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Abstract
Stonitsch and Markowski perform multiple-Doppler radar analyses of a cold front over Oklahoma and Kansas. Despite their interesting results, their explanations include a number of misconceptions about cold fronts. These misconceptions include the proper interpretation of the frontogenesis function, the role of entrainment versus differential surface sensible heat flux toward weakening the virtual potential temperature gradient across a cold front, a separation of the wind shift from the virtual potential temperature gradient, and the factors that affect the motion of the cold front.
Abstract
Stonitsch and Markowski perform multiple-Doppler radar analyses of a cold front over Oklahoma and Kansas. Despite their interesting results, their explanations include a number of misconceptions about cold fronts. These misconceptions include the proper interpretation of the frontogenesis function, the role of entrainment versus differential surface sensible heat flux toward weakening the virtual potential temperature gradient across a cold front, a separation of the wind shift from the virtual potential temperature gradient, and the factors that affect the motion of the cold front.
Abstract
The conceptual model of a classical surface-based cold front consists of a sharp temperature decrease coincident with a pressure trough and a distinct wind shift at the surface. Many cold fronts, however, do not conform to this model—time series at a single surface station may possess a pressure trough and wind shift in the warm air preceding the cold front (hereafter called a prefrontal trough and prefrontal wind shift, respectively). Although many authors have recognized these prefrontal features previously, a review of the responsible mechanisms has not been performed to date. This paper presents such a review. Ten disparate mechanisms with different frontal structures have been identified from the previous literature. These mechanisms include those external to the front (i.e., those not directly associated with the cold front itself): synoptic-scale forcing, interaction with lee troughs/drylines, interaction with fronts in the mid- and upper troposphere, and frontogenesis associated with inhomogeneities in the prefrontal air. Mechanisms internal to the front (i.e., those directly associated with the structure and dynamics of the front) include the following: surface friction, frontogenesis acting on alongfront temperature gradients, moist processes, descent of air, ascent of air at the front, and generation of prefrontal bores/gravity waves. Given the gaps in our knowledge of the structure, evolution, and dynamics of surface cold fronts, this paper closes with an admonition for improving the links between theory, observations, and modeling to advance understanding and develop better conceptual models of cold fronts, with the goal of improving both scientific understanding and operational forecasting.
Abstract
The conceptual model of a classical surface-based cold front consists of a sharp temperature decrease coincident with a pressure trough and a distinct wind shift at the surface. Many cold fronts, however, do not conform to this model—time series at a single surface station may possess a pressure trough and wind shift in the warm air preceding the cold front (hereafter called a prefrontal trough and prefrontal wind shift, respectively). Although many authors have recognized these prefrontal features previously, a review of the responsible mechanisms has not been performed to date. This paper presents such a review. Ten disparate mechanisms with different frontal structures have been identified from the previous literature. These mechanisms include those external to the front (i.e., those not directly associated with the cold front itself): synoptic-scale forcing, interaction with lee troughs/drylines, interaction with fronts in the mid- and upper troposphere, and frontogenesis associated with inhomogeneities in the prefrontal air. Mechanisms internal to the front (i.e., those directly associated with the structure and dynamics of the front) include the following: surface friction, frontogenesis acting on alongfront temperature gradients, moist processes, descent of air, ascent of air at the front, and generation of prefrontal bores/gravity waves. Given the gaps in our knowledge of the structure, evolution, and dynamics of surface cold fronts, this paper closes with an admonition for improving the links between theory, observations, and modeling to advance understanding and develop better conceptual models of cold fronts, with the goal of improving both scientific understanding and operational forecasting.
Abstract
Despite the popularity of the conveyor-belt model for portraying the airflow through midlatitude cyclones, questions arise as to the path of the cold conveyor belt, the lower-tropospheric airflow poleward of and underneath the warm front. Some studies, beginning with Carlson's analysis of the eastern U.S. cyclone of 5 December 1977, depict the cold conveyor belt moving westward, reaching the northwest quadrant of the storm, turning abruptly anticyclonically, rising to jet level, and departing the cyclone downstream (hereafter, the anticyclonic path). Other studies depict the cold conveyor belt reaching the northwest quadrant, turning cyclonically around the low center, and remaining in the lower troposphere (the cyclonic path). To clarify the path of the cold conveyor belt, the present study reexamines Carlson's analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 December 1977 cyclone.
