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JOHN M. LEWIS

Abstract

Sasaki's variational analysis method is used to describe the subsynoptic surface conditions accompanying severe local storms. Observations are extracted from the network of surface stations that routinely report every hour. The variational analysis filters the observations by constraining the meteorological fields to satisfy a set of governing prognostic equations. The filtering is monotonic and is designed to admit space and time scales of the order of 500 km and 10 hr, respectively.

The analysis is applied to a severe storm situation on June 10, 1968. The development of an intense squall line from the incipient to mature stage is depicted by an index coupling vertical motion and surface moisture. The results demonstrate that dynamically consistent time continuity can be achieved by using the variational method.

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SMAGORINSKY'S GFDL

Building the Team

John M. Lewis

Joseph Smagorinsky (1924–2005) was a forceful and powerful figure in meteorology during the last half of the twentieth century. He served as director of the Geophysical Fluid Dynamics Laboratory (GFDL) for nearly 30 yr (1955–83); and during his tenure as director, this organization substantially contributed to advances in weather forecasting and climate diagnostics/prediction. The purpose of this research is to explore Smagorinsky s philosophy of science and style of management which were central to the success of GFDL. Information herein comes from his early scientific publications, personal letters and notes in the possession of his family, several oral histories, and letters of reminiscence from scientists who worked within and outside GFDL.

The principal results of the study are that 1) early inspiration and development of Smagorinsky's scientific philosophy came from his contact with Jule Charney and Harry Wexler, 2) his doctoral dissertation ideally prepared him for appointment as director of the U.S. Weather Bureau's long-range numerical prediction project in 1955—the General Circulation Research Section (later renamed GFDL), 3) he masterfully assembled a team of researchers to attack the challenging problem of general circulation modeling, and 4) he exhibited an authoritarian style of rule tempered by protection of the scientists from disrupting outside influence while celebrating the elitism and esprit de corps that characterized the laboratory.

A list of Smagorinsky's management principles is found in the appendix. Several of these tenets have been interspersed in the main body of the paper in support of actions he took at GFDL.

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John M. Lewis

Abstract

Inaccuracy in the numerical prediction of the moisture content of return-flow air over the Gulf of Mexico continues to plague operational forecasters. At the Environmental Modeling Center/National Centers for Environmental Prediction in the United States, the prediction errors have exhibited bias—typically too dry in the early 1990s and too moist from the mid-1990s to present. This research explores the possible sources of bias by using a Lagrangian formulation of the classic mixed-layer model. Justification for use of this low-order model rests on careful examination of the upper-air thermodynamic structure in a well-observed event during the Gulf of Mexico Experiment. The mixed-layer constraints are shown to be appropriate for the first phase of return flow, namely, the northerly-flow or outflow phase. The theme of the research is estimation of sensitivity—change in the model output (at termination of outflow) in response to inaccuracies or uncertainties in the elements of the control vector (the initial conditions, the boundary conditions, and the physical and empirical parameters). The first stage of research explores this sensitivity through a known analytic solution to a reduced form of the mixed-layer equations. Numerically calculated sensitivity (via Runge–Kutta integration of the equations) is compared to the exact values and found to be most credible. Further, because the first- and second-order terms in the solution about the base state can be found exactly for the analytic case, the degree of nonlinearity in the dynamical system can be determined. It is found that the system is “weakly nonlinear”; that is, solutions that result from perturbations to the control vector are well approximated by the first-order terms in the Taylor series expansion. This bodes well for the sensitivity analysis. The second stage of research examines sensitivity for the general case that includes moisture and imposed subsidence. Results indicate that uncertainties in the initial conditions are significant, yet they are secondary to uncertainties in the boundary conditions and physical/empirical parameters. The sea surface temperatures and associated parameters, the saturation mixing ratio at the sea surface and the turbulent transfer coefficient, exert the most influence on the moisture forecast. Uncertainty in the surface wind speed is also shown to be a major source of systematic error in the forecast. By assuming errors in the elements of the control vector that reflect observational error and uncertainties in the parameters, the bias error in the moisture forecast is estimated. These bias errors are significantly greater than random errors as explored through Monte Carlo experiments. Bias errors of 1–2 g kg−1 in the moisture forecast are possible through a variety of systematic errors in the control vector. The sensitivity analysis also makes it clear that judiciously chosen incorrect specifications of the elements can offset each other and lead to a good moisture forecast. The paper ends with a discussion of research approaches that hold promise for improved operational forecasts of moisture in return-flow events.

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John M. Lewis

In the early 1930s, Heinz Lettau and Werner Schwerdtfeger made direct measurements of air motion in the lowest 4 km of the troposphere by using the manned free balloon as an instrumented platform. The experiment was motivated by Wilhelm Schmidt's and Ludwig Prandtl's work on Austausch (exchange) theory in the second and third decades of the twentieth century. As a prelude to investigating the Lettau–Schwerdtfeger experiment, historical developments that had bearing on the field program are reviewed. Following this review, the experiment is analyzed by 1) documenting the scientific goals, 2) discussing the strategy for data collection, 3) examining one flight in detail (the flight of 25 February 1934), and 4) summarizing results from the experiment. The paper ends with a retrospective view of Austausch theory.

