This study presents airborne in situ and satellite remote sensing climatologies of cirrus clouds and humidity. The climatologies serve as a guide to the properties of cirrus clouds, with the new in ...situ database providing detailed insights into boreal midlatitudes and the tropics, while the satellite-borne data set offers a global overview.
The Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) field mission based at Ellington Field, Texas, during August and September 2013 ...employed the most comprehensive airborne payload to date to investigate atmospheric composition over North America. The NASA ER‐2, DC‐8, and SPEC Inc. Learjet flew 57 science flights from the surface to 20 km. The ER‐2 employed seven remote sensing instruments as a satellite surrogate and eight in situ instruments. The DC‐8 employed 23 in situ and five remote sensing instruments for radiation, chemistry, and microphysics. The Learjet used 11 instruments to explore cloud microphysics. SEAC4RS launched numerous balloons, augmented AErosol RObotic NETwork, and collaborated with many existing ground measurement sites. Flights investigating convection included close coordination of all three aircraft. Coordinated DC‐8 and ER‐2 flights investigated the optical properties of aerosols, the influence of aerosols on clouds, and the performance of new instruments for satellite measurements of clouds and aerosols. ER‐2 sorties sampled stratospheric injections of water vapor and other chemicals by local and distant convection. DC‐8 flights studied seasonally evolving chemistry in the Southeastern U.S., atmospheric chemistry with lower emissions of NOx and SO2 than in previous decades, isoprene chemistry under high and low NOx conditions at different locations, organic aerosols, air pollution near Houston and in petroleum fields, smoke from wildfires in western forests and from agricultural fires in the Mississippi Valley, and the ways in which the chemistry in the boundary layer and the upper troposphere were influenced by vertical transport in convective clouds.
Key Points
The SEAC4RS field mission was based near Houston, Texas during August and September of 2013
The paper overviews the mission to aid those interested in this data set to understand its context
The data can be accessed at http://www‐air.larc.nasa.gov/cgi‐bin/ArcView/seac4rs
The Asian summer monsoon (ASM) anticyclone circulation system is recognized to be a significant transport pathway for water vapor and pollutants to enter the stratosphere. The observational evidence, ...however, is largely based on satellite retrievals. We report the first coincident in situ measurements of water vapor and ozone within the ASM anticyclone. The combined water vapor and ozonesondes were launched from Kunming, China in August 2009 and Lhasa, China in August 2010. In total, 11 and 12 sondes were launched in Kunming and Lhasa, respectively. We present the key characteristics of these measurements, and provide a comparison to similar measurements from an equatorial tropical location, during the Tropical Composition, Cloud and Climate Coupling (TC4) campaign in July and August of 2007. Results show that the ASM anticyclone region has higher water vapor and lower ozone concentrations in the upper troposphere and lower stratosphere than the TC4 observations. The results also show that the cold point tropopause in the ASM region has a higher average height and potential temperature. The in situ observations therefore support the satellite‐based conclusion that the ASM is an effective transport pathway for water vapor to enter stratosphere.
Key Points
First in situ measurements of water vapor and ozone within the ASM anticyclone
ASM anticyclone has higher water vapor and lower ozone in the UTLS
ASM region has a higher cold point tropopause level
Four years of temperature profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate GPS satellite retrievals are used to examine the difference between the World ...Meteorological Organization lapse rate definition and the cold point definition of the tropopause in the tropics. The separation between the cold point tropopause (CPT) and lapse rate tropopause (LRT) heights is quantified in seasonal averages and with the frequency of occurrence. In seasonal averages, small separations, <0.5 km, are found in the deep tropics, increasing to ~1 km toward higher latitudes and maximizing at ~1.5 km near the jet streams. The seasonal average separations show significant longitudinal structures in the December‐January‐February (DJF) and June‐July‐August (JJA) seasons. Case studies indicate that breaking Rossby waves and their effects extending into the equatorial region are responsible for the longitudinal structure in the DJF season. The seasonal average CPT‐LRT separation therefore identifies the regions of the tropical upper troposphere‐lower stratosphere that are controlled by extratropical forcing. Examination of individual profiles shows that a small yet significant fraction (~12%) of temperature profiles has CPT‐LRT separations of 1 km or larger in the region of small seasonal average separation. These large separations are produced by wave perturbations of the upper tropospheric temperature structure. The impact of tropopause separation on the cloud top‐tropopause relationship is examined using colocated CALIPSO cloud top data. We find that the frequency of clouds above the tropopause is reduced by approximately 50% if the CPT is used instead of LRT. The occurrence of clouds above the CPT is nevertheless significant, especially over the western Pacific in the DJF season and over the Asian monsoon region in the JJA season.
