Is there a trend in cirrus cloud cover due to aircraft traffic?

Abstract. Trends in cirrus cloud cover have been estimated based on 16 years of data from ISCCP (International Satellite Cloud Climatology Project). The results have been spatially correlated with aircraft density data to determine the changes in cirrus could cover due to aircraft traffic. Main emphasis has been on the area covered by the METEOSAT satellite, to avoid trends in the ISCCP data resulting from changing satellite positions. An alternative retrieval of high clouds in this region has been used to complement the analysis based on ISCCP data. In Europe, which is within the METEOSAT region, we find indications of a trend of about 2%/decade due to aircraft, in reasonable agreement with previous studies. The positive trend in cirrus in areas of high aircraft traffic seems to have contrasted a general negative trend in cirrus. Extrapolation in time to cover the entire period of aircraft operations and in space to cover the global scale yields a best estimate of 0.05 Wm−2 for the radiative forcing due to aircraft. This is close to the value given by IPCC (1999) as an upper limit.

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Is there a trend in cirrus cloud cover due to aircraft traffic?

Atmospheric Chemistry and Physics ◽

10.5194/acp-5-2155-2005 ◽

2005 ◽

Vol 5 (8) ◽

pp. 2155-2162 ◽

Cited By ~ 54

Author(s):

F. Stordal ◽

G. Myhre ◽

E. J. G. Stordal ◽

W. B. Rossow ◽

D. S. Lee ◽

...

Keyword(s):

Radiative Forcing ◽

Cloud Cover ◽

Reasonable Agreement ◽

Global Scale ◽

Cirrus Cloud ◽

Positive Trend ◽

Spatially Correlated ◽

Upper Limit ◽

Main Emphasis ◽

The Mean

Abstract. Trends in cirrus cloud cover have been estimated based on 16 years of data from ISCCP (International Satellite Cloud Climatology Project). The results have been spatially correlated with aircraft density data to determine the changes in cirrus cloud cover due to aircraft traffic. The correlations are only moderate, as many other factors have also contributed to changes in cirrus. Still we regard the results to be indicative of an impact of aircraft on cirrus amount. The main emphasis of our study is on the area covered by the METEOSAT satellite to avoid trends in the ISCCP data resulting from changing satellite viewing geometry. In Europe, which is within the METEOSAT region, we find indications of a trend of about 1-2% cloud cover per decade due to aircraft, in reasonable agreement with previous studies. The positive trend in cirrus in areas of high aircraft traffic contrasts with a general negative trend in cirrus. Extrapolation in time to cover the entire period of aircraft operations and in space to cover the global scale yields a mean estimate of 0.03 Wm-2 (lower limit 0.01, upper limit 0.08 Wm-2) for the radiative forcing due to aircraft induced cirrus. The mean is close to the value given by IPCC (1999) as an upper limit.

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A Climatology of Midlatitude Continental Clouds from the ARM SGP Central Facility. Part II: Cloud Fraction and Surface Radiative Forcing

Journal of Climate ◽

10.1175/jcli3710.1 ◽

2006 ◽

Vol 19 (9) ◽

pp. 1765-1783 ◽

Cited By ~ 81

Author(s):

Xiquan Dong ◽

Baike Xi ◽

Patrick Minnis

Keyword(s):

