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Abstract
Visual data on Jovian spot motions for 1897–1966 are assembled to show the variation of zonal velocity with Jovian latitude. The Northern and Southern Hemispheres show asymmetric zonal motions away from the equatorial jet. The mean velocities change appreciably over the years and transient anomalous velocities occur in subtropical latitudes. There is evidence for anticylconic shear to be correlated with bright zones and cyclonic shear with dark belts, but the correlation is imperfect. Certain zonal currents are very stable in latitude, despite shifts in latitude of the visible belts; other currents may be tied to the belts. No physical interpretation of these observations is attempted.
Abstract
Visual data on Jovian spot motions for 1897–1966 are assembled to show the variation of zonal velocity with Jovian latitude. The Northern and Southern Hemispheres show asymmetric zonal motions away from the equatorial jet. The mean velocities change appreciably over the years and transient anomalous velocities occur in subtropical latitudes. There is evidence for anticylconic shear to be correlated with bright zones and cyclonic shear with dark belts, but the correlation is imperfect. Certain zonal currents are very stable in latitude, despite shifts in latitude of the visible belts; other currents may be tied to the belts. No physical interpretation of these observations is attempted.
Abstract
A recent study by Bryson and Starr suggests that there is an observable atmospheric tide forced by the 14-month Chandler wobble of the earth’s rotation axis. Both the theoretical arguments and the observational evidence supporting this theory appear to be weak. Power spectra of non-seasonal barometric pressure fluctuations show no special behavior at periods near 14 months, suggesting that the response to the Chandler wobble is buried in the low-frequency continuum of atmospheric variations.
Abstract
A recent study by Bryson and Starr suggests that there is an observable atmospheric tide forced by the 14-month Chandler wobble of the earth’s rotation axis. Both the theoretical arguments and the observational evidence supporting this theory appear to be weak. Power spectra of non-seasonal barometric pressure fluctuations show no special behavior at periods near 14 months, suggesting that the response to the Chandler wobble is buried in the low-frequency continuum of atmospheric variations.
Abstract
Mean winds and tides at meteoric heights have been observed with a meteor radar system located at Durham, N. H. Measurements show that mean winds are, in general, larger than periodic components and that the semidiurnal tide does conform to model predictions. Diurnal and longer period variations, however, are quite variable and show much less coherence.
Abstract
Mean winds and tides at meteoric heights have been observed with a meteor radar system located at Durham, N. H. Measurements show that mean winds are, in general, larger than periodic components and that the semidiurnal tide does conform to model predictions. Diurnal and longer period variations, however, are quite variable and show much less coherence.
The 1929–64 precipitation record at La Porte was analyzed through the use of a budgetary hydrologic model. Pre- and postanomaly data allowed accurate estimation of stream discharge for the La Porte region, but use of the anomaly period data caused consistent significant overestimation of discharge. If both the La Porte data and the stream discharge data are accurate, then La Porte can only be a small-scale phenomenon, affecting a small portion of the basin. The post-1960 disappearence of the anomaly could be explained by the movement of a local anomaly, dissipation of the anomaly mechanism by a reduction of atmospheric particulates, or elimination of gage and/or observer error. Of the three, gage and/or observer error appears most likely to be the cause of the anomaly.
The 1929–64 precipitation record at La Porte was analyzed through the use of a budgetary hydrologic model. Pre- and postanomaly data allowed accurate estimation of stream discharge for the La Porte region, but use of the anomaly period data caused consistent significant overestimation of discharge. If both the La Porte data and the stream discharge data are accurate, then La Porte can only be a small-scale phenomenon, affecting a small portion of the basin. The post-1960 disappearence of the anomaly could be explained by the movement of a local anomaly, dissipation of the anomaly mechanism by a reduction of atmospheric particulates, or elimination of gage and/or observer error. Of the three, gage and/or observer error appears most likely to be the cause of the anomaly.
Abstract
This paper describes research in formulating objective weather analysis and forecasting aids for calculation by an electronic computer. Methods based upon single-station techniques for analysis of rawinsoundings are presented for computing wind shear, lapse rate, thermal advection and a parcel stability index. These quantities are useful in identifying phenomena such as fronts, troughs, the tropopause and the level of maximum wind. Average values of height, temperature, humidity and wind components are computed in six arbitrarily defined layers for purposes of representing the gross atmospheric structure. A simple computer technique for calculating kinematical values of horizontal divergence, vorticity, deformation, vertical motion and geostrophic departures from layer-averaged wind and height data at three stations is developed and demonstrated for an area comprised of the midwestern United States. For this region, the computations require only 20 min on a computer of modest speed; therefore, the magnitude of the calculations is no longer an obstacle to their routine application. Limitations of the methods are described. Our experience indicates that these computer routines are adaptable to several operational and research problems even though the multiple-station computations are subject to considerable noise. Further developments of objective techniques and possible means of suppressing noise are described.
