Skip to main content
Home
Department Of Physics text logo
  • Research
    • Our research
    • Our research groups
    • Our research in action
    • Research funding support
    • Summer internships for undergraduates
  • Study
    • Undergraduates
    • Postgraduates
  • Engage
    • For alumni
    • For business
    • For schools
    • For the public
Menu
von Kármán vortex street over Canary Islands
Credit: NASA

Philip Stier

Professor of Atmospheric Physics

Research theme

  • Climate physics

Sub department

  • Atmospheric, Oceanic and Planetary Physics

Research groups

  • Climate processes
philip.stier@physics.ox.ac.uk
Telephone: 01865 (2)72887
Atmospheric Physics Clarendon Laboratory, room 103
  • About
  • Research
  • Teaching
  • CV
  • Publications

AEROCOM and AEROSAT AAOD and SSA study – Part 1: Evaluation and intercomparison of satellite measurements

Atmospheric Chemistry and Physics Copernicus Publications 21:9 (2021) 6895-6917

Authors:

Nick Schutgens, Oleg Dubovik, Otto Hasekamp, Omar Torres, Hiren Jethva, Peter Leonard, Pavel Litvinov, Jens Redemann, Yohei Shinozuka, Gerrit de Leeuw, Stefan Kinne, Thomas Popp, Michael Schulz, Philip Stier

Abstract:

Global measurements of absorbing aerosol optical depth (AAOD) are scarce and mostly provided by the ground network AERONET (AErosol RObotic NETwork). In recent years, several satellite products of AAOD have been developed. This study's primary aim is to establish the usefulness of these datasets for AEROCOM (Aerosol Comparisons between Observations and Models) model evaluation with a focus on the years 2006, 2008 and 2010. The satellite products are super-observations consisting of  min aggregated retrievals.

This study consists of two papers, the current one that deals with the assessment of satellite observations and a second paper (Schutgens et al., 2021) that deals with the evaluation of models using those satellite data. In particular, the current paper details an evaluation with AERONET observations from the sparse AERONET network as well as a global intercomparison of satellite datasets, with a focus on how minimum AOD (aerosol optical depth) thresholds and temporal averaging may improve agreement between satellite observations.

All satellite datasets are shown to have reasonable skill for AAOD (three out of four datasets show correlations with AERONET in excess of 0.6) but less skill for SSA (single-scattering albedo; only one out of four datasets shows correlations with AERONET in excess of 0.6). In comparison, satellite AOD shows correlations from 0.72 to 0.88 against the same AERONET dataset. However, we show that performance vs. AERONET and inter-satellite agreements for SSA improve significantly at higher AOD. Temporal averaging also improves agreements between satellite datasets. Nevertheless multi-annual averages still show systematic differences, even at high AOD. In particular, we show that two POLDER (Polarization and Directionality of the Earth's Reflectances) products appear to have a systematic SSA difference over land of ∼0.04, independent of AOD. Identifying the cause of this bias offers the possibility of substantially improving current datasets.

We also provide evidence that suggests that evaluation with AERONET observations leads to an underestimate of true biases in satellite SSA.

In the second part of this study we show that, notwithstanding these biases in satellite AAOD and SSA, the datasets allow meaningful evaluation of AEROCOM models.

More details from the publisher
Details from ORA
More details

An Energetic View on the Geographical Dependence of the Fast Aerosol Radiative Effects on Precipitation

Journal of Geophysical Research: Atmospheres American Geophysical Union (AGU) 126:9 (2021)

Authors:

G Dagan, P Stier, D Watson-Parris

Abstract:

