M. A. Shapiro

A Review of the Structure and Dynamics of Upper-Level Frontal Zones

Abstract This article presents a review of upper-level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves. The discussion begins by tracing present-day concepts concerning the structure of upper-level frontal systems, which are based on composite analyses of radiosonde and aircraft data, from their origins in the pioneering analyses of upper-air data in the 1930s. Perspectives from scales both smaller and larger than upper-level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper-level frontogenesis. The dynamics of upper-level fronts are shown to comprise the interactions between the primary (geostrophic) and secondary (ageostrophic) cir...

Fronts, Jet Streams and the Tropopause

The advent of kite and balloon-borne meteorograph soundings during the early 1900s and the subsequent deployment of regional rawinsonde networks provided the observational basis for the study of the spatial and temporal evolution of fronts, jet streams and the tropopause. During the mid-century years (1935–1965), researchers focused on the structural characteristics of fronts and their associated jet streams near the tropopause, and on the diagnosis of the frontogenetic processes and secondary circulations governing their life cycles. The pioneering observational study by J. Bjerknes and E. Palm n (1937) showed fronts to be transitional zones of finite width (~100 km) and depth (~1 km), rather than near zero-order discontinuities extending from the surface to the tropopause. Newton (1954) presented the most comprehensive diagnosis of all components of upper-level frontogenesis during this period, and Sawyer (1956) and Eliassen (1962) derived the diagnostic theory for geostrophically forced secondary circulations about fronts based on the semigeostrophic equations, which was later expanded to the temporal dimension by Hoskins (1971) and Hoskins and Bretherton (1972).

The Fronts and Atlantic Storm-Track Experiment (FASTEX): Scientific Objectives and Experimental Design

The Fronts and Atlantic Storm-Track Experiment (FASTEX) will address the life cycle of cyclones evolving over the North Atlantic Ocean in January and February 1997. The objectives of FASTEX are to improve the forecasts of end-of-storm-track cyclogenesis (primarily in the eastern Atlantic but with applicability to the Pacific) in the range 24 to 72 h, to enable the testing of theoretical ideas on cyclone formation and development, and to document the vertical and the mesoscale structure of cloud systems in mature cyclones and their relation to the dynamics. The observing system includes ships that will remain in the vicinity of the main baroclinic zone in the central Atlantic Ocean, jet aircraft that will fly and drop sondes off the east coast of North America or over the central Atlantic Ocean, turboprop aircraft that will survey mature cyclones off Ireland with dropsondes, and airborne Doppler radars, including ASTRAIA/ELDORA. Radiosounding frequency around the North Atlantic basin will be increased, as ...

The North Pacific Experiment (NORPEX-98): Targeted Observations for Improved North American Weather Forecasts

Abstract The objectives and preliminary results of an interagency field program, the North Pacific Experiment (NORPEX), which took place between 14 January and 27 February 1998, are described. NORPEX represents an effort to directly address the issue of observational sparsity over the North Pacific basin, which is a major contributing factor in short-range (less than 4 days) forecast failures for land-falling Pacific winter-season storms that affect the United States, Canada, and Mexico. The special observations collected in NORPEX include approximately 700 targeted tropospheric soundings of temperature, wind, and moisture from Global Positioning System (GPS) dropsondes obtained in 38 storm reconnaissance missions using aircraft based primarily in Hawaii and Alaska. In addition, wind data were provided every 6 h over the entire North Pacific during NORPEX, using advanced and experimental techniques to extract information from multispectral geostationary satellite imagery. Preliminary results of NORPEX dat...

The Life Cycle of an Extratropical Marine Cyclone. Part I: Frontal-Cyclone Evolution and Thermodynamic Air-Sea Interaction

Abstract The Experiment on Rapidly Intensifying Cyclones over the Atlantic was carried out over the western North Atlantic Ocean to provide temporally continuous comprehensive datasets from which to document the life cycle of extratropical marine cyclones. The most intense cyclogenetic event occurred on 4-5 January 1989 over the warm (>20°C) Gulf Stream current; the cyclones central sea level pressure decreased by 60 mb in 24 h, from 996 to 936 mb. This study presents the synoptic-scale and mesoscale life cycle of this cyclone in two parts. Part I, presented here, describes the 24-h frontal-cyclone evolution through 6-h analyses of observations taken by specially deployed observing systems from air, land, and sea. The analyses of temperature, wind, and pressure about the incipient cyclone first illustrate the precursor signatures to cyclogenesis. The 850- and 500-mb temperature evolutions show a significant departure from the Norwegian frontal-cyclone model. In particular, the 850-mb analyses document 1)...

