The Aerosols, Radiation and Clouds in Southern Africa Field Campaign in Namibia: Overview, Illustrative Observations, and Way Forward

AbstractThe Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role of aerosols on the regional climate of southern Africa. This is a unique environment where natural and anthropogenic aerosols and a semipermanent and widespread stratocumulus (Sc) cloud deck are found. The project aims to understand the dynamical, chemical, and radiative processes involved in aerosol–cloud–radiation interactions over land and ocean and under various meteorological conditions. The AEROCLO-sA field campaign was conducted in August and September of 2017 over Namibia. An aircraft equipped with active and passive remote sensors and aerosol in situ probes performed a total of 30 research flight hours. In parallel, a ground-based mobile station with state-of-the-art in situ aerosol probes and remote sensing instrumentation was implemented over coastal Namibia, and complemented by ground-based and balloonborne observations of the dynamical, thermodynamical, and physical properties of the lower troposphere. The focus laid on mineral dust emitted from salty pans and ephemeral riverbeds in northern Namibia, the advection of biomass-burning aerosol plumes from Angola subsequently transported over the Atlantic Ocean, and aerosols in the marine boundary layer at the ocean–atmosphere interface. This article presents an overview of the AEROCLO-sA field campaign with results from the airborne and surface measurements. These observations provide new knowledge of the interactions of aerosols and radiation in cloudy and clear skies in connection with the atmospheric dynamics over southern Africa. They will foster new advanced climate simulations and enhance the capability of spaceborne sensors, ultimately allowing a better prediction of future climate and weather in southern Africa.

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In-situ estimates of the role of radiative cooling for shallow convective organization

10.5194/egusphere-egu21-4953 ◽

2021 ◽

Author(s):

Benjamin Fildier ◽

Caroline Muller ◽

Ludovic Touze-Peiffer ◽

Anna Lea Albright

Keyword(s):

Boundary Layer ◽

Radiative Transfer ◽

Radiative Cooling ◽

Shallow Convection ◽

Field Campaign ◽

Radiative Processes ◽

Horizontal Gradients ◽

Convective Organization

This study investigates the role of radiative processes in shaping the spatial distribution of shallow clouds, using in-situ measurements retrieved during the EUREC4A field campaign. Horizontal gradients in atmospheric radiative cooling above the boundary layer had been advanced as important drivers of shallow circulation and low-level winds, through their effect on surface pressure gradients. Modeling studies first recognized their importance in idealized simulations of deep convection in radiative-convective equilibrium, then found a weaker role for idealized cases of very shallow convection; but recent work using remote-sensing data argued for their importance in strengthening the circulation close to the margin between dry and moist regions, on synoptic scales, arguing for a possible significance for these radiative effects on observed cloud structures.Here we investigate cases of intermediate scale, observed during the EUREC4A field campaign, where shallow convection extends vertically up to 4 km, and whose spatial organization can be described on mesoscales as &#8220;fish&#8221; or &#8220;flower&#8221; patterns. We perform careful radiative transfer calculations, using state-of-the-art spectroscopic data and over two thousand of dropsondes and radiosondes launched, to capture the fine details of radiative cooling profiles usually missed by satellite measurements. The large number of sondes allows us to sample radiative cooling information for the organization pattern of interest and analyze it in conjunction with the direct wind and humidity measurements. We also use geostationary estimates of precipitable water in clear-sky in order to cross-check the sonde data, and connect them to the organization pattern and to the position of the moist margin.Our results target the following relationships previously identified in idealized simulations: (a) between horizontal gradients in moisture and in top-of-the-boundary-layer radiative cooling, (b) between these radiative cooling gradients and surface wind anomalies across the moist margin, and (c) between the strength of surface winds as a function of the distance from the moist margin. These results will allow us to test the importance of radiative transfer processes in a real case of shallow convective organization.

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A regional real-time forecast of marine boundary layers during VOCALS-REx

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-421-2011 ◽

2011 ◽

Vol 11 (2) ◽

pp. 421-437 ◽

Cited By ~ 29

Author(s):

S. Wang ◽

L. W. O'Neill ◽

Q. Jiang ◽

S. P. de Szoeke ◽

X. Hong ◽

...