By interacting with radiation, aerosols perturb the Earth’s energy budget and thus the global precipitation amount. It was previously shown that aerosol-radiation interactions lead to a reduction in the global-mean precipitation amount. We have further demonstrated in aqua-planet simulations that the local response to absorbing aerosols differs between the tropics and the extra-tropics. In this study we incorporate an energy budget perspective to further examine the latitudinal-dependence of the effect of aerosol-radiation interaction on precipitation in idealized global simulations. We demonstrate that the transition between a positive local precipitation response in the tropics and a negative local precipitation response in the extra-tropics occurs at relatively low latitudes (∼10°), indicating a transition between the deep-tropics (in which the Coriolis force is low, hence direct thermally driven circulation, and associated divergence/convergence of energy/moisture, can form as a result of the diabatic-heating) and their surroundings. In addition, we gradually increase the level of complexity of the simulations and demonstrate that, in the case of absorbing aerosols, the effect of land is to counteract some of the response both inside and outside the deep-tropics due to the reduction in surface latent-heat flux that opposes the diabatic-heating. The effect of scattering aerosols is also examined and demonstrates a decrease in precipitation over land in both the tropics and extra-tropics and no effect over the ocean. Finally, we examine these results in a more realistic set-up and demonstrate that, although the physical mechanisms still operate, they are not significant enough to be discerned from the model’s natural-variability.
More details from the publisher

Impacts of varying concentrations of cloud condensation nuclei on deep convective cloud updrafts: A multimodel assessment

Journal of the Atmospheric Sciences American Meteorological Society 78:4 (2021) 1147-1172

Authors:

Peter Marinescu, Sue van den Heever, Max Heikenfeld, Andrew Barret, Christian Barthlott, Corinna Hoose, Jiwen Fan, Ann Fridlind, Toshihisa Matsui, Annette Miltenberger, Philip Stier, Benoit Vie, Bethan White, Yuwei Zhang

Abstract:

This study presents results from a model intercomparison project, focusing on the range of responses in deep convective cloud updrafts to varying cloud condensation nuclei (CCN) concentrations among seven state-of-the-art cloud-resolving models. Simulations of scattered convective clouds near Houston, Texas, are conducted, after being initialized with both relatively low and high CCN concentrations. Deep convective updrafts are identified, and trends in the updraft intensity and frequency are assessed. The factors contributing to the vertical velocity tendencies are examined to identify the physical processes associated with the CCN-induced updraft changes. The models show several consistent trends. In general, the changes between the High-CCN and Low-CCN simulations in updraft magnitudes throughout the depth of the troposphere are within 15% for all of the models. All models produce stronger (~+5%–15%) mean updrafts from ~4–7 km above ground level (AGL) in the High-CCN simulations, followed by a waning response up to ~8 km AGL in most of the models. Thermal buoyancy was more sensitive than condensate loading to varying CCN concentrations in most of the models and more impactful in the mean updraft responses. However, there are also differences between the models. The change in the amount of deep convective updrafts varies significantly. Furthermore, approximately half the models demonstrate neutral-to-weaker (~−5% to 0%) updrafts above ~8 km AGL, while the other models show stronger (~+10%) updrafts in the High-CCN simulations. The combination of the CCN-induced impacts on the buoyancy and vertical perturbation pressure gradient terms better explains these middle- and upper-tropospheric updraft trends than the buoyancy terms alone.
More details from the publisher
Details from ORA
More details

Anthropogenic aerosols modulated twentieth-century Sahel rainfall variability via impacts on North Atlantic sea surface temperature

Copernicus Publications (2021)

Authors:

Shipeng Zhang, Philip Stier, Guy Dagan, Minghuai Wang
More details from the publisher

Using the learnings of machine learning to distill cloud controlling environmental regimes from satellite observations

Copernicus Publications (2021)

Authors:

Alyson Douglas, Philip Stier
More details from the publisher

Pagination

  • First page First
  • Previous page Prev
  • …
  • Page 21
  • Page 22
  • Page 23
  • Page 24
  • Current page 25
  • Page 26
  • Page 27
  • Page 28
  • Page 29
  • …
  • Next page Next
  • Last page Last

Footer Menu

  • Contact us
  • Giving to the Dept of Physics
  • Work with us
  • Media

User account menu

  • Log in

Follow us

FIND US

Clarendon Laboratory,

Parks Road,

Oxford,

OX1 3PU

CONTACT US

Tel: +44(0)1865272200

University of Oxfrod logo Department Of Physics text logo
IOP Juno Champion logo Athena Swan Silver Award logo

© University of Oxford - Department of Physics

Cookies | Privacy policy | Accessibility statement

Built by: Versantus

  • Home
  • Research
  • Study
  • Engage
  • Our people
  • News & Comment
  • Events
  • Our facilities & services
  • About us
  • Current students
  • Staff intranet