Water Vapor ◽

Radiative Forcing ◽

Cloud Cover ◽

Surface Albedo ◽

Cloud Fraction ◽

Total Cloud Cover ◽

Cloud Radiative Forcing ◽

Low Clouds ◽

High Clouds ◽

Central Facility

Abstract Data collected at the Department of Energy Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility (SCF) are analyzed to determine the monthly and hourly variations of cloud fraction and radiative forcing between January 1997 and December 2002. Cloud fractions are estimated for total cloud cover and for single-layered low (0–3 km), middle (3–6 km), and high clouds (>6 km) using ARM SCF ground-based paired lidar–radar measurements. Shortwave (SW) and longwave (LW) fluxes are derived from up- and down-looking standard precision spectral pyranometers and precision infrared radiometer measurements with uncertainties of ∼10 W m−2. The annual averages of total and single-layered low-, middle-, and high-cloud fractions are 0.49, 0.11, 0.03, and 0.17, respectively. Both total- and low-cloud amounts peak during January and February and reach a minimum during July and August; high clouds occur more frequently than other types of clouds with a peak in summer. The average annual downwelling surface SW fluxes for total and low clouds (151 and 138 W m−2, respectively) are less than those under middle and high clouds (188 and 201 W m−2, respectively), but the downwelling LW fluxes (349 and 356 W m−2) underneath total and low clouds are greater than those from middle and high clouds (337 and 333 W m−2). Low clouds produce the largest LW warming (55 W m−2) and SW cooling (−91 W m−2) effects with maximum and minimum absolute values in spring and summer, respectively. High clouds have the smallest LW warming (17 W m−2) and SW cooling (−37 W m−2) effects at the surface. All-sky SW cloud radiative forcing (CRF) decreases and LW CRF increases with increasing cloud fraction with mean slopes of −0.984 and 0.616 W m−2 %−1, respectively. Over the entire diurnal cycle, clouds deplete the amount of surface insolation more than they add to the downwelling LW flux. The calculated CRFs do not appear to be significantly affected by uncertainties in data sampling and clear-sky screening. Traditionally, cloud radiative forcing includes not only the radiative impact of the hydrometeors, but also the changes in the environment. Taken together over the ARM SCF, changes in humidity and surface albedo between clear and cloudy conditions offset ∼20% of the NET radiative forcing caused by the cloud hydrometeors alone. Variations in water vapor, on average, account for 10% and 83% of the SW and LW CRFs, respectively, in total cloud cover conditions. The error analysis further reveals that the cloud hydrometeors dominate the SW CRF, while water vapor changes are most important for LW flux changes in cloudy skies. Similar studies over other locales are encouraged where water and surface albedo changes from clear to cloudy conditions may be much different than observed over the ARM SCF.

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Responses of Tropical and Subtropical High-Cloud Statistics to Global Warming

Journal of Climate ◽

10.1175/jcli-d-14-00179.1 ◽

2014 ◽

Vol 27 (20) ◽

pp. 7753-7768 ◽

Cited By ~ 14

Author(s):

A. T. Noda ◽

M. Satoh ◽

Y. Yamada ◽

C. Kodama ◽

T. Seiki

Keyword(s):

Climate Change ◽

Global Warming ◽

High Resolution ◽

Radiative Forcing ◽

Cloud Cover ◽

High Cloud ◽

Cloud Radiative Forcing ◽

Almost All ◽

High Clouds ◽

Horizontal Grid

Abstract Data from global high-resolution, nonhydrostatic simulations, covering a 1-yr period and with horizontal grid sizes of 7 and 14 km, were analyzed to evaluate the response of high cloud to global warming. The results indicate that, in a warmer atmosphere, high-cloud cover increases robustly and associated longwave (LW) cloud radiative forcing (CRF) increases on average. To develop a better understanding of high-cloud responses to climate change, the geographical distribution of high-cloud size obtained from the model was analyzed and compared with observations. In warmer atmospheres, the contribution per cloud to CRF decreases for both the LW and shortwave (SW) components. However, because of significant increases in the numbers of high clouds in almost all cloud size categories, the magnitude of both LW and SW CRF increases in the simulations. In particular, the contribution from an increase in the number of smaller clouds has more effect on the CRF change. It was also found that the ice and liquid water paths decrease in smaller clouds and that particularly the former contributes to reduced LW CRF per high cloud.

