The Atmospheric Sciences Entering the Twenty-First Century (1998) / Chapter Skim
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3 Atmospheric Dynamics and Weather Forecasting Research Entering the Twenty-First Century
3 Atmospheric Dynamics and Weather Forecasting Research Entering the Twenty-First Century
Pages 169-198
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From page 169... ...
Basic research in atmospheric science has been one of the most cost-effective investments that society has made in science. Progress in the basic understanding of phenomena such as severe thunderstorms has led directly to improved warnings and the reduction of loss of life, while technical advances in numerical weather prediction, application of statistics to model output, and advanced satellite and radar technology have contributed to much improved forecasts of all kinds.
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From page 170... ...
Great strides in the basic understanding of the dynamics of weather systems and the development of new techniques such as ensemble forecasting combine with the deployment of new measurement systems and advanced means of communicating information to offer the promise of much improved forecasts to the American public. To realize these potential improvements, new means of measuring the atmosphere, oceans, and land surface must be developed and implemented, and existing measurement systems such as rawinsondes, mobile radars, and research aircraft must be maintained and upgraded.
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From page 171... ...
1. The fundamental physics of land-air interaction: Basic understanding of the nature of the interaction between atmospheric and land surface processes is at the threshold of major advances and has the potential, when coupled with greatly improved routine measurements of land surface properties, to lead to substantial improvements in understanding and forecasting convection, boundary layer cloud cover, and regional climate anomalies.
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From page 172... ...
10. The dynamics of landfallen tropical cyclones, particularly as they relate to flash floods: Some of the worst disasters in U.S.
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From page 173... ...
Fundamental improvements in forecasting in the two- to seven-day range have enormous potential economic benefits but require far better collection and utilization of data over the oceans and other data-sparse areas. We strongly encourage the support of research seeking to determine optimal combinations of satellite and ground-based remote sensing, and aircraft, balloon, and surface observations, as well as the support of key technological developments such as satellite-borne active sensing techniques, near-field remote sensing of atmospheric water vapor, and observations from commercial and pilotless aircraft.
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From page 174... ...
4. Much-improved understanding of land-atmosphere interaction and far better measurements of land surface properties, especially soil moisture, would constitute a major intellectual advance and may hold the key to dramatic improvements in a number of forecasting problems, including the location and timing of the onset of deep convection over land, quantitative precipitation forecasting in general, and seasonal climate prediction.
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From page 175... ...
Modeling studies show that this feedback has an important effect on hurricane intensity, but observations of this interaction are lacking. We strongly encourage enhanced observations of the upper ocean during the passage of tropical and some extratropical cyclones.
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From page 176... ...
However, current numerical weather prediction techniques may not be uniformly applicable at the mesoscale. A large issue that must be faced is the initialization problem.
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From page 177... ...
Adaptive observational strategies may serve to help optimize observations in aid of numerical weather prediction. Tropical Cyclones Landfalling hurricanes can have catastrophic societal impacts in terms of loss of life and property near the U.S.
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From page 178... ...
The aircraft are relatively slow, however, and the information derived from the sondes does not cover the important region above flight level. The remote-sensing satellite data are limited in accuracy and coverage, particularly at the critical middle-tropospheric levels." More accurate tropical cyclone forecasts and warnings require that improved understanding of basic physical processes and improved depictions of the hurricane and its environment be incorporated into forecast models.
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From page 179... ...
Research on this aspect of tropical cyclone physics would profit from better measurements of the ocean response during and after passage of tropical cyclones. Although the axisymmetric dynamics of hurricane evolution are reasonably well understood, the asymmetric interactions with the environment that influence a storm's intensity are just beginning to be established.
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From page 180... ...
Perhaps research aircraft could be directed toward an investigation of landfallen tropical cyclones. Atmospheric Convection There has been considerable progress in the basic understanding of moist convection in the atmosphere over the past two decades.
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From page 181... ...
Data provided by the demonstration wind profiler network, local mesonetworks, and the Geostationary Operational Environmental Satellite (GOES) 8 and 9; a plethora of numerical guidance produced by more frequent update cycles of mesoscale numerical weather prediction (NWP)
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From page 182... ...
Another area of opportunity involves boundary layer and land surface properties, particularly soil moisture. There is increasing evidence that the evolution of the planetary boundary layer over land is strongly influenced by the distribution of soil moisture, through its effect on the temperature and moisture of overlying air, but routine measurements of soil properties are seriously inadequate.
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From page 183... ...
Examples showing definite seasonal forecast skill include weather anomalies associated with E1 Nino and seasonal forecasts of Atlantic hurricane activity based on long-period fluctuations such as E1 Nino and the quasi-biennial oscillation as well as land surface conditions in sub-Saharan Africa. Sea ice and snow cover on land may also prove to be significant components of the coupled system on seasonal time scales.
