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Author: Timothy Wallace Cronin Publisher: ISBN: Category : Languages : en Pages : 171
Book Description
I present work on several topics related to land-atmosphere interaction and radiative-convective equilibrium: the first two research chapters invoke ideas related to land-atmosphere interaction to better understand radiative-convective equilibrium; the last two research chapters use the framework of radiative-convective equilibrium to better understand land-atmosphere interaction. First, I calculate how averaging the incident solar radiation can lead to biases in idealized climate models. I derive an expression for the absorption-weighted solar zenith angle, which minimizes the bias in mean absorbed shortwave radiation, and I find that it is closely matched by the insolation-weighted zenith angle. Common use of daytime-weighted zenith angle likely leads to high biases in albedo by ~3%. Second, I explore the time scales of approach to radiative-convective equilibrium with both a simple linearized two-variable model, and a single-column model with full physics. I show that there is a long time scale of approach to radiative-convective equilibrium that is order hundreds of days even when the surface heat capacity vanishes. The impact of water vapor on the effective atmospheric heat capacity can more than double this time scale for warm temperatures and low surface heat capacities. Third, I develop an analytic theory for the sensitivity of near-surface temperature to properties of the land surface. I show that the theory compares well against a simple numerical model of the coupled boundary layer-surface system, as well as a more complex two-column model, and discuss application of the theory to questions of how changes in land use or ecosystem function may affect climate change. Finally, I find that the diurnal cycle of convection is important for the spatial distribution of rainfall in idealized simulations of radiative-convective equilibrium with a cloud-resolving model. In a region that is partly an island and mostly ocean, precipitation over the island falls primarily in a regular, strong, afternoon thunderstorm, with a time-mean rainfall rate more than double the domain average. I explore mechanisms for this island rainfall enhancement, investigate the importance of island size for my results, and find that the upper troposphere warms with the inclusion of an island, which may have implications for the large-scale tropical circulation.
Author: Timothy Wallace Cronin Publisher: ISBN: Category : Languages : en Pages : 171
Book Description
I present work on several topics related to land-atmosphere interaction and radiative-convective equilibrium: the first two research chapters invoke ideas related to land-atmosphere interaction to better understand radiative-convective equilibrium; the last two research chapters use the framework of radiative-convective equilibrium to better understand land-atmosphere interaction. First, I calculate how averaging the incident solar radiation can lead to biases in idealized climate models. I derive an expression for the absorption-weighted solar zenith angle, which minimizes the bias in mean absorbed shortwave radiation, and I find that it is closely matched by the insolation-weighted zenith angle. Common use of daytime-weighted zenith angle likely leads to high biases in albedo by ~3%. Second, I explore the time scales of approach to radiative-convective equilibrium with both a simple linearized two-variable model, and a single-column model with full physics. I show that there is a long time scale of approach to radiative-convective equilibrium that is order hundreds of days even when the surface heat capacity vanishes. The impact of water vapor on the effective atmospheric heat capacity can more than double this time scale for warm temperatures and low surface heat capacities. Third, I develop an analytic theory for the sensitivity of near-surface temperature to properties of the land surface. I show that the theory compares well against a simple numerical model of the coupled boundary layer-surface system, as well as a more complex two-column model, and discuss application of the theory to questions of how changes in land use or ecosystem function may affect climate change. Finally, I find that the diurnal cycle of convection is important for the spatial distribution of rainfall in idealized simulations of radiative-convective equilibrium with a cloud-resolving model. In a region that is partly an island and mostly ocean, precipitation over the island falls primarily in a regular, strong, afternoon thunderstorm, with a time-mean rainfall rate more than double the domain average. I explore mechanisms for this island rainfall enhancement, investigate the importance of island size for my results, and find that the upper troposphere warms with the inclusion of an island, which may have implications for the large-scale tropical circulation.
Author: E.F. Wood Publisher: Springer Science & Business Media ISBN: 9400921551 Category : Science Languages : en Pages : 302
Book Description
It is well known that the interactions between land surfaces and the atmosphere, and the resulting exchanges in water and energy have a tremendous affect on climate. The inadequate representation of land-atmosphere interactions is a major weakness in current climate models, and is providing the motivation for the HAPEX and ISLSCP experiments as well as the proposed Global Energy and Water Experiment (GEWEX) and the Earth Observing System (EOS) mission. The inadequate representation reflects the recognition that the well-known phys ical relationships, which are well described at small scales, result in different relationships when represented at the scales used in climate models. Understanding this transition in the mathematical relationships with increased space-time scales appears to be very difficult, and has led to different approaches; at one extreme, the famous "bucket" model where the land-surface is a simple one layer storage without vegetation; the other extreme may be Seller's Simple Biosphere Model (Sib) where one big leaf covers the climate model grid. Given the heterogeneous nature of landforms, soils and vegetation within a climate model grid, the development of new land surface parameterizations, and their verification through large scale experiments is perceived to be a challenging area of research for the hydrology and meteorology communities. This book evolved from a workshop held at Princeton University to explore the status of land surface parameterizations within climate models, and how observa tional data can be used to assess these parameterizations and improve models.
