► We use a 1-D photochemistry-diffusion model to simulate the chemical system in the middle atmosphere of Venus. ► A sulfur source is required to explain the SO and SO
2 profiles observed by Venus ...Express. ► The evaporation of the aerosols composed of sulfuric acid or polysulfur above 90
km could provide the sulfur source. ► Measurements of SO
3 abundance and SO (
a
1Δ
→
X
3Σ
-) emission at 1.7
μm may be the key to distinguish between the two models.
Venus Express measurements of the vertical profiles of SO and SO
2 in the middle atmosphere of Venus provide an opportunity to revisit the sulfur chemistry above the middle cloud tops (∼58
km). A one dimensional photochemistry-diffusion model is used to simulate the behavior of the whole chemical system including oxygen-, hydrogen-, chlorine-, sulfur-, and nitrogen-bearing species. A sulfur source is required to explain the SO
2 inversion layer above 80
km. The evaporation of the aerosols composed of sulfuric acid (model A) or polysulfur (model B) above 90
km could provide the sulfur source. Measurements of SO
3 and SO (
a
1Δ
→
X
3Σ
-) emission at 1.7
μm may be the key to distinguish between the two models.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A new multilayer (ML) cloud detection algorithm based on three shortwave infrared (SWIR) and two longwave infrared (LWIR) channels is developed and applied to the Visible Infrared Imager Radiometer ...Suite (VIIRS) onboard the Suomi-NPP satellite. The algorithm identifies ML clouds, i.e., ice clouds overlying water clouds, based on satellite multispectral observations in the 1.38, 1.6, 2.25, 8.5, and 11 μm channels. We perform synthetic radiative transfer simulations to understand the sensitivities of the aforementioned channels on ML and single-layer (SL) clouds. Active CALIOP observations are used to evaluate the algorithm. Compared with the collocated CALIOP results, the algorithm can determine SL and ML clouds correctly with success rates of approximately 80% and 60%, respectively, and has similar performance to that of the current MODIS operational ML cloud detection algorithm. The misclassification of ML clouds as SL clouds is primarily caused by thin ice clouds that are practically undetectable using LWIR tests. Furthermore, the algorithm is extended to analyze data from radiometers onboard the geostationary Himawari-8 and FengYun-4A satellites, and results similar to those of VIIRS are obtained.
•A new algorithm for multilayer cloud detection is developed for VIIRS radiometer.•Accurate radiative transfer is performed for model understanding and development.•The model is evaluated using collocated MODIS and CALIOP observations.•It is extended for multilayer cloud detection of two geostationary radiometers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
There has been a growing concern that most climate models predict precipitation that is too frequent, likely due to lack of reliable subgrid variability
and vertical variations in microphysical ...processes in low-level warm clouds.
In this study, the warm-cloud physics parameterizations in the singe-column
configurations of NCAR Community Atmospheric Model version 6 and 5 (SCAM6
and SCAM5, respectively) are evaluated using ground-based and airborne
observations from the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Aerosol and Cloud Experiments in the Eastern
North Atlantic (ACE-ENA) field campaign near the Azores islands during
2017–2018. The 8-month single-column model (SCM) simulations show that both SCAM6 and SCAM5 can
generally reproduce marine boundary layer cloud structure, major
macrophysical properties, and their transition. The improvement in warm-cloud properties from the Community Atmospheric Model 5 and 6 (CAM5 to CAM6) physics can be found through comparison with the observations. Meanwhile, both physical schemes underestimate cloud liquid
water content, cloud droplet size, and rain liquid water content but
overestimate surface rainfall. Modeled cloud condensation nuclei (CCN)
concentrations are comparable with aircraft-observed ones in the summer but are
overestimated by a factor of 2 in winter, largely due to the biases in the
long-range transport of anthropogenic aerosols like sulfate. We also test
the newly recalibrated autoconversion and accretion parameterizations that
account for vertical variations in droplet size. Compared to the
observations, more significant improvement is found in SCAM5 than in SCAM6.
This result is likely explained by the introduction of subgrid variations
in cloud properties in CAM6 cloud microphysics, which further suppresses the
scheme's sensitivity to individual warm-rain microphysical parameters. The
predicted cloud susceptibilities to CCN perturbations in CAM6 are within a
reasonable range, indicating significant progress since CAM5 which produces an
aerosol indirect effect that is too strong. The present study emphasizes the
importance of understanding biases in cloud physics parameterizations by
combining SCM with in situ observations.
Mid‐tropospheric Carbonyl sulfide (OCS) retrievals from the Tropospheric Emission Spectrometer (TES) are utilized to study OCS distributions during the dry/wet seasons over the Amazon rainforest. TES ...OCS retrievals reveal positive OCS anomalies (∼16 ppt) over the central and southern parts of the Amazon during August–October (dry season) compared to January–March (wet season). There is less OCS taken up by vegetation and soil and more OCS released from biomass burning during the dry season, which causes an increase in OCS concentrations. Strong sinking air during the dry season also helps to trap OCS and this contributes to positive OCS anomalies. MOZART‐4 model captures positive OCS anomalies over the central and southern regions of the Amazon and negative OCS anomalies over the northern part of the Amazon, which are similar to those from TES mid‐tropospheric OCS retrievals. Our studies can help us better understand OCS variations and photosynthetic activities.