This reexamination raises several previously unappreciated and underappreciated issues. First, airflow in the vicinity of the warm front is shown to be composed of three different airstreams: air-parcel trajectories belonging to the ascending warm conveyor belt, air-parcel trajectories belonging to the cyclonic path of the cold conveyor belt that originate from the lower troposphere, and air-parcel trajectories belonging to the anticyclonic path of the cold conveyor belt that originate within the midtroposphere. Thus, the 5 December 1977 storm consists of a cold conveyor belt with both cyclonic and anticyclonic paths. Second, the anticyclonic path represents a transition between the warm conveyor belt and the cyclonic path of the cold conveyor belt, which widens with height. Third, the anticyclonic path of the cold conveyor belt is related to the depth of the closed circulation associated with the cyclone, which increases as the cyclone deepens and evolves. When the closed circulation is strong and deep, the anticyclonic path of the cold conveyor belt is not apparent and the cyclonic path of the cold conveyor belt dominates. Fourth, Carlson's analysis of the anticyclonic path of the cold conveyor belt was fortuitous because his selection of isentropic surface occurred within the transition zone, whereas, if a slightly colder isentropic surface were selected, the much broader lower-tropospheric cyclonic path would have been evident in his analysis instead. Finally, whereas Carlson concludes that the clouds and precipitation in the cloud head were associated with the anticyclonic path of the cold conveyor belt, results from the model simulation suggest that the clouds and precipitation originated within the ascending warm conveyor belt.
As a consequence of the reexamination of the 5 December 1977 storm using air-parcel trajectories, this paper clarifies the structure of and terminology associated with the cold conveyor belt. It is speculated that cyclones with well-defined warm fronts will have a sharp demarcation between the cyclonic and anticyclonic paths of the cold conveyor belt. In contrast, cyclones with weaker warm fronts will have a broad transition zone between the two paths. Finally, the implications of this research for forecasting warm-frontal precipitation amount and type are discussed.
Abstract
Despite the popularity of the conveyor-belt model for portraying the airflow through midlatitude cyclones, questions arise as to the path of the cold conveyor belt, the lower-tropospheric airflow poleward of and underneath the warm front. Some studies, beginning with Carlson's analysis of the eastern U.S. cyclone of 5 December 1977, depict the cold conveyor belt moving westward, reaching the northwest quadrant of the storm, turning abruptly anticyclonically, rising to jet level, and departing the cyclone downstream (hereafter, the anticyclonic path). Other studies depict the cold conveyor belt reaching the northwest quadrant, turning cyclonically around the low center, and remaining in the lower troposphere (the cyclonic path). To clarify the path of the cold conveyor belt, the present study reexamines Carlson's analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 December 1977 cyclone.
This reexamination raises several previously unappreciated and underappreciated issues. First, airflow in the vicinity of the warm front is shown to be composed of three different airstreams: air-parcel trajectories belonging to the ascending warm conveyor belt, air-parcel trajectories belonging to the cyclonic path of the cold conveyor belt that originate from the lower troposphere, and air-parcel trajectories belonging to the anticyclonic path of the cold conveyor belt that originate within the midtroposphere. Thus, the 5 December 1977 storm consists of a cold conveyor belt with both cyclonic and anticyclonic paths. Second, the anticyclonic path represents a transition between the warm conveyor belt and the cyclonic path of the cold conveyor belt, which widens with height. Third, the anticyclonic path of the cold conveyor belt is related to the depth of the closed circulation associated with the cyclone, which increases as the cyclone deepens and evolves. When the closed circulation is strong and deep, the anticyclonic path of the cold conveyor belt is not apparent and the cyclonic path of the cold conveyor belt dominates. Fourth, Carlson's analysis of the anticyclonic path of the cold conveyor belt was fortuitous because his selection of isentropic surface occurred within the transition zone, whereas, if a slightly colder isentropic surface were selected, the much broader lower-tropospheric cyclonic path would have been evident in his analysis instead. Finally, whereas Carlson concludes that the clouds and precipitation in the cloud head were associated with the anticyclonic path of the cold conveyor belt, results from the model simulation suggest that the clouds and precipitation originated within the ascending warm conveyor belt.
As a consequence of the reexamination of the 5 December 1977 storm using air-parcel trajectories, this paper clarifies the structure of and terminology associated with the cold conveyor belt. It is speculated that cyclones with well-defined warm fronts will have a sharp demarcation between the cyclonic and anticyclonic paths of the cold conveyor belt. In contrast, cyclones with weaker warm fronts will have a broad transition zone between the two paths. Finally, the implications of this research for forecasting warm-frontal precipitation amount and type are discussed.