Author: Samuel Pennypacker Publisher: ISBN: Category : Languages : en Pages : 97
Book Description
Boundary layer clouds are fundamental components of the climate system because of their first order impacts on the global energy balance. While marine boundary layer clouds have received most of the attention in this field because of their connection to global climate sensitivity and radiative forcing, continental boundary layer clouds also play a crucial role in controlling the amount of radiation reaching the land surface. Sitting at the top of the atmospheric boundary layer, these clouds are fundamentally linked to underlying land surface processes. We present three studies that explore the connection between land-atmosphere interactions and shallow clouds with eye toward improving process-based understanding of this system. The first shows that marine boundary layer clouds are an important sink for aerosol particles over the southeast Atlantic Ocean, helping mitigate the impact of continental African biomass burning aerosols transported to the vicinity of these low clouds. Then, we look to ground our mechanistic understanding of the response of continental shallow cumulus clouds to two different land cover changes, boreal forest expansion and tropical deforestation, using an idealized modeling framework. This analysis reveals the importance of environmental context, especially soil moisture availability and background atmospheric humidity, in determining the response of the convective boundary layer and cloud cover to these land surface perturbations. The co-evolution of boundary layer and lifting condensation level heights also emerges as key and should motivate examination of results from models that cannot faithfully represent these parameters. Finally, using a combination of the same idealized modeling system and observations from two ARM sites, we explore the effects of variations in the surface energy budget, in response to both land cover change and natural variability, on boundary layer convective velocities, initial shallow cumulus updraft speeds and the number of aerosol particles activated into cloud droplets. While the simulations and observations show that surface heat fluxes are not likely the dominant driver of changes in shallow cumulus droplet number in most settings, environments with lower evaporative fractions do favor a stronger coupling. We connect each of these studies to larger questions in cloud physics and land-atmosphere interactions, and hope to motivate further work on the detailed properties of this system.
Author: Jiangfeng Wei Publisher: ISBN: Category : Plant-atmosphere relationships Languages : en Pages :
Book Description
Land-atmosphere interaction includes complex feedbacks among radiative, hydrological, and ecological processes, and the understanding of it is hindered by many factors such as the heterogeneity of land surface properties, the chaotic nature of the atmosphere, and the lack of observational data. In this study, several different methods are used to investigate the land-atmosphere interaction processes and their relationship with climate variability. Firstly, a simple one-dimensional model is developed to simulate the dominant soil-vegetation-atmosphere interaction processes in the warm climate. Although the physical processes are described coarsely, the model can be more easily used to find some relationships which may be drown out or distorted by noise. The influence of land on climate variability mainly lies in it memory, which is greatly related with the atmospheric forcing, so this model is used to investigate the influence of different forcing strengths on land-atmosphere interaction and its difference at different land covers. The findings from the simple model can provide guidance for other studies. The second part of the study compares a lagged soil moisture-precipitation (S-P) correlation (soil moisture in current day and precipitation in future 30 days) in three atmospheric reanalysis products (ERA-40, NCEP/DOE reanalysis-2, and North American Regional Reanalysis (NARR)), Global Soil Wetness Project Phase 2 (GSWP-2) data, and NCAR CAM3 simulations. Different datasets and model simulations come to a similar negative-dominant S-P correlation pattern. This is different from the traditional view that the soil moisture should have positive influence on future precipitation. Further analysis shows that this correlation pattern is not caused by the soil moisture feedback but due to the combined effect of the precipitation oscillation and the memory of soil moisture. Theoretical analysis confirms the above results and finds that the precipitation time series with the strongest oscillation at 32-60 day period is most likely to induce a significantly negative S-P correlation, and regions with longer soil water retention time are more likely to have a significantly negative S-P correlation. This study illustrates that a lagged correlation does not always indicate a causal relation.
Author: Dennis L. Hartmann Publisher: Academic Press ISBN: 0080571638 Category : Science Languages : en Pages : 425
Book Description
Global Physical Climatology is an introductory text devoted to the fundamental physical principles and problems of climate sensitivity and change. Addressing some of the most critical issues in climatology, this text features incisive coverage of topics that are central to understanding orbital parameter theory for past climate changes, and for anthropogenic and natural causes of near-future changes--Key Features* Covers the physics of climate change* Examines the nature of the current climate and its previous changes* Explores the sensitivity of climate and the mechanisms by which humans are likely to produce near-future climate changes* Provides instructive end-of-chapter exercises and appendices
Author: National Research Council Publisher: National Academies Press ISBN: 0309133505 Category : Science Languages : en Pages : 222
Book Description
Changes in climate are driven by natural and human-induced perturbations of the Earth's energy balance. These climate drivers or "forcings" include variations in greenhouse gases, aerosols, land use, and the amount of energy Earth receives from the Sun. Although climate throughout Earth's history has varied from "snowball" conditions with global ice cover to "hothouse" conditions when glaciers all but disappeared, the climate over the past 10,000 years has been remarkably stable and favorable to human civilization. Increasing evidence points to a large human impact on global climate over the past century. The report reviews current knowledge of climate forcings and recommends critical research needed to improve understanding. Whereas emphasis to date has been on how these climate forcings affect global mean temperature, the report finds that regional variation and climate impacts other than temperature deserve increased attention.
Author: Timothy Wallace Cronin
Author: Timothy Wallace Cronin
Author: Julie Ega Kiang
Author: James Coles Barnard
Author: E.F. Wood
Author: Samuel Pennypacker
Author: Jiangfeng Wei
Author: Aneela Laurel Qureshi
Author: Dennis L. Hartmann
Author: National Research Council
Author: Michael Eugene Brown