The Life Cycle of an Extratropical Marine Cyclone. Part II: Mesoscale Structure and Diagnostics

Abstract This is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) field program. Part I describes the 24-h frontal-cyclone evolution through 6-h horizontal analyses of observations taken by specially deployed observing systems from air, land, and sea. Part II presents frontal-scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclones life cycle. Horizontal analyses at 350 m above ground level describe the cyclones mesoscale frontal baroclinic structure and associated flow patterns. The vertical structure and evolution of the cyclones cold front, warm front, and bent-back front are illustrated in cross-sectional analyses of potential temperature, wind velocity, potential vorticity (PV), front-relative transverse flow vecto...

The Arctic Tropopause Fold

Abstract Analyses of research aircraft observation, satellite total columnar ozone retrievals and synoptic upper-air soundings are used to describe the structure of Arctic jetstreams and their associated frontal zones and tropopause folds. These analyses document the presence of major tropopause folding events within the Arctic that occur at the flanks of large-scale (∼2000 km) polar vortices. One example shows a polar vortex and its associated tropopause fold and Arctic front that migrated from the high Canadian Arctic southward into midlatitudes over central North America. The frigid cold-air outbreak associated with this migration was an important component in the record setting daily minimum temperatures that were recorded from the Great Lakes to southern Florida. Total columnar ozone measurements from the Total Ozone Mapping Spectrometer (TOMS) are shown to identify the location of polar vortices and the mesoscale (∼200 km) ozone gradients at the flanks of these vortices which coincide with regions o...

Collaboration of the weather and climate communities to advance subseasonal-to-seasonal prediction.

The World Weather Research Programme (WWRP) and the World Climate Research Programme (WCRP) have identified collaborations and scientific priorities to accelerate advances in analysis and prediction at subseasonalto-seasonal time scales, which include i) advancing knowledge of mesoscale–planetary-scale interactions and their prediction; ii) developing high-resolution global–regional climate simulations, with advanced representation of physical processes, to improve the predictive skill of subseasonal and seasonal variability of high-impact events, such as seasonal droughts and floods, blocking, and tropical and extratropical cyclones; iii) contributing to the improvement of data assimilation methods for monitoring and predicting used in coupled ocean–atmosphere–land and Earth system models; and iv) developing and transferring diagnostic and prognostic information tailored to socioeconomic decision making. The document puts forward specific underpinning research, linkage, and requirements necessary to achi...

Large-Amplitude Mountain Wave Breaking over Greenland

Abstract A large-amplitude mountain wave generated by strong southwesterly flow over southern Greenland was observed during the Fronts and Atlantic Storm-Track Experiment (FASTEX) on 29 January 1997 by the NOAA G-IV research aircraft. Dropwindsondes deployed every 50 km and flight level data depict a vertically propagating large-amplitude wave with deep convectively unstable layers, potential temperature perturbations of 25 K that deformed the tropopause and lower stratosphere, and a vertical velocity maximum of nearly 10 m s−1 in the stratosphere. The wave breaking was associated with a large vertical flux of horizontal momentum and dominated by quasi-isotropic turbulence. The Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) nonhydrostatic model with four-nested grid meshes with a minimum resolution of 1.7 km accurately simulates the amplitude, location, and timing of the mountain wave and turbulent breakdown. Finescale low-velocity plumes that resemble wakelike structures emanate from highl...

Multiscale Convective Organization and the YOTC Virtual Global Field Campaign

The Year of Tropical Convection (YOTC) project recognizes that major improvements are needed in how the tropics are represented in climate models. Tropical convection is organized into multiscale precipitation systems with an underlying chaotic order. These organized systems act as building blocks for meteorological events at the intersection of weather and climate (time scales up to seasonal). These events affect a large percentage of the worlds population. Much of the uncertainty associated with weather and climate derives from incomplete understanding of how meteorological systems on the mesoscale (~1–100 km), synoptic scale (~1,000 km), and planetary scale (~10,000 km) interact with each other. This uncertainty complicates attempts to predict high-impact phenomena associated with the tropical atmosphere, such as tropical cyclones, the Madden–Julian oscillation, convectively coupled tropical waves, and the monsoons. These and other phenomena influence the extratropics by migrating out of the tropics a...