Keyword(s):

Real Time ◽

Large Scale ◽

Marine Boundary Layer ◽

Surface Wind ◽

Lower Troposphere ◽

Temporal Distribution ◽

Satellite Observations ◽

Naval Research ◽

Strong Wind

Abstract. This paper presents an evaluation and validation of the Naval Research Laboratory's COAMPS® real-time forecasts during the VOCALS-REx over the area off the west coast of Chile/Peru in the Southeast Pacific during October and November 2008. The analyses focus on the marine boundary layer (MBL) structure. These forecasts are compared with lower troposphere soundings, in situ surface measurements, and satellite observations. The predicted mean MBL cloud and surface wind spatial distributions are in good agreement with the satellite observations. The large-scale longitudinal variation of the MBL structure along 20° S is captured by the forecasts. That is, the MBL height increases westward toward the open ocean, the moisture just above the inversion decreases, and the MBL structure becomes more decoupled offshore. The observed strong wind shear across the cloud-top inversion near 20° S was correctly predicted by the model. The model's cloud spatial and temporal distribution in the 15 km grid mesh is sporadic compared to satellite observations. Our results suggest that this is caused by grid-scale convection likely due to a lack of a shallow cumulus convection parameterization in the model. Both observations and model forecasts show wind speed maxima near the top of MBL along 20° S, which is consistent with the westward upslope of the MBL heights based on the thermal wind relationship. The forecasts produced well-defined diurnal variations in the spatially-averaged MBL structure, although the overall signal is weaker than those derived from the in situ measurements and satellite data. The MBL heights are generally underpredicted in the nearshore area. An analysis of the sensitivity of the MBL height to horizontal and vertical grid resolution suggests that the underprediction is likely associated with overprediction of the mesoscale downward motion and cold advection near the coast.

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Global carbon monoxide vertical distributions from spaceborne high-resolution FTIR nadir measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-5-2901-2005 ◽

2005 ◽

Vol 5 (11) ◽

pp. 2901-2914 ◽

Cited By ~ 40

Author(s):

B. Barret ◽

S. Turquety ◽

D. Hurtmans ◽

C. Clerbaux ◽

J. Hadji-Lazaro ◽

...

Keyword(s):

High Resolution ◽

Estimation Method ◽

Lower Troposphere ◽

Optimal Estimation ◽

Vertical Distributions ◽

Surface Measurements ◽

The Vertical Distribution ◽

Global Carbon ◽

Good Agreement

Abstract. This paper presents the first global distributions of CO vertical profiles retrieved from a thermal infrared FTS working in the nadir geometry. It is based on the exploitation of the high resolution and high quality spectra measured by the Interferometric Monitor of Greenhouse gases (IMG) which flew onboard the Japanese ADEOS platform in 1996-1997. The retrievals are performed with an algorithm based on the Optimal Estimation Method (OEM) and are characterized in terms of vertical sensitivity and error budget. It is found that most of the IMG measurements contain between 1.5 and 2.2 independent pieces of information about the vertical distribution of CO from the lower troposphere to the upper troposphere-lower stratosphere (UTLS). The retrievals are validated against coincident NOAA/CMDL in situ surface measurements and NDSC/FTIR total columns measurements. The retrieved global distributions of CO are also found to be in good agreement with the distributions modeled by the GEOS-CHEM 3D CTM, highlighting the ability of IMG to capture the horizontal as well as the vertical structure of the CO distributions.

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Tropospheric ozone variations at the Nepal climate observatory – pyramid (Himalayas, 5079 m a.s.l.) and influence of stratospheric intrusion events

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-1483-2010 ◽

2010 ◽

Vol 10 (1) ◽

pp. 1483-1516 ◽

Cited By ~ 5

Author(s):

P. Cristofanelli ◽

A. Bracci ◽

M. Sprenger ◽

A. Marinoni ◽

U. Bonafè ◽

...

Keyword(s):