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John M. Lewis

LeRoy Meisinger was a U.S. Weather Bureau meteorologist and aeronaut who worked vigorously to bring meteorology to the aid of aviation in the post–World War I period. He was killed at the age of 29 in a scientific ballooning accident that has been detailed in a companion paper by Lewis and Moore. Meisinger's personality and scientific profile are reconstructed by examination of his oeuvre, which contains research contributions augmented by popular articles in the magazines of the period.

Meisinger's personal characteristics were those of a quiet, scholarly man with strong interests in science, music, and art. His experiences as a Signal Corps weather officer during World War I inclined him toward a career in meteorology. While stationed at the Fort Omaha Balloon School, he became intrigued with the possibilities of using the free balloon as a platform for tracking air currents.

As a research meteorologist with the U.S. Weather Bureau after the war, Meisinger melded adventurous scientific ballooning with the more painstaking and arduous task of scrutinizing data from the limited upper-air network of kite stations. His principal research contribution was a form of differential analysis that extrapolated surface data to the 1- and 2-km levels by using climatological statistics from the upper-air network. The impressive line of research he pioneered at the bureau came to an immediate and abrupt end with his accidental death in 1924.

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John M. Lewis

Philip Thompson (1922–94) pioneered innovative approaches to weather analysis and prediction that blended determinism and probability. He generally posed problems in terms of simplified dynamics that were amenable to analytic solution. His preciseness in problem formulation and presentation in a forceful didactical manner are linked to his early home-schooling and experiences with a coterie of young intellectuals. Four of Thompson's contributions are examined with the intention of highlighting their impact on the current state of operational analysis and prediction.

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John M. Lewis

In the late 1960s, well before the availability of computer power to produce ensemble weather forecasts, Edward Epstein (1931–2008) developed a stochastic–dynamic prediction (SDP) method for calculating the temporal evolution of mean value, variance, and covariance of the model variables: the statistical moments of a time-varying probability density function that define an ensemble forecast. This statistical–dynamical approach to ensemble forecasting is an alternative to the Monte Carlo formulation that is currently used in operations. The stages of Epstein's career that led to his development of this methodology are presented with the benefit of his oral history and supporting documentation that describes the retreat of strict deterministic weather forecasting. The important follow-on research by two of Epstein's protégés, Rex Fleming and Eric Pitcher, is also presented.

A low-order nonlinear dynamical system is used to discuss the rudiments of SDP and Monte Carlo and to compare these approximate methods with the exact solution found by solving Liouville's equation. Graphical results from these various methods of solution are found in the main body of the paper while mathematical development is contained in an online supplement. The paper ends with a discussion of SDP's strengths and weaknesses and its possible future as an operational and research tool in probabilistic–dynamic weather prediction.

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John M. Lewis

Abstract

The dynamical adjustment scheme of P.D. Thompson (1969) has been adapted to the two-parameter baroclinic model which has potential vorticity as the constraint. In contrast to Thompson's approach, which used a differential-difference form of the constraint in space-time, the governing equations are discretized. Analyses simulated from analytic functions and analyses derived at the National Meteorological Center (NMC) are used to test the adjustment procedure. The reduction in error variance is related to the characteristics of the analysis error and the consequences of discretization, i.e., truncation error in the constraint and associated Euler–Lagrange equations.

The principal results are as follows:

1) Significant reduction in mean square error of vorticity can be accomplished with systematic or random error sources when r = |V| Δts < 1, where |V| is the geostrophic advection speed, Δt is one-half the time interval between maps, and Δs is the spatial resolution along the steering contours.

2) The limit of error reduction is reached as r→0, and the limiting values obtained from experiment compare favorably with the theoretical results of Thompson.

3) Height fields that are post-processed from adjusted vorticities also exhibit reduced error variance.

4) Results from the two-parameter model indicate that the strategy of adjustment will be useful in assimilating a sequence of mean temperature (thickness) fields derived from the VISSR Atmospheric Sounder (VAS) which is to be carded on all GOES satellites during this decade.

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John M. Lewis

In the mid-1950s, amid heated debate over the physical mechanisms that controlled the known features of the atmosphere's general circulation, Norman Phillips simulated hemispheric motion on the high-speed computer at the Institute for Advanced Study. A simple energetically consistent model was integrated for a simulated time of approximately 1 month. Analysis of the model results clarified the respective roles of the synoptic-scale eddies (cyclones-anticyclones) and mean meridional circulation in the maintenance of the upper-level westerlies and the surface wind regimes. Furthermore, the modeled cyclones clearly linked surface frontogenesis with the upper-level Charney–Eady wave. In addition to discussing the model results in light of the controversy and ferment that surrounded general circulation theory in the 1940s–1950s, an effort is made to follow Phillips's scientific path to the experiment.

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John M Lewis

Meteorologist Carl-Gustaf Rossby is examined as a mentor. In order to evaluate him, the mentor–protégé concept is discussed with the benefit of existing literature on the subject and key examples from the recent history of science. In addition to standard source material, oral histories and letters of reminiscence from approximately 25 former students and associates have been used.

The study indicates that Rossby expected an unusually high degree of independence on the part of his protégés, but that he was exceptional in his ability to engage the protégés on an intellectual basis—to scientifically excite them on issues of importance to him. Once they were entrained, however, Rossby was not inclined to follow their work closely.

He surrounded himself with a cadre of exceptional teachers who complemented his own heuristic style, and he further used his influence to establish a steady stream of first-rate visitors to the institutes. In this environment that bristled with ideas and discourse, the protégés thrived.

A list of Rossby's protégés and the titles of their doctoral dissertations are also included.

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