scholarly journals Enhanced upward motion through the troposphere over the tropical western Pacific and its implication to transport of trace gases from the troposphere to the stratosphere

2021 ◽  
Author(s):  
Kai Qie ◽  
Wuke Wang ◽  
Wenshou Tian ◽  
Rui Huang ◽  
Mian Xu ◽  
...  
Keyword(s):  
Climate Model ◽  
Dominant Role ◽  
Deep Convection ◽  
Trace Gases ◽  
Walker Circulation ◽  
Western Pacific ◽  
Upward Motion ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Tropical Western Pacific

Abstract. The tropical western Pacific (TWP) is a preferential area of air uplifting from the surface to the upper troposphere. A significantly intensified upward motion through the troposphere over the TWP in the boreal wintertime (November to March of the next year) has been detected from 1958 to 2017 using the reanalysis datasets. Model simulations using the Whole Atmosphere Community Climate Model, version 4 (WACCM4) suggest that warming global sea surface temperatures (SSTs), particularly TWP SSTs, play a dominant role in the intensification of the upward motion by strengthening the Pacific Walker circulation and enhancing the deep convection over the TWP. Using CO as a tropospheric tracer, numeric simulations show that more CO could be elevated to the tropical tropopause layer (TTL) by the enhanced upward motion over the TWP and subsequently into the stratosphere by the strengthened Brewer-Dobson (BD) circulation which is also mainly caused by global SST warming. This implies that more tropospheric trace gases and aerosols may enter the stratosphere through the TWP region and affect the stratospheric chemistry and climate.

scholarly journals Tropical convective transport and the Walker circulation

2012 ◽  
Vol 12 (20) ◽  
pp. 9791-9797 ◽  
Author(s):  
J. S. Hosking ◽  
M. R. Russo ◽  
P. Braesicke ◽  
J. A. Pyle
Keyword(s):  
Climate Model ◽  
Deep Convection ◽  
Walker Circulation ◽  
Reanalysis Data ◽  
Convective Transport ◽  
Boreal Winter ◽  
Transport Pathways ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
The Walker Circulation

Abstract. We introduce a methodology to visualise rapid vertical and zonal tropical transport pathways. Using prescribed sea-surface temperatures in four monthly model integrations for 2005, we characterise preferred transport routes from the troposphere to the stratosphere in a high resolution climate model. Most efficient transport is modelled over the Maritime Continent (MC) in November and February, i.e., boreal winter. In these months, the ascending branch of the Walker Circulation over the MC is formed in conjunction with strong deep convection, allowing fast transport into the stratosphere. In the model the upper tropospheric zonal winds associated with the Walker Circulation are also greatest in these months in agreement with ERA-Interim reanalysis data. We conclude that the Walker circulation plays an important role in the seasonality of fast tropical transport from the lower and middle troposphere to the upper troposphere and so impacts at the same time the potential supply of surface emissions to the tropical tropopause layer (TTL) and subsequently to the stratosphere.

scholarly journals Bromine partitioning in the tropical tropopause layer: implications for stratospheric injection

2014 ◽  
Vol 14 (12) ◽  
pp. 17857-17905 ◽  
Author(s):  
R. P. Fernandez ◽  
R. J. Salawitch ◽  
D. E. Kinnison ◽  
J.-F. Lamarque ◽  
A. Saiz-Lopez
Keyword(s):  
Geographic Distribution ◽  
State Of The Art ◽  
Convective Transport ◽  
Global Model ◽  
Western Pacific ◽  
Annual Average ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Tropical Western Pacific ◽  
Inorganic Species