Plain Language Summary
As a photosynthetic tracer, OCS can help us better understand photosynthetic activities, the biosphere‐atmosphere interaction, and the carbon sink. There are positive OCS anomalies (∼16 ppt) over the central and southern parts of the Amazon during August–October (dry season), which is related to reduced OCS uptake from vegetation and soil, enhanced OCS emission from biomass burning, and strengthened sinking air. MOZART‐4 is used to simulate the OCS variations during dry/wet seasons. Model results are similar to those from Tropospheric Emission Spectrometer OCS retrievals. However, there are some differences between the spatial distributions of OCS in the MOZART‐4 model and the satellite retrievals. Results in this study can help us better understand the variability of OCS and photosynthetic activities over the Amazon rainforest, which is the biggest rainforest and one of the largest sinks of OCS.
Key Points
Tropospheric Emission Spectrometer OCS concentrations are higher over the central and southern parts of the Amazon during the dry season than the wet season
High OCS concentrations are related to reduced vegetation uptake, enhanced biomass burning, and increased sinking air
MOZART‐4 captures the observed positive OCS anomalies over the central and southern Amazon during August–October (dry season)
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Vertical profiles of aerosols are inadequately observed and poorly represented in climate models, contributing to the current large uncertainty associated with aerosol–cloud interactions. The US ...Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) aircraft field campaign near the Azores islands provided ample observations of vertical distributions of aerosol and cloud properties. Here we utilize the in situ aircraft measurements from the ACE-ENA and ground-based remote-sensing data along with an aerosol-aware Weather Research and Forecast (WRF) model to characterize the aerosols due to long-range transport over a remote region and to assess their possible influence on marine-boundary-layer (MBL) clouds. The vertical profiles of aerosol and cloud properties measured via aircraft during the ACE-ENA campaign provide detailed information revealing the physical contact between transported aerosols and MBL clouds. The European Centre for Medium-Range Weather Forecasts Copernicus Atmosphere Monitoring Service (ECMWF-CAMS) aerosol reanalysis data can reproduce the key features of aerosol vertical profiles in the remote region. The cloud-resolving WRF sensitivity experiments with distinctive aerosol profiles suggest that the transported aerosols and MBL cloud interactions (ACIs) require not only aerosol plumes to get close to the marine-boundary-layer top but also large cloud top height variations. Based on those criteria, the observations show that the occurrence of ACIs involving the transport of aerosol over the eastern North Atlantic (ENA) is about 62 % in summer. For the case with noticeable long-range-transport aerosol effects on MBL clouds, the susceptibilities of droplet effective radius and liquid water content are −0.11 and +0.14, respectively. When varying by a similar magnitude, aerosols originating from the boundary layer exert larger microphysical influence on MBL clouds than those entrained from the free troposphere.
Aerosol effects on convective clouds and associated precipitation constitute an important open-ended question in climate research. Previous studies have linked an increase in aerosol concentration to ...a delay in the onset of rain, invigorated clouds and stronger rain rates. Here, using observational data, we show that the aerosol effect on convective clouds shifts from invigoration to suppression with increasing aerosol optical depth. We explain this shift in trend (using a cloud model) as the result of a competition between two types of microphysical processes: cloud-core-based invigorating processes vs. peripheral suppressive processes. We show that the aerosol optical depth value that marks the shift between invigoration and suppression depends on the environmental thermodynamic conditions. These findings can aid in better parameterizing aerosol effects in climate models for the prediction of climate trends.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
When retrieving Aerosol Optical Depth (AOD) from passive satellite sensors, the vertical distribution of aerosols usually needs to be assumed, potentially causing uncertainties in the retrievals. In ...this study, we use the Moderate Resolution Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) sensors as examples to investigate the impact of aerosol vertical distribution on AOD retrievals. A series of sensitivity experiments was conducted using radiative transfer models with different aerosol profiles and surface conditions. Assuming a 0.2 AOD, we found that the AOD retrieval error is the most sensitive to the vertical distribution of absorbing aerosols; a −1 km error in aerosol scale height can lead to a ~30% AOD retrieval error. Moreover, for this aerosol type, ignoring the existence of the boundary layer can further result in a ~10% AOD retrieval error. The differences in the vertical distribution of scattering and absorbing aerosols within the same column may also cause −15% (scattering aerosols above absorbing aerosols) to 15% (scattering aerosols below absorbing aerosols) errors. Surface reflectance also plays an important role in affecting the AOD retrieval error, with higher errors over brighter surfaces in general. The physical mechanism associated with the AOD retrieval errors is also discussed. Finally, by replacing the default exponential profile with the observed aerosol vertical profile by a micro-pulse lidar at the Beijing-PKU site in the VIIRS retrieval algorithm, the retrieved AOD shows a much better agreement with surface observations, with the correlation coefficient increased from 0.63 to 0.83 and bias decreased from 0.15 to 0.03. Our study highlights the importance of aerosol vertical profile assumption in satellite AOD retrievals, and indicates that considering more realistic profiles can help reduce the uncertainties.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract
Point-source spectrophotometric (single-point) light curves of Earth-like planets contain a surprising amount of information about the spatial features of those worlds. Spatially resolving ...these light curves is important for assessing time-varying surface features and the existence of an atmosphere, which in turn is critical to life on Earth and significant for determining habitability on exoplanets. Given that Earth is the only celestial body confirmed to harbor life, treating it as a proxy exoplanet by analyzing time-resolved spectral images provides a benchmark in the search for habitable exoplanets. The Earth Polychromatic Imaging Camera (EPIC) on the Deep Space Climate Observatory (DSCOVR) provides such an opportunity, with observations of ∼5000 full-disk sunlit Earth images each year at 10 wavelengths with high temporal frequency. We disk-integrate these spectral images to create single-point light curves and decompose them into principal components (PCs). Using machine-learning techniques to relate the PCs to six preselected spatial features, we find that the first and fourth PCs of the single-point light curves, contributing ∼83.23% of the light-curve variability, contain information about low and high clouds, respectively. Surface information relevant to the contrast between land and ocean reflectance is contained in the second PC, while individual land subtypes are not easily distinguishable (<0.1% total light-curve variation). We build an Earth model by systematically altering the spatial features to derive causal relationships to the PCs. This model can serve as a baseline for analyzing Earth-like exoplanets and guide wavelength selection and sampling strategies for future observations.
The abundance of SO dimers (SO)
in the upper atmosphere of Venus and their implications for the enigmatic ultraviolet absorption has been investigated in several studies over the past few years. ...However, the photochemistry of sulfur species in the upper atmosphere of Venus is still not well understood and the identity of the missing ultraviolet absorber(s) remains unknown. Here we update an existing photochemical model of Venus' upper atmosphere by including the photochemistry of SO dimers. Although the spectral absorption profile of SO dimers fits the unknown absorber, their abundance is found to be too low for them to contribute significantly to the absorption. It is more likely that their photolysis and/or reaction products could contribute more substantively. Reactions of SO dimers are found to be important sources of S
O, and possibly higher order S
O species and polysulfur, S
. All of these species absorb in the critical ultraviolet region and are expected to be found in both the aerosol and gas phase. indicating that in-situ high resolution aerosol mass spectrometry might be a useful technique for identifying the ultraviolet absorber on Venus.
•The Alice instrument on New Horizons measured a UV solar occultation by Pluto's atmosphere in 2015.•Densities were derived for N2, CH4, C2H2, C2H4, C2H6, and haze.•These imply low escape rates ...(CH4-dominated), a stable lower atmosphere, direct evidence for C2Hx photochemistry, and haze whose extinction coefficient is roughly proportional to N2 density.
The Alice instrument on NASA's New Horizons spacecraft observed an ultraviolet solar occultation by Pluto's atmosphere on 2015 July 14. The transmission vs. altitude was sensitive to the presence of N2, CH4, C2H2, C2H4, C2H6, and haze. We derived line-of-sight abundances and local number densities for the 5 molecular species, and line-of-sight optical depth and extinction coefficients for the haze. We found the following major conclusions: (1) We confirmed temperatures in Pluto's upper atmosphere that were colder than expected before the New Horizons flyby, with upper atmospheric temperatures near 65–68 K. The inferred enhanced Jeans escape rates were (3–7) × 1022 N2 s−1 and (4–8) × 1025 CH4 s−1 at the exobase (at a radius of ∼ 2900 km, or an altitude of ∼1710 km). (2) We measured CH4 abundances from 80 to 1200 km above the surface. A joint analysis of the Alice CH4 and Alice and REX N2 measurements implied a very stable lower atmosphere with a small eddy diffusion coefficient, most likely between 550 and 4000 cm2 s−1. Such a small eddy diffusion coefficient placed the homopause within 12 km of the surface, giving Pluto a small planetary boundary layer. The inferred CH4 surface mixing ratio was ∼ 0.28–0.35%. (3) The abundance profiles of the “C2Hx hydrocarbons” (C2H2, C2H4, C2H6) were not simply exponential with altitude. We detected local maxima in line-of-sight abundance near 410 km altitude for C2H4, near 320 km for C2H2, and an inflection point or the suggestion of a local maximum at 260 km for C2H6. We also detected local minima near 200 km altitude for C2H4, near 170 km for C2H2, and an inflection point or minimum near 170–200 km for C2H6. These compared favorably with models for hydrocarbon production near 300–400 km and haze condensation near 200 km, especially for C2H2 and C2H4 (Wong et al., 2017). (4) We found haze that had an extinction coefficient approximately proportional to N2 density.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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