1. PREPARE: Projected Responses in Extreme Precipitation and Atmospheric Radiative Energy
Richard P. Allan, Matthias Zahn
Department of Meteorology, University of Reading
Met Office Collaborators: Viju John, Mark Ringer, Alejandro Bodas- Salcedo, Peili Wu
International Collaborators: Martin Wild (ETH, Zurich) Brian Soden (RSMAS, University of Miami), Igor Zveryaev (PP Shirshov, Moscow)‏
Projected Responses in Extreme Precipitation and Atmospheric Radiative Energy 1

2. PREPARE project: details
Funded by NERC; collaboration with Met Office and ETH Zurich
1 March April 2013
Also: NERC Changing Water Cycle (CWC):
PAGODA CWC project (Reading/Edinburgh/Exeter/Met Office)
Imperial College CWC project (Imperial/Reading)
TAMSAT group (Reading)
Work toward AR5
Aim of today: to to make each other aware of current work relating to PREPARE and opportunities for collaboration. In particular, how can the project be of use to the Met Office and what resources, for example model experiments/datasets, would the Met Office be able to contribute to the project.

3. How will precipitation change in the future?
How is precipitation currently changing?
Do we understand projected responses?
Wet/Dry region responses
Extreme precipitation
Model Precipitation Change (%)‏
Allan et al. (2010) Environ. Res. Lett. 3

4. Current Understanding
Observations and simple physics help to confirm robust model projections
Increased precipitation (~2%/K)
Increased precipitation intensity (~7%/K)
Extratropics and wet regions of tropics get wetter
Dry regions of sub-tropics get drier
Transient response to GHG stabilisation
Outstanding Issues
Inaccurate simulation of precipitation events
Limitations of satellite and gauge data
Cloud Feedback and Aerosol Forcing
is Walker circulation modulated by contrasting effects of SST and forcing (e.g. CO2)?
Detecting and attributing signals
Projected Responses in Extreme Precipitation and Atmospheric Radiative Energy 4

5. Recent Advances
Surface and atmosphere energy balance constraint (Allen and Ingram, 2002; Stephens and Ellis, 2008; Lambert and Webb, 2008, Andrews et al. 2009; Richter and Xie 2008 JGR)
Moisture transport constraint (Held and Soden, 2006)
Dynamical considerations (O’Gorman and Schneider, 2009; Lendering and Van Meijgaard, 2008; Turner and Slingo 2009 ASL)
Mass flux and moist adiabat arguments (e.g. Vecchi and Soden 2006 Nature; Sohn and Park 2010 JGR)
Transient response (Andrews et al ERL; Wu et al GRL; Bala et al Clim Dyn)
Hydrological forcing and absorbing aerosol (Andrews et al GRL; Ming et al GRL)
Observed responses (Zhang et al Nature; Wentz et al Science; Allan and Soden 2008 Science, Adler et al JGR; Wild et al GRL; Zolina et al GRL)

6. PREPARE proposal Hypothesis:
Core datasets, including improvement of surface radiation budget using BSRN and empirical formula (WP1)
Quantifying trends and physical relationships (WP2)
Precipitation Extremes (WP3)
Modelling Experiments (WP4)
Implications for Climate Projections (WP5)
Hypothesis:
Current observing systems are inadequate for monitoring current changes in the hydrological cycle
Changes in aerosol, in particular absorbing aerosols, are key to understanding current changes in precipitation
Projected responses in extreme precipitation are primarily related to parametrizations and relate to present day bias in the probability distribution of precipitation events
2010
2012
2012
2013

7. PREPARE proposal Hypothesis:
Core datasets, including improvement of surface radiation budget using BSRN and empirical formula (WP1)
Quantifying trends and physical relationships (WP2)
Precipitation Extremes (WP3)
Modelling Experiments (WP4)
Implications for Climate Projections (WP5)
Hypothesis:
Current observing systems are inadequate for monitoring current changes in the hydrological cycle
Changes in aerosol, in particular absorbing aerosols, are key to understanding current changes in precipitation
Projected responses in extreme precipitation are primarily related to parametrizations and relate to present day bias in the probability distribution of precipitation events