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From page 184... ...
Preliminary studies using the forecast model of the European Centre for Medium Range Weather Forecasts indicate the importance of soil moisture representations for heavy-rainfall forecasting. Properties of the land surface, especially soil moisture content, exercise an
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From page 185... ...
Orographic Effects on Weather The Earth's terrain is known to cause or modify many types of atmospheric phenomena, including the following: topographically enhanced rain and rain shadows, torrential rain and flash floods, forest fire storms, shear lines controlling tornado formation, sheltering of lee-side locations from strong winds, severe downslope and channel winds, gravity waves that remotely interact with larger-scale flows, cold air damming, modification of fronts and cyclones, diurnal control of thunderstorms, valley pollution and long-range pollution transport, and clear-air turbulence. There are three fundamental difficulties facing researchers and practitioners dealing with meteorology in mountainous areas: 1.
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From page 186... ...
Among other things, the internal waves excited by flow over topography often break in the troposphere and lower stratosphere, providing a net drag on the large-scale flow. Weather prediction models prove sensitive to the way in which this is formulated, and it is clear that progress in basic research on flow over topography with a continuum of scales is necessary before internal wave breaking can be adequately represented in models.
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From page 187... ...
Current forecast models provide reasonable guidance for predicting areas at risk for fires. If the forest is dry, the synoptic meteorological conditions favoring fire formation are low relative humidity, high temperature and winds, and thunderstorms creating cloud-to ground lightning with little precipitation.
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From page 188... ...
The improvement in the forecast models and data base is outside the area of this Disciplinary Assessment, but it should be noted that any improvement in these components immediately results in improvement of the data assimilation system. Since instruments do not work perfectly and data are collected through a number of different paths (some still using manual means of transmission)
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From page 189... ...
It may be based on the extension of a three-dimensional variational system to a four-dimensional system or some approximation of a Kalman filter. One exciting potential by-product of ensemble forecasting and data assimilation schemes is the concept of adaptive observations.
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From page 190... ...
Parameterization of Physical Processes Accurate prediction of the moisture field, including horizontal and vertical cloud distributions, is one of the most important items for both numerical weather prediction and climate forecasting. Recent studies have shown the importance of predicting the horizontal distribution of shallow clouds for the coupled oceanatmosphere system.
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From page 191... ...
The water vapor content of the atmosphere is very sensitive to assumed cloud physical processes, and better prediction of water vapor content will be necessary for improvement in quantitative precipitation forecasts, longer-range numerical weather prediction, and climate simulation. Considerable effort has been made to improve the parameterization of surface physics, particularly ground hydrology.
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From page 192... ...
A hybrid-coordinate approach has been proposed to overcome the lack of resolution near the ground and the problem of isentropic surfaces intersecting the ground. More investigation is needed into the feasibility of using such hybrid coordinates and determining whether there is an advantage to their use in numerical weather prediction and climate modeling.
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From page 193... ...
Technological Developments Ground- and Aircraft-Based Measurement Systems In situ measurements from surface stations, ships, aircraft, and balloons remain the backbone of the global observing system in aid of weather forecasting. Improvements of this in situ measurement capability and of ground- and aircraftbased remote sensors offer the promise of much improved knowledge of the overall state of the atmosphere, which should lead to improved understanding of weather dynamics and physics and to improved forecasts.
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From page 194... ...
Even so, DIAL offers much improved sampling of lower-tropospheric water vapor. Some information about atmospheric water vapor content can be obtained from the GPS.
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From page 195... ...
Several active sensing techniques can be used to detect atmospheric winds. One such technique is Doppler lidar, which operates much like Doppler radar in that signals returned to the receiver from distant targets are analyzed spectrally to recover the Doppler shifts imposed by the motion of the target.
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From page 196... ...
In the range of 2-3 m/s, scatterometer winds agree to within 2 m/s and 20° of other estimates, barring contamination from sea ice or precipitation. Moreover, assimilation of ERS-1 scatterometer wind data can improve operational weather forecasts, particularly of tropical cyclone formation and location.
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From page 197... ...
If numerical weather prediction is to be done with kilometer-scale resolution over synoptic-scale (1,000 km) domains, massively parallel machines are presently the only ones that could in theory deliver the 1,000-gigaflop speed required.
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From page 198... ...
Better measurements of atmospheric water vapor and of cloud microphysical processes, particularly those involving ice, may allow us to solve a number of outstanding problems such as predicting the development and movement of mesoscale convective systems and the response of atmospheric water vapor and cloud cover to climate change. Advanced applications of ensemble and adjoins techniques to numerical weather prediction may reveal, in near real time, those parts of the atmosphere that are particularly susceptible to initial error, allowing us to target such regions for observational scrutiny and thereby greatly reduce numerical forecast errors.
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