The NCEP and NCAR are cooperating in a project (denoted “reanalysis”) to produce a 40-year record of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involves the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data; quality controlling and assimilating these data with a data assimilation system that is kept unchanged over the reanalysis period 1957–96. This eliminates perceived climate jumps associated with changes in the data assimilation system. The NCEP/NCAR 40-yr reanalysis uses a frozen state-of-the-art global data assimilation system and a database as complete as possible. The data assimilation and the model used are identical to the global system implemented operationally at the NCEP on 11 January 1995, except that the horizontal resolution is T62 (about 210 km). The database has been enhanced with many sources of observations not available in real time for operations, provided b...

The NCEP/NCAR 40-Year Reanalysis Project

ERA-Interim is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim project was conducted in part to prepare for a new atmospheric reanalysis to replace ERA-40, which will extend back to the early part of the twentieth century. This article describes the forecast model, data assimilation method, and input datasets used to produce ERA-Interim, and discusses the performance of the system. Special emphasis is placed on various difficulties encountered in the production of ERA-40, including the representation of the hydrological cycle, the quality of the stratospheric circulation, and the consistency in time of the reanalysed fields. We provide evidence for substantial improvements in each of these aspects. We also identify areas where further work is needed and describe opportunities and objectives for future reanalysis projects at ECMWF. Copyright © 2011 Royal Meteorological Society

The ERA-Interim reanalysis: configuration and performance of the data assimilation system

Land use has generally been considered a local environmental issue, but it is becoming a force of global importance. Worldwide changes to forests, farmlands, waterways, and air are being driven by the need to provide food, fiber, water, and shelter to more than six billion people. Global croplands, pastures, plantations, and urban areas have expanded in recent decades, accompanied by large increases in energy, water, and fertilizer consumption, along with considerable losses of biodiversity. Such changes in land use have enabled humans to appropriate an increasing share of the planet’s resources, but they also potentially undermine the capacity of ecosystems to sustain food production, maintain freshwater and forest resources, regulate climate and air quality, and ameliorate infectious diseases. We face the challenge of managing trade-offs between immediate human needs and maintaining the capacity of the biosphere to provide goods and services in the long term.

/pdf/global-consequences-of-land-use-map7a6ziel.pdf

Global Consequences of Land Use

世界経済・社会統計 = World development indicators

Drafting Authors: Neil Adger, Pramod Aggarwal, Shardul Agrawala, Joseph Alcamo, Abdelkader Allali, Oleg Anisimov, Nigel Arnell, Michel Boko, Osvaldo Canziani, Timothy Carter, Gino Casassa, Ulisses Confalonieri, Rex Victor Cruz, Edmundo de Alba Alcaraz, William Easterling, Christopher Field, Andreas Fischlin, Blair Fitzharris, Carlos Gay García, Clair Hanson, Hideo Harasawa, Kevin Hennessy, Saleemul Huq, Roger Jones, Lucka Kajfež Bogataj, David Karoly, Richard Klein, Zbigniew Kundzewicz, Murari Lal, Rodel Lasco, Geoff Love, Xianfu Lu, Graciela Magrín, Luis José Mata, Roger McLean, Bettina Menne, Guy Midgley, Nobuo Mimura, Monirul Qader Mirza, José Moreno, Linda Mortsch, Isabelle Niang-Diop, Robert Nicholls, Béla Nováky, Leonard Nurse, Anthony Nyong, Michael Oppenheimer, Jean Palutikof, Martin Parry, Anand Patwardhan, Patricia Romero Lankao, Cynthia Rosenzweig, Stephen Schneider, Serguei Semenov, Joel Smith, John Stone, Jean-Pascal van Ypersele, David Vaughan, Coleen Vogel, Thomas Wilbanks, Poh Poh Wong, Shaohong Wu, Gary Yohe

Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change

We examined changes in several independent intensity indices of four major tropical monsoonal circulations for the period 1950-1998. These intensity indices included observed land surface precipitation and observed ocean surface pressure in the monsoon regions as well as upper- level divergence calculated at several standard levels from the NCAR/NCEP reanalysis. These values were averaged seasonally over appropriate regions of southeastern Asian, western Africa, eastern Africa and the Australia/Maritime continent and adjacent ocean areas. As a consistency check we also examined two secondary indices: mean sea level pressure trends and low level convergence both from the NCEP reanalysis. We find that in each of the four regions examined, a consistent picture emerges indicating signi- ficantly diminished monsoonal circulations over the period of record, evidence of diminished spatial maxima in the global hydrological cycle since 1950. Trends since 1979, the period of strongest reported surface warming, do not indicate any change in monsoon circulations. When strong ENSO years are removed from each of the time series the trends still show a general, significant reduc- tion of monsoon intensity indicating that ENSO variability is not the direct cause for the observed weakening. Most previously reported model simulations of the effects of rising CO2 show an increase in monsoonal activity with rising global surface temperature. We find no support in these data for an increasing hydrological cycle or increasing extremes as hypothesized by greenhouse warming scenarios.