Abstract
Time series of cold fronts from stations in the central United States possess incredible variety. For example, time series of some cold fronts exhibit a sharp temperature decrease coincident with a pressure trough and a distinct wind shift. Other time series exhibit a prefrontal trough and wind shift that precedes the temperature decrease associated with the front by several hours. In early March 2003, two cold fronts passed through Oklahoma City, Oklahoma (OKC), representing each of the above scenarios. The cold front on 4 March was characterized by a coincident sharp wind shift, pressure trough, and a strong temperature decrease of 10°C in 2 min. On the other hand, the cold-frontal passage on 8 March was characterized by a prefrontal wind shift occurring over a 7-h period before the temperature decrease of 10°C in 2 h. Twelve hours before frontal passage at OKC, both fronts had the same magnitude of the horizontal potential temperature gradient and Petterssen frontogenesis. By the time of frontal passage at OKC, the magnitude of the horizontal potential temperature gradient for the 4 March front was double that of the 8 March front, and the frontogenesis was nearly four times as great. The simultaneity of the surface horizontal potential temperature gradient and deformation and convergence maxima (coincident with the wind shift) was primarily responsible for the greater strength of the cold front in OKC on 4 March compared to that on 8 March. Whether a prefrontal wind shift occurred was determined by the timing and location of cyclogenesis in the central United States. On 4 March, a cyclone was adjacent to the slope of the Rocky Mountains and developed on the cold front as it moved through Oklahoma, permitting greater frontogenesis and resulting in a cold-frontal passage at OKC with a simultaneous temperature decrease and wind shift. On 8 March, the cyclone moved eastward through Oklahoma before the arrival of the cold front, resulting in a prefrontal wind shift associated with the northerlies behind the cyclone, followed by the frontal passage. A 2-yr climatology of cold-frontal passages at OKC supports the results from the two cases above, indicating that the timing and location of cyclogenesis was responsible for these two different cold-frontal structures. These results imply that, for situations resembling those of this study, the prefrontal trough is not directly associated with the cold front, but is caused by external processes related to the lee troughing.
Abstract
Time series of cold fronts from stations in the central United States possess incredible variety. For example, time series of some cold fronts exhibit a sharp temperature decrease coincident with a pressure trough and a distinct wind shift. Other time series exhibit a prefrontal trough and wind shift that precedes the temperature decrease associated with the front by several hours. In early March 2003, two cold fronts passed through Oklahoma City, Oklahoma (OKC), representing each of the above scenarios. The cold front on 4 March was characterized by a coincident sharp wind shift, pressure trough, and a strong temperature decrease of 10°C in 2 min. On the other hand, the cold-frontal passage on 8 March was characterized by a prefrontal wind shift occurring over a 7-h period before the temperature decrease of 10°C in 2 h. Twelve hours before frontal passage at OKC, both fronts had the same magnitude of the horizontal potential temperature gradient and Petterssen frontogenesis. By the time of frontal passage at OKC, the magnitude of the horizontal potential temperature gradient for the 4 March front was double that of the 8 March front, and the frontogenesis was nearly four times as great. The simultaneity of the surface horizontal potential temperature gradient and deformation and convergence maxima (coincident with the wind shift) was primarily responsible for the greater strength of the cold front in OKC on 4 March compared to that on 8 March. Whether a prefrontal wind shift occurred was determined by the timing and location of cyclogenesis in the central United States. On 4 March, a cyclone was adjacent to the slope of the Rocky Mountains and developed on the cold front as it moved through Oklahoma, permitting greater frontogenesis and resulting in a cold-frontal passage at OKC with a simultaneous temperature decrease and wind shift. On 8 March, the cyclone moved eastward through Oklahoma before the arrival of the cold front, resulting in a prefrontal wind shift associated with the northerlies behind the cyclone, followed by the frontal passage. A 2-yr climatology of cold-frontal passages at OKC supports the results from the two cases above, indicating that the timing and location of cyclogenesis was responsible for these two different cold-frontal structures. These results imply that, for situations resembling those of this study, the prefrontal trough is not directly associated with the cold front, but is caused by external processes related to the lee troughing.
Based on a talk given at the sixth annual meeting of the Atmospheric Science Librarians International, this paper explores the author;s experiences performing reviews of the scientific literature as a tool to advancing meteorology and studying the history of science. Three phases of performing literature searches with varying degrees of interaction with a research librarian are considered: do it yourself, librarian assisted, and librarian as collaborator. Examples are given for each phase: occluded fronts, conditional symmetric instability, and static instability terminology, respectively. Electronic availability of information is changing the relationship between scientists and librarians. Yet, despite these changes, books on library shelves and knowledgeable human librarians remain essential to the scientific enterprise.
Based on a talk given at the sixth annual meeting of the Atmospheric Science Librarians International, this paper explores the author;s experiences performing reviews of the scientific literature as a tool to advancing meteorology and studying the history of science. Three phases of performing literature searches with varying degrees of interaction with a research librarian are considered: do it yourself, librarian assisted, and librarian as collaborator. Examples are given for each phase: occluded fronts, conditional symmetric instability, and static instability terminology, respectively. Electronic availability of information is changing the relationship between scientists and librarians. Yet, despite these changes, books on library shelves and knowledgeable human librarians remain essential to the scientific enterprise.