Key Points
CPT‐LRT separation is smallest in the deep tropics and largest in the subtropics
In deep tropics, warm phase of waves creates CPT‐LRT separation
About 50% of clouds that are above the tropical LRT are below the CPT
Chemical transport associated with the dynamics of the Asian summer monsoon (ASM) system is investigated using model output from the National Center for Atmospheric Research (NCAR) Whole Atmosphere ...Community Climate Model run in specified dynamics mode. The 3‐D day‐to‐day behavior of modeled carbon monoxide is analyzed together with dynamical fields and transport boundaries to identify preferred locations of uplifting from the boundary layer, the role of subseasonal‐scale dynamics in the upper troposphere and lower stratosphere (UTLS), and the relationship of ASM transport and the stratospheric residual circulation. The model simulation of CO shows the intraseasonal east‐west oscillation of the anticyclone may play an essential role in transporting convectively pumped boundary layer pollutants in the UTLS. A statistical analysis of 11 year CO also shows that the southern flank of the Tibetan plateau is a preferred location for boundary layer tracers to be lofted to the tropopause region. The vertical structure of a model tracer (E90) further shows that the rapid ASM vertical transport is only effective up to the tropopause level (around 400 K). The efficiency of continued vertical transport into the deep stratosphere is limited by the slow ascent associated with the zonal‐mean residual circulation in the lower stratosphere during northern summer. Quasi‐isentropic transport near the 400 K potential temperature level is likely the most effective process for ASM anticyclone air to enter the stratosphere.
Key Points
Model results indicate that there is a preferred location of vertical transport from the boundary layer to UTLS
Subseasonal‐scale dynamics of the Asian monsoon anticyclone is an important driver of UTLS chemical transport
The season's slow ascent in residual circulation limits the efficiency of vertical transport into the stratosphere from the ASM
We present data and analysis of a set of balloon‐borne sounding profiles, which includes co‐located O3, CO, CH4, and particles, over the northern Tibetan Plateau during an Asian summer monsoon (ASM) ...season. These novel measurements shed light on the ASM transport behavior near the northern edge of the anticyclone. Joint analyses of these species with the temperature and wind profiles and supported by back trajectory modeling identify three distinct transport processes that dominate the vertical chemical structure in the middle troposphere, upper troposphere (UT), and the tropopause region. The correlated changes in profile structures in the middle troposphere highlight the influence of the strong westerly jet. Elevated constituent concentrations in the UT identify the main level of convective transport at the upstream source regions. Observed higher altitude maxima for CH4 characterize the airmasses' continued ascent following convection. These data complement constituent observations from other parts of the ASM anticyclone.
Plain Language Summary
Asian summer monsoon deep convection transports surface pollutants to the stratosphere. Although satellite data have provided clear evidence of this transport, in situ measurements are critical for characterizing how monsoon is vertically re‐distributing the regional emissions. We report new balloon‐borne measurements over the Tibetan Plateau that provide a unique data set on the northern edge of the anticyclone, complementing other observations.
Key Points
A novel set of in‐situ profile measurements of O3, CO, CH4 and particles from Tibetan Plateau during Asian summer monsoon are presented
Joint analyses of the profiles provide insights into transport processes controlling the northern edge of the Asian monsoon anticyclone
Observed CO profile maxima at 13–14 km (∼360–370 K) identify the level of convective transport at the upstream source regions
Although the tropopause is a well‐established concept, its definition and physical properties remain an active research topic. In the tropics, both the World Meteorological Organization established ...lapse rate tropopause definition and the minimum in the temperature profile (the cold point) are used to determine the tropopause height. We examine the differences produced by these two definitions using high‐resolution airborne in situ measurements of temperature, water vapor, and ozone in the tropical tropopause layer from a recent experiment over the western Pacific using the National Aeronautics and Space Administration (NASA) Global Hawk unmanned aircraft system. When the two definitions do not produce the same tropopause height, which is in about half of the cases, the combined temperature and trace gas analysis shows that the lapse rate definition better identifies the transition from the troposphere to the stratosphere.
Plain Language Summary
Discovered more than a century ago, the tropopause is known to mark the boundary of two dynamically and chemically distinct layers of atmosphere, the stratosphere, and the troposphere. In the tropics, the location, temperature, and physical/chemical gradients of the tropopause are important as part of the fundamental knowledge of the atmosphere and for regulating the amount of water vapor entering the stratosphere, which has a significant contribution to climate forcing. The tropopause over the tropical western Pacific, in particular, is known as the decisive region for determining the amount of stratospheric water vapor. High‐resolution measurements for this region are rare because the region is remote and tropopause altitudes are difficult to access. An airborne experiment targeting this decisive region was conducted in 2014, using the National Aeronautics and Space Administration (NASA) Global Hawk unmanned aircraft system. These high‐resolution temperature and trace gas data provided an unprecedented opportunity to examine the physical meaning of the two tropical tropopause definitions, known as the lapse‐rate tropopause and the cold‐point tropopause. In this work, we demonstrate how the relationship of two chemical tracers, ozone and water vapor, can unambiguously identify the transition from troposphere to stratosphere and therefore serve to diagnose the effectiveness of the different tropopause definitions.
