We think you have liked this presentation. If you wish to download it, please recommend it to your friends in any social system. Share buttons are a little bit lower. Thank you!
Presentation is loading. Please wait.
Published byClaire Duffy
Modified over 5 years ago
Met Office Hadley Centre, FitzRoy Road, Exeter, Devon, EX1 3PB United Kingdom Tel: +44 (0)1392 886905 Fax: +44 (0)1392 885681 Email: email@example.com We have run a full set of CFMIP-2 experiments with HadGEM2-A, an atmosphere-only version of the HadGEM2-ES Earth System Model. These include an AMIP control forced with observed SSTs, a 4xCO 2 perturbation experiment with observed SSTs, uniform and patterned +4K SST perturbation experiments, and aquaplanet equivalents. All include CFMIP Observation Simulator Package outputs, temperature, humidity and cloud increments and time-step outputs at 119 locations. Here we show some preliminary results to illustrate the use of increments and time-step outputs to investigate feedback mechanisms. Fig 1a shows that the cloud component of the CO 2 forcing is consistent with what would be expected from cloud masking in the global mean (roughly -0.5 Wm -2 ), but there is a suggestion of positive cloud adjustment over land and the trade wind regions, and a negative adjustment over mid-latitude oceans and some stratocumulus to cumulus transition regions. The SST forced experiments show strong positive cloud feedbacks in the subtropical stratocumulus regions. Negative cloud feedbacks are seen off the edge of the sea ice in the Southern Ocean. The patterned SST experiment has a less positive feedback overall because of a less positive feedback poleward of 40 o S and a less extensive area of positive feedback in the south-east Tropical Pacific. Instantaneous time-step data have been saved from all of the experiments at the 119 locations shown on Fig 1c. We focus on [137W,26N] (location shown with a square) which shows a strong positive feedback in patterned and uniform +4K experiments. 1a) CFMIP-2 4CO 2 response in Net Cloud Radiative Effect (CRE) 30 year annual mean Global 2CO 2 Equivalent = -0.44 Wm -2 1b) +4K Uniform SST Net CRE response 30 year annual mean. Global Cloud Feedback = 0.31 Wm-2K-1 1c) +4K Patterned SST Net CRE response 0.23 Wm -2 K -1 and CFMIP time-step output locations 2c) Frequency distribution of instantaneous cloud fraction [137W,26N] AMIP + 4K Patterned SST July 1979-2008 2b) Frequency distribution of instantaneous cloud fraction [137W,26N] AMIP Control July 1979-2008 Height (km) Frequency of Cloud Fraction cloud fraction Fig 2a shows a substantial reduction in boundary layer cloud fraction at 1km in the +4K patterned SST experiment at [137W,26N]. Relative humidity is reduced by 5% at 1km. Free tropospheric relative humidity increases, presumably due to remote processes such as deep convection. Although the long term mean cloud fraction is less than 0.5 (Fig 2a), a histogram of instantaneous time-step outputs (Fig 2b) shows that instantaneous cloud fractions are mostly either close to unity (stratocumulus diagnosed by the large scale cloud scheme) or less than 0.2. In the +4K Patterned SST experiment, the frequency of occurrence of stratocumulus is greatly reduced, contributing to the strongly positive cloud feedback in this location. (Fig 2c) 3a) AMIP Temperature Tendencies [137W,26N] July 1979-2008 3b) AMIP +4K Pattern Temperature Tendencies [137W,26N] Fig 3a shows temperature tendencies at the same location for the AMIP run. At 1km (the level of maximum cloud) the longwave radiative cooling is balanced mainly by heating from the boundary layer and large scale cloud schemes, and also shortwave absorption. The boundary layer scheme heats the cloud layer by mixing warm air from below and by entraining warm air from above, while the cloud scheme heats it via latent heat release due to cloud condensation. Fig 3b shows the tendencies for the patterned SST perturbation experiment. We see large reductions in longwave