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  • 1
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    Online Resource
    Measurements of nitrogen oxides at the tropopause: Attribution to convection and correlation with lightning
    American Geophysical Union (AGU) ; 2000
    In:  Journal of Geophysical Research: Atmospheres Vol. 105, No. D3 ( 2000-02-16), p. 3679-3700
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 105, No. D3 ( 2000-02-16), p. 3679-3700
    Abstract: NO x (NO and NO 2 ) and ozone were measured on 98 flights during August to November 1997 in the framework of the projects Pollution From Aircraft Emissions in the North Atlantic Flight Corridor (POLINAT 2) and Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX). The fully automated measurement system Nitrogen Oxides and Ozone Along Air Routes (NOXAR) was permanently installed aboard an inservice Swissair B‐747 airliner operating in the North Atlantic Flight Corridor. Below the tropopause, predominantly over the U.S. east coast, the patchy occurrence of NO x enhancements up to 3000 parts per trillion by volume (pptv) was observed frequently and led to a lognormal probability density function of NO x . These plumes extend over several hundred kilometers. In three case studies the origin of such plumes was investigated using back trajectories, satellite infrared images, and lightning observations from the U.S. National Lightning Detection Network (NLDN) and the Optical Transient Detector (OTD) satellite instrument. In the case of frontal activity above the continental United States, the location of NO x plumes was explained with maps of convective influence. In another case, NO x seems to have been produced by lightning in a marine thunderstorm over the eastern Atlantic. Lightning activity triggered over the warm Gulf Stream is found to be an important source for the regional upper tropospheric NO x budget, at least for the time period considered. With a method that we call “lightning tracing” we show for the first time that (in some cases) the number of lightning flashes, accumulated along back trajectories, was proportional to the NO x concentrations observed several hundred kilometers downwind of the anvil outflows. We suggest that mixing processes in convective clouds reduce the initially highly heterogeneous NO x field rapidly, but that following this phase, the structure of large‐scale plumes remains stable over relatively long periods of time (as they decay).
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/1999JD901053
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2000
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  • 2
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    Ubiquitous influence of waves on tropical high cirrus clouds
    American Geophysical Union (AGU) ; 2016
    In:  Geophysical Research Letters Vol. 43, No. 11 ( 2016-06-16), p. 5895-5901
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 43, No. 11 ( 2016-06-16), p. 5895-5901
    Abstract: Extensive airborne measurements reveal widespread influence of waves on tropical high cirrus clouds Cirrus clouds preferentially occur at cold anomalies with ongoing cooling Vertical scales of waves affect vertical scales of cirrus layers
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Issue
    URL: Article
    DOI: 10.1002/grl.v43.11
    DOI: 10.1002/2016GL069293
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2016
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  • 3
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    Preface [to special section on 'The Tropical Experiment of the Stratosphere‐Troposphere Exchange Project (STEP Tropical)]
    American Geophysical Union (AGU) ; 1993
    In:  Journal of Geophysical Research: Atmospheres Vol. 98, No. D5 ( 1993-05-20), p. 8561-8562
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 98, No. D5 ( 1993-05-20), p. 8561-8562
    Abstract: The Tropical Experiment of the Stratosphere‐Troposphere Exchange Project (STEP) was an international effort to answer two major questions: (1) How is air moved from the tropical troposphere to the overlying stratosphere and (2) Why is the stratosphere so dry? These issues are in fact coupled, since, excepting the lower middle stratosphere during Antarctic winter, only the tropical tropopause is cold enough to dehydrate air (by freezing and subsequent precipitation) to the zonally averaged mixing ratios of 2.5–3 parts per million by volume (ppmv) observed in the tropical lower stratosphere. Indeed, the dryness of the global stratosphere has historically been the key piece of evidence indicating that the tropics are the region of upward mass transfer.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/93JD00860
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1993
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  • 4
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    In-situ observations of mid-latitude forest fire plumes deep in the stratosphere : FOREST FIRE PLUMES IN THE STRATOSPHERE
    American Geophysical Union (AGU) ; 2004
    In:  Geophysical Research Letters Vol. 31, No. 11 ( 2004-06), p. n/a-n/a
