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Clifford Mass

Abstract

A 10-level, linearized primitive equation model with boundary-layer friction, latent heating and cumulus momentum mixing is used to explore the instability properties of the environment of African wave disturbances. It is found that a realistic mean jet profile, constructed from a one-week average of the zonal wind at 5°E, produces a most unstable mode with propagation and structural characteristics close to the observed. The inclusion of parameterizations of diabatic heating and convective momentum transport results in a substantial increase in the mid-tropospheric vertical motions as well as the wind and divergence perturbations in the upper and lower troposphere. This suggests an important role for convection in extending and coupling the influence of the disturbances away from the jet level, where barotropic instability appears to dominate in both the model and observations.

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Clifford Mass

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Western Washington State is a region where both land-water and topographic contrasts result in diurnal circulations that produce significant diurnal variations in parameters such as wind speed and direction, cloudiness and precipitation. These circulations are most apparent from late spring through early fall and are manifested on several interacting scales. In this paper resultant winds are examined both at the surface and aloft in order to describe the origin, structure and effects of Washington State's diurnal circulations and their influence on forecasting. It is shown that during the summer months the surface winds undergo a large diurnal variation with onshore and upslope winds during the day and offshore and downslope winds at night. This diurnal evolution, which is large only in the lowest 50 mb, results in a diurnal variation of low-level divergence in Puget Sound and produces a substantial modulation of precipitation frequency. It is shown that the winter months also possess diurnal wind variations but of far lesser magnitude. Finally, the relative roles of sea breeze and topographic effect are discussed.

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Clifford Mass

Abstract

Several times a year when the low-level winds from off the Pacific Ocean are within a narrow range of speed and direction, air passes both north and south of the Olympic Mountains of Washington State and is forced to converge in Puget Sound by the north-south oriented Cascade Range. This phenomenon, termed the Puget Sound convergence zone, often results in a band of cloudiness and precipitation in northern and central Puget Sound with clear, subsiding air to the north and south. This paper presents the results of a series of case studies in which the structure of the zone, its meteorological manifestations, and the environmental conditions necessary for its formation are explored. It is shown that the convergence zone is skillfully forecast by surface coastal winds and undergoes a strong annual and diurnal cycle, being most frequent during the late spring and early summer months and during the afternoon and early evening. It is also found that the zone is structurally similar to a shallow cold front and has a significant influence on the precipitation climatology of the region.

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Clifford Mass

Nowcasting combines a description of the current state of the atmosphere and a short-term forecast of how the atmosphere will evolve during the next several hours. A convergence of technical developments has set the stage for a major jump in nowcasting capabilities and the ability to apply those advances to important societal needs. New communications technologies, including broadband Internet, wireless communication, social media, and smartphones, have made the distribution and application of real-time weather information possible nearly anywhere. Rapid increases in the quantity and quality of surface, aircraft, and remote-sensing data now provide a real-time description of atmospheric conditions from the global to regional scales. Improved modeling and data assimilation offer the potential to more effectively apply mesoscale observations and to produce highresolution analyses and forecasts. Finally, improvements in communication, computation, and control have provided society with the ability to effectively access and use nowcasting information for the protection of life and property, as well as facilitating commerce and recreation. This paper describes these individual advances, the synergies of their combination, and how the forecast process might change as a result during the next few decades.

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Clifford Mass

Although the large U.S. meteorological community has made significant strides in weather diagnosis and prediction, progress has been slowed by a lack of cooperation, coordination, and pooling of resources. This paper analyzes such problems in a number of areas, ranging from numerical weather prediction to forecast dissemination, and proposes an alternative approach of greater community involvement in decision making, coupled with closely coordinated research and application, which might facilitate improvement in our ability to predict the weather and to apply weather information to societal needs.

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Clifford F. Mass

Abstract

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Lynn McMurdie and Clifford Mass

Abstract

Strong North Pacific storms that impact the North American west coast are sometimes poorly predicted in the short term (up to 48 h) by operational models, with cyclone position errors of hundreds of kilometers and central pressure errors of tens of millibars. These major numerical forecast failures still occur despite continuing improvements in modeling and data assimilation. In this paper, the frequency and intensity of sea level pressure errors at buoy and coastal locations are documented by comparing the National Centers for Environmental Prediction (NCEP) Eta Model forecasts to observations and through case studies of two poorly forecast cyclones from the 2001/02 winter season.

Using data from October 1999 through March 2003 at coastal and offshore sites along the west coast of North America, it was found that large forecast errors (48-h sea level pressure errors greater than 10 mb) by the Eta Model occur 10–15 times each winter, and extremely large errors (48-h errors greater than 15 mb) occur 3–4 times per winter. Such substantial forecast errors are often associated with large position errors of surface low pressure centers. For example, storms associated with large 48-h forecast errors greater than 10 mb at nearshore and coastal sites had average forecast position errors of 453 km and mean absolute central pressure errors of 7.5 mb.

To illustrate the nature of such large forecast errors, two major cyclones that were poorly predicted by several operational models are examined. The 7–8 February 2002 storm was a compact, but powerful, cyclone that struck western Oregon with strong winds, injured four people, and produced extensive damage and power outages. The 24-h numerical forecasts for this event were poor and had a variety of solutions. Two operational models forecast lows of sufficient depth, but displaced them more than 150 km to the east or southeast of the verifying position. Three other operational models did not produce a low at all but only predicted weak troughs. The comparison of the initial conditions of the various models revealed large differences, with the more accurate models starting with sharper, more intense features. The 13–14 December 2001 storm developed rapidly offshore of British Columbia, Canada, and brought extensive rain, winds, and snow to the mountains along the west coast. The 48-h forecasts of sea level pressure by five different operational numerical models had very large errors, with cyclone position errors greater than 400 km and central pressure errors on the order of 10 mb. Differences among the initial conditions of these operational models were smaller than in the February case. Comparison of the initial conditions to surface observations revealed potentially significant errors in the vicinity of the incipient cyclone.

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Clifford F. Mass

This paper describes the current application of compact discs (CD-ROM) to the storage and distribution of datasets for atmospheric sciences and related disciplines. CD-ROM technology is reviewed, currently available discs are listed, and a look at future developments is provided.

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Clifford F. Mass
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Clifford Mass and Carl Sagan

Abstract

A quasi-geostrophic numerical model, including friction, radiation and the observed planetary topography is applied to the general circulation of the Martian atmosphere in the Southern Hemisphere at latitudes south of about −35°. Near-equilibrium weather systems developed after about 5 model days. To avoid violating the quasi-geostrophic approximation, only 0.8 of the already smoothed relief was employed. Weather systems and velocity fields are strikingly tied to topography. A 2 mb middle-latitude jet stream is found of remarkably terrestrial aspect. Highest surface velocities, both horizontal and vertical, are predicted in western Hellas Planitia and eastern Argyre Planitia, which are common sites of orgin of major Martian dust storms. Mean horizontal velocities >30 m s−1 and mean vertical velocities >0.2 m s are sometimes found just above the surface velocity boundary layer, apart from eddy velocity contributions. When consideration is taken of scaling to full topography and the probable gustiness of Martian winds, it seems very likely that the general circulation is adequate, at certain times and places, to transport dust from the surface of Mars, as observed. Certain sources and sinks of vertical dust streaming are suggested; the entire south circumpolar zone appears to be a dust sink in winter.

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