Summer Monsoon ◽

Radiative Forcing ◽

Surface Ozone ◽

Regional Climate ◽

Lower Troposphere ◽

Back Trajectory ◽

Winter Period ◽

Air Mass ◽

Tropospheric O3

Abstract. The paper presents the first 2-years of continuous surface ozone (O3) observations and systematic assessment of the influence of stratospheric intrusions (SI) at the Nepal Climate Observatory at Pyramid (NCO-P; 27°57' N, 86°48' E), located in the Southern Himalayas at 5079 m a.s.l. Continuous O3 monitoring has been carried out at this GAW-WMO station in the framework of the Ev-K2-CNR SHARE and UNEP ABC projects since March 2006. Over the period March 2006–February 2008, an average O3 value of 49±12 ppbv (±1δ) was recorded, with a large annual cycle characterized by a maximum during the pre-monsoon (61±9 ppbv) and a minimum during the monsoon (39±10 ppbv). In general, the average O3 diurnal cycles had different shapes in the different seasons, suggesting an important interaction between the synoptic-scale circulation and the local mountain wind regime. Short-term O3 behaviour in the middle/lower troposphere (e.g. at the altitude level of NCO-P) can be significantly affected by deep SI which, representing the most important natural input for tropospheric O3, can also influence the regional atmosphere radiative forcing. To identify days possibly influenced by SI at the NCO-P, analyses were performed on in-situ observations (O3 and meteorological parameters), total column O3 data from OMI satellite and air-mass potential vorticity provided by the LAGRANTO back-trajectory model. In particular, a specially designed statistical methodology was applied to the time series of the observed and modelled stratospheric tracers. On this basis, during the 2-year investigation, 14.1% of analysed days were found to be affected by SI. The SI frequency showed a clear seasonal cycle, with minimum during the summer monsoon (1.2%) and higher values during the rest of the year (21.5%). As suggested by the LAGRANTO analysis, the position of the subtropical jet stream could play an important role in determining the occurrence of deep SI transport on the Southern Himalayas. In order to estimate the fraction of O3 due to air-mass transport from the stratosphere at the NCO-P, the 30 min O3 concentrations recorded during the detected SI days were analysed. In particular, in-situ relative humidity and black carbon observations were used to exclude influence from wet and polluted air-masses transported by up-valley breezes. This analysis led to the conclusion that during SI O3 significantly increased by 27.1% (+13 ppbv) with respect to periods not affected by such events. Moreover, the integral contribution of SI (O3S) to O3 at the NCO-P was also calculated, showing that 13.7% of O3 recorded at the measurement site could be attributed to SI. On a seasonal basis, the lowest SI contributions were found during the summer monsoon (less than 0.1%), while the highest were found during the winter period (24.2%). These results indicated that, during non-monsoon periods, high O3 levels could affect NCO-P during SI, thus influencing the variability of tropospheric O3 over the Southern Himalayas. Being a powerful regional greenhouse gas, these results indicate that the evaluation of the current and future regional climate cannot be assessed without properly taking into account the influence of SI to tropospheric O3 in this important area.

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Instabilities, Dynamics, and Energetics accompanying Atmospheric Layering (IDEAL) Campaign: High-Resolution in situ Observations above the Nocturnal Boundary Layer

10.5194/amt-2021-173 ◽

2021 ◽

Author(s):

Abhiram Doddi ◽

Dale Lawrence ◽

David Fritts ◽

Ling Wang ◽

Thomas Lund ◽

...

Keyword(s):

High Resolution ◽

Lower Troposphere ◽

Unmanned Aircraft ◽

Lower Atmosphere ◽

Second Phase ◽

Field Campaign ◽

Stable Conditions ◽

In Situ Observations ◽

The Ideal

Abstract. The Instabilities, Dynamics, and Energetics accompanying Atmospheric Layering (IDEAL) project was conceived to improve our understanding of the dynamics of sheet and layer (S&L) structures in the lower troposphere under strongly stable conditions. The approach employed a synergistic combination of targeted multi-point observations using small unmanned aircraft systems (sUAS) guiding direct numerical simulation (DNS) modeling to characterize the dynamics driving the S&L structures and associated flow features. The IDEAL research program consisted of two phases. The first was an observational field campaign to systematically probe stable lower atmosphere conditions using multiple DataHawk-2 (DH2) sUAS. Coordinated, simultaneous multi-DH2 flights were guided by concurrent Integrated Sounding System (ISS) wind profiler radar and radiosonde soundings performed by NCAR Earth Observing Laboratory (EOL) participants. Additional sUAS flight guidance was obtained from real-time sUAS measurements. Following the field campaign, the second phase focused on high-resolution DNS modeling efforts guided by in-situ observations made during the first phase. This overview focuses on the details of the observational phase that took place from 24 October to 15 November 2017 at Dugway Proving Ground (DPG), Utah. A total of 72 DH2 flights coordinated with 93 balloon-borne radiosondes were deployed in support of the IDEAL field campaign. Our discussion addresses the average atmospheric conditions, the observation strategy, and the objectives of the field campaign. Also presented are representative flight sorties and sUAS environmental and turbulence measurements.