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 31, No. 11 ( 2004-06), p. n/a-n/a
    Type of Medium: Online Resource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2003GL019253
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2004
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  • 5
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    Observational Evidence of Horizontal Transport‐Driven Dehydration in the TTL
    American Geophysical Union (AGU) ; 2019
    In:  Geophysical Research Letters Vol. 46, No. 13 ( 2019-07-16), p. 7848-7856
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 46, No. 13 ( 2019-07-16), p. 7848-7856
    Abstract: Airborne measurements over the western Pacific provide insight into the TTL hypothesis of horizontal transport‐driven dehydration The observed final dehydration is dominated by quasi‐horizontal transport between the lapse rate and the cold point tropopause The measured water vapor in the upper tropical tropopause layer corresponds to the coldest temperatures in the observation region
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/2019GL083647
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2019
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  • 6
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    CRISTA observations of cirrus clouds around the tropopause : CIRRUS CLOUDS DETECTED BY CRISTA
    American Geophysical Union (AGU) ; 2002
    In:  Journal of Geophysical Research: Atmospheres Vol. 107, No. D23 ( 2002-12-16), p. CRI 2-1-CRI 2-18
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 107, No. D23 ( 2002-12-16), p. CRI 2-1-CRI 2-18
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2001JD000698
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2002
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  • 7
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    Characteristics of the atmospheric CO 2 signal as observed over the conterminous United States during INTEX-NA
    American Geophysical Union (AGU) ; 2008
    In:  Journal of Geophysical Research Vol. 113, No. D7 ( 2008-04-01)
    Details
    In: Journal of Geophysical Research, American Geophysical Union (AGU), Vol. 113, No. D7 ( 2008-04-01)
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2007JD008899
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2008
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  • 8
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    A meteorological overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) campaign over the southeastern Atlantic during 2016–2018: Part 1 – Climatology
    Copernicus GmbH ; 2021
    In:  Atmospheric Chemistry and Physics Vol. 21, No. 22 ( 2021-11-16), p. 16689-16707
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 21, No. 22 ( 2021-11-16), p. 16689-16707
    Abstract: Abstract. In 2016–2018, the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) project undertook 3-month-long deployments to the southeastern (SE) Atlantic Ocean using research aircraft to better understand the impact of biomass burning (BB) aerosol transport to the SE Atlantic Ocean on climate. In this (part 1 of the meteorological overview) paper, the climatological features at monthly timescales are investigated. The southern African easterly jet (AEJ-S), defined as the zonal easterlies over 600–700 hPa exceeding 6 m s−1 around 5–15∘ S, is a characteristic feature of the mid-level circulation over southern Africa that was also during the deployment months of August 2017, September 2016, and October 2018. Climatologically, the AEJ-S develops at lower altitudes (∼ 3 km; 700 hPa) between 5–10∘ S in August, while it develops at around 4 km (∼ 600 hPa) and further south (5–15∘ S) in September and October, largely driven by the strong sensible heating over the African plateau. Notable meteorological anomalous characteristics during the 3 deployment months, compared to climatology (2000–2018), include the following: (1) during August 2017, the AEJ-S was weaker than the climatological mean, with an additional anomalous upper-level jet aloft (∼ 6 km) around 10∘ S. August 2017 was also drier over the SE Atlantic at 600–700 hPa than climatology, with a stronger Benguela low-level jet (LLJ) at 925–950 hPa along the Namibian coast of the SE Atlantic. Consistent with this, the southern Atlantic anticyclone was also stronger and closer to the coast than the August climatological mean. (2) During September 2016, the AEJ-S intensity was similar to the climatological mean, although the heat low and vertical motion over the land was slightly stronger compared to the September climatology. The LLJ and the large-scale southern Atlantic anticyclone were stronger than the climatological mean. (3) During October 2018, the AEJ-S was slightly weaker compared to the climatological mean, as was the LLJ and the southern Atlantic anticyclone. October 2018 was wetter over the Benguela coastal region at 600 hPa than the climatological mean. During all the deployment months, the sea surface temperatures (SST) over the SE Atlantic were warmer than the climatological means, but the monthly mean low cloud fraction was only noticeably reduced in August 2017. A weak August 2017 AEJ-S can explain low offshore black carbon (BC) mixing ratios within the European Centre for Medium-Range Weather Forecasts (ECMWF) Copernicus Atmosphere Monitoring Service (CAMS) reanalysis, although the BC peak altitude, at 2–3 km, is below that of the AEJ-S. The upper-level wave disturbance and the associated anomalous circulation also explain the weakening of AEJ-S through the reduction of the strength of the heat low over the land during August 2017.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    URL: Article
