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Sonia M. Kreidenweis, Markus Petters, and Ulrike Lohmann

anthropogenic sulfate aerosol forcing (W m −2 ) (global = 1.8 W m −2 ). [Figure and caption from Kiehl and Briegleb (1993) . Reprinted with permission from AAAS.] Charlson et al. (1992) included in their analysis of aerosol climate forcing a discussion of the “indirect radiative influence” of sulfate aerosols that arises due to the interactions of atmospheric particles with cloud formation and development. Sufficiently large numbers of particles are always present in the atmosphere, such that all water

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Pavlos Kollias, Eugene E. Clothiaux, Thomas P. Ackerman, Bruce A. Albrecht, Kevin B. Widener, Ken P. Moran, Edward P. Luke, Karen L. Johnson, Nitin Bharadwaj, James B. Mead, Mark A. Miller, Johannes Verlinde, Roger T. Marchand, and Gerald G. Mace

. Ahmad , and D. Hartmann , 1989 : Cloud-radiative forcing and climate: Results from the Earth Radiation Budget Experiment . Science , 243 , 57 – 63 , doi: 10.1126/science.243.4887.57 . Sassen , K. , C. J. Grund , J. D. Spinhirne , M. H. Hardesty , and J. M. Alvarez , 1990 : The 27–28 October FIRE IFO cirrus case study: A five lidar overview of cloud structure and evolution . Mon. Wea. Rev. , 118 , 2288 – 2311 , doi: 10.1175/1520-0493(1990)118<2288:TOFICC>2.0.CO;2 . Sassen

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Andrew J. Heymsfield, Martina Krämer, Anna Luebke, Phil Brown, Daniel J. Cziczo, Charmaine Franklin, Paul Lawson, Ulrike Lohmann, Greg McFarquhar, Zbigniew Ulanowski, and Kristof Van Tricht

(EULAG) to perform idealized simulations with different concentrations of INPs in a dynamically dominated regime with high vertical velocities. They showed that, even under these conditions, low number concentrations of INP on the order of 0–50 L −1 are able to strongly decrease the simulated ice crystal number burden, the ice water path, and optical depth of the cloud. The shortwave, longwave, and net cloud forcings are also reduced with increasing INP concentrations. Kuebbeler et al. (2014

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Robert G. Fovell, Yizhe Peggy Bu, Kristen L. Corbosiero, Wen-wen Tung, Yang Cao, Hung-Chi Kuo, Li-huan Hsu, and Hui Su

shortwave (SW) radiation, effectively rendering clouds transparent. Track variation with respect to MP virtually disappeared, which demonstrated that the interplay of hydrometeors with radiation—which we term cloud-radiative forcing (CRF)—was a distinguishing factor among microphysics schemes. The interaction between condensed water and radiation is species dependent, and the MPs that generate more radiatively active particles also developed more radially extensive convective activity, different

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V. Ramaswamy, W. Collins, J. Haywood, J. Lean, N. Mahowald, G. Myhre, V. Naik, K. P. Shine, B. Soden, G. Stenchikov, and T. Storelvmo

. (a) From top to bottom, the forcings are due to changes in CO 2 , non-CO 2 WMGHGs, tropospheric ozone, stratospheric ozone, aerosol–radiation interaction, aerosol–cloud interaction, surface albedo, total anthropogenic RF, and solar irradiance. The forcings are color coded to indicate the “confidence level” (or LOSU as was presented in and before AR4, which used “consensus” rather than “agreement” to assess confidence level). Dark green is “high agreement and robust evidence”; light green is

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Ulrich Schumann and Andrew J. Heymsfield

, doi: 10.1175/1520-0493(2002)130<0398:OOADTF>2.0.CO;2 . 10.1175/1520-0493(2002)130<0398:OOADTF>2.0.CO;2 Duda , D. P. , P. Minnis , and L. Nguyen , 2001 : Estimates of cloud radiative forcing in contrail clusters using GOES imagery . J. Geophys. Res. , 106 , 4927 – 4937 , doi: 10.1029/2000JD900393 . 10.1029/2000JD900393 Duda , D. P. , P. Minnis , L. Nyuyen , and R. Palikonda , 2004 : A case study of the development of contrail clusters over the Great Lakes . J. Atmos. Sci

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W.-K. Tao, Y. N. Takayabu, S. Lang, S. Shige, W. Olson, A. Hou, G. Skofronick-Jackson, X. Jiang, C. Zhang, W. Lau, T. Krishnamurti, D. Waliser, M. Grecu, P. E. Ciesielski, R. H. Johnson, R. Houze, R. Kakar, K. Nakamura, S. Braun, S. Hagos, R. Oki, and A. Bhardwaj

advection terms on the RHS of Eq. (2-1) have been used to force CRMs (or cumulus ensemble models) to study the response of convective systems to large and mesoscale processes ( Soong and Tao 1980 ). This CRM approach to studying cloud and precipitation processes is called cloud ensemble modeling [ Soong and Tao 1980 ; Tao and Soong 1986 ; Tao et al. 1987 ; Krueger 1988 ; Moncrieff et al. 1997 ; also see review papers by Tao (2003 , 2007 ) and Tao and Moncrieff (2009) ]. It allows many clouds

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Daniel Rosenfeld and William L. Woodley

Abstract

Spaceborne inferences of cloud microstructure and precipitation-forming processes with height have been used to investigate the effect of ingested aerosols on clouds and to integrate the findings with past cloud physics research. The inferences were made with a method that analyzes data from National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (NOAA AVHRR) and Tropical Rainfall Measuring Mission Visible and Infrared Scanner (TRMM VIRS) sensors to determine the effective radius of cloud particles with height. In addition, the TRMM Precipitation Radar (PR) made it possible to measure the rainfall simultaneously with the microphysical retrievals, which were validated by aircraft cloud physics measurements under a wide range of conditions. For example, the satellite inferences suggest that vigorous convective clouds over many portions of the globe remain supercooled to near −38°C, the point of homogeneous nucleation. These inferences were then validated in Texas and Argentina by in situ measurements using a cloud physics jet aircraft.

This unique satellite vantage point has documented enormous variability of cloud conditions in space and time and the strong susceptibility of cloud microstructure and precipitation to the ingested aerosols. This is in agreement with past cloud physics research. In particular, it has been documented that smoke and air pollution can suppress both water and ice precipitation-forming processes over large areas. Measurements in Thailand of convective clouds suggest that the suppression of coalescence can decrease areal rainfall by as much as a factor of 2. It would appear, therefore, that pollution has the potential to alter the global climate by suppressing rainfall and decreasing the net latent heating to the atmosphere and/or forcing its redistribution. In addition, it appears that intense lightning activity, as documented by the TRMM Lightning Imaging Sensor (LIS), is usually associated with microphysically highly “continental” clouds having large concentrations of ingested aerosols, great cloud-base concentrations of tiny droplets, and high cloud water contents. Conversely, strongly “maritime” clouds, having intense coalescence, early fallout of the hydrometeors, and glaciation at warm temperatures, show little lightning activity. By extension these results suggest that pollution can enhance lightning activity.

The satellite inferences suggest that the effect of pollution on clouds is greater and on a much larger scale than any that have been documented for deliberate cloud seeding. They also provide insights for cloud seeding programs. Having documented the great variability in space and time of cloud structure, it is likely that the results of many cloud seeding efforts have been mixed and inconclusive, because both suitable and unsuitable clouds have been seeded and grouped together for evaluation. This can be addressed in the future by partitioning the cases based on the microphysical structure of the cloud field at seeding and then looking for seeding effects within each partition.

This study is built on the scientific foundation laid by many past investigators and its results can be viewed as a synthesis of the new satellite methodology with their findings. Especially noteworthy in this regard is Dr. Joanne Simpson, who has spent much of her career studying and modeling cumulus clouds and specifying their crucial role in driving the hurricane and the global atmospheric circulation. She also was a pioneer in early cloud seeding research in which she emphasized cloud dynamics rather than just microphysics in her seeding hypotheses and in her development and use of numerical models. It is appropriate, therefore, that this paper is offered to acknowledge Dr. Joanne Simpson and her many colleagues who paved the way for this research effort.

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William M. Gray

Abstract

This paper uses extensive aircraft, composited rawinsonde data, and an idealized hurricane structure model to analyze the physical processes that maintain the transverse circulation of the steady-state hurricane. It is shown that convective available potential energy (CAPE) or processes other than frictional forcing plays an important role in maintaining the hurricane's inner-core (radius < 60 km) in-up-and-out radial circulation. But this is not true at outer radii (60–250 km or 250–700 km) where surface friction forcing is dominant and larger than the resulting upward vertical motion.

Overall, there is less vertical motion within the hurricane's 0–250-km area than that specified by frictional forcing and, overall, CAPE or buoyancy plays a negative role in enhancing vertical motion. But this is not true of the inner-core eye-wall cloud region where nonfrictionally driven eye-wall vertical motion has an important buoyant contribution and a strong ocean-to-air energy flux is present. Frictionally forced vertical motion resulting from low-level relative vorticity is typically not balanced locally. Quasi balance between frictional forcing and vertical motion is observed only for the larger-scale vortex (approximately 0°–3° radius) as a whole.

PROLOGUE

Joanne Simpson tells the story that in the mid-1940s, when she was a young (and precocious!) graduate student at the University of Chicago, she told Carl Rossby that she wanted to study clouds and that he responded by saying that that was a good subject for a girl. We now more fully appreciate the role of clouds as the fundamental component of the hydrologic cycle. Most of us would agree that understanding the physics behind cumulus convection is a fundamental challenge for all, girl or boy. Joanne's choice of cloud studies as a career endeavor was a wiser choice than most meteorologists of that day (and many of this day) realized. Attention in the 1940s and 1950s had been focused more on the requirements of wind for the transfer of energy from the tropical to the polar regions. There is no doubt that horizontal transport of energy is a fundamental ingredient of the general circulation. But vertical energy transport to balance the troposphere's continuous radiational cooling of ∼1°C per day is more important. Globally averaged, the required vertical transport of energy from the surface up into the troposphere is about four times larger than the required horizontal transport. It is this vertical energy transport that is so messy and so difficult to understand, and so hard to treat in a realistic and quantitative fashion. Many modelers and theoreticians have chosen to neglect the many hydrologic cycle complications (by assuming that the troposphere's radiational cooling is balanced by condensation warming) and to concentrate only on the horizontal energy imbalances. This has been the approach of the dishpan or annulus experiments. But this is not satisfactory for a full understanding of how the troposphere really functions. We have to face up to the need for the development of a realistic quantitative treatment of the globe's hydrologic cycle. The cumulus convection schemes in current GCMs are still inadequate. It is this continuing need to better understand the full range of cloud processes that has made Joanne's decision in the mid-1940s to concentrate on clouds such a wise one. She has since made many contributions to the understanding of the role of clouds. The paper she wrote with Herbert Riehl in 1958 (Riehl and Malkus) had much influence on the thinking of the important role of cumulus convection. Her recent work with the Tropical Rainfall Measuring Mission (TRMM) experiment is an example of her continuing drive to better understand clouds and the hydrologic cycle.

I first met and worked with Joanne in the late 1950s when I was a graduate student of Herbert Riehl's at the University of Chicago. I participated in the study she was directing on the variations of tropical Pacific cloudiness from aircraft time-lapse photography. This was before the satellite and the computer. We had more time to think and to speculate in those days. I have been most grateful to both Joanne and Bob Simpson for their interest and encouragement of my research efforts since that time.

It is a pleasure to make a contribution to this symposium honoring Joanne. The paper to follow has many similarities to the early and original paper of Joanne in 1958 titled “The Structure and Maintenance of the Mature Hurricane Eye.”

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Steven Ghan and Joyce E. Penner

of the earth. The term radiative forcing (RF) refers to the impact of anthropogenic aerosols on the shortwave and longwave radiative fluxes without considering the adjustment of clouds to the aerosol. RFari is the component of RF due to aerosol–radiation interactions, specifically scattering and absorption of radiation, while RFaci is the component of RF due to aerosol–cloud interactions, specifically aerosol effects on droplet and ice crystal number but not liquid water or ice mass concentration

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