Remote Sensing of Droplet Number Concentration in Warm Clouds: A Review of the Current State of Knowledge and Perspectives

Grosvenor, Daniel P.; Sourdeval, Odran; Zuidema, Paquita; Ackerman, A. S.; Alexandrov, Mikhail D.; Bennartz, Ralf; Boers, R.; Cairns, Brian; Chiu, J. Christine; Christensen, Matthew; Deneke, Hartwig; Diamond, Michael; Feingold, Graham; Fridlind, A. M.; Hünerbein, Anja; Knist, Christine; Kollias, Pavlos; Marshak, Alexander; McCoy, Daniel; Merk, Daniel; Painemal, David; Rausch, John; Rosenfeld, Daniel; Russchenberg, H.W.J.; Seifert, Patric; Sinclair, Kenneth; Stier, Philip; Diedenhoven, Bastiaan van; Wendisch, Manfred; Werner, Frank; Wood, Robert; Zhang, Zhibo; Quaas, Johannes

doi:10.1029/2017rg000593

Cited by 264 publications

(413 citation statements)

References 251 publications

(419 reference statements)

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“…For the analysis here the 2.1‐μm effective radius values are used to compute N d from MODIS. While acknowledging the large uncertainties in satellite retrievals of N d (Grosvenor et al, ) and the sparsity of retrievals at high latitudes in winter months a distinct seasonal cycle in N d over the Southern Ocean is observed. Peak concentrations occur in the austral summer months and coincide with peak marine biogenic emissions (McCoy et al, ).…”

Section: Model Developmentssupporting

confidence: 89%

“…Retrieved data have been removed north of 60°N and south of 60°S where retrievals are most uncertain. The simulated N d distributions from GA7 and GA7.1 are in very good agreement with Grosvenor et al () with highest N d concentrations over land and downwind of key source regions. The stratocumulus cloud regions also appear well represented although N d is lower in this region in Bennartz and Rausch ().…”

Section: Discussionmentioning

confidence: 99%

“…Figure evaluates the simulated PD seasonal cycle of N d over the Southern Ocean (averaged between 35°S and 55°S) against Moderate Resolution Imaging Spectroradiometer (MODIS) satellite retrievals following McCoy et al (), which was based on the N d data set described in Grosvenor and Wood (). As McCoy et al () use only 1 year of MODIS observations we extend the evaluation to also include multiannual retrievals of MODIS N d (Grosvenor et al, ) from 2003 to 2014. This better reflects the interannual variability in Southern Ocean N d .…”

Section: Model Developmentsmentioning

confidence: 99%

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Improved Aerosol Processes and Effective Radiative Forcing in HadGEM3 and UKESM1

Mulcahy

Jones

Sellar

et al. 2018

J Adv Model Earth Syst

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166

212

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Aerosol processes and, in particular, aerosol‐cloud interactions cut across the traditional physical‐Earth system boundary of coupled Earth system models and remain one of the key uncertainties in estimating anthropogenic radiative forcing of climate. Here we calculate the historical aerosol effective radiative forcing (ERF) in the HadGEM3‐GA7 climate model in order to assess the suitability of this model for inclusion in the UK Earth system model, UKESM1. The aerosol ERF, calculated for the year 2000 relative to 1850, is large and negative in the standard GA7 model leading to an unrealistic negative total anthropogenic forcing over the twentieth century. We show how underlying assumptions and missing processes in both the physical model and aerosol parameterizations lead to this large aerosol ERF. A number of model improvements are investigated to assess their impact on the aerosol ERF. These include an improved representation of cloud droplet spectral dispersion, updates to the aerosol activation scheme, and black carbon optical properties. One of the largest contributors to the aerosol forcing uncertainty is insufficient knowledge of the preindustrial aerosol climate. We evaluate the contribution of uncertainties in the natural marine emissions of dimethyl sulfide and organic aerosol to the ERF. The combination of model improvements derived from these studies weakens the aerosol ERF by up to 50% of the original value and leads to a total anthropogenic historical forcing more in line with assessed values.

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Section: Model Developmentssupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Section: Model Developmentsmentioning

confidence: 99%

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Improved Aerosol Processes and Effective Radiative Forcing in HadGEM3 and UKESM1

Mulcahy

Jones

Sellar

et al. 2018

J Adv Model Earth Syst

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166

212

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“…We used SEVIRI-based cloud products (CF, cloud optical depth c , drop effective radius r e , and LWP) generated with the Meteosat Second Generation-Cloud Physical Properties algorithm developed at the Royal Netherlands Meteorological Institute available via http://data.knmi.nl (Roebeling et al, 2006). Potential uncertainties in N d arise from the high sensitivity of N d retrieval to r e (Grosvenor et al, 2018;Szczodrak et al, 2001), especially when r e is relatively small. In order to reduce uncertainty in cloud property retrieval, pixels having c and r e smaller than 3 are excluded from the analysis as these retrievals are less reliable (Sourdeval et al, 2015).…”

