Publications by Philip Stier

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

REVIEWS OF GEOPHYSICS 56 (2018) 409-453

DP Grosvenor, O Sourdeval, P Zuidema, A Ackerman, MD Alexandrov, R Bennartz, R Boers, B Cairns, JC Chiu, M Christensen, H Deneke, M Diamond, G Feingold, A Fridlind, A Huenerbein, C Knist, P Kollias, A Marshak, D McCoy, D Merk, D Painemal, J Rausch, D Rosenfeld, H Russchenberg, P Seifert, K Sinclair, P Stier, B van Diedenhoven, M Wendisch, F Werner, R Wood, Z Zhang, J Quaas

How Well Can We Represent the Spectrum of Convective Clouds in a Climate Model? Comparisons between Internal Parameterization Variables and Radar Observations


L Labbouz, Z Kipling, P Stier, A Protat

Quantifying the effects of horizontal grid length and parameterised convection on the degree of convective organisation using a metric of the potential for convective interaction

Journal of the Atmospheric Sciences (2017)

BA White, AM Buchanan, CE Birch, P Stier, KJ Pearson

The chemistry-climate model ECHAM6.3-HAM2.3-MOZ1.0


MG Schultz, S Stadtler, S Schroeder, D Taraborrelli, B Franco, J Krefting, A Henrot, S Ferrachat, U Lohmann, D Neubauer, C Siegenthaler-Le Drian, S Wahl, H Kokkola, T Kuehn, S Rast, H Schmidt, P Stier, D Kinnison, GS Tyndall, JJ Orlando, C Wespes

Limited impact of sulfate-driven chemistry on black carbon aerosol aging in power plant plumes

AIMS Environmental Science 5 (2018) 195-215

M Z. Markovic, A E. Perring, R-S Gao, J Liao, A Welti, N L. Wagner, I B. Pollack, A M. Middlebrook, T B. Ryerson, M K. Trainer, C Warneke, J A. de Gouw, D W. Fahey, P Stier, J P. Schwarz

How Well Can We Represent the Spectrum of Convective Clouds in a Climate Model? Comparisons between Internal Parameterization Variables and Radar Observations

Journal of the Atmospheric Sciences American Meteorological Society (2018)

L Labbouz, Z Kipling, P Stier

THE GLOBAL AEROSOL SYNTHESIS AND SCIENCE PROJECT (GASSP): Measurements and Modeling to Reduce Uncertainty


CL Reddington, KS Carslaw, P Stier, N Schutgens, H Coe, D Liu, J Allan, J Browse, KJ Pringle, LA Lee, M Yoshioka, JS Johnson, LA Regayre, DV Spracklen, GW Mann, A Clarke, M Hermann, S Henning, H Wex, TB Kristensen, WR Leaitch, U Poeschl, D Rose, MO Andreae, J Schmale, Y Kondo, N Oshima, JP Schwarz, A Nenes, B Andersrson, GC Roberts, JR Snider, C Leck, PK Quinn, X Chi, A Ding, JL Jimenez, Q Zhang

Aerosols at the poles: an AeroCom Phase II multi-model evaluation


M Sand, BH Samset, Y Balkanski, S Bauer, N Bellouin, TK Berntsen, H Bian, M Chin, T Diehl, R Easter, SJ Ghan, T Iversen, A Kirkevag, J-F Lamarque, G Lin, X Liu, G Luo, G Myhre, T van Noije, JE Penner, M Schulz, O Seland, RB Skeie, P Stier, T Takemura, K Tsigaridis, F Yu, K Zhang, H Zhang

On the spatio-temporal representativeness of observations

Atmospheric Chemistry and Physics European Geosciences Union (EGU) (2017)

NJ Schutgens, S Tsyro, E Gryspeerdt, D Goto, N Weigum, M Schulz, P Stier

Constraining the instantaneous aerosol influence on cloud albedo.

