Understanding the Extratropical Liquid Water Path Feedback in Mixed-Phase Clouds with an Idealized Global Climate Model

2022 ◽  
pp. 1-48
Author(s):  
Yi Ming
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Climate Model ◽  
Global Climate Model ◽  
Cloud Water ◽  
Mixed Phase ◽  
Liquid Water Path ◽  
Water Path ◽  
Cloud Water Content ◽  
Mixed Phase Clouds

Abstract A negative shortwave cloud feedback associated with higher extratropical liquid water content in mixed-phase clouds is a common feature of global warming simulations, and multiple mechanisms have been hypothesized. A set of process-level experiments performed with an idealized global climate model (a dynamical core with passive water and cloud tracers and full Rotstayn-Klein single-moment microphysics) show that the common picture of the liquid water path (LWP) feedback in mixed-phase clouds being controlled by the amount of ice susceptible to phase change is not robust. Dynamic condensate processes—rather than static phase partitioning—directly change with warming, with varied impacts on liquid and ice amounts. Here, three principal mechanisms are responsible for the LWP response, namely higher adiabatic cloud water content, weaker liquid-to-ice conversion through the Bergeron-Findeisen process, and faster melting of ice and snow to rain. Only melting is accompanied by a substantial loss of ice, while the adiabatic cloud water content increase gives rise to a net increase in ice water path (IWP) such that total cloud water also increases without an accompanying decrease in precipitation efficiency. Perturbed parameter experiments with a wide range of climatological LWP and IWP demonstrate a strong dependence of the LWP feedback on the climatological LWP and independence from the climatological IWP and supercooled liquid fraction. This idealized setup allows for a clean isolation of mechanisms and paints a more nuanced picture of the extratropical mixed-phase cloud water feedback than simple phase change.

scholarly journals The importance of mixed-phase clouds for climate sensitivity in the global aerosol-climate model ECHAM6-HAM2

2018 ◽  
Author(s):  
Ulrike Lohmann ◽  
David Neubauer
Keyword(s):  
Southern Ocean ◽  
Climate Sensitivity ◽  
Liquid Water ◽  
Climate Model ◽  
Global Climate Model ◽  
Supercooled Liquid ◽  
Mixed Phase ◽  
Radiation Budget ◽  
Shortwave Radiation ◽  
Mixed Phase Clouds

Abstract. Clouds are important in the climate system because of their large influence on the radiation budget. On the one hand, they scatter solar radiation and with that cool the climate. On the other hand, they absorb and re-emit terrestrial radiation, which causes a warming. How clouds change in a warmer climate is one of the largest uncertainties for the equilibrium climate sensitivity (ECS). While a large spread in the cloud feedback arises from low-level clouds, it was recently shown that also mixed-phase clouds are important for ECS. If mixed-phase clouds in the current climate contain too few supercooled cloud droplets, too much ice will change to liquid water in a warmer climate. As shown by Tan et al. (2016), this overestimates the negative cloud phase feedback and underestimates ECS in the CAM global climate model (GCM). Here we are using the newest version of the ECHAM6-HAM2 GCM to investigate the importance of mixed-phase clouds for ECS. Although we also considerably underestimate the fraction of supercooled liquid water globally in the reference version of ECHAM6-HAM2 GCM, we do not obtain increases in ECS in simulations with more supercooled liquid water in the present-day climate, contrary to the findings by Tan et al. (2016). We hypothesize that it is not the global supercooled liquid water fraction that matters, but only how well low- and mid-level mixed-phase clouds with cloud top temperatures in the mixed-phase temperature range between 0 and −35 ºC are simulated. These occur most frequent in mid-latitudes, in particular over the Southern Ocean where they determine the amount of absorbed shortwave radiation. In ECHAM6-HAM2 the amount of absorbed shortwave radiation over the Southern Ocean is only overestimated if all clouds below 0 ºC consist exclusively of ice and only in this simulation is ECS is significantly smaller than in all other simulations. Hence, the negative cloud phase feedback seems to be important only if the optically thin low- and mid-level mid-latitude clouds have the wrong phase (ice instead of liquid water) in the absence of overlying clouds. In all other simulations, changes in cloud feedbacks associated with cloud amount and cloud top pressure, dominate.

scholarly journals Formation and Development of Orographic Mixed-Phase Clouds

2017 ◽  
Vol 74 (11) ◽  
pp. 3703-3724 ◽  
Author(s):  
Olga Henneberg ◽  
Jan Henneberger ◽  
Ulrike Lohmann
Keyword(s):  
Liquid Water ◽  
Sensitivity Study ◽  
Horizontal Resolution ◽  
Mixed Phase ◽  
Liquid Water Path ◽  
Water Path ◽  
Orographic Forcing ◽  
Mixed Phase Clouds ◽  
Ice Water ◽  
Saturation Vapor

Abstract Orographic forcing can stabilize mixed-phase clouds (MPCs), which are thermodynamically unstable owing to the different saturation vapor pressure over liquid water and ice. This study presents simulations of MPCs in orographically complex terrain over the Alpine ridge with the regional model COSMO using a horizontal resolution of 1 km. Two case studies provide insights into the formation of Alpine MPCs. Trajectory studies show that the majority of the air parcels lifted by more than 600 m are predominantly in the liquid phase even if they originate from glaciated clouds. The interplay between lifted and advected air parcels is crucial for the occurrence of MPCs. Within a sensitivity study, the orography is reduced to 80%, which changed both the total barrier height and steepness. The changes in total water path (TWP), liquid water path (LWP), and ice water path (IWP) vary in sign and strength as the affected precipitation does. LWP can experience changes up to 500% resulting in a transformation from an ice-dominated MPC to a liquid-dominated MPC. In further simulations with increased steepness and maintained surface height at Jungfraujoch, TWP experiences a reduction between 25% and 40% during different time periods, which results in reduced precipitation by around 30%. An accurate representation of the steepness and the height of mountains in models is crucial for the formation and development of MPCs.

scholarly journals Cloud albedo changes in response to anthropogenic sulfate and non-sulfate aerosol forcings in CMIP5 models

2017 ◽  
Vol 17 (14) ◽  
pp. 9145-9162 ◽  
Author(s):  
Lena Frey ◽  
Frida A.-M. Bender ◽  
Gunilla Svensson
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Coupled Model ◽  
Cmip5 Models ◽  
Liquid Water Path ◽  
Anthropogenic Aerosols ◽  
Aerosol Composition ◽  
Cloud Albedo ◽  
Cloud Water Content ◽  
Absorbing Aerosols

Abstract. The effects of different aerosol types on cloud albedo are analysed using the linear relation between total albedo and cloud fraction found on a monthly mean scale in regions of subtropical marine stratocumulus clouds and the influence of simulated aerosol variations on this relation. Model experiments from the Coupled Model Intercomparison Project phase 5 (CMIP5) are used to separately study the responses to increases in sulfate, non-sulfate and all anthropogenic aerosols. A cloud brightening on the month-to-month scale due to variability in the background aerosol is found to dominate even in the cases where anthropogenic aerosols are added. The aerosol composition is of importance for this cloud brightening, that is thereby region dependent. There is indication that absorbing aerosols to some extent counteract the cloud brightening but scene darkening with increasing aerosol burden is generally not supported, even in regions where absorbing aerosols dominate. Month-to-month cloud albedo variability also confirms the importance of liquid water content for cloud albedo. Regional, monthly mean cloud albedo is found to increase with the addition of anthropogenic aerosols and more so with sulfate than non-sulfate. Changes in cloud albedo between experiments are related to changes in cloud water content as well as droplet size distribution changes, so that models with large increases in liquid water path and/or cloud droplet number show large cloud albedo increases with increasing aerosol. However, no clear relation between model sensitivities to aerosol variations on the month-to-month scale and changes in cloud albedo due to changed aerosol burden is found.

scholarly journals On the Definition of the Cloud Water Content Fluctuations and Its Effects on the Computation of a Second-Order Liquid Water Correlation

2007 ◽  
Vol 64 (2) ◽  
pp. 665-669 ◽  
Author(s):  
E. Bouzereau ◽  
L. Musson-Genon ◽  
B. Carissimo
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Climate Models ◽  
Cloud Water ◽  
Second Order ◽  
Subgrid Scale ◽  
Eddy Flux ◽  
Cloud Models ◽  
Cloud Water Content ◽  
Definition Of

Abstract In subgrid-scale condensation schemes of cloud models, the majority of previous authors have relied on results presented in a paper by Bougeault. In the present paper, second-order liquid water correlations are restated that differ from the former paper but are coherent with the corrigendum of Mellor. These differences are explained here through two different underlying definitions of cloud water content fluctuations; they can be summarized by whether or not unsaturated air within a grid box contributes to the eddy flux of the cloud water content. Taking into account the issue mentioned above, the “buoyancy flux” is also derived. Although the full impact of these changes has not been evaluated here, it may become important for future global cloud-resolving climate models.

scholarly journals Cloud Liquid Water Path from Satellite-Based Passive Microwave Observations: A New Climatology over the Global Oceans

2008 ◽  
Vol 21 (8) ◽  
pp. 1721-1739 ◽  
Author(s):  
Christopher W. O’Dell ◽  
Frank J. Wentz ◽  
Ralf Bennartz
Keyword(s):  
Liquid Water ◽  
Systematic Errors ◽  
Cloud Water ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Water Path ◽  
Microwave Imager ◽  
Cloud Liquid Water Path ◽  
The Tropics ◽  
Global Oceans

Abstract This work describes a new climatology of cloud liquid water path (LWP), termed the University of Wisconsin (UWisc) climatology, derived from 18 yr of satellite-based passive microwave observations over the global oceans. The climatology is based on a modern retrieval methodology applied consistently to the Special Sensor Microwave Imager (SSM/I), the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), and the Advanced Microwave Scanning Radiometer (AMSR) for Earth Observing System (EOS) (AMSR-E) microwave sensors on eight different satellite platforms, beginning in 1988 and continuing through 2005. It goes beyond previously published climatologies by explicitly solving for the diurnal cycle of cloud liquid water by providing statistical error estimates, and includes a detailed discussion of possible systematic errors. A novel methodology for constructing the climatology is used in which a mean monthly diurnal cycle as well as monthly means of the liquid water path are derived simultaneously from the data on a 1° grid; the methodology also produces statistical errors for these quantities, which decrease toward the end of the time record as the number of observations increases. The derived diurnal cycles are consistent with previous findings in the tropics, but are also derived for higher latitudes and contain more information than in previous studies. The new climatology exhibits differences with previous observationally based climatologies and is found to be more consistent with the 40-yr ECMWF Re-Analysis (ERA-40) than are the previous climatologies. Potential systematic errors of the order of 15%–30% or higher exist in the LWP climatology. A previously unexplored source of systematic error is caused by the assumption that all microwave-based retrievals of LWP must make regarding the partitioning of cloud water and rainwater, which cannot be determined using microwave observations alone. The potentially large systematic errors that result may hamper the usefulness of microwave-based climatologies of both cloud liquid water and especially rain rate, particularly in certain regions of the tropics and midlatitudes where the separation of rain from liquid cloud water is most critical.

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