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The Atmospheric Energy Constraint on Precipitation Change 1

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The Atmospheric Energy Constraint on Precipitation Change 1 The atmospheric energy constraint on precipitation change 1 Angeline G. Pendergrass A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2013 Reading Committee: Dennis L. Hartmann, Chair Dargan M. W. Frierson Gerard H. Roe Program Authorized to Offer Degree: Department of Atmospheric Sciences 1Updated to correct typos. University of Washington Abstract The atmospheric energy constraint on precipitation change 1 Angeline G. Pendergrass Chair of the Supervisory Committee: Professor Dennis L. Hartmann Department of Atmospheric Sciences How does rain change with global warming? This dissertation investigates the rate of global-mean precipitation increase, changes in atmospheric radiative cooling, and the changes in frequency and intensity of rain events. We examine changes in global-mean precipitation and atmospheric radiative cool- ing in comprehensive climate model simulations. In a realistic forcing scenario includ- ing both greenhouse gases and aerosols, clear-sky absorption of shortwave radiation is correlated with the rate of global-mean precipitation increase. In a scenario forced by increasing carbon dioxide alone, we make radiative transfer calculations to separate the responses of clear-sky atmospheric radiative cooling due to warming, moistening, and the carbon dioxide itself. Clear-sky atmospheric radiative cooling increases in response to vertically uniform warming and constant relative humidity moistening of the atmosphere. These increases are partially offset by decreases due to the di- rect radiative effects of carbon dioxide and black carbon. Global-mean precipitation increases by the same rate as the change in clear-sky atmospheric radiative cooling. Changes in the frequency of rain and the rate at which it falls constitute the increase in global-mean precipitation. We develop a methodology for characterizing the frequency and amount of rainfall as functions of the rain rate. We define two 1Updated to correct typos. modes of response, one in which the distribution of rainfall increases in equal fraction at all rain rates (the increase mode) and one in which the rainfall shifts to higher or lower rain rates without a change in mean rainfall (the shift mode). We apply this description of change to simulations of global warming in climate models. We also calculate the response of the tropical rainfall distribution to ENSO phases in models and observations and apply the increase and shift modes. In addition to the increase and shift modes of change, some models show a substantial increase in rainfall at the highest rain rates. In some models this extreme mode can be shown to be associated with increases in grid-scale precipitation. TABLE OF CONTENTS Page ListofFigures ................................... iii ListofTables.................................... vi Chapter1: Introduction ............................ 1 1.1 Precipitationasatransferofenergy . ... 2 1.2 Changes in global-mean precipitation and atmospheric radiative cooling 3 1.3 The distribution of precipitation and its change . ...... 5 1.4 Outlineofthedissertation . 7 Chapter 2: Global-mean precipitation and black carbon in AR4 simulations 9 2.1 Introduction................................ 9 2.2 Data.................................... 10 2.3 Changes in global-mean precipitation and components of the atmo- sphericenergybudget. 12 2.4 Patterns of change in clear-sky atmospheric SW absorption...... 12 2.5 Thetimeseriesofblackcarbonforcing . .. 14 2.6 Contrast with CO2-doublingscenario . 18 2.7 Conclusions ................................ 19 Chapter 3: The atmospheric energy constraint on global-mean precipitation change................................ 22 3.1 Introduction................................ 22 3.2 Atmospheric energy and precipitation change. ..... 24 3.3 Radiative response to changes in moisture and temperature at a par- ticularheight ............................... 25 3.4 Atmospheric column radiative responses to idealized changes in tem- perature, moisture, and CO2 ....................... 29 i 3.5 Inter-model spread in atmospheric radiative cooling response to CO2 forcing................................... 42 3.6 Discussion................................. 49 3.7 Conclusion................................. 53 Chapter 4: Changes in the distribution of rain in response to warming in modelsandobservations . 55 4.1 Introduction................................ 55 4.2 Dataandmethods ............................ 56 4.3 Therain amount distribution and its change . ... 62 4.4 Implications for changes in frequency distribution . ........ 84 4.5 Differencesacrossmodels. 95 4.6 Discussion................................. 