Tropical Variability and the Validation of Convective Parameterizations PDF Download

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 22

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Book Description
The weather in the tropics is dominated by the effects of cumulus convection, be it the daily cycle of rain over the continents, tropical cyclones or the seasonal monsoon rains. In turn, the heating associated with cumulus convection is the dominant driving mechanism for tropical circulation. In the last two decades, observation of the tropics by satellites have revealed a rich tapestry of space and time scales in convective activity. These range from individual clouds, to cloud clusters associated with synoptic scale disturbances, through to super cloud clusters which display intraseasonal behavior. On the planetary scale, tropical convection shoes seasonal and interannual variability associated with, for example, monsoons and the effects of ENSO. One of the main purposed of this paper is to demonstrate the type of diagnostics which should be applied to GCMs when assessing the skill of the model and the validity of the convection scheme. In the final section, a technique for studying the behavior of tropical weather systems in a statistical manner will be described, and its application to ECMWF ReAnalyses (ERA) and to geostationary satellite imagery will be discussed.

Author: Robert S Plant
Publisher: World Scientific
ISBN: 1783266929
Category : Technology & Engineering
Languages : en
Pages : 1169

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Book Description
Precipitating atmospheric convection is fundamental to the Earth's weather and climate. It plays a leading role in the heat, moisture and momentum budgets. Appropriate modelling of convection is thus a prerequisite for reliable numerical weather prediction and climate modelling. The current standard approach is to represent it by subgrid-scale convection parameterization.Parameterization of Atmospheric Convection provides, for the first time, a comprehensive presentation of this important topic. The two-volume set equips readers with a firm grasp of the wide range of important issues, and thorough coverage is given of both the theoretical and practical aspects. This makes the parameterization problem accessible to a wider range of scientists than before. At the same time, by providing a solid bottom-up presentation of convection parameterization, this set is the definitive reference point for atmospheric scientists and modellers working on such problems.Volume 1 of this two-volume set focuses on the basic principles: introductions to atmospheric convection and tropical dynamics, explanations and discussions of key parameterization concepts, and a thorough and critical exploration of the mass-flux parameterization framework, which underlies the methods currently used in almost all operational models and at major climate modelling centres. Volume 2 focuses on the practice, which also leads to some more advanced fundamental issues. It includes: perspectives on operational implementations and model performance, tailored verification approaches, the role and representation of cloud microphysics, alternative parameterization approaches, stochasticity, criticality, and symmetry constraints.

Author: Kerry Emanuel
Publisher: Springer
ISBN: 1935704133
Category : Science
Languages : en
Pages : 242

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Book Description
This book presents descriptions of numerical models for testing cumulus in cloud fields. It is divided into six parts. Part I provides an overview of the problem, including descriptions of cumulus clouds and the effects of ensembles of cumulus clouds on mass, momentum, and vorticity distributions. A review of closure assumptions is also provided. A review of "classical" convection schemes in widespread use is provided in Part II. The special problems associated with the representation of convection in mesoscale models are discussed in Part III, along with descriptions of some of the commonly used mesoscale schemes. Part IV covers some of the problems associated with the representation of convection in climate models, while the parameterization of slantwise convection is the subject of Part V.