Section: Satellite Observationsmentioning

confidence: 99%

Anthropogenic Air Pollution Delays Marine Stratocumulus Breakup to Open Cells

Goren

Kazil

Hoffmann

et al. 2019

Geophysical Research Letters

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Marine stratocumulus cloud (Sc) decks with high cloud fraction typically breakup when sufficient drizzle forms. Cloud breakup leads to a lower cloud radiative effect due to the lower cloud amount. Here we use realistic Lagrangian large eddy simulations along a 3-day trajectory, evaluated with satellite observations, to investigate the timing of Sc breakup in response to aerosol conditions. We show that the timing of the breakup is strongly modulated by the diurnal cycle and large-scale meteorology but varies systematically with the initial aerosol concentration: the more polluted the clouds, the later the breakup. This indicates that the cloud radiative effect via cloud cover adjustments is not saturated, in contrast to the effect of aerosol on cloud albedo at fixed cloudiness, which weakens with increasing aerosol levels. The results also show that the cloud radiative impact of anthropogenic aerosol is strongest far from its origin over land.Plain Language Summary Marine stratocumulus clouds (Sc) cover large areas of the subtropical oceans. They frequently form as fully overcast cloud decks near the western coasts of continents, and break up as they move westwards, driven by the prevailing winds, towards the remote ocean. Their breakup is accompanied by a reduction in cloud cover, which in turn reduces the amount of solar radiation that is reflected by the cloud deck. Aerosol particles, as well as meteorological factors, determine the time it takes for a fully overcast cloud deck to break up. Here we use high-resolution simulations of Sc combined with satellite observations to investigate the roles of aerosol and meteorology in Sc break-up time and location. We demonstrate that an observed Sc deck off the coast of Western Europe would have broken up sooner had it not been influenced by anthropogenic aerosol from Europe. Aerosol was the main factor determining the break-up time of the cloud deck, with a sometimes significant contribution by largescale meteorology. Our results show that even at present-day pollution levels, aerosol perturbations can extend the lifetime of the Sc deck in its overcast state, and exert a significant cooling effect.Sc covers extensive regions over the eastern parts of the major subtropical oceans (Klein & Hartmann, 1993;Muhlbauer et al., 2014). These regions are characterized by decks of closed cells that form near the coast and breakup into open cells and trade wind cumulus as they move westward towards the remote oceans

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“…For liquid clouds, N d can for instance be inferred through relationships between satellite retrievals of τ c and the droplet r eff (Brenguier et al, 2000). These relationships rely on strong assumptions that have shortcomings 25 (Grosvenor et al, 2018) but nonetheless provide N d values that compare well against in situ observations (Painemal and Zuidema, 2011) and can be used to establish climatologies (Bennartz and Rausch, 2017). Such relationships are less trivial for ice clouds due to the high complexity and variability of ice nucleation processes Lohmann, 2002, 2003;Ickes et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

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

Sourdeval¹,

Gryspeerdt²,

Krämer³

et al. 2018

Preprint

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Abstract. The number concentration of cloud particles is a key quantity for understanding aerosol-cloud interactions and describing clouds in climate and numerical weather prediction models. In contrast with recent advances for liquid clouds, few observational constraints exist on the ice crystal number concentration (N i ). This study investigates how combined lidar-radar measurements can be used to provide satellite estimates of N i , using a methodology that constrains moments of a parameterized particle size distribution (PSD). The operational liDAR-raDAR (DARDAR) product serves as an existing base for this method, 5 which focuses on ice clouds with temperatures T c < -30°C.Theoretical considerations demonstrate the capability for accurate retrievals of N i , apart from a possible bias in the concentration in small crystals when T c -50°C, due to the assumption of a monomodal PSD shape in the current method. This is verified by comparing satellite estimates to co-incident in situ measurements, which additionally demonstrates the sufficient sensitivity of lidar-radar observations to N i . Following these results, satellite estimates of N i are evaluated in the context of a 10 case study and a preliminary climatological analysis based on 10 years of global data. Despite of a lack of other large-scale references, this evaluation shows a reasonable physical consistency in N i spatial distribution patterns. Notably, increases in N i are found towards cold temperatures and, more significantly, in the presence of strong updraughts, such as those related to convective or orographic uplifts. Further evaluation and improvements of this method are necessary but these results already constitute a first encouraging step towards large-scale observational constraints for N i . Part two of this series uses this new 15 dataset to examine the controls on N i .

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Remote Sensing of Droplet Number Concentration in Warm Clouds: A Review of the Current State of Knowledge and Perspectives

Cited by 264 publications

References 251 publications

Improved Aerosol Processes and Effective Radiative Forcing in HadGEM3 and UKESM1

Improved Aerosol Processes and Effective Radiative Forcing in HadGEM3 and UKESM1

Anthropogenic Air Pollution Delays Marine Stratocumulus Breakup to Open Cells

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

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