/pdf/changes-in-global-monsoon-circulations-since-1950-3ksuwj7wur.pdf

Changes in Global Monsoon Circulations Since 1950

We compare the first local Lyapunov vector (LLV) and the leading optimal vectors in a T10/18 level truncated version of the National Centers for Environmental Prediction global spectral model. The leading LLV is a vector toward which all other perturbations turn and hence it is characterized by the fastest possible growth over infinitely long time periods, while the optimal vectors are perturbations that maximize growth for a finite time period, with respect to a chosen norm. Linear tangent model breeding experiments without convection at T10 resolution show that arbitrary random perturbations converge within a transition period of 3 to 4 days to a single LLV. We computed optimal vectors with the Lanczos algorithm, using the total energy norm. For optimization periods shorter than the transition period (about 3 days), the  horizontal structure of the leading initial optimal vectors differs substantially from that of the leading LLV, which provides maximum sustainable growth. There are also profound differences between the two types of vectors in their vertical structure. While the 24- h optimal vectors rapidly become similar to the LLV in their vertical structure, changes in their horizontal structure are very slow. As a consequence, their amplification factor drops and stays well below that of the LLV for an extended period after the optimization period ends. This may have an adverse effect when optimal vectors with short optimization periods are used as initial perturbations for medium-range ensemble forecasts. The optimal vectors computed for 3 days or longer are different. In these vectors, the fastest growing initial perturbation has a horizontal structure similar to that of the leading LLV, and its major difference from the LLV, in the vertical structure, tends to disappear by the end of the optimization period. Initially, the optimal vectors are highly unbalanced and the rapid changes in their vertical structure are associated with geostrophic adjustment. The kinetic energy of the initial optimal vectors peaks in the lower troposphere, whereas in the LLV the maximum is around the jet level. During the integration the phase of the streamfunction field of the optimal vectors, with respect to their corresponding temperature field, is rapidly shifted 180°. And, due to drastic changes that also take place in the vertical temperature distribution, the maximum baroclinic shear shifts from the lower troposphere to just below the jet level. Just after initial time, when the geostrophic adjustment dominates, the leading optimal vectors exhibit a growth rate significantly higher than that of the LLV. By the end of the period of optimization, however, the growth rate associated with the leading optimal vectors drops to or below the level of the Lyapunov exponent. The transient super-Lyapunov growth associated with the leading optimal vectors is due to a one-time-only rapid rotation of the optimal vectors toward the leading LLVs. The nature of this rapid rotation depends on the length of the optimization period and the norm chosen. We speculate that the initial optimal vectors computed with commonly used norms may not be realizable DOI: 10.1034/j.1600-0870.1997.00004.x

https://www.tandfonline.com/doi/pdf/10.3402/tellusa.v49i2.14467

A comparison of Lyapunov and optimal vectors in a low-resolution GCM

Our work has addressed several issues relating to Ensemble Kalman Filter (EnKF) for assimilating real data, 1) model errors, 2) inconvenience or infeasibility of manually tuning the inflation factor when it is regional and/or variable dependent and 3) erroneously specified observation error statistics. A Local Ensemble Transform Kalman Filter (LETKF) is used as an efficient representative of other EnKF systems. For the model errors issue, we assimilate observations generated from the NCEP/NCAR reanalysis fields into the SPEEDY model. Several methods to handle model errors including model bias and system-noise are investigated. We address the second and third issues by simultaneously estimating both inflation factor and observation error variance on-line. Our research in this book suggests the need to develop a more advanced LETKF with both bias correction and adaptive estimation of inflation within the system.

Data Assimilation with the Local Ensemble Transform Kalman Filter

In atmospheric models that include vertical diffusion and surface fluxes of heat and moisture it is common to observe large amplitude “fibrillations” associated with these noniinear damping terms. In this paper this phenomenon is studied through the analysis of a simple nonlinear damping equation, ∂X/∂t = −(KXP)X + S. It is concluded that the behavior of several time schemes for the strongly nonlinear damping equations currently used can be quite pathological, with either large amplitude oscillations, or even nonoscillatory but incorrect solutions. Also presented are new simple schemes, which are easy to implement and have a much wider range of stability. These schemes are applied in the new National Meteorological Center (NMC) spectral model.

Time Schemes for Strongly Nonlinear Damping Equations

This study investigates the degree to which data from the space-borne FGGE observing systems are able to determine the complete state of the atmosphere when incorporated into a global objective analysis cycle. Three data assimilation experiments are performed with the Goddard Laboratory for Atmospheric Sciences (GLAS) analysis/forecast system, using different combinations of the FGGE level II–b data collected during the first Special Observing Period (SOP-1), 5 January through 5 March 1979. The control experiment is an assimilation cycle with the complete FGGE II–b data. The other two assimilation/forecast experiments consist of i) the conventional system without the satellite data and special FGGE data sets; and ii) the FGGE II–b surface and satellite temperature soundings and cloud-track winds, aircraft data, and special FGGE data sets, but without the conventional rawinsonde/pilot balloon network. From these experiments, we attempt to assess the accuracy of the inferred mass and motion fields over data...

Eugenia Kalnay

Papers

Changes in Global Monsoon Circulations Since 1950

A comparison of Lyapunov and optimal vectors in a low-resolution GCM

Data Assimilation with the Local Ensemble Transform Kalman Filter

Time Schemes for Strongly Nonlinear Damping Equations

An Assessment of the FGGE Satellite Observing System during SOP-1