cooling and in the heating from the boundary layer and cloud schemes at 1km. We have considered a number of physical mechanisms and ruled out several which are inconsistent with temperature and humidity tendencies changes – for example changes in shallow convection. Our results are consistent with a mechanism proposed by Stevens and Brenguier (2009) whereby increases in free tropospheric humidity inhibit cloud top cooling, breaking up stratocumulus clouds. We plan to test this hypothesis by repeating our experiments with fixed free tropospheric relative humidity. Conclusions High frequency instantaneous model outputs can be used to separate the effects of stratocumulus vs trade cumulus feedbacks. Tendency term analysis can be a useful tool for generating and selecting hypotheses relating to physical mechanisms. The suggested role of changes in free tropospheric RH has implications for CGILS, in which free tropospheric RH is fixed. References Stevens, B. & Brenguier, J.-L. in Clouds in the Perturbed Climate System: Their Relationship to Energy Balance, Atmospheric Dynamics and Precipitation (eds Heintzenberg, J. & Charlson, R. J.) Ch. 8 (MIT Press, 2009) Frequency of Cloud Fraction 2a) Cloud fraction and Relative Humidity [137W,26N] July 1979-2008 © Crown copyright 2011 11/0188 Met Office and the Met Office logo are registered trademarks Early results from HadGEM2-A CFMIP-2 experiments M. J. Webb, A.P.Lock, A. Bodas-Salcedo, Y. Tsushima, T.Andrews
© Crown copyright 2006Page 1 CFMIP II sensitivity experiments Mark Webb (Met Office Hadley Centre) Johannes Quaas (MPI) Tomoo Ogura (NIES) With thanks.
Page 1© Crown copyright 2007 CFMIP2: Options for SST-forced and slab experiments Mark Ringer, Brian Soden Hadley Centre,UK & RSMA/MPO, US CFMIP/ENSEMBLES.
Page 1© Crown copyright 2007 Initial tendencies of cloud regimes in the Met Office Unified Model Keith Williams and Malcolm Brooks Met Office, Hadley Centre.
© Crown copyright Met Office Towards understanding the mechanisms responsible for different cloud-climate responses in GCMs. Mark Webb, Adrian Lock (Met.
Page 1© Crown copyright 2007 Constraining the range of climate sensitivity through the diagnosis of cloud regimes Keith Williams 1 and George Tselioudis.
What’s quasi-equilibrium all about?
Links Between Clear-sky Radiation, Water Vapour and the Hydrological Cycle Richard P. Allan 1, Viju O. John 2 1 Environmental Systems Science Centre, University.
1 PV Generation in the Boundary Layer Robert Plant 18th February 2003 (With thanks to S. Belcher)
The effect of doubled CO 2 and model basic state biases on the monsoon- ENSO system: the mean response and interannual variability Andrew Turner, Pete.
Moisture Transport in Baroclinic Waves Ian Boutle a, Stephen Belcher a, Bob Plant a Bob Beare b, Andy Brown c 24 April 2014.
1 Dynamical Polar Warming Amplification and a New Climate Feedback Analysis Framework Ming Cai Florida State University Tallahassee, FL 32306
Water Vapor and Lapse Rate Feedbacks Neil Gordon ESP Seminar April 14, 2006.
Recent Evidence for Reduced Climate Sensitivity Roy W. Spencer, Ph.D Principal Research Scientist The University of Alabama In Huntsville March 4, 2008.
The syllabus says: Atmosphere and change Describe the functioning of the atmospheric system in terms of the energy balance between solar and long- wave.
Ocean-Atmosphere Interaction: A Tropical Thermostat for Global Warming
Clouds and Climate A. Pier Siebesma KNMI What are clouds? How do they form? Cloud climatology Clouds and Radiation Clouds in Climate models Cloud Climate.
Hurricanes and climate ATOC 4720 class22. Hurricanes Hurricanes intense rotational storm that develop in regions of very warm SST (typhoons in western.
Observed Tropical Expansion: Impact on the Hydrological and Energy Cycles New Investigator Research Summary Joel Norris (Lead PI, UC San Diego) Robert.
Circulation in the atmosphere
Double ITCZ Phenomena in GCM’s Marcus D. Williams.
© 2018 SlidePlayer.com Inc. All rights reserved.