Author: Nicholas Weber
Publisher:
ISBN:
Category :
Languages : en
Pages : 14

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Book Description
Although accurate weather and climate prediction beyond one to two weeks is of great value to society, the skill of such extended prediction is limited in current operational global numerical models, whose coarse horizontal grid spacing necessitates the parameterization of atmospheric processes. Of particular concern is the parameterization of convection and specifically convection in the tropics, which impacts global weather at all time scales through atmospheric teleconnections. Global convection-permitting models (CPMs), which forego convective parameterization by explicitly resolving cumulus-scale motions using fine (1-4 km) horizontal grid spacing, can improve operational global weather prediction at extended time scales by more faithfully simulating tropical convection and associated teleconnections. Beyond this, global CPMs are also useful tools for studying processes important for simulating realistic tropical variability. Month-long simulations targeting four Madden-Julian Oscillation events made with several global model configurations are verified against observations not only with the above operational and scientific goals in mind, but also to assess the roles of grid spacing and convective parameterization in global models. Specifically, the performance of a global CPM configuration with a uniform 3-km mesh is compared to that of a global 15-km configuration with and without convective parameterization, and of a variable-resolution "channel" simulation using 3-km grid spacing in the tropics and 15-km in the extratropics with a scale-aware convection scheme over the entire domain. It is shown that global 3-km simulations produce realistic tropical precipitation statistics, except for an overall wet bias and delayed diurnal cycle. The channel simulation performs similarly, though with an unrealistically high frequency of heavy rain. The 15-km simulations with and without cumulus schemes produce too much light and heavy tropical precipitation, respectively. A deeper look at the environmental sensitivity of simulated precipitation reveals that the 15-km model with a cumulus parameterization triggers convection under unrealistically stringent environmental stability and moisture conditions; specifically, convection in the 15-km configuration is unrealistically dependent on environmental stability and lacks nonlinear sensitivity to moisture variations. These problems are alleviated in the global CPM configuration. Only the global CPM configuration is able to capture eastward-propagating Madden-Julian Oscillation events, while the 15-km runs favor stationary or westward-propagating convection organized at the planetary scale. A case study of a convectively coupled Kelvin wave during the first simulation case is conducted to identify the instability/coupling mechanisms necessary for such waves and other important tropical convective features. Results suggest that the 15-km simulation lacks strong wave-convection coupling because of its aforementioned lack of sensitivity to moisture. The 3-km simulation realistically simulates the nonlinear relationship between moisture and precipitationboth in its mean state and throughout the life cycle a convectively coupled Kelvin wave. The global 3-km CPM exhibits the highest extratropical forecast skill aloft and at the surface (particularly during week-3), consistent with its superior MJO representation. While more cases are needed to statistically verify these results, this study highlights the benefits of using global CPMs for identifying flaws in current-generation models, examining tropical convection and its relationship to environmental factors, and improving subseasonal forecasting. Furthermore, results show that alternatives to global convection-permitting resolution (using coarser resolution or a scale-aware channel configuration) exhibit drawbacks that reduce their predictive skill.

Author: Kathleen Anne Schiro
Publisher:
ISBN:
Category :
Languages : en
Pages : 148

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Book Description
Constraining precipitation processes in climate models with observations is crucial to accurately simulating current climate and reducing uncertainties in future projections. This work presents robust relationships between tropical deep convection, column-integrated water vapor (CWV), and other thermodynamic quantities analyzed with data from the DOE Atmospheric Radiation Measurement (ARM) Mobile Facility in Manacapuru, Brazil as part of the GOAmazon campaign and are directly compared to such relationships at DOE ARM sites in the tropical western Pacific. A robust relationship between CWV and precipitation, as explained by variability in lower tropospheric humidity, exists just as strongly in a tropical continental region as it does in a tropical oceanic region. Given sufficient mixing in the lower troposphere, higher CWV generally results in greater plume buoyancies through a deep convective layer. Although sensitivity of convection to other controls is suggested, such as microphysical processes and dynamical lifting mechanisms, the increase in buoyancy with CWV is consistent with the sharp increase in precipitation observed. Entraining plume buoyancy calculations confirm that CWV is a good proxy for the conditional instability of the environment, yet differences in convective onset as a function of CWV exist over land and ocean, as well as seasonally and diurnally over land. This is largely due to variability in the contribution of lower tropospheric humidity to the total column moisture. Over land, the relationship between deep convection and lower free tropospheric moisture is robust across all seasons and times of day, whereas the relation to boundary layer moisture is robust for the daytime only. Using S-Band radar, these transition statistics are examined separately for unorganized and mesoscale-organized convection, which exhibit sharp increases in probability of occurrence with increasing moisture throughout the column, particularly in the lower free troposphere. An observational basis for an integrated buoyancy measure from a single plume buoyancy formulation that provides a strong relation to precipitation can be useful for constraining convective parameterizations. A mixing scheme corresponding to deep inflow of environmental air into a plume that grows with height provides a weighting of boundary layer and free tropospheric air that yields buoyancies consistent with the observed onset of deep convection across seasons and times of day, across land and ocean sites, and for all convection types. This provides a substantial improvement relative to more traditional constant mixing assumptions, and a dramatic improvement relative to no mixing. Furthermore, it provides relationships that are as strong or stronger for mesoscale-organized convection as for unorganized convection. Downdrafts and their associated parameters are poorly constrained in models, as physical and microphysical processes of leading order importance are difficult to observe with sufficient frequency for development of robust statistics. Downdrafts and cold pool characteristics for mesoscale convective systems (MCSs) and isolated, unorganized deep precipitating convection in the Amazon are composited and both exhibit similar signatures in wind speed, surface fluxes, surface equivalent potential temperature () and precipitation. For both MCSs and unorganized convection, downdrafts associated with the strongest modifications to surface thermodynamics have increasing probability of occurrence with decreasing height through the lowest 4 km and show similar mean downdraft magnitudes with height. If is approximately conserved following descent, a large fraction of the air reaching the surface likely originates at altitudes in the lowest 2 km. Mixing computations suggest that, on average, air originating at heights greater than 3 km would require substantial mixing, particularly in the case of isolated cells, to match the observed cold pool . Statistics from two years of surface meteorological data at the GOAmazon site and 15 years of data at the DOE ARM site on Manus Island in the tropical western Pacific show that conditioned on precipitation levels off with increasing precipitation rate, bounded by the maximum difference between surface and its minimum in the profile aloft. Robustness of these statistics observed across scales and regions suggests their potential use as model diagnostic tools for the improvement of downdraft parameterizations in climate models.