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Global Analysis of Atmospheric Transmissivity Using Cloud Cover, Aridity and Flux Network Datasets

Remote Sensing ◽

10.3390/rs13091716 ◽

2021 ◽

Vol 13 (9) ◽

pp. 1716

Author(s):

Ankur Srivastava ◽

Jose F. Rodriguez ◽

Patricia M. Saco ◽

Nikul Kumari ◽

Omer Yetemen

Keyword(s):

Cloud Cover ◽

Climatic Factors ◽

Global Analysis ◽

Empirical Relationship ◽

Aridity Index ◽

Global Scale ◽

Empirical Models ◽

Coefficient Of Determination ◽

Crop Modeling ◽

Atmospheric Transmissivity

Atmospheric transmissivity (τ) is a critical factor in climatology, which affects surface energy balance, measured at a limited number of meteorological stations worldwide. With the limited availability of meteorological datasets in remote areas across different climatic regions, estimation of τ is becoming a challenging task for adequate hydrological, climatic, and crop modeling studies. The availability of solar radiation data is comparatively less accessible on a global scale than the temperature and precipitation datasets, which makes it necessary to develop methods to estimate τ. Most of the previous studies provided region specific datasets of τ, which usually provide local assessments. Hence, there is a necessity to give the empirical models for τ estimation on a global scale that can be easily assessed. This study presents the analysis of the τ relationship with varying geographic features and climatic factors like latitude, aridity index, cloud cover, precipitation, temperature, diurnal temperature range, and elevation. In addition to these factors, the applicability of these relationships was evaluated for different climate types. Thus, empirical models have been proposed for each climate type to estimate τ by using the most effective factors such as cloud cover and aridity index. The cloud cover is an important yet often overlooked factor that can be used to determine the global atmospheric transmissivity. The empirical relationship and statistical indicator provided the best performance in equatorial climates as the coefficient of determination (r2) was 0.88 relatively higher than the warm temperate (r2 = 0.74) and arid regions (r2 = 0.46). According to the results, it is believed that the analysis presented in this work is applicable for estimating the τ in different ecosystems across the globe.

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Anthropogenic forcing and response yield observed positive trend in Earth’s energy imbalance

Nature Communications ◽

10.1038/s41467-021-24544-4 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Shiv Priyam Raghuraman ◽

David Paynter ◽

V. Ramaswamy

Keyword(s):

Radiative Forcing ◽

Climate Model ◽

Solar Spectrum ◽

Internal Variability ◽

Satellite Observations ◽

Positive Trend ◽

Energy Imbalance ◽

Model Simulations ◽

Heat Uptake ◽

Climate Model Simulations

AbstractThe observed trend in Earth’s energy imbalance (TEEI), a measure of the acceleration of heat uptake by the planet, is a fundamental indicator of perturbations to climate. Satellite observations (2001–2020) reveal a significant positive globally-averaged TEEI of 0.38 ± 0.24 Wm−2decade−1, but the contributing drivers have yet to be understood. Using climate model simulations, we show that it is exceptionally unlikely (<1% probability) that this trend can be explained by internal variability. Instead, TEEI is achieved only upon accounting for the increase in anthropogenic radiative forcing and the associated climate response. TEEI is driven by a large decrease in reflected solar radiation and a small increase in emitted infrared radiation. This is because recent changes in forcing and feedbacks are additive in the solar spectrum, while being nearly offset by each other in the infrared. We conclude that the satellite record provides clear evidence of a human-influenced climate system.

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Large contribution to secondary organic aerosol from isoprene cloud chemistry

Science Advances ◽

10.1126/sciadv.abe2952 ◽

2021 ◽

Vol 7 (13) ◽

pp. eabe2952

Author(s):

Houssni Lamkaddam ◽

Josef Dommen ◽

Ananth Ranjithkumar ◽

Hamish Gordon ◽

Günther Wehrle ◽

...