Abstract
This paper describes research in formulating objective weather analysis and forecasting aids for calculation by an electronic computer. Methods based upon single-station techniques for analysis of rawinsoundings are presented for computing wind shear, lapse rate, thermal advection and a parcel stability index. These quantities are useful in identifying phenomena such as fronts, troughs, the tropopause and the level of maximum wind. Average values of height, temperature, humidity and wind components are computed in six arbitrarily defined layers for purposes of representing the gross atmospheric structure. A simple computer technique for calculating kinematical values of horizontal divergence, vorticity, deformation, vertical motion and geostrophic departures from layer-averaged wind and height data at three stations is developed and demonstrated for an area comprised of the midwestern United States. For this region, the computations require only 20 min on a computer of modest speed; therefore, the magnitude of the calculations is no longer an obstacle to their routine application. Limitations of the methods are described. Our experience indicates that these computer routines are adaptable to several operational and research problems even though the multiple-station computations are subject to considerable noise. Further developments of objective techniques and possible means of suppressing noise are described.
Abstract
Observations from a mesoscale network of automatic weather stations are analyzed for 15 U.K. cold fronts exhibiting narrow cold frontal rainbands (NCFRs). Seven of the NCFRs produced tornadoes. A time-compositing approach is applied to the minute-resolution data using the radar-observed motion vectors of NCFR precipitation segments. Interpolated onto a 5-km grid, the analyses resolve much of the small-mesoscale structure in surface wind, temperature, and pressure fields. Postfrontal winds varied substantially between cases. Tornadic NCFRs exhibited a near-90° wind veer and little or no reduction in wind speed on NCFR passage; these attributes were generally associated with large vertical vorticity, horizontal convergence, and vorticity stretching at the NCFR. Nontornadic NCFRs exhibited smaller wind veers and/or marked decreases in wind speed across the NCFR, and weaker vorticity, convergence, and vorticity stretching. In at least four tornadic NCFRs, increases in vorticity stretching preceded tornadogenesis. Doppler radar observations of two tornadic NCFRs revealed the development of misocyclones, some tornadic, during the latter stages of vorticity-stretching increase. The presence of cyclonic vortices only, in one case occurring at regular intervals along the NCFR, provides limited circumstantial evidence for horizontal shearing instability (HSI), though other vortex-genesis mechanisms cannot be discounted. Vorticity-stretching increases were associated with coherent mesoscale structures in the postfrontal wind field, which modified the cross-frontal convergence. Where cross-frontal convergence was large, extremely narrow, intense shear zones were observed; results suggest that tornadoes occurred when such shear zones developed in conjunction with conditional instability in the prefrontal environment.
Abstract
Observations from a mesoscale network of automatic weather stations are analyzed for 15 U.K. cold fronts exhibiting narrow cold frontal rainbands (NCFRs). Seven of the NCFRs produced tornadoes. A time-compositing approach is applied to the minute-resolution data using the radar-observed motion vectors of NCFR precipitation segments. Interpolated onto a 5-km grid, the analyses resolve much of the small-mesoscale structure in surface wind, temperature, and pressure fields. Postfrontal winds varied substantially between cases. Tornadic NCFRs exhibited a near-90° wind veer and little or no reduction in wind speed on NCFR passage; these attributes were generally associated with large vertical vorticity, horizontal convergence, and vorticity stretching at the NCFR. Nontornadic NCFRs exhibited smaller wind veers and/or marked decreases in wind speed across the NCFR, and weaker vorticity, convergence, and vorticity stretching. In at least four tornadic NCFRs, increases in vorticity stretching preceded tornadogenesis. Doppler radar observations of two tornadic NCFRs revealed the development of misocyclones, some tornadic, during the latter stages of vorticity-stretching increase. The presence of cyclonic vortices only, in one case occurring at regular intervals along the NCFR, provides limited circumstantial evidence for horizontal shearing instability (HSI), though other vortex-genesis mechanisms cannot be discounted. Vorticity-stretching increases were associated with coherent mesoscale structures in the postfrontal wind field, which modified the cross-frontal convergence. Where cross-frontal convergence was large, extremely narrow, intense shear zones were observed; results suggest that tornadoes occurred when such shear zones developed in conjunction with conditional instability in the prefrontal environment.
Abstract
This paper compares upper-tropospheric humidity from the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite with European Centre for Medium-Range Weather Forecasts (ECMWF) data. MLS measurements are not included in the ECMWF analyses, and so a comparison of two independent datasets is possible. The focus of this paper is on the tropical region from 1991 to 1997 when MLS measurements are available and, to be more specific, from 1991 to 1994 during the ECMWF 15-yr reanalysis period (ERA-15). It is found that the contrast between moist and dry areas, or areas of convection and subsidence, is less pronounced in ECMWF data than in MLS measurements. This result applies on the scale of both global and regional circulations and results in a semiannual cycle of high and low correlations between the two datasets that is particularly pronounced over South America. Time series show that the impact of model changes to the absolute values of humidity make long-term comparison with MLS difficult.
