and in-situ observations (SHADOZ), CLaMS simulations show above ≈360 K potential temperature, a pronounced annual cycle in O3 and in the mean age of air with highest values in the late boreal summer. Within the model, this seasonality is driven by the seasonality of both upwelling and in-mixing. The latter process describes enhanced meridional transport from the extratropics into the TTL. The strongest in-mixing occurs from the Northern Hemisphere during the boreal summer in the potential temperature range between 380 and 420 K. Contrary, an increase of upwelling with highest values in winter reduces O3 up to the lowest values in early spring. Both, CLaMS simulations and Aura MLS O3 observations show that this enhanced equatorward transport in summer is mainly driven by the Asian monsoon anticyclone.

scholarly journals Tropopause Characteristics and Variability from 11 yr of SHADOZ Observations in the Southern Tropics and Subtropics

2011 ◽  
Vol 50 (7) ◽  
pp. 1403-1416 ◽  
Author(s):  
V. Sivakumar ◽  
H. Bencherif ◽  
N. Bègue ◽  
A. M. Thompson
Keyword(s):  
Southern Hemisphere ◽  
Southern Oscillation ◽  
Lower Boundary ◽  
Lapse Rate ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Decadal Trend ◽  
Cold Point ◽  
The Tropics

AbstractIn this paper, tropopause characteristics observed from tropical to subtropical Southern Hemisphere stations using Southern Hemisphere Additional Ozonesonde (SHADOZ) data are presented for the 11-yr period of 1998–2008. Three different definitions of tropopause—cold-point tropopause (CPT), lapse-rate tropopause (LRT), and ozone tropopause (OT)—are determined, and their variability for nine different SHADOZ sites is studied for the purpose of evaluating their usefulness as indicators of possible tropopause trends. For each station, the OT is uniquely defined by the ozone gradient and is found to be more variable than either LRT or CPT. The OT roughly coincides with the upper boundary of the region of most active convective mixing over the western Pacific Ocean and with the lower boundary of the transition region from the troposphere to the lower stratosphere that is generally referred to as the tropical tropopause layer. The monthly and year-to-year variations in the tropopause are examined, and the annual cycle in OT, the dominant signal, is described. The distance of separation of the OT from the CPT or LRT is smaller for the tropics (stations at 0°–15°S) than for the subtropics (15°–25°S). The decadal trend in tropopause heights is measured using a statistical model that accounts for natural variations expressed in El Niño–Southern Oscillation, the quasi-biennial oscillation, and the Indian Ocean dipole. The decadal trend estimation shows no statistically significant trend for the CPT and LRT in the tropics, in contrast to other studies. A decrease in altitude for the OT is significant. In the subtropics, the CPT and LRT decline significantly, by −240 and −190 m (10 yr)−1, respectively, but the OT increases.

scholarly journals Regional modelling of tracer transport by tropical convection – Part 2: Sensitivity to model resolutions

2009 ◽  
Vol 9 (18) ◽  
pp. 7101-7114 ◽  
Author(s):  
J. Arteta ◽  
V. Marécal ◽  
E. D. Rivière
Keyword(s):  
Horizontal Resolution ◽  
Convective Transport ◽  
Limited Area ◽  
Tracer Transport ◽  
Regional Modelling ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Long Duration ◽  
Cold Point ◽  
The Impact

Abstract. The general objective of this series of two papers is to evaluate long duration limited-area simulations with idealised tracers as a possible tool to assess the tracer transport in chemistry-transport models (CTMs). In this second paper we analyse the results of three simulations using different horizontal and vertical resolutions. The goal is to study the impact of the model spatial resolution on convective transport of idealized tracer in the tropics. The reference simulation (REF) uses a 60 km horizontal resolution and 300 m vertically in the upper troposphere/lower stratosphere (UTLS). A 20 km horizontal resolution simulation (HR) is run as well as a simulation with 850 m vertical resolution in the UTLS (CVR). The simulations are run for one month during the SCOUT-O3 field campaign. Aircraft data, TRMM rainrate estimates and radiosoundings have been used to evaluate the simulations. They show that the HR configuration gives generally a better agreement with the measurements than the REF simulation. The CVR simulation gives generally the worst results. The vertical distribution of the tropospheric tracers for the simulations has a similar shape with a ~15 km altitude maximum for the 6h-lifetime tracer of 0.4 ppbv for REF, 1.2 for HR and 0.04 for CVR. These differences are related to the dynamics produced by the three simulations that leads to larger values of the upward velocities on average for HR and lower for CVR compared to REF. HR simulates more frequent and stronger convection leading to enhanced fluxes compared to REF and higher detrainment levels compared to CVR. HR provides also occasional overshoots over the cold point dynamical barrier. For the stratospheric tracers the differences between the three simulations are small. The diurnal cycle of the fluxes of all tracers in the Tropical Tropopause Layer exhibits a maximum linked to the maximum of convective activity.

scholarly journals The Impact of Cloud Radiative Effects on the Tropical Tropopause Layer Temperatures