Keyword(s):

Radiative Forcing ◽

Flow Reactor ◽

Secondary Organic Aerosol ◽

Cloud Droplet ◽

Organic Aerosol ◽

Global Scale ◽

Oxidation Products ◽

Oh Radicals ◽

Large Contribution ◽

Cloud Processing

Aerosols still present the largest uncertainty in estimating anthropogenic radiative forcing. Cloud processing is potentially important for secondary organic aerosol (SOA) formation, a major aerosol component: however, laboratory experiments fail to mimic this process under atmospherically relevant conditions. We developed a wetted-wall flow reactor to simulate aqueous-phase processing of isoprene oxidation products (iOP) in cloud droplets. We find that 50 to 70% (in moles) of iOP partition into the aqueous cloud phase, where they rapidly react with OH radicals, producing SOA with a molar yield of 0.45 after cloud droplet evaporation. Integrating our experimental results into a global model, we show that clouds effectively boost the amount of SOA. We conclude that, on a global scale, cloud processing of iOP produces 6.9 Tg of SOA per year or approximately 20% of the total biogenic SOA burden and is the main source of SOA in the mid-troposphere (4 to 6 km).

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Upper limits on the extent of seafloor anoxia during the PETM from uranium isotopes

Nature Communications ◽

10.1038/s41467-020-20486-5 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Matthew O. Clarkson ◽

Timothy M. Lenton ◽

Morten B. Andersen ◽

Marie-Laure Bagard ◽

Alexander J. Dickson ◽

...

Keyword(s):

Carbon Cycle ◽

Global Scale ◽

Uranium Isotopes ◽

Biogeochemical Model ◽

Emission Scenarios ◽

Isotope Data ◽

Upper Limit ◽

Thermal Maximum ◽

Upper Limits ◽

Anoxic Events

AbstractThe Paleocene Eocene Thermal Maximum (PETM) represents a major carbon cycle and climate perturbation that was associated with ocean de-oxygenation, in a qualitatively similar manner to the more extensive Mesozoic Oceanic Anoxic Events. Although indicators of ocean de-oxygenation are common for the PETM, and linked to biotic turnover, the global extent and temporal progression of de-oxygenation is poorly constrained. Here we present carbonate associated uranium isotope data for the PETM. A lack of resolvable perturbation to the U-cycle during the event suggests a limited expansion of seafloor anoxia on a global scale. We use this result, in conjunction with a biogeochemical model, to set an upper limit on the extent of global seafloor de-oxygenation. The model suggests that the new U isotope data, whilst also being consistent with plausible carbon emission scenarios and observations of carbon cycle recovery, permit a maximum ~10-fold expansion of anoxia, covering <2% of seafloor area.

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Decadal increase in Arctic dimethylsulfide emission

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1904378116 ◽

2019 ◽

Vol 116 (39) ◽

pp. 19311-19317 ◽

Cited By ~ 13

Author(s):

Martí Galí ◽

Emmanuel Devred ◽

Marcel Babin ◽

Maurice Levasseur

Keyword(s):

Sea Ice ◽

Radiative Forcing ◽

Positive Trend ◽

Aerosol Formation ◽

Atmospheric Measurements ◽

Sea Ice Extent ◽

Phytoplankton Productivity ◽

Physical Forcing ◽

Ice Retreat ◽

Aerosol Cloud Interactions

Dimethylsulfide (DMS), a gas produced by marine microbial food webs, promotes aerosol formation in pristine atmospheres, altering cloud radiative forcing and precipitation. Recent studies suggest that DMS controls aerosol formation in the summertime Arctic atmosphere and call for an assessment of pan-Arctic DMS emission (EDMS) in a context of dramatic ecosystem changes. Using a remote sensing algorithm, we show that summertime EDMS from ice-free waters increased at a mean rate of 13.3 ± 6.7 Gg S decade−1 (∼33% decade−1) north of 70°N between 1998 and 2016. This trend, mostly explained by the reduction in sea-ice extent, is consistent with independent atmospheric measurements showing an increasing trend of methane sulfonic acid, a DMS oxidation product. Extrapolation to an ice-free Arctic summer could imply a 2.4-fold (±1.2) increase in EDMS compared to present emission. However, unexpected regime shifts in Arctic geo- and ecosystems could result in future EDMS departure from the predicted range. Superimposed on the positive trend, EDMS shows substantial interannual changes and nonmonotonic multiyear trends, reflecting the interplay between physical forcing, ice retreat patterns, and phytoplankton productivity. Our results provide key constraints to determine whether increasing marine sulfur emissions, and resulting aerosol–cloud interactions, will moderate or accelerate Arctic warming in the context of sea-ice retreat and increasing low-level cloud cover.