A 14-week laboratory course at the University of Helsinki was offered to improve undergraduate and graduate students' writing and speaking skills, as well as their scientific skills. To emphasize active learning, the course avoided long lecture sessions and featured intensive homework assignments and in-class exercises. Examples of these assignments included a title-writing exercise, brainstorming, peer-reviewing, and précis. To reveal their attitudes about and approaches toward scientific writing, gauge their opinions and knowledge of scientific communication skills, and guide the course content, the students completed a survey during week 1. The survey asked questions on such varied topics as the use of first-person pronouns in scientific writing, willingness to publish in open-access journals, and attitudes regarding coauthorship between students and professors. A final in-class presentation involved the students asking for funding for their research project from a panel of nonspecialists, forcing the students to convince others of the value of their research. The challenges of teaching this kind of laboratory course included encouraging student participation and the amount of grading, although these challenges could be overcome by small-group exercises and changing the approach to grading, respectively. Finally, this article discusses the opportunities for these exercises to be applied to regular curriculum courses in the atmospheric sciences.
A 14-week laboratory course at the University of Helsinki was offered to improve undergraduate and graduate students' writing and speaking skills, as well as their scientific skills. To emphasize active learning, the course avoided long lecture sessions and featured intensive homework assignments and in-class exercises. Examples of these assignments included a title-writing exercise, brainstorming, peer-reviewing, and précis. To reveal their attitudes about and approaches toward scientific writing, gauge their opinions and knowledge of scientific communication skills, and guide the course content, the students completed a survey during week 1. The survey asked questions on such varied topics as the use of first-person pronouns in scientific writing, willingness to publish in open-access journals, and attitudes regarding coauthorship between students and professors. A final in-class presentation involved the students asking for funding for their research project from a panel of nonspecialists, forcing the students to convince others of the value of their research. The challenges of teaching this kind of laboratory course included encouraging student participation and the amount of grading, although these challenges could be overcome by small-group exercises and changing the approach to grading, respectively. Finally, this article discusses the opportunities for these exercises to be applied to regular curriculum courses in the atmospheric sciences.
Characteristics of 63 journals publishing peer-reviewed articles on atmospheric science were collected from online information and through a survey e-mailed to the journals. The rate that submitted manuscripts were rejected for publication (hereafter, the rejection rate) was available for 47 (75%) of the journals. Although the range in rejection rates is quite large (2%–91%), most journals reject between 25% and 60% of submitted manuscripts, with a mean of 38.7%, a result of more than 6,000 manuscripts a year rejected for publication. Some journals have a policy of the editor vigorously rejecting manuscripts without peer review, whereas others send either all or nearly all of the manuscripts out for peer review. Measures of journal volume and quality (i.e., number of submissions, number of published articles, number of citations, impact factor, immediacy index, article half-life) show little, if any, relationship to rejection rates, indicating that rejection rates are not higher for journals of higher perceived quality. Nonprofit journals have significantly lower rejection rates than for-profit journals, and journals with page charges have significantly lower rejection rates than those without page charges. That few journals have rejection rates less than 25% indicates that some minimum standard for quality of submitted manuscripts is met at nearly all journals, which is some of the evidence for consensus (defined as the shared conceptions of research problems and techniques) within the atmospheric sciences. Because many factors go into choosing a journal for manuscript submission, the results of this study should not be used as a menu for authors to decide to which journals they should submit their manuscripts.
Characteristics of 63 journals publishing peer-reviewed articles on atmospheric science were collected from online information and through a survey e-mailed to the journals. The rate that submitted manuscripts were rejected for publication (hereafter, the rejection rate) was available for 47 (75%) of the journals. Although the range in rejection rates is quite large (2%–91%), most journals reject between 25% and 60% of submitted manuscripts, with a mean of 38.7%, a result of more than 6,000 manuscripts a year rejected for publication. Some journals have a policy of the editor vigorously rejecting manuscripts without peer review, whereas others send either all or nearly all of the manuscripts out for peer review. Measures of journal volume and quality (i.e., number of submissions, number of published articles, number of citations, impact factor, immediacy index, article half-life) show little, if any, relationship to rejection rates, indicating that rejection rates are not higher for journals of higher perceived quality. Nonprofit journals have significantly lower rejection rates than for-profit journals, and journals with page charges have significantly lower rejection rates than those without page charges. That few journals have rejection rates less than 25% indicates that some minimum standard for quality of submitted manuscripts is met at nearly all journals, which is some of the evidence for consensus (defined as the shared conceptions of research problems and techniques) within the atmospheric sciences. Because many factors go into choosing a journal for manuscript submission, the results of this study should not be used as a menu for authors to decide to which journals they should submit their manuscripts.