Abstract
This paper compares upper-tropospheric humidity from the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite with European Centre for Medium-Range Weather Forecasts (ECMWF) data. MLS measurements are not included in the ECMWF analyses, and so a comparison of two independent datasets is possible. The focus of this paper is on the tropical region from 1991 to 1997 when MLS measurements are available and, to be more specific, from 1991 to 1994 during the ECMWF 15-yr reanalysis period (ERA-15). It is found that the contrast between moist and dry areas, or areas of convection and subsidence, is less pronounced in ECMWF data than in MLS measurements. This result applies on the scale of both global and regional circulations and results in a semiannual cycle of high and low correlations between the two datasets that is particularly pronounced over South America. Time series show that the impact of model changes to the absolute values of humidity make long-term comparison with MLS difficult.
Abstract
A linear multiple regression equation was developed for each of 27 ozone monitoring sites in the north-eastern United States to forecast the next day's maximum 1 h average ozone concentration. Thirty-five prognostic meteorological variables, the climatological daily maximum surface temperature, the length and direction of 12 and 24 h backward trajectories, and three air quality variables relating to the seasonality or the upwind ozone concentrations were considered as possible predictors in each of the regression equations. Data pertaining to 244 randomly selected days formed the developmental or the dependent data set, while the data pertaining to the remaining 122 days in the months of June, July, August and September of 1975, 1976 and 1977 were used to assess the performance of the regression equations. Performance was assessed and compared to that of persistence, via statistical evaluations of site-specific forecasts. In addition, areas of the Northeast where the 1 h ozone standard was predicted to be exceeded, were compared to the areas where the standard was exceeded.
The results indicated that approximately half of the predictions generated from the independent data set were within 20% of the observations, while 77% were within 40% of the observations. A tendency for the underprediction of the maximum concentrations was noted. Overall, the regression equations performed best in forecasting the trends and patterns of the daily 1 h average ozone concentrations.
Abstract
A linear multiple regression equation was developed for each of 27 ozone monitoring sites in the north-eastern United States to forecast the next day's maximum 1 h average ozone concentration. Thirty-five prognostic meteorological variables, the climatological daily maximum surface temperature, the length and direction of 12 and 24 h backward trajectories, and three air quality variables relating to the seasonality or the upwind ozone concentrations were considered as possible predictors in each of the regression equations. Data pertaining to 244 randomly selected days formed the developmental or the dependent data set, while the data pertaining to the remaining 122 days in the months of June, July, August and September of 1975, 1976 and 1977 were used to assess the performance of the regression equations. Performance was assessed and compared to that of persistence, via statistical evaluations of site-specific forecasts. In addition, areas of the Northeast where the 1 h ozone standard was predicted to be exceeded, were compared to the areas where the standard was exceeded.
The results indicated that approximately half of the predictions generated from the independent data set were within 20% of the observations, while 77% were within 40% of the observations. A tendency for the underprediction of the maximum concentrations was noted. Overall, the regression equations performed best in forecasting the trends and patterns of the daily 1 h average ozone concentrations.
Abstract
An ERTS-1 Data Collection Platform instrumented with meteorological sensors has been operated for more than a year at 3536 m in the Front Range, Colorado.
The interface system and sensor performance are shown to operate well although the message interval is suitable only for certain types of parameter with the present interface system.
Abstract
An ERTS-1 Data Collection Platform instrumented with meteorological sensors has been operated for more than a year at 3536 m in the Front Range, Colorado.
The interface system and sensor performance are shown to operate well although the message interval is suitable only for certain types of parameter with the present interface system.
Abstract
Micro-oscillations in the atmosphere of the order of magnitude of minutes have been known and studied for many years. In 1936 Macelwane, and in 1939 Benioff, with their respective electromagnetic microbarographs showed that the spectrum of these micro-oscillations extends down into the order of seconds. The two different types of microbarographs respond to the same types of stimuli and low-level turbulence is an important source of the micro-oscillations. It is shown that fronts, as such, are not a source of these micro-oscillations, although micro-oscillations may accompany a front. The microbarograph has produced observational evidence supporting Haurwitz's theoretically derived conclusion that there is a similarity between internal wave patterns and convective patterns. It is shown that electromagnetic microbarographs are useful in studying cumulus activity.
Abstract
Micro-oscillations in the atmosphere of the order of magnitude of minutes have been known and studied for many years. In 1936 Macelwane, and in 1939 Benioff, with their respective electromagnetic microbarographs showed that the spectrum of these micro-oscillations extends down into the order of seconds. The two different types of microbarographs respond to the same types of stimuli and low-level turbulence is an important source of the micro-oscillations. It is shown that fronts, as such, are not a source of these micro-oscillations, although micro-oscillations may accompany a front. The microbarograph has produced observational evidence supporting Haurwitz's theoretically derived conclusion that there is a similarity between internal wave patterns and convective patterns. It is shown that electromagnetic microbarographs are useful in studying cumulus activity.