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Recent changes of relative humidity: regional connection with land and ocean processes

10.5194/esd-2017-43 ◽

2017 ◽

Cited By ~ 3

Author(s):

Sergio M. Vicente-Serrano ◽

Raquel Nieto ◽

Luis Gimeno ◽

Cesar Azorin-Molina ◽

Anita Drumond ◽

...

Keyword(s):

Relative Humidity ◽

Interannual Variability ◽

Air Temperature ◽

Spatial Scales ◽

Global Scale ◽

Sea Surface ◽

Positive Trend ◽

Source Regions ◽

Strong Agreement

Abstract. We analyzed changes in surface relative humidity (RH) at the global scale from 1979 to 2014 using both observations and ERA-Interim dataset. We compared the variability and trends of RH with those of land evapotranspiration and ocean evaporation in moisture source areas across a range of selected regions worldwide. The sources of moisture for each particular region were identified by integrating different observational data and model outputs into a lagrangian approach. The aim was to account for the possible role of changes in air temperature over land, in comparison to sea surface temperature (SST), on RH variability. Results demonstrate a strong agreement between the interannual variability of RH and the interannual variability of precipitation and land evapotranspiration in regions with continentally-originated humidity. In contrast, albeit with the dominant positive trend of air temperature/SST ratio in the majority of the analyzed regions, the interannual variability of RH in the target regions did not show any significant correlation with this ratio over the source regions. Also, we did not find any significant association between the interannual variability of oceanic evaporation in the oceanic humidity source regions and RH in the target regions. Our findings stress the need for further investigation of the role of both dynamic and radiative factors in the evolution of RH over continental regions at different spatial scales.

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Total and partial cloud amount detection during summermonths 2005 at Westerland (Sylt, Germany)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-13479-2008 ◽

2008 ◽

Vol 8 (4) ◽

pp. 13479-13505 ◽

Cited By ~ 1

Author(s):

N. H. Schade ◽

A. Macke ◽

H. Sandmann ◽

C. Stick

Keyword(s):

Cloud Cover ◽

Cloud Amount ◽

Cirrus Clouds ◽

Total Cloud Amount ◽

The North ◽

Seaside Resort ◽

The North Sea ◽

Sky Imager ◽

Downward Radiation ◽

High Clouds

Abstract. The detection of cloudiness is investigated by means of partial and total cloud amount estimations from pyrgeometer radiation measurements and all-sky imager observations. The measurements have been performed in Westerland, a seaside resort on the North Sea island of Sylt, Germany, during summer 2005. An improvement to previous studies on this subject results from the fact that for the first time partial cloud amount (PCA), defined as total cloud amounts without high clouds, calculations from longwave downward radiation (LDR) according to the APCADA-Algorithm (Dürr and Philipona, 2004) are validated against both human observations from the German Weather Service DWD at the nearby airport of Sylt and digital all-sky imaging. Differences between the resulting total cloud amounts (TCA's), defined as total cloud amount for all-cloud situations, derived from the camera images and from human observations are within ±1 octa in 72% and within ±2 octa in 85% of the cases. Compared to human observations PCA measurements according to APCADA underestimate the observed cloud cover in 47% of all cases and the differences are within ±1 octa in 60% and ±2 octa in 74% of all cases. Since high cirrus clouds can not be derived from LDR, separate comparisons for all cases without high clouds have been performed showing an agreement within ±1(2) octa in 73(90)% for PCA and also for camera derived TCA. For this coastal mid-latitude site under investigation we find similar though slightly smaller agreements to human observations as reported in Dürr and Philipona (2004). Though limited to day-time the cloud cover retrievals from the sky imager are not much affected by cirrus clouds and provide a more reliable cloud climatology for all-cloud conditions than APCADA.

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