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In the normal use of pilot-balloon reports as an aid to drawing upper-air charts, these reports are usually assumed to represent the mean air flow undisturbed by turbulence. This assumption needs to be justified if the pibals are used in the preparation of wind convergence charts.
The failure of the pibal to represent the mean undisturbed wind is due to (1) inaccuracy and (2) unrepresentativeness of the pibal observation. Most of the inaccuracy arises from incorrectly prescribed heights of the balloon based on a constant rate of ascent. In the cases studied, the average error (Table I) was 4.1° in direction and 3.3 miles/hour in speed. The unrepresentativeness due to turbulence averaged 1.3° and 2.5 miles/hour. The total inaccuracy and unrepresentativeness together averaged 5.6° and 4.1 miles/hour.
In the normal use of pilot-balloon reports as an aid to drawing upper-air charts, these reports are usually assumed to represent the mean air flow undisturbed by turbulence. This assumption needs to be justified if the pibals are used in the preparation of wind convergence charts.
The failure of the pