The western U.S. receives precipitation predominantly during the cold season when storms approach from the Pacific Ocean. The snowpack that accumulates during winter storms provides about 70-90% of water supply for the region. Understanding and modeling the fundamental processes that govern the large precipitation variability and extremes in the western U.S. is a critical test for the ability of climate models to predict the regional water cycle, including floods and droughts. Two elements of significant importance in predicting precipitation variability in the western U.S. are atmospheric rivers and aerosols. Atmospheric rivers (ARs) are narrow bands of enhanced water vapor associated with the warm sector of extratropical cyclones over the Pacific and Atlantic oceans. Because of the large lower-tropospheric water vapor content, strong atmospheric winds and neutral moist static stability, some ARs can produce heavy precipitation by orographic enhancement during landfall on the U.S. West Coast. While ARs are responsible for a large fraction of heavy precipitation in that region during winter, much of the rest of the orographic precipitation occurs in post-frontal clouds, which are typically quite shallow, with tops just high enough to pass the mountain barrier. Such clouds are inherently quite susceptible to aerosol effects on both warm rain and ice precipitation-forming processes.
The purpose of this Atmospheric Radiation Measurement (ARM) Science Plan is to articulate the scientific issues driving the ARM Program, and to relate them to DOE's programmatic objectives for ARM, based on the experience and scientific progress gained over the past five years. ARM programmatic objectives are to: (1) Relate observed radiative fluxes and radiances in the atmosphere, spectrally resolved and as a function of position and time, to the temperature and composition of the atmosphere, specifically including water vapor and clouds, and to surface properties, and sample sufficient variety of situations so as to span a wide range of climatologically relevant possibilities; (2) develop and test parameterizations that can be used to accurately predict the radiative properties and to model the radiative interactions involving water vapor and clouds within the atmosphere, with the objective of incorporating these parameterizations into general circulation models. The primary observational methods remote sending and other observations at the surface, particularly remote sensing of clouds, water vapor and aerosols.
This book is the standard reference based on roughly 20 years of research on atmospheric rivers, emphasizing progress made on key research and applications questions and remaining knowledge gaps. The book presents the history of atmospheric-rivers research, the current state of scientific knowledge, tools, and policy-relevant (science-informed) problems that lend themselves to real-world application of the research—and how the topic fits into larger national and global contexts. This book is written by a global team of authors who have conducted and published the majority of critical research on atmospheric rivers over the past years. The book is intended to benefit practitioners in the fields of meteorology, hydrology and related disciplines, including students as well as senior researchers.
Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water path (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 05/27/2011 at the Southern Great Plains (SGP) measurement site established by Department of Energy's Atmospheric Radiation Measurement (ARM) Program using a single column version of a global climate model (Community Atmosphere Model or CAM) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near cloud top, resulting in an overall decrease in LWP. Our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.
Field Measurements for Environmental Remote Sensing: Instrumentation, Intensive Campaigns, and Satellite Applications is an academic synthesis of invaluable in situ measurements and techniques leveraged by the science of environmental remote sensing. Sections cover in situ datasets and observing methods used for satellite remote sending applications and validation, synthesizing the various techniques utilized by well-established application areas under a common paradigm. The book serves as both a textbook for students (upper-level undergraduate to graduate level) and a reference book for practitioners and researchers in the atmospheric, oceanic and remote sensing fields. Presents chapters organized according to subdiscipline, with each written by established experts in their relevant field Includes literature reviews, case studies and applications for each subdivision Features a synthesis of the suite of invaluable in situ measurements and techniques leveraged by the science of environmental remote sensing
The studies in this dissertation aim at advancing our scientific understandings about physical processes involved in the aerosol-cloud-precipitation interaction and quantitatively assessing the impacts of aerosols on the cloud systems with diverse scales over the globe on the basis of the observational data analysis and various modeling studies. As recognized in the Fifth Assessment Report by the Inter-government Panel on Climate Change, the magnitude of radiative forcing by atmospheric aerosols is highly uncertain, representing the largest uncertainty in projections of future climate by anthropogenic activities. By using a newly implemented cloud microphysical scheme in the cloud-resolving model, the thesis assesses aerosol-cloud interaction for distinct weather systems, ranging from individual cumulus to mesoscale convective systems. This thesis also introduces a novel hierarchical modeling approach that solves a long outstanding mismatch between simulations by regional weather models and global climate models in the climate modeling community. More importantly, the thesis provides key scientific solutions to several challenging questions in climate science, including the global impacts of the Asian pollution. As scientists wrestle with the complexities of climate change in response to varied anthropogenic forcing, perhaps no problem is more challenging than the understanding of the impacts of atmospheric aerosols from air pollution on clouds and the global circulation.
This book recommends the initiation of an "integrated" research program to study the role of aerosols in the predicted global climate change. Current understanding suggest that, even now, aerosols, primarily from anthropogenic sources, may be reducing the rate of warming caused by greenhouse gas emissions. In addition to specific research recommendations, this book forcefully argues for two kinds of research program integration: integration of the individual laboratory, field, and theoretical research activities and an integrated management structure that involves all of the concerned federal agencies.
The role of multiple groups of primary biological aerosol particles (PBAPs) as ice nucleating particles (INPs), and of ice formation processes such as time-dependent freezing of various INPs, and various secondary ice production (SIP) mechanisms in overall ice concentration has been evaluated in a range of cloud systems by simulating them numerically with the state-of-the-art 'Aerosol-Cloud' (AC) model in a 3D mesoscale domain. Also, the mechanisms of aerosol indirect effects (AIEs) arising from anthropogenic INPs, and the responses to these AIEs from time-dependent INP freezing and SIP processes are investigated in the simulated clouds. The cloud systems simulated with AC are: events of summertime deep convection observed over Oklahoma, USA during the Midlatitude Continental Convective Cloud Experiment (MC3E) in 2011 on 1) 11 May, and 2) 20 May, and wintertime 3) orographic clouds observed during the Atmospheric Radiation Measurement Cloud Aerosol Precipitation Experiment (ACAPEX) on 07 February 2015 over North California, and 4) supercooled layer clouds observed over Larkhill, UK, during the Aerosol Properties, Processes And Influences on the Earth's climate (APPRAISE) campaign on 18 February 2009. AC uses the dynamical core of the Weather Research and Forecasting (WRF) model, modified Geophysical Fluid Dynamic Laboratory (GFDL) radiation scheme, and hybrid bin-bulk microphysics scheme. AC is validated adequately with the coincident aircraft, ground-based, and satellite observations for all four cases. AC forms secondary ice through the Hallett-Mossop (HM) process of rime-splintering, and fragmentation during ice-ice collisions, raindrop freezing, and sublimation of dendritic snow and graupel. A measure of SIP is defined using the term 'ice enhancement' (IE) ratio which is the ratio between the number concentration of total ice particles and active INPs at cloud tops. For both cases in MC3E, overall, PBAPs have little effect (+1-6%) on the cloud-liquid (droplet mean sizes, number concentrations, and their water contents) properties, overall ice concentration, and on precipitation. AC predicts the activity of various INPs with an empirical parameterization (EP). The EP is modified to represent the time-dependent approach of INP freezing in light of our published laboratory observations. It is predicted that the time dependence of INP freezing is not the main cause for continuous ice nucleation and precipitation in all simulated cases. Rather, the main mechanism of precipitation formation is the combination of various SIP mechanisms (in convection) and recirculation-reactivation of dust particles (in APPRAISE layer cloud episode). Also, for all cases, the inclusion of time dependence of INP freezing causes little increase (about 10-20%) in the total ice concentration and ice from all SIP. Regarding SIP, in young developing convective clouds of MC3E (11 May), with tops > −15oC, the initial explosive growth is from the fast HM process, creating IE ratios as high as 103. By contrast, in mature convective clouds (tops
One of the most significant and uncertain aspects of climate change projections is the impact of aerosols on the climate system. Aerosols influence the climate indirectly by interacting with nearby clouds leading to small changes in cloud cover, thickness, and altitude, which significantly affect Earth's radiative balance. Advancements have been made in recent years on understanding the complex processes and atmospheric interactions involved when aerosols interact with surrounding clouds, but further progress has been hindered by limited observations. The National Academies of Sciences, Engineering, and Medicine organized a workshop to discuss the usefulness of the classified observing systems in advancing understanding of cloud and aerosol interactions. Because these systems were not developed with weather and climate modeling as a primary mission objective, many participants said it is necessary for scientists to find creative ways to utilize the data. The data from these systems have the potential to be useful in advancing understanding of cloud and aerosol interactions. This publication summarizes the presentations and discussions from the workshop.