Abstract. Very short-lived (VSL) bromocarbons are produced at a prodigious rate by ocean biology and these source compounds (SGVSL), together with their degradation inorganic products (PGVSL), are lofted by vigorous convection to the tropical tropopause layer (TTL). Using a state-of-the-art photochemical mechanism within a global model, we calculate annual average stratospheric injection of total bromine due to VSL sources to be 5 pptv, with ~3 pptv entering the stratosphere as PGVSL and ~2 pptv as SGVSL. The geographic distribution and partitioning of VSL bromine within the TTL, and its consequent stratospheric injection, is highly dependent on the oceanic flux, the strength of convection and the occurrence of heterogeneous recycling reactions. Our calculations indicate atomic Br should be the dominant inorganic species in large regions of the TTL during daytime, due to the low ozone and cold conditions of this region. We propose the existence of a "tropical ring of atomic bromine" located approximately between 15 and 19 km and 30° N to 30° S. Daytime Br / BrO ratios of up to ~4 are predicted within the Br ring in regions of highly convective transport, such as the tropical Western Pacific. Then, we suggest experimental programs designed to quantify the bromine budget of the TTL and the stratospheric injection of VSL biogenic bromocarbons should include a strategy for the measurement of atomic Br during daytime and HOBr or BrCl during nighttime.

Longitudinal Asymmetric Trends of Tropical Cold-Point Tropopause Temperature and Their Link to Strengthened Walker Circulation

2016 ◽  
Vol 29 (21) ◽  
pp. 7755-7771 ◽  
Author(s):  
Dingzhu Hu ◽  
Wenshou Tian ◽  
Zhaoyong Guan ◽  
Yipeng Guo ◽  
Sandip Dhomse
Keyword(s):  
Climate Model ◽  
Walker Circulation ◽  
Warm Pool ◽  
Tropical Regions ◽  
Model Simulations ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Climate Model Simulations ◽  
Cold Point ◽  
Tropopause Temperature

Abstract The zonal structure of trends in the tropical tropopause layer during 1979–2014 is investigated by using reanalysis datasets and chemistry–climate model simulations. The analysis herein reveals that the tropical cold-point tropopause temperature (CPTT) trends during 1979–2014 are zonally asymmetric; that is, over the tropical central and eastern Pacific (CEP; 20°S–20°N, 160°E–100°W), the CPTT shows an increasing trend of 0.22 K decade−1, whereas over the rest of the tropical regions (non-CEP regions) the CPTT shows a decreasing trend of −0.08 K decade−1. Model simulations suggest that this zonal asymmetry in the tropical CPTT trends can be partly attributed to Walker circulation (WC) changes induced by zonally asymmetric changes of the sea surface temperatures (SSTs). The increasing (decreasing) SSTs over the western Pacific (CEP) result in a larger zonal gradient in sea level pressure over the tropical Pacific and intensified surface easterlies. The increased pressure gradient leads to enhanced convection over the Indo-Pacific warm pool and weakened convection over the CEP, facilitating a stronger WC. The downward branch of the intensified WC induces a dynamical warming over the CEP and the upward branch of the intensified WC induces a dynamical cooling over the non-CEP regions below 150 hPa. The significant warming in the upper troposphere and lower stratosphere (UTLS) caused by the WC descending and wave activity changes in the UTLS over the CEP shifts the cold-point tropopause height to a higher level, while the radiative effects of greenhouse gases, ozone, and water vapor changes in the UTLS make less important contributions to the trend of the tropical CPTT than SST changes.

scholarly journals Convective transport of very short lived bromocarbons to the stratosphere

2014 ◽  
Vol 14 (11) ◽  
pp. 5781-5792 ◽  
Author(s):  
Q. Liang ◽  
E. Atlas ◽  
D. Blake ◽  
M. Dorf ◽  
K. Pfeilsticker ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Climate Model ◽  
Degradation Products ◽  
Deep Convection ◽  
Gas Injection ◽  
Tropical Indian Ocean ◽  
Convective Transport ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause

Abstract. We use the NASA Goddard Earth Observing System (GEOS) Chemistry Climate Model (GEOSCCM) to quantify the contribution of the two most important brominated very short lived substances (VSLSs), bromoform (CHBr3) and dibromomethane (CH2Br2), to stratospheric bromine and its sensitivity to convection strength. Model simulations suggest that the most active transport of VSLSs from the marine boundary layer through the tropopause occurs over the tropical Indian Ocean, the tropical western Pacific, and off the Pacific coast of Mexico. Together, convective lofting of CHBr3 and CH2Br2 and their degradation products supplies ~8 ppt total bromine to the base of the tropical tropopause layer (TTL, ~150 hPa), similar to the amount of VSLS organic bromine available in the marine boundary layer (~7.8–8.4 ppt) in the active convective lofting regions mentioned above. Of the total ~8 ppt VSLS bromine that enters the base of the TTL at ~150 hPa, half is in the form of organic source gases and half in the form of inorganic product gases. Only a small portion (<10%) of the VSLS-originated bromine is removed via wet scavenging in the TTL before reaching the lower stratosphere. On average, globally, CHBr3 and CH2Br2 together contribute ~7.7 pptv to the present-day inorganic bromine in the stratosphere. However, varying model deep-convection strength between maximum (strongest) and minimum (weakest) convection conditions can introduce a ~2.6 pptv uncertainty in the contribution of VSLSs to inorganic bromine in the stratosphere (BryVSLS). Contrary to conventional wisdom, the minimum convection condition leads to a larger BryVSLS as the reduced scavenging in soluble product gases, and thus a significant increase in product gas injection (2–3 ppt), greatly exceeds the relatively minor decrease in source gas injection (a few 10ths ppt).

scholarly journals Effects of convective ice evaporation on interannual variability of tropical tropopause layer water vapor

2018 ◽  
Vol 18 (7) ◽  
pp. 4425-4437 ◽  
Author(s):  
Hao Ye ◽  
Andrew E. Dessler ◽  
Wandi Yu
Keyword(s):  
Water Vapor ◽  
Interannual Variability ◽  
Climate Model ◽  
Deep Convection ◽  
Tropospheric Temperature ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause Layer ◽  
Earth Observing System ◽  
Tropical Tropopause ◽  
The Impact

Abstract. Water vapor interannual variability in the tropical tropopause layer (TTL) is investigated using satellite observations and model simulations. We break down the influences of the Brewer–Dobson circulation (BDC), the quasi-biennial oscillation (QBO), and the tropospheric temperature (ΔT) on TTL water vapor as a function of latitude and longitude using a two-dimensional multivariate linear regression. This allows us to examine the spatial distribution of the impact of each process on TTL water vapor. In agreement with expectations, 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 the troposphere warms. Tests using a chemistry–climate model, the Goddard Earth Observing System Chemistry Climate Model (GEOSCCM), support this hypothesis.

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.

scholarly journals Ozonesonde profiles from the West Pacific Warm Pool

2015 ◽  
Vol 15 (12) ◽  
pp. 16655-16696 ◽  
Author(s):  
R. Newton ◽  
G. Vaughan ◽  
H. M. A. Ricketts ◽  
L. L. Pan ◽  
A. J. Weinheimer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ozone Concentration ◽  
Deep Convection ◽  
Warm Pool ◽  
Atmospheric Composition ◽  
Measured Signal ◽  
Background Current ◽  
West Pacific ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause

Abstract. We present a series of ozonesonde profiles measured from Manus Island, Papua New Guinea, during February 2014. The experiment formed a part of a wider airborne campaign involving three aircraft based in Guam, to characterise the atmospheric composition above the tropical West Pacific in unprecedented detail. Thirty-nine ozonesondes were launched between 2 and 25 February, of which 34 gave good ozone profiles. Particular attention was paid to measuring the background current of the ozonesonde before launch, as this can amount to half the measured signal in the tropical tropopause layer (TTL). An unexpected contamination event affected these measurements and required a departure from standard operating procedures for the ozonesondes. Comparison with aircraft measurements allows validation of the measured ozone profiles and confirms that for well-characterized sondes (background current <50 nA) a constant background current should be assumed throughout the profile, equal to the minimum value measured during preparation just before launch. From this set of 34 ozonesondes, the minimum reproducible ozone concentration measured in the TTL was 12–13 ppbv; no examples of near-zero ozone concentration as reported by other recent papers were measured. The lowest ozone concentrations coincided with outflow from extensive deep convection to the east of Manus, consistent with uplift of ozone-poor air from the boundary layer. However, these minima were lower than the ozone concentration measured through most of the boundary layer, and were matched only by measurements at the surface in Manus.

