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J. M. Lewis

Carl-Gustaf Rossby (1898–1957) was chosen to head the first U.S. program in modern meteorology at the Massachusetts Institute of Technology (MIT) in 1928. The steps that led to this appointment are briefly reviewed as well as the academic environment at MIT in the early 1930s. It has been argued that Rossby's development as a research scientist was closely tied to his connection with oceanographers at the Woods Hole Oceanographic Institution. His work on geostrophic adjustment, an outgrowth of his research on the Gulf Stream, was marked by bold simplification of the governing dynamical equations. This allowed him to capture the essence of adjustments between pressure and velocity in unbalanced geophysical flow. His work on the adjustment problem is summarized and related to earlier work by Ekman and Margules.

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J. M. Lewis

In response to the needs of the ocean traders and military shipping during the nineteenth century, Matthew Maury (1806–73) and Wladimir Köppen (1846–1940) worked in tandem to create wind charts for the World Ocean. In the early part of the century, Maury organized and supervised the production of the Wind and Current Charts for all navigable seas. In the latter part of the century, Köppen simplified these charts by use of a synoptically innovative stratification of the data, and these analyses became centerpieces of the Segelhandbiicher (Sail Handbooks) produced by the German Marine Observatory (Seewarte).

The charts produced by each of these men are examined in an effort to clarify their separate but unique contributions. Maury and Köppen were complementary in their approach to marine meteorology: Maury possessed organizational skills and an empirical approach to science, while Köppen was more academic and interested in the basic sciences. Köppen's exceptional background in both physics and biology was instrumental to his success in simplifying Maury's charts. These appealing synoptic charts served Bergeron in his quest for a global understanding of air masses and ultimately gave Köppen a viewpoint on climatology that embraced the entire world.

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J. M. Lewis

Out of the nearly 6000 U.S. military officers who were trained to be weather forecasters during World War II, there were approximately 100 women. They were recruited into the Women Accepted for Volunteer Emergency Service (WAVES) by the U.S. Navy and underwent training with the military men in the so-called cadet program. Letters of reminiscence from six WAVES forecasters are combined with official navy correspondence, archival information from universities, and newspaper articles of the period to reconstruct the recruitment, training, duty assignments, and postwar careers of these women.

With limited information, an effort has also been made to document the training of civilian women in the cadet program, and to estimate the number of women who served as forecasters in foreign countries during the war. The status of women in meteorology prior to the United States' entry into the war is examined as a backdrop to the study. Principal results of the study are as follows:

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J. M. Lewis

Ira Sprague Bowen (1898–1973) was a prominent astrophysicist during the twentieth century. In his impressive oeuvre of work over the 50-year span (1920–70), there appears a lone contribution to the geophysical sciences on the subject of evaporation and conduction from water surfaces. This theoretical development led to an expression for the ratio of heat conduction to evaporative flux at the air–water interface, labeled the Bowen ratio by Harald Sverdrup in the early 1940s. The circumstances that led to this contribution are examined with attention to the character of education and research at the California Institute of Technology during the 1920s. Bowen was unaware of the important precedent work in meteorology and fluid dynamics that is also reviewed.

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J. M. Lewis

The California Institute of Technology (Cal Tech) established a course of study in meteorology in 1933. It was intimately tied to the upsurge of activity in commercial and military aviation that occurred in the period between the world wars. The tragic crash of the airship U.S.S. Akron provided the stimulus for including meteorology as a subprogram in the aeronautics department at Cal Tech. Theodore von Kármán, head of the department and director of the school's Guggenheim Aeronautics Laboratory, masterminded the design of the program and geared it toward the solution of practical problems using the principles of dynamic meteorology. One of his doctoral students, Irving Krick, was groomed to develop the program.

Robert Millikan, head of the institute, fostered an approach to science that encouraged the faculty to consult and work with industry. In this environment, Krick established links with aviation, motion picture studios, and public utilities that would set the stage for the research thrust in meteorology. The program was primarily designed for training at the master's degree level, and a significant number of the graduates became entrepreneurs in meteorology. Based on letters of reminiscence and oral histories from some of these consulting meteorologists, it has been concluded that the Millikan/von Karman philosophy of science played an important part in directing the meteorologists into the private sector.

Following World War II, Lee DuBridge replaced Millikan as head of the institute. DuBridge's efforts were directed toward making the small elite school scientifically competitive in the changed conditions of a postwar world. In this climate, the merging of private business with academic work fell into disfavor. Without champions such as Millikan and von Karman, the meteorology program was unable to survive.

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Robert M. Lewis
and
Richard J. Reed

Abstract

No abstract available.

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J. M. Lewis
,
Y. Ogura
, and
L. Gidel

Abstract

A case of squall line generation in the National Severe Storms Laboratory (NSSL) network has been examined with the intention of capturing synoptic-scale influences. A telescopic analysis approach was used whereby observations from both synoptic and mesoscale networks were combined.