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Environmental Conditions for Nighttime Offshore Migration of Precipitation Area as Revealed by In Situ Observation off Sumatra Island

Monthly Weather Review ◽

10.1175/mwr-d-18-0412.1 ◽

2019 ◽

Vol 147 (9) ◽

pp. 3391-3407 ◽

Cited By ~ 9

Author(s):

Satoru Yokoi ◽

Shuichi Mori ◽

Fadli Syamsudin ◽

Urip Haryoko ◽

Biao Geng

Keyword(s):

Wind Shear ◽

Lower Troposphere ◽

Radiosonde Data ◽

In Situ Observation ◽

Western Coast ◽

Field Campaign ◽

Southwesterly Wind ◽

Sumatra Island ◽

Precipitation Area

Abstract The diurnal cycle over tropical coastal waters is characterized by offshore migration of precipitation area during nighttime. This study analyzes in situ observational data collected during the YMC-Sumatra 2017 field campaign around the western coast of Sumatra Island, Indonesia, to examine the offshore migration phenomenon during 5–31 December 2017, when the Research Vessel Mirai was deployed about 90 km off the coast to perform observation. The offshore migration is observed in only less than a half of the 27 days. A comparison of radiosonde data at the vessel between days with and without the offshore migration reveals that vertical wind shear in the lower troposphere is a key environmental condition. In late afternoon of the days with the offshore migration, offshore (northeasterly) wind shear with height with considerable magnitude is observed, which is due to weaker daily mean southwesterly wind in the lower free troposphere, stronger southwesterly wind in the boundary layer, and sea breeze. As this condition is considered favorable for regeneration of convective cells to the offshore side of old ones, these results support an idea that the regeneration process is critical for the offshore migration. The Madden–Julian oscillation and cold surges play some roles in the weakening of the free-tropospheric wind. The migration speed is estimated at 2–3 m s−1, which is lower than that observed in another field campaign conducted in 2015 (Pre-YMC 2015). This difference is partly due to the difference in the environmental wind in the lower to midtroposphere.

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Aircraft measurements of water vapor heavy isotope ratios in the marine boundary layer and lower troposphere during ORACLES

10.5194/essd-2021-238 ◽

2021 ◽

Author(s):

Dean Henze ◽

David Noone ◽

Darin Toohey

Keyword(s):

Boundary Layer ◽

Water Vapor ◽

Marine Boundary Layer ◽

Lower Troposphere ◽

Isotope Ratios ◽

Specific Humidity ◽

Heavy Isotope ◽

Ratio Measurement ◽

Data Usage

Abstract. This paper presents the water vapor heavy isotope ratio measurement system developed for aircraft in-situ measurements and used in the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) project. The resultant dataset collected, which includes measurements of specific humidity and the heavy isotope ratios D / H and 18O / 16O, is also presented. Aircraft sampling took place in the southeast Atlantic marine boundary layer and lower troposphere (equator to 22° S) over the months of Sept. 2016, Aug. 2017, and Oct. 2018. Isotope measurements were made using cavity ring-down spectroscopic analyzers integrated into the Water Isotope System for Precipitation and Entrainment Research (WISPER). The water concentration and isotopic data accompanied a suite of other variables including standard meteorological quantities (wind, temperature, moisture), trace gas and aerosol concentrations, radar, and lidar remote sensing. From an isotope perspective, the 300+ hours of 1 Hz in-situ data at levels in the atmosphere ranging from 70 m to 6 km represents a remarkably large and vertically resolved dataset. This paper provides a brief overview of the ORACLES mission and describes how water vapor heavy isotope ratios fit within the experimental design. Overviews of the sampling region and WISPER system setup are presented, along with calibration details, measurement uncertainties, and suggested data usage. Characteristics in the spatial variability of the study region over the three sampling periods are highlighted with latitude-altitude curtains. A number of individual tropospheric profiles are presented to illustrate the fidelity with which a series of different hydrologic processes are captured by the observations. The curtains and profiles demonstrate the dataset’s potential to provide a comprehensive perspective on moisture transport and isotopic content in this region. Readers interested in a quick reference to data usage and uncertainty estimation can consult the beginning of section 5. Data for the Sept. 2016, Aug. 2017, and Oct. 2018 sampling periods can be accessed at https://doi.org/10.5067/Suborbital/ORACLES/P3/2016_V2, https://doi.org/10.5067/Suborbital/ORACLES/P3/2017_V2, and https://doi.org/10.5067/Suborbital/ORACLES/P3/2018_V2, respectively (see references for ORACLES Science Team, 2020 – 2016 P3 data, 2017 P3 data, and 2018 P3 data).