Proceedings of the National Academy of Sciences of the United States of America 114 (2017) 4899-4904

E Gryspeerdt, J Quaas, S Ferrachat, A Gettelman, S Ghan, U Lohmann, H Morrison, D Neubauer, DG Partridge, P Stier, T Takemura, H Wang, M Wang, K Zhang

Much of the uncertainty in estimates of the anthropogenic forcing of climate change comes from uncertainties in the instantaneous effect of aerosols on cloud albedo, known as the Twomey effect or the radiative forcing from aerosol-cloud interactions (RFaci), a component of the total or effective radiative forcing. Because aerosols serving as cloud condensation nuclei can have a strong influence on the cloud droplet number concentration (Nd ), previous studies have used the sensitivity of the Nd to aerosol properties as a constraint on the strength of the RFaci. However, recent studies have suggested that relationships between aerosol and cloud properties in the present-day climate may not be suitable for determining the sensitivity of the Nd to anthropogenic aerosol perturbations. Using an ensemble of global aerosol-climate models, this study demonstrates how joint histograms between Nd and aerosol properties can account for many of the issues raised by previous studies. It shows that if the anthropogenic contribution to the aerosol is known, the RFaci can be diagnosed to within 20% of its actual value. The accuracy of different aerosol proxies for diagnosing the RFaci is investigated, confirming that using the aerosol optical depth significantly underestimates the strength of the aerosol-cloud interactions in satellite data.

Strong constraints on aerosol-cloud interactions from volcanic eruptions.

Nature 546 (2017) 485-491

FF Malavelle, JM Haywood, A Jones, A Gettelman, L Clarisse, S Bauduin, RP Allan, IHH Karset, JE Kristjánsson, L Oreopoulos, N Cho, D Lee, N Bellouin, O Boucher, DP Grosvenor, KS Carslaw, S Dhomse, GW Mann, A Schmidt, H Coe, ME Hartley, M Dalvi, AA Hill, BT Johnson, CE Johnson, JR Knight, FM O'Connor, DG Partridge, P Stier, G Myhre, S Platnick, GL Stephens, H Takahashi, T Thordarson

Aerosols have a potentially large effect on climate, particularly through their interactions with clouds, but the magnitude of this effect is highly uncertain. Large volcanic eruptions produce sulfur dioxide, which in turn produces aerosols; these eruptions thus represent a natural experiment through which to quantify aerosol-cloud interactions. Here we show that the massive 2014-2015 fissure eruption in Holuhraun, Iceland, reduced the size of liquid cloud droplets-consistent with expectations-but had no discernible effect on other cloud properties. The reduction in droplet size led to cloud brightening and global-mean radiative forcing of around -0.2 watts per square metre for September to October 2014. Changes in cloud amount or cloud liquid water path, however, were undetectable, indicating that these indirect effects, and cloud systems in general, are well buffered against aerosol changes. This result will reduce uncertainties in future climate projections, because we are now able to reject results from climate models with an excessive liquid-water-path response.

Dynamic subgrid heterogeneity of convective cloud in a global model: Description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6-HAM2

Atmospheric Chemistry and Physics 17 (2017) 327-342

Z Kipling, P Stier, L Labbouz, T Wagner

© 2017 The Author(s). The Convective Cloud Field Model (CCFM) attempts to address some of the shortcomings of both the commonly used bulk mass-flux parameterisations and those using a prescribed spectrum of clouds. By considering the cloud spectrum as a competitive system in which cloud types interact through their environment in competition for convective available potential energy (CAPE), the spectrum is able to respond dynamically to changes in the environment. An explicit Lagrangian entraining plume model for each cloud type allows for the representation of convective-cloud microphysics, paving the way for the study of aerosol-convection interactions at the global scale where their impact remains highly uncertain. In this paper, we introduce a new treatment of convective triggering, extending the entraining plume model below cloud base to explicitly represent the unsaturated thermals which initiate convection. This allows for a realistic vertical velocity to develop at cloud base, so that the cloud microphysics can begin with physically based activation of cloud condensation nuclei (CCN). We evaluate this new version of CCFM in the context of the global model ECHAM6-HAM, comparing its performance to the standard Tiedtke-Nordeng parameterisation used in that model. We find that the spatio-temporal distribution of precipitation is improved, both against a climatology from the Global Precipitation Climatology Project (GPCP) and also against diurnal cycles from the Tropical Rainfall Measurement Mission (TRMM) with a reduced tendency for precipitation to peak too early in the afternoon. Cloud cover is quite sensitive to the vertical level from which the dry convection is initiated, but when this is chosen appropriately the cloud cover compares well with that from Tiedtke-Nordeng. CCFM can thus perform as well as, or better than, the standard scheme while providing additional capabilities to represent convective-cloud microphysics and dynamic cloud morphology at the global scale.

