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Ice crystal number concentration estimates from lidar–radar satellite remote sensing – Part 1: Method and evaluation

The number concentration of ice crystals (N_i) is a key cloud property that remains very uncertain due to difficulties in determining it using satellites. This lack of global observational constraints limits our ability to constrain this property in models responsible for predicting future climate. This pair of papers fills this gap by showing and analyzing the first rigorously evaluated global climatology of N_i, leading to new information shedding light on the processes that control high clouds.

Trends in China’s anthropogenic emissions since 2010 as the consequence of clean air actions

To tackle the problem of severe air pollution, China has implemented active clean air policies in recent years. We quantified China’s anthropogenic emissions during 2010–2017 and identified the major driving forces of these trends by using a combination of bottom-up emission inventory and index decomposition analysis (IDA) approaches. The major air pollutants have reduced their emissions by 17–62 % during 2010–2017. The IDA results suggest that emission control measures are the main drivers.

How well do stratospheric reanalyses reproduce high-resolution satellite temperature measurements?

Reanalyses (RAs) are models which assimilate observations and are widely used as proxies for the true atmospheric state. Here, we resample six leading RAs using the weighting functions of four high-res satellite instruments, allowing a like-for-like comparison. We find that the RAs generally reproduce the satellite data well, except at high altitudes and in the tropics. However, we also find that the RAs more tightly correlate with each other than with observations, even those they assimilate.

Inverse modelling of CF₄ and NF₃ emissions in East Asia

Emissions of carbon tetrafluoride CF₄, NF₃ and CHF₃ in east Asia have been calculated using atmospheric measurements and an atmospheric transport model. We calculate emissions of CF₄ to be quite constant between the years 2008 and 2015 for both China and South Korea, with 2015 emissions calculated at 4.33 ± 2.65 Gg yr^-1 and 0.36 ± 0.11 Gg yr^-1, respectively. Emission estimates of NF₃ from South Korea could be made with relatively small uncertainty at 0.6 ± 0.07 Gg yr^-1 in 2015.

The climate effects of increasing ocean albedo: an idealized representation of solar geoengineering

Marine cloud brightening has been proposed as a means of geoengineering/climate intervention, or deliberately altering the climate system to offset anthropogenic climate change. In idealized simulations that highlight contrasts between land and ocean, we find that the globe warms, including the ocean due to transport of heat from land. This study reinforces that no net energy input into the Earth system does not mean that temperature will necessarily remain unchanged.

Radiative feedbacks of dust in snow over eastern Asia in CAM4-BAM

This study extends our previous investigation in dust–radiation interactions to investigate SRF and its feedbacks on the regional climate and the dust cycle over east Asia by use of the CAM4-BAM. Our results show that SRF increases the east Asian dust emissions significantly by 13.7 % in the spring, in contrast to −7.6 % of decreased dust emissions by DRF. Hence, a significant feature of SRF on the Tibetan Plateau can create a positive feedback loop to enhance the dust cycle over east Asia.

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Connecting regional aerosol emissions reductions to local and remote precipitation responses

Small particles in Earth’s atmosphere (also referred to as atmospheric aerosols) emitted by human activities impact Earth’s climate in complex ways and play an important role in Earth’s water cycle. We use a climate modeling approach and find that aerosols from the United States and Europe can have substantial effects on rainfall in far-away regions such as Africa’s Sahel or the Mediterranean. Air pollution controls in these regions may help reduce the likelihood and severity of Sahel drought.

Extreme levels of Canadian wildfire smoke in the stratosphere over central Europe on 21–22 August 2017

Extremely large light extinction coefficients of 500 Mm^-1, about 20 times higher than after the Pinatubo volcanic eruptions in 1991, were observed by EARLINET lidars in the stratosphere over central Europe from 21 to 22 August, 2017. This paper provides an overview based on ground-based (lidar, AERONET) and satellite (MODIS, OMI) remote sensing.

Formation and evolution of tar balls from northwestern US wildfires

This paper presents the first direct atmospheric observations of the formation and evolution of tar balls (TBs) in forest fires collected during the Department of Energy’s Biomass Burning Observation Project (BBOP). We quantify, for the first time, the TB mass fraction in the BB plumes and show that this mass fraction increases from less than 1 % to 50 % within the first couple of hours of plume aging. Using Mie theory we find that TBs are consistent with being weak light absorbers.

HTAP2 multi-model estimates of premature human mortality due to intercontinental transport of air pollution and emission sectors

Emissions from one continent affect air quality and health elsewhere. Here we quantify the effects of intercontinental PM_2.5 and ozone transport on human health using a new multi-model ensemble, evaluating the health effects of emissions from six world regions and three emission source sectors. Emissions from one region have significant health impacts outside of that source region; similarly, foreign emissions contribute significantly to air-pollution-related deaths in several world regions.

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