    DOI: 10.5194/acp-21-16689-2021
    DOI: 10.5194/acp-21-16689-2021-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
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  • 9
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    On the differences in the vertical distribution of modeled aerosol optical depth over the southeastern Atlantic
    Copernicus GmbH ; 2023
    In:  Atmospheric Chemistry and Physics Vol. 23, No. 7 ( 2023-04-12), p. 4283-4309
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 23, No. 7 ( 2023-04-12), p. 4283-4309
    Abstract: Abstract. The southeastern Atlantic is home to an expansive smoke aerosol plume overlying a large cloud deck for approximately a third of the year. The aerosol plume is mainly attributed to the extensive biomass burning activities that occur in southern Africa. Current Earth system models (ESMs) reveal significant differences in their estimates of regional aerosol radiative effects over this region. Such large differences partially stem from uncertainties in the vertical distribution of aerosols in the troposphere. These uncertainties translate into different aerosol optical depths (AODs) in the planetary boundary layer (PBL) and the free troposphere (FT). This study examines differences of AOD fraction in the FT and AOD differences among ESMs (WRF-CAM5, WRF-FINN, GEOS-Chem, EAM-E3SM, ALADIN, GEOS-FP, and MERRA-2) and aircraft-based measurements from the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign. Models frequently define the PBL as the well-mixed surface-based layer, but this definition misses the upper parts of decoupled PBLs, in which most low-level clouds occur. To account for the presence of decoupled boundary layers in the models, the height of maximum vertical gradient of specific humidity profiles from each model is used to define PBL heights. Results indicate that the monthly mean contribution of AOD in the FT to the total-column AOD ranges from 44 % to 74 % in September 2016 and from 54 % to 71 % in August 2017 within the region bounded by 25∘ S–0∘ N–S and 15∘ W–15∘ E (excluding land) among the ESMs. ALADIN and GEOS-Chem show similar aerosol plume patterns to a derived above-cloud aerosol product from the Moderate Resolution Imaging Spectroradiometer (MODIS) during September 2016, but none of the models show a similar above-cloud plume pattern to MODIS in August 2017. Using the second-generation High Spectral Resolution Lidar (HSRL-2) to derive an aircraft-based constraint on the AOD and the fractional AOD, we found that WRF-CAM5 produces 40 % less AOD than those from the HSRL-2 measurements, but it performs well at separating AOD fraction between the FT and the PBL. AOD fractions in the FT for GEOS-Chem and EAM-E3SM are, respectively, 10 % and 15 % lower than the AOD fractions from the HSRL-2. Their similar mean AODs reflect a cancellation of high and low AOD biases. Compared with aircraft-based observations, GEOS-FP, MERRA-2, and ALADIN produce 24 %–36 % less AOD and tend to misplace more aerosols in the PBL. The models generally underestimate AODs for measured AODs that are above 0.8, indicating their limitations at reproducing high AODs. The differences in the absolute AOD, FT AOD, and the vertical apportioning of AOD in different models highlight the need to continue improving the accuracy of modeled AOD distributions. These differences affect the sign and magnitude of the net aerosol radiative forcing, especially when aerosols are in contact with clouds.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    URL: Article
    DOI: 10.5194/acp-23-4283-2023
    DOI: 10.5194/acp-23-4283-2023-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2023
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  • 10
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    Microphysical Properties of Tropical Tropopause Layer Cirrus
    American Geophysical Union (AGU) ; 2018
    In:  Journal of Geophysical Research: Atmospheres Vol. 123, No. 11 ( 2018-06-16), p. 6053-6069
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 123, No. 11 ( 2018-06-16), p. 6053-6069
    Abstract: Ice particles were predominantly quasi‐spheroidal, especially at coldest temperatures Growth‐sedimentation is dominant in determining TTL cirrus size distributions and habits Aggregation is negligible in TTL in situ cirrus
    Type of Medium: Online Resource
    ISSN: 2169-897X , 2169-8996
    URL: Article
    DOI: 10.1029/2017JD028068
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2018
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