Author: Kevin Hamilton
Publisher: Springer Science & Business Media
ISBN: 0387497919
Category : Science
Languages : en
Pages : 298

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This highly relevant text documents the first international meeting focused specifically on high-resolution atmospheric and oceanic modeling. It was held recently at the Earth Simulator Center in Yokohama, Japan. Rather than producing a standard conference proceedings volume, the editors have decided to compose this volume entirely of papers written by invited speakers at the meeting, who report on their most exciting recent results involving high resolution modeling.

Author: Tropical Rainfall Measuring Mission. Science Steering Group
Publisher:
ISBN:
Category : Government publications
Languages : en
Pages : 108

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"The Tropical Rainfall Measuring Mission (TRMM), a satellite program now being studied jointly by the United States and Japan, would carry out the systematic study of tropical rainfall required for major strides in weather and climate research ... This report presents the scientific justification for TRMM and outlines the implementation process for the scientific community."--Preface.

Author: Venugopal Vuruputur
Publisher: Elsevier
ISBN: 0128092572
Category : Science
Languages : en
Pages : 366

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Book Description
Tropical Extremes: Natural Variability and Trends features the most up-to-date information on present and future trends related to climate change and tropical extremes. Including contributions from the foremost experts in the field, this important reference addresses the science behind climate change and natural variability in relation to tropical extremes. The book also includes practical insight into modeling and observation approaches. In a warming world, the increase of weather extremes presents a scientifically complex and societally relevant challenge. The book confronts these challenges with observational evidence, modeling studies and expected impacts. This is an essential reference for researchers, modelers and students in the fields of climate and atmospheric science looking to better understand the causes and effects of tropical extremes and natural variability. Illuminates the role of natural variability and climate change in determining the fate and state of tropical extremes Offers a robust guide for analysis relating to the impacts of extremes, thus providing a potential roadmap for navigating the future of risk analysis and the water-food-energy nexus Edited by a diverse team of global experts Includes contributions from leading researchers in the field, comprising the most up-to-date understanding of tropical extremes

Author: Tim Li
Publisher: Springer
ISBN: 3319595970
Category : Science
Languages : en
Pages : 236

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Book Description
This textbook introduces fundamental dynamics of tropical atmosphere and ocean useful for advanced graduate courses in atmospheric and climate sciences. It presents an overview of simple atmospheric and oceanic models, as well as the observed phenomena associated with major climate modes in the tropics. It provides students with an up-to-date understanding of the dynamics of tropical climate and weather phenomena. A particular focus is given to scale interactions and atmosphere-ocean interactions associated with tropical mean climate (such as ITCZ asymmetry and annual cycles), synoptic-scale variability (such as synoptic wave trains, easterly waves and tropical cyclones), intraseasonal oscillations (such as Madden-Julian Oscillation and boreal summer intraseasonal oscillation), and interannual variability (such as El Niño-Southern Oscillation and Indian Ocean Dipole). Theoretical and conceptual models are presented for better understanding of physical mechanisms behind the observational phenomena. This book aims to motivate graduate students in atmospheric sciences and oceanography by providing them with the key methods and tools necessary to conduct research.

Author: Charles Jones
Publisher:
ISBN:
Category :
Languages : en
Pages : 186

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