scholarly journals Water vapor anomaly over the tropical western Pacific in El Niño winters from radiosonde and satellite observations

2021 ◽  
Author(s):  
Minkang Du ◽  
Kaiming Huang ◽  
Shaodong Zhang ◽  
Chunming Huang ◽  
Yun Gong ◽  
...  
Keyword(s):  
Water Vapor ◽  
El Niño ◽  
El Nino ◽  
Walker Circulation ◽  
Western Pacific ◽  
Monsoon Circulation ◽  
Circulation Anomaly ◽  
Tropical Western Pacific ◽  
Ep El Niño ◽  
The Walker Circulation

Abstract. Using radiosonde observations at five stations in the tropical western Pacific and reanalysis data for 15 years from 2005 to 2019, we report an extremely negative anomaly in atmospheric water vapor during the super El Niño winter of 2015/16, and compare the anomaly with that in the other three El Niño winters. Strong specific humidity anomaly is concentrated below 8 km of the troposphere with a peak at 2.5–3.5 km, and column integrated water vapor mass anomaly over the five radiosonde sites has a large negative correlation coefficient of −0.63 with oceanic Niño3.4 index, but with a lag of about 2–3 months. In general, the tropical circulation anomaly in the El Niño winter is characterized by divergence (convergence) in the lower troposphere over the tropical western (eastern) Pacific, thus the water vapor decreases over the tropical western Pacific as upward motion is suppressed. The variability of the Hadley circulation is quite small and has little influence on the observed water vapor anomaly. The anomaly of the Walker circulation makes a considerable contribution to the total anomaly in all the four El Niño winters, especially in the 2006/07 and 2015/16 eastern-Pacific (EP) El Niño events. The monsoon circulation shows a remarkable change from one to the other event, and its anomaly is large in the 2009/10 and 2018/19 central-Pacific (CP) El Niño winters and small in the two EP El Niño winters. The observed water vapor anomaly is caused mainly by the Walker circulation anomaly in the supper EP event of 2015/16 but by the monsoon circulation anomaly in the strong CP event of 2009/10. Owing to the anomalous decrease in upward transport of water vapor during the El Niño winter, less cloud amount and more outgoing longwave radiation over the five stations are clearly presented in satellite observation.

scholarly journals The impact of overshooting deep convection on local transport and mixing in the tropical upper troposphere/lower stratosphere (UTLS)

2015 ◽  
Vol 15 (11) ◽  
pp. 6467-6486 ◽  
Author(s):  
W. Frey ◽  
R. Schofield ◽  
P. Hoor ◽  
D. Kunkel ◽  
F. Ravegnani ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Transport Processes ◽  
Convective System ◽  
Upper Troposphere ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Transport And Mixing ◽  
The Impact

Abstract. In this study we examine the simulated downward transport and mixing of stratospheric air into the upper tropical troposphere as observed on a research flight during the SCOUT-O3 campaign in connection with a deep convective system. We use the Advanced Research Weather and Research Forecasting (WRF-ARW) model with a horizontal resolution of 333 m to examine this downward transport. The simulation reproduces the deep convective system, its timing and overshooting altitudes reasonably well compared to radar and aircraft observations. Passive tracers initialised at pre-storm times indicate the downward transport of air from the stratosphere to the upper troposphere as well as upward transport from the boundary layer into the cloud anvils and overshooting tops. For example, a passive ozone tracer (i.e. a tracer not undergoing chemical processing) shows an enhancement in the upper troposphere of up to about 30 ppbv locally in the cloud, while the in situ measurements show an increase of 50 ppbv. However, the passive carbon monoxide tracer exhibits an increase, while the observations show a decrease of about 10 ppbv, indicative of an erroneous model representation of the transport processes in the tropical tropopause layer. Furthermore, it could point to insufficient entrainment and detrainment in the model. The simulation shows a general moistening of air in the lower stratosphere, but it also exhibits local dehydration features. Here we use the model to explain the processes causing the transport and also expose areas of inconsistencies between the model and observations.

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

&lt;p&gt;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.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document