Atmosphere ◽  
2018 ◽  
Vol 9 (10) ◽  
pp. 377 ◽  
Author(s):  
Qiang Fu ◽  
Maxwell Smith ◽  
Qiong Yang
Keyword(s):  
Maximum Temperature ◽  
Radiative Effects ◽  
Heating Rates ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Cloud Radiative Effect ◽  
Single Column ◽  
Cloud Radiative Effects ◽  
Cold Point ◽  
The Impact

A single-column radiative-convective model (RCM) is a useful tool to investigate the physical processes that determine the tropical tropopause layer (TTL) temperature structures. Previous studies on the TTL using the RCMs, however, omitted the cloud radiative effects. In this study, we examine the impact of cloud radiative effects on the simulated TTL temperatures using an RCM. We derive the cloud radiative effects based on satellite observations, which show heating rates in the troposphere but cooling rates in the stratosphere. We find that the cloud radiative effect warms the TTL by as much as 2 K but cools the lower stratosphere by as much as −1.5 K, resulting in a thicker TTL. With (without) considering cloud radiative effects, we obtain a convection top of ≈167 hPa (≈150 hPa) with a temperature of ≈213 K (≈209 K), and a cold point at ≈87 hPa (≈94 hPa) with a temperature of ≈204 K (≈204 K). Therefore, the cloud radiative effects widen the TTL by both lowering the convection-top height and enhancing the cold-point height. We also examine the impact of TTL cirrus radiative effects on the RCM-simulated temperatures. We find that the TTL cirrus warms the TTL with a maximum temperature increase of ≈1.3 K near 110 hPa.

scholarly journals The radiative role of ozone and water vapour in the annual temperature cycle in the tropical tropopause layer

2017 ◽  
Vol 17 (9) ◽  
pp. 5677-5701 ◽  
Author(s):  
Alison Ming ◽  
Amanda C. Maycock ◽  
Peter Hitchcock ◽  
Peter Haynes
Keyword(s):  
Water Vapour ◽  
Annual Cycle ◽  
Vertical Structure ◽  
Temperature Response ◽  
Dynamical Response ◽  
Annual Cycles ◽  
Temperature Changes ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Cold Point

Abstract. The structure and amplitude of the radiative contributions of the annual cycles in ozone and water vapour to the prominent annual cycle in temperatures in the tropical tropopause layer (TTL) are considered. This is done initially through a seasonally evolving fixed dynamical heating (SEFDH) calculation. The annual cycle in ozone is found to drive significant temperature changes predominantly locally (in the vertical) and roughly in phase with the observed TTL annual cycle. In contrast, temperature changes driven by the annual cycle in water vapour are out of phase with the latter. The effects are weaker than those of ozone but still quantitatively significant, particularly near the cold point (100 to 90 hPa) where there are substantial non-local effects from variations in water vapour in lower layers of the TTL. The combined radiative heating effect of the annual cycles in ozone and water vapour maximizes above the cold point and is one factor contributing to the vertical structure of the amplitude of the annual cycle in lower-stratospheric temperatures, which has a relatively localized maximum around 70 hPa. Other important factors are identified here: radiative damping timescales, which are shown to maximize over a deep layer centred on the cold point; the vertical structure of the dynamical heating; and non-radiative processes in the upper troposphere that are inferred to impose a strong constraint on tropical temperature perturbations below 130 hPa. The latitudinal structure of the radiative contributions to the annual cycle in temperatures is found to be substantially modified when the SEFDH assumption is relaxed and the dynamical response, as represented by a zonally symmetric calculation, is taken into account. The effect of the dynamical response is to reduce the strong latitudinal gradients and inter-hemispheric asymmetry seen in the purely radiative SEFDH temperature response, while leaving the 20° N–20° S average response relatively unchanged. The net contribution of the annual ozone and water vapour cycles to the peak-to-peak amplitude in the annual cycle of TTL temperatures is found to be around 35 % of the observed 8 K at 70 hPa, 40 % of 6 K at 90 hPa, and 45 % of 3 K at 100 hPa. The primary sensitivity of the calculated magnitude of the temperature response is identified as the assumed annual mean ozone mixing ratio in the TTL.

scholarly journals The impact of temperature resolution on trajectory modeling of stratospheric water vapour

2014 ◽  
Vol 14 (21) ◽  
pp. 29209-29236 ◽  
Author(s):  
T. Wang ◽  
A. E. Dessler ◽  
M. R. Schoeberl ◽  
W. J. Randel ◽  
J.-E. Kim
Keyword(s):  
Water Vapour ◽  
Vertical Resolution ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Finite Resolution ◽  
Cold Point ◽  
Wave Induced ◽  
The Impact ◽  
Modern Era ◽  
Stratospheric Water Vapour

