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14 - Tagging systematic errors arising from different components of dynamics and physics in forecast models
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- By T. N. Krishnamurti, Florida State University, USA, Vinay Kumar, Florida State University, USA
- Edited by Pinhas Alpert, Tel-Aviv University, Tatiana Sholokhman, Tel-Aviv University
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- Book:
- Factor Separation in the Atmosphere
- Published online:
- 03 May 2011
- Print publication:
- 10 February 2011, pp 219-236
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Summary
This study summarizes the results from a large number of forecast experiments with a global model with the objective of tagging errors that arise from different components of model dynamics and physics. To sort out such errors in non-linear systems is generally very difficult. In this study, we show examples of model forecasts that illustrate deficiencies (i.e., errors) that arise in the parameterization of cumulus convection and in the planetary boundary layer (PBL) physics. Our proposed Factor Separation method enables us to tag the systematic errors in our PBL formulation of moisture convergence. We note that the PBL scheme overestimates by roughly a factor of 2 the convergence near the tropical cloud base. These errors were the largest over meso-convective regions of deep convection. With such efforts at error tagging further improvements in modeling and forecasts can be achieved. We also address further work in this area of research.
Introduction
Factor Separation (FS), introduced by Stein and Alpert (1993) and Alpert et al. (2006), permits an explicit separation of atmospheric synergies among several salient features of a forecast model. They have exploited the FS method covering many scales of modeling to answer questions on issues such as the role of water and carbon dioxide for the understanding of global change. Their proposed method has many wide-ranging applications, as seen from the contents of this book. Our proposed study follows the same rationale in asking how one can sort out and tag errors that arise from different components of a non-linear model during the evolution of weather or climate.
Chapter 20 - Weather and seasonal climate forecasts using the superensemble approach
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- By T. N. Krishnamurti, Department of Meteorology, Florida State University, Tallahassee, T. S. V. Vijaya Kumar, Department of Meteorology, Florida State University, Tallahassee, Won-Tae Yun, Department of Meteorology, Florida State University, Tallahassee, Arun Chakraborty, Department of Meteorology, Florida State University, Tallahassee, Lydia Stefanova, Department of Meteorology, Florida State University, Tallahassee
- Edited by Tim Palmer, Renate Hagedorn
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- Book:
- Predictability of Weather and Climate
- Published online:
- 03 December 2009
- Print publication:
- 27 July 2006, pp 532-560
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Summary
In this chapter we present a short overview of the Florida State University (FSU) superensemble methodology for weather and seasonal climate forecasts and cite some examples on application for hurricanes, numerical weather prediction (NWP) and seasonal climate forecasts. This is a very powerful method for producing a consensus forecast from a suite of multimodels and the use of statistical algorithms. The message conveyed here is that the superensemble reduces the errors considerably compared with those of the member models and of the ensemble mean. This is based on results from several recent publications, where varieties of skill scores such as anomaly correlation, root-mean-square (rms) errors and threat scores have been examined. The improvements in several categories such as seasonal climate prediction from coupled atmosphere–ocean multimodels and NWP forecasts for precipitation exceed those of the best models in a consistent manner and are more accurate compared with the ensemble mean. It is difficult to state, soon after a forecast is made, as to which among the member models would have the highest skill. The superensemble is very consistent in this regard and is thus more reliable. In this study, we show walk-through tables that illustrate the workings of the superensemble for a hurricane track and heavy rain forecast for a flooding event. A number of features of the superensemble – number of training days, behaviour as the number of models increased, reduction of systematic errors and use of a synthetic superensemble – illustrate the strength of this new forecast experience.
2 - Northern summer planetary-scale monsoons during drought and normal rainfall months
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- By T. N. Krishnamurti, Florida State University, M. Kanamitsu, Japan Meteorological Agency
- James Lighthill, R. P. Pearce
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- Book:
- Monsoon Dynamics
- Published online:
- 05 November 2011
- Print publication:
- 19 March 1981, pp 19-48
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Summary
In this paper the 200 mb flow regimes during a drought year (1972) are contrasted with those during a normal rainfall year (1967) over the global tropics for the northern summer months. It is shown that the deficient rainfall over central India and western Africa during 1972 may be related to the following: (i) warm sea-surface temperatures over the equatorial Pacific; (ii) an excessive number of typhoon days over the equatorial Pacific; (iii) strong east-northeasterlies over the equatorial eastern Indian Ocean (related to upper-level outflows from the typhoons); (iv) a weaker tropical easterly jet; (v) a weaker meridional pressure gradient over India; (vi) a weaker Tibetan High; (vii) a south-eastward shift over the major circulation patterns as well as of several dynamical parameters; (viii) a weaker vertical wind shear and a weaker measure of the combined barotropicbaroclinic instability over west Africa; and (ix) weaker westward steering for rain-producing disturbances over India and a consequent stronger influence of the mountains.
A sequential interrelationship of the above aspects of the drought problem are discussed in this paper.
Introduction
The monsoonal rainfall over south Asia and west Africa undergoes interannual variations. Although some of the anomalous periods have more of a regional character, i.e., a period of drought over parts of a continent may not occur at the same period in other regions, there do exist periods of widespread drought that extend from west Africa to India. Such droughts occurred during the summers of 1877, 1899, 1918 and 1972.