Key Points
The tropical tropopause definitions are examined using airborne in situ measurements over the tropical western Pacific
O3 and H2O relationship is used to identify the air mass change from the troposphere to the stratosphere
The lapse rate definition is shown to more consistently identify the tropopause based on the tracer diagnostic
An enhanced aerosol layer near the tropopause over Asia during the June–September period of the Asian summer monsoon (ASM) was recently identified using satellite observations. Its sources and ...climate impact are presently not well-characterized. To improve understanding of this phenomenon, we made in situ aerosol measurements during summer 2015 from Kunming, China, then followed with a modeling study to assess the global significance. The in situ measurements revealed a robust enhancement in aerosol concentration that extended up to 2 km above the tropopause. A climate model simulation demonstrates that the abundant anthropogenic aerosol precursor emissions from Asia coupled with rapid vertical transport associated with monsoon convection leads to significant particle formation in the upper troposphere within the ASM anticyclone. These particles subsequently spread throughout the entire Northern Hemispheric (NH) lower stratosphere and contribute significantly (∼15%) to the NH stratospheric column aerosol surface area on an annual basis. This contribution is comparable to that from the sum of small volcanic eruptions in the period between 2000 and 2015. Although the ASM contribution is smaller than that from tropical upwelling (∼35%), we find that this region is about three times as efficient per unit area and time in populating the NH stratosphere with aerosol. With a substantial amount of organic and sulfur emissions in Asia, the ASM anticyclone serves as an efficient smokestack venting aerosols to the upper troposphere and lower stratosphere. As economic growth continues in Asia, the relative importance of Asian emissions to stratospheric aerosol is likely to increase.
Every year during the Asian summer monsoon season from about mid-June to early September, a stable anticyclonic circulation system forms over the Himalayas. This Asian summer monsoon (ASM) ...anticyclone has been shown to promote transport of air into the stratosphere from the Asian troposphere, which contains large amounts of anthropogenic pollutants. Essential details of Asian monsoon transport, such as the exact timescales of vertical transport, the role of convection in cross-tropopause exchange, and the main location and level of export from the confined anticyclone to the stratosphere are still not fully resolved. Recent airborne observations from campaigns near the ASM anticyclone edge and centre in 2016 and 2017, respectively, show a steady decrease in carbon monoxide (CO) and increase in ozone (O3) with height starting from tropospheric values of around 100 ppb CO and 30–50 ppb O3 at about 365 K potential temperature. CO mixing ratios reach stratospheric background values below ∼25 ppb at about 420 K and do not show a significant vertical gradient at higher levels, while ozone continues to increase throughout the altitude range of the aircraft measurements. Nitrous oxide (N2O) remains at or only marginally below its 2017 tropospheric mixing ratio of 333 ppb up to about 400 K, which is above the local tropopause. A decline in N2O mixing ratios that indicates a significant contribution of stratospheric air is only visible above this level. Based on our observations, we draw the following picture of vertical transport and confinement in the ASM anticyclone: rapid convective uplift transports air to near 16 km in altitude, corresponding to potential temperatures up to about 370 K. Although this main convective outflow layer extends above the level of zero radiative heating (LZRH), our observations of CO concentration show little to no evidence of convection actually penetrating the tropopause. Rather, further ascent occurs more slowly, consistent with isentropic vertical velocities of 0.7–1.5 K d−1. For the key tracers (CO, O3, and N2O) in our study, none of which are subject to microphysical processes, neither the lapse rate tropopause (LRT) around 380 K nor the cold point tropopause (CPT) around 390 K marks a strong discontinuity in their profiles. Up to about 20 to 35 K above the LRT, isolation of air inside the ASM anticyclone prevents significant in-mixing of stratospheric air (throughout this text, the term in-mixing refers specifically to mixing processes that introduce stratospheric air into the predominantly tropospheric inner anticyclone). The observed changes in CO and O3 likely result from in situ chemical processing. Above about 420 K, mixing processes become more significant and the air inside the anticyclone is exported vertically and horizontally into the surrounding stratosphere.
Air masses within the Asian monsoon anticyclone (AMA) show anomalous signatures in various trace gases. In this study, we investigate how air masses are transported from the planetary boundary layer ...(PBL) to the AMA based on multiannual trajectory analyses. In particular, we focus on the climatological perspective and on the intraseasonal and interannual variability. Further, we also discuss the relation of the interannual east-west displacements of the AMA with the transport from the PBL to the AMA. The analysis of both model data sets highlights the interannual and intraseasonal variability of the PBL source regions of the AMA. Although there are differences in the transport pathways, the interannual east-west displacement of the AMA - which we find to be related to the monsoon Hadley index - is not connected to considerable differences in the overall transport characteristics.
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