The squall line formed in the warm air behind the surface position of the cold front. Large-scale circulation was responsible for creating a shallow layer (∼1-km thick) of convectively unstable air immediately above this front. Horizontal gradient of low-level moisture, pronounced low-level wind shear, and surface convergence were the large-scale factors that combined to produce the unstable region.

Mesoscale analysis showed that vertical velocity in the low levels exhibited a persistent small-scale variation prior to convective activity. The horizontal variation in vertical velocity was ultimately responsible for creating a favored position within the mesonetwork.

Conservation of potential temperature and specific humidity is examined as well as the relative importance of horizontal and vertical advection.

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S. Lakshmivarahan
,
J. M. Lewis
, and
D. Phan

Abstract

A data assimilation strategy based on feedback control has been developed for the geophysical sciences—a strategy that uses model output to control the behavior of the dynamical system. Whereas optimal tracking through feedback control had its early history in application to vehicle trajectories in space science, the methodology has been adapted to geophysical dynamics by forcing the trajectory of a deterministic model to follow observations in accord with observation accuracy. Fundamentally, this offline (where it is assumed that the observations in a given assimilation window are all given) approach is based on Pontryagin’s minimum principle (PMP) where a least squares fit of idealized path to dynamic law follows from Hamiltonian mechanics. This utilitarian process optimally determines a forcing function that depends on the state (the feedback component) and the observations. It follows that this optimal forcing accounts for the model error. From this model error, a correction to the one-step transition matrix is constructed. The above theory and technique is illustrated using the linear Burgers’ equation that transfers energy from the large scale to the small scale.

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Lewis M. Rothstein
,
Michael J. McPhaden
, and
Jeffrey A. Proehl

Abstract

A numerical model is designed to study the effects of the strong, near-surface associated with the equatorial current system on energy transmission of time-periodic equatorial waves into the deep mean. The present paper is confined to long wavelength, low-frequency Kelvin waves forced by a longitudinally confined patch of zonal wind. Energy transmission into the deep ocean is investigated as a function of mean current shear amplitude and geometry and the forcing frequency.

Solutions form well-defined beams of energy that radiate energy eastward and vertically toward the deep ocean in the absence of mean flow. However, the presence of critical surfaces associated with mean currents inhibits low-frequency energy from reaching the deep ocean. For a given zonal wavenumber, longitudinal propagation through mean currents will be less inhibited as the frequency increases (phase speed increases). When the mean current amplitude is large enough, the beam encounters multiple critical surfaces (i.e., critical surfaces for different wavenumber components of the beam) where significant and momentum can take place with the men currents via Reynolds stress transfers. Work against the dominant vertical shear is the dominant wave energy loss for the case of a mean South Equatorial Current–Equatorial Undercurrent system, illustrating the need for high vertical resolution in equatorial ocean models.

The model also describes the possible induction of a mean zonal acceleration as well as a mean meridional circulation. Eliassen-Palm fluxes are used to diagnose these dynamics. The presence of critical surfaces result in mean field accelerations on the equator above the core of the Equatorial Undercurrent. Implications of these results with regard to observations in the equatorial waveguide are discussed.

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Dake Chen
,
Lewis M. Rothstein
, and
Antonio J. Busalacchi

Abstract

A novel hybrid vertical mixing scheme, based jointly on the Kraus–Turner-type mixed layer model and Price's dynamic instability model, is introduced to aid in parameterization of vertical turbulent mixing in numerical ocean models. The scheme is computationally efficient and is capable of simulating the three major mechanisms of vertical turbulent mixing in the upper ocean, that is, wind stirring, shear instability, and convective overturning.

The hybrid scheme is first tested in a one-dimensional model against the Kraus–Turner-type bulk mixed layer model and the Mellor–Yamada level 2.5 (MY2.5) turbulence closure model. As compared with those two models, the hybrid model behaves more reasonably in both idealized experiments and realistic simulations. The improved behavior of the hybrid model can be attributed to its more complete physics. For example, the MY2.5 model underpredicts mixed layer depth at high latitudes due to its lack of wind stirring and penetrative convection, while the Kraus–Turner bulk model produces rather shallow mixed layers in the equatorial region because of its lack of shear-produced mixing. The hybrid model reproduces the good results of the MY2.5 model toward the equator and the bulk model toward high latitudes, thereby taking the advantages of those two models while avoiding their shortcomings.

The hybrid scheme is then implemented in a three-dimensional model of the tropical Pacific Ocean. This leads to an improved simulation of the large-scale equatorial circulation. Compared with the other two commonly used mixing schemes tested in this experiment, the hybrid scheme helps to produce more realistic velocity profiles in the eastern and central equatorial Pacific. This is mainly due to the improved parameterization of interior mixing related to the large shears of the Equatorial Undercurrent. Another feature in this model that is sensitive to the vertical mixing scheme is the equatorial instability waves; in the eastern Pacific Ocean these waves are most energetic when the hybrid scheme is used. The meridional heat flux associated with these waves can be locally important in the mixed layer heat budget.

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