Can models robustly represent aerosol–convection interactions if their cloud microphysics is uncertain?

Atmospheric Chemistry and Physics Discussions European Geosciences Union (EGU) (2016)

B White, E Gryspeerdt, P Stier, H Morrison, G Thompson

Limitations of passive remote sensing to constrain global cloud condensation nuclei


P Stier

Will a perfect model agree with perfect observations? The impact of spatial sampling


NAJ Schutgens, E Gryspeerdt, N Weigum, S Tsyro, D Goto, M Schulz, P Stier

Challenges in constraining anthropogenic aerosol effects on cloud radiative forcing using present-day spatiotemporal variability (vol 113, pg 5804, 2016)


S Ghan, M Wang, S Zhang, S Ferrachat, A Gettelman, J Griesfeller, Z Kipling, U Lohmann, H Morrison, D Neubauer, DG Partridge, P Stier, T Takemura, H Wang, K Zhang

Evaluation of the aerosol vertical distribution in global aerosol models through comparison against CALIOP measurements: AeroCom phase II results


B Koffi, M Schulz, F-M Breon, F Dentener, BM Steensen, J Griesfeller, D Winker, Y Balkanski, SE Bauer, N Bellouin, T Berntsen, H Bian, M Chin, T Diehl, R Easter, S Ghan, DA Hauglustaine, T Iversen, A Kirkevag, X Liu, U Lohmann, G Myhre, P Rasch, O Seland, RB Skeie, SD Steenrod, P Stier, J Tackett, T Takemura, K Tsigaridis, MR Vuolo, J Yoon, K Zhang

Effect of aerosol sub-grid variability on aerosol optical depth and cloud condensation nuclei: Implications for global aerosol modelling

Atmospheric Chemistry and Physics Discussions (2016) 1-36

N Weigum, N Schutgens, P Stier

Jury is still out on the radiative forcing by black carbon.

Proceedings of the National Academy of Sciences of the United States of America 113 (2016) E5092-E5093

O Boucher, Y Balkanski, Ø Hodnebrog, CL Myhre, G Myhre, J Quaas, BH Samset, N Schutgens, P Stier, R Wang

Will a perfect model agree with perfect observations? the impact of spatial sampling

Atmospheric Chemistry and Physics Discussions 2016 (2016)

NAJ Schutgens, E Gryspeerdt, N Weigum, S Tsyro, D Goto, M Schulz, P Stier

© Author(s) 2016. The spatial resolution of global climate models with interactive aerosol and the observations used to evaluate them is very different. Current models use grid-spacings of ∼ 200 km, while satellite observations of aerosol use so-called pixels of ∼ 10 km. Ground site or air-borne observations concern even smaller spatial scales. We study the errors incurred due to different resolutions by aggregating high-resolution simulations (10 km grid-spacing) over either the large areas of global model grid-boxes ("perfect" model data) or small areas corresponding to the pixels of satellite measurements or the field-of-view of ground-sites ("perfect" observations). Our analysis suggests that instantaneous RMS differences between these perfect observations and perfect global models can easily amount to 30-160%, for a range of observables like AOT (Aerosol Optical Thickness), extinction, black carbon mass concentrations, PM2.5, number densities and CCN (Cloud Condensation Nuclei). These differences, due entirely to different spatial sampling of models and observations, are often larger than measurement errors in real observations. Temporal averaging over a month of data reduces these differences more strongly for some observables (e.g. a three-fold reduction i.c. AOT), than for others (e.g. a two-fold reduction for surface black carbon concentrations), but significant RMS differences remain (10-75%). Note that this study ignores the issue of temporal sampling of real observations, which is likely to affect our present monthly error estimates. We examine several other strategies (e.g. spatial aggregation of observations, interpolation of model data) for reducing these differences and show their effectiveness. Finally, we examine consequences for the use of flight campaign data in global model evaluation and show that significant biases may be introduced depending on the flight strategy used.