Abstract. Lagrangian trajectories driven by reanalysis meteorological fields are frequently used to study water vapour (H2O) in the stratosphere, in which the tropical cold-point temperatures regulate H2O amount entering the stratosphere. Therefore, the accuracy of temperatures in the tropical tropopause layer (TTL) is of great importance for trajectory studies. 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 introduce uncertainties in the simulations. In this paper, we quantify this uncertainty by comparing the trajectory results using MERRA temperatures on model levels (traj.MER-T) to those using temperatures in finite resolutions, including GPS temperatures (traj.GPS-T) and MERRA temperatures adjusted to recover wave-induced variability underrepresented by the current ~1.2 km vertical resolution (traj.MER-Twave). Comparing with traj.MER-T, traj.GPS-T has little impact on simulated stratospheric H2O (changes ~0.1 ppmv), whereas traj.MER-Twave tends to dry air by 0.2–0.3 ppmv. The bimodal dehydration peaks in traj.MER-T due to limited vertical resolution disappear in traj.GPS-T and traj.MER-Twave by allowing the cold-point tropopause to be found at finer vertical levels. 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 the finite resolution of temperature has limited impact on predicted H2O in the trajectory model.

scholarly journals Annual cycle of ozone at and above the tropical tropopause: observations versus simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS)

2010 ◽  
Vol 10 (1) ◽  
pp. 121-132 ◽  
Author(s):  
P. Konopka ◽  
J.-U. Grooß ◽  
G. Günther ◽  
F. Ploeger ◽  
R. Pommrich ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Potential Temperature ◽  
Early Spring ◽  
Lagrangian Model ◽  
Boreal Summer ◽  
Tropical Tropopause Layer ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
In Situ Observations

Abstract. Multi-annual simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) were conducted to study the seasonality of O3 within the stratospheric part of the tropical tropopause layer (TTL), i.e. above θ=360 K potential temperature level. In agreement with satellite (HALOE) and in-situ observations (SHADOZ), CLaMS simulations show a pronounced annual cycle in O3, at and above θ=380 K, with the highest mixing ratios in the late boreal summer. Within the model, this cycle is driven by the seasonality of both upwelling and in-mixing. The latter process occurs through enhanced horizontal transport from the extratropics into the TTL that is mainly driven by the meridional, isentropic winds. The strongest in-mixing occurs during the late boreal summer from the Northern Hemisphere in the potential temperature range between 370 and 420 K. Complementary, the strongest upwelling occurs in winter reducing O3 to the lowest values in early spring. Both CLaMS simulations and Aura MLS O3 observations consistently show that enhanced in-mixing in summer is mainly driven by the Asian monsoon anticyclone.

scholarly journals Model study of the cross-tropopause transport of biomass burning pollution

2007 ◽  
Vol 7 (14) ◽  
pp. 3713-3736 ◽  
Author(s):  
B. N. Duncan ◽  
S. E. Strahan ◽  
Y. Yoshida ◽  
S. D. Steenrod ◽  
N. Livesey
Keyword(s):  
Biomass Burning ◽  
El Niño ◽  
Fossil Fuels ◽  
Extreme Event ◽  
El Nino ◽  
Deep Convection ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
El Niño Event ◽  
The Impact

Abstract. We present a modeling study of the troposphere-to-stratosphere transport (TST) of pollution from major biomass burning regions to the tropical upper troposphere and lower stratosphere (UT/LS). TST occurs predominately through 1) slow ascent in the tropical tropopause layer (TTL) to the LS and 2) quasi-horizontal exchange to the lowermost stratosphere (LMS). We show that biomass burning pollution regularly and significantly impacts the composition of the TTL, LS, and LMS. Carbon monoxide (CO) in the LS in our simulation and data from the Aura Microwave Limb Sounder (MLS) shows an annual oscillation in its composition that results from the interaction of an annual oscillation in slow ascent from the TTL to the LS and seasonal variations in sources, including a semi-annual oscillation in CO from biomass burning. The impacts of CO sources that peak when ascent is seasonally low are damped (e.g. Southern Hemisphere biomass burning) and vice-versa for sources that peak when ascent is seasonally high (e.g. extra-tropical fossil fuels). Interannual variation of CO in the UT/LS is caused primarily by year-to-year variations in biomass burning and the locations of deep convection. During our study period, 1994–1998, we find that the highest concentrations of CO in the UT/LS occurred during the strong 1997–1998 El Niño event for two reasons: i. tropical deep convection shifted to the eastern Pacific Ocean, closer to South American and African CO sources, and ii. emissions from Indonesian biomass burning were higher. This extreme event can be seen as an upper bound on the impact of biomass burning pollution on the UT/LS. We estimate that the 1997 Indonesian wildfires increased CO in the entire TTL and tropical LS (>60 mb) by more than 40% and 10%, respectively, for several months. Zonal mean ozone increased and the hydroxyl radical decreased by as much as 20%, increasing the lifetimes and, subsequently TST, of trace gases. Our results indicate that the impact of biomass burning pollution on the UT/LS is likely greatest during an El Niño event due to favorable dynamics and historically higher burning rates.

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