107 4.7 Conclusions ................................ 113 Chapter5: Concludingremarks . 115 AppendixA: Modelsimulations . 130 Appendix B: Rain amount and rain frequency distribution calculations. 133 ii LIST OF FIGURES Figure Number Page 2.1 Rate of precipitation increase versus change in atmospheric radiative cooling................................... 13 2.2 Maps of clear-sky atmospheric shortwave absorption change in NCAR CCSM3andGFDLCM2.1 ....................... 15 2.3 Timeseries of clear-sky shortwave absorption and precipitation in NCAR CCSM3.0andGFDLCM2.0and2.1 . 17 2.4 Rate of precipitation increase versus change in clear-sky shortwave ab- sorption for carbon dioxide increase forcing scenario . ...... 20 3.1 Global-mean precipitation increase in CMIP5 models . ...... 24 3.2 Zonal-mean cross sections of temperature and moisture changes in CMIP5models .............................. 27 3.3 TOA, surface, and atmospheric column radiative responses to the ver- ticalstructureofwarmingandmoistening . 29 3.4 Atmospheric column LW and SW radiative responses to the vertical structureofwarmingandmoistening . 30 3.5 Global mean of the baseline temperature and relative humidity profiles usedforidealizedcalculations . 31 3.6 Radiative response to vertically-uniform warming, constant-relative- humidity moistening, and carbon dioxide increase . ... 34 3.7 Radiative response to vertically-varying warming with constant-relative- humiditymoistening ........................... 37 3.8 Radiative response to idealized low and high clouds . ...... 41 3.9 Clear-sky atmospheric radiative cooling and the rate of global-mean precipitation increase across CMIP5 models . 44 3.10 Comparison of GCM radiative responses with radiative transfer model calculations ................................ 45 3.11 Contributing factors to inter-model spread in precipitation and radia- tive response at the TOA and in the atmospheric column . 46 iii 3.12 The compensation between TOA and atmospheric column radiative responsestolapserateandwatervaporchange . 47 3.13 Relationship of the radiative response to vertically-varying and vertically- uniform constant-RH moistening with the response to changing lapse rate .................................... 49 4.1 Rain amount and rain frequency distributions in the CMIP5 multi- modelmeanandobservations . 64 4.2 Rain amount distribution in CMIP5 models compared with GPCP ob- servations ................................. 66 4.3 Schematic of the modes of change of the rain distribution ....... 69 4.4 Modes of change of the rain distribution compared to the CMIP5 multi- modelmeanresponse........................... 71 4.5 Rain amount response to carbon dioxide increase, with fitted shift and increase modes, for the CMIP5 multi-model mean . 75 4.6 Rain amount response to carbon dioxide increase, with fitted shift and increasemodes,forCMIP5models . 77 4.7 Shiftmodeversuserroroffit. 78 4.8 Increase mode versus global-mean precipitation change ........ 79 4.9 Rain amount response to ENSO phases, with fitted shift and increase modes,inobservationsandmodels . 81 4.10 Magnitude of the shift and increase modes fit to response to ENSO phases in observations and models over land and ocean . .. 83 4.11 Magnitude of the shift and increase modes fit to responses to CO2 increase and ENSO phases in models over land and ocean . 85 4.12 Rain frequency response to carbon dioxide increase in CMIP5 multi- modelmean................................ 87 4.13 Extreme rain rate response to carbon dioxide increase in the CMIP5 multi-modelmean............................. 90 4.14 Extreme rain rate response to carbon dioxide increase in CMIP5 models 92 4.15 Extreme rain rate response to carbon dioxide increase and ENSO phases overland.................................. 93 4.16 Extreme rain rate response to ENSO phases in models and observations 94 4.17 Unresolved (convective) rain distribution in three models ....... 98 4.18 Maps of the rain amount falling in heavy events in observations and MPI-ESM-LR and GFDL-ESM2G model simulations . 101 iv 4.19 Evolution of a heavy rain event in MPI-ESM-LR. ... 103 4.20 Evolution of a heavy rain event in GFDL-ESM2G . 104 4.21 Rain amount and extreme rain rate responses to carbon dioxide dou- blingandquadruplinginthreemodels . 105 4.22 Rain amount and extreme rain rate response to ENSO phases in two models................................... 109 4.23 Vertical velocity and its change as a function of rain rate in three models112 v LIST OF TABLES Table Number Page 2.1 CMIP3 models ranked by rate of precipitation increase . ...... 11 3.1 Changes in CMIP5 multi-model, global-mean atmospheric energy bud- getcomponents .............................. 25 3.2 Clear-sky radiative response to warming, moistening, and carbon diox- idefromradiativetransfercalculations . .. 33 3.3 Comparison
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