8. Initial Results: Sensitivity to dataset
GPCP Ascent Region Precipitation (mm/day)
Initial Results: Sensitivity to dataset
Allan (2009) J. Clim
Robust response: wet regions become wetter at the expense of dry regions
Large uncertainty in magnitude of change: satellite datasets and models & time period
TRMM
John et al. (2009) GRL

9. PREPARE: Initial Results
Opposing trends in wet and dry regions of the tropics
Response to ENSO
Mechanisms:
Aerosol forcing?
Circulation changes?
Data inhomogeneity?
Does Walker circulation respond to SST/CO2 forcing (e.g. rising SST reduces Walker circulation, CO2 forcing enhances Walker circulation).
Allan et al. (2010) Environ. Res. Lett.

10. Increases in the frequency of the heaviest rainfall with warming: daily data from models and microwave satellite data (SSM/I)
Daily data from AMIP climate model simulations (observed SST forcing) and microwave data from the F08/F11/F13 SSM/I series of satellite microwave measurements. The heaviest rainfall events are separated into bins ranging from heavy up to torrential events and the variation in the frequency of events in each bin is calculated (red=more frequent, blue=less frequent). The response of the heaviest rainfall events is consistent with models but the models appear to underestimate the response to warming and the details of the changes away from the heaviest rainfall regimes are not in agreement.
Reduced frequency Increased frequency
Allan et al. (2010) Environ. Res. Lett. 10

11. SSM/I satellite observations at upper limit of model range
Increase in intense rainfall with tropical ocean warming (close to Clausius Clapeyron)‏
SSM/I satellite observations at upper limit of model range
Model intense precipitation constrained by moist adiabatic lapse rate; responses highly sensitive to model-specific changes in upward velocities (O’Gorman &Schneider, 2009, PNAS; Gastineau & Soden 2009; Turner and Slingo, 2009 ASL). 11

12. Can we understand regional changes in water cycle?
Water vapour Precipitation
Allan and Zveryaev (2010) Int J Climatology

13. Binning Precipitation by ω-Ts
CMIP AMIP
Percentiles of global temperature (warmer -->) 13

14. Matthias…

15. Datasets (WP1)
PREPARE

16. Current Plans
i) Consolidation/intercomparison/analysis of datasets (WP1/2)
Explore use of BSRN and SSM/I water vapour data to constrain decadal changes in surface fluxes; EOF analysis
ii) Calculation of moisture transports (WP2)
DryWet; Tropics Extra Tropics
iii) Evaluation of precipitation extremes: AR4/AR5 (WP2/3)
iv) Define/identify AMIP (or other) experiments (WP4)
Explore sensitivity to aerosol: fast responses
v) Explore available QUMP experiments (WP4)
Sensitivity to parametrization
vi) Links between surface radiation/Hydrological forcing (WP1/4)
See Andrews et al GRL and Ming et al GRL
The idea is to just run or adapt some simple AMIP experiments from 1979-present as follows:
1) A control with increasing GHG but no changes in aerosol
2) Realistic changes in main aerosol types
3) As 1 but changing each main aerosol species separately (e.g. Sulphate and Black Carbon)
4) Some experiments in which we allow aerosol to vary by a larger amount, in particular Black Carbon.
In particular I'd be interested how different the decadal precipitation responses could be, in particular for Black Carbon.
Andy Jones:
Points 1-4 sound perfectly sensible - it's what you say just before point 1 that doesn't! If you're using an AMIP setup (i.e. atmosphere-only with prescribed SSTs and sea-ice) then any impact of aerosols on climate is going to be negated as the model will just evolve following the SSTs. It seems to me that to look at what you're interested in you need to use a fully coupled model.
Me:
But AMIP experiments can provide information on FAST feedbacks (e.g. direct responses to forcings).
Could consider slab ocean experiments from Tim Andrews et al. also.