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A study on the direct effect of anthropogenic aerosols on near surface air temperature over Southeastern Europe during summer 2000 based on regional climate modeling

Annales Geophysicae ◽

10.5194/angeo-27-3977-2009 ◽

2009 ◽

Vol 27 (10) ◽

pp. 3977-3988 ◽

Cited By ~ 23

Author(s):

P. Zanis

Keyword(s):

Atmospheric Circulation ◽

Air Temperature ◽

Radiative Forcing ◽

Regional Climate ◽

Lower Troposphere ◽

Balkan Peninsula ◽

Southeastern Europe ◽

Anthropogenic Aerosols ◽

Near Surface ◽

Induced Changes

Abstract. In the present work it is investigated the direct shortwave effect of anthropogenic aerosols on the near surface temperature over Southeastern Europe and the atmospheric circulation during summer 2000. In summer 2000, a severe heat-wave and droughts affected many countries in the Balkans. The study is based on two yearly simulations with and without the aerosol feedback of the regional climate model RegCM3 coupled with a simplified aerosol model. The surface radiative forcing associated with the anthropogenic aerosols is negative throughout the European domain with the more negative values in Central and Central-eastern Europe. A basic pattern of the aerosol induced changes in air temperature at the lower troposphere is a decrease over Southeastern Europe and the Balkan Peninsula (up to about 1.2°C) thus weakening the pattern of the climatic temperature anomalies of summer 2000. The aerosol induced changes in air temperature from the lower troposphere to upper troposphere are not correlated with the respective pattern of the surface radiative forcing implying the complexity of the mechanisms linking the aerosol radiative forcing with the induced atmospheric changes through dynamical feedbacks of aerosols on atmospheric circulation. Investigation of the aerosol induced changes in the circulation indicates a southward shift of the subtropical jet stream playing a dominant role for the decrease in near surface air temperature over Southeastern Europe and the Balkan Peninsula. The southward shift of the jet exit region over the Balkan Peninsula causes a relative increase of the upward motion at the northern flank of the jet exit region, a relative increase of clouds, less solar radiation absorbed at the surface and hence relative cooler air temperatures in the lower troposphere between 45° N and 50° N. The southward extension of the lower troposphere aerosol induced negative temperature changes in the latitudinal band 35° N–45° N over the Balkan Peninsula is justified from the prevailing northerly flow advecting the relatively cooler air from the latitudinal band 45° N–50° N towards the lower latitudes. The present regional climate modeling study indicates the important role of anthropogenic aerosols for the regional climate and their dynamical feedback on atmospheric circulation.

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Global carbon monoxide vertical distributions from spaceborne high-resolution FTIR nadir measurements

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-5-4599-2005 ◽

2005 ◽

Vol 5 (4) ◽

pp. 4599-4639 ◽

Cited By ~ 3

Author(s):

B. Barret ◽

S. Turquety ◽

D. Hurtmans ◽

C. Clerbaux ◽

J. Hadji-Lazaro ◽

...

Keyword(s):

High Resolution ◽

Estimation Method ◽

Lower Troposphere ◽

Optimal Estimation ◽

Vertical Distributions ◽

Surface Measurements ◽

The Vertical Distribution ◽

Global Carbon ◽

Good Agreement

Abstract. This paper presents the first global distributions of CO vertical profiles retrieved from a thermal infrared FTS working in the nadir geometry. It is based on the exploitation of the high resolution and high quality spectra measured by the Interferometric Monitor of Greenhouse gases (IMG) which flew onboard the Japanese ADEOS platform in 1996–1997. The retrievals are performed with an algorithm based on the Optimal Estimation Method (OEM) and are characterized in terms of vertical sensitivity and error budget. It is found that most of the IMG measurements contain between 1.5 and 2.2 independent pieces of information about the vertical distribution of CO from the lower troposphere to the upper troposphere-lower stratosphere (UTLS). The retrievals are validated against coincident NOAA/CMDL in situ surface measurements and NDSC/FTIR total columns measurements. The retrieved global distributions of CO are also found to be in good agreement with the distributions modeled by the GEOS-CHEM 3D CTM, highlighting the ability of IMG to capture the horizontal as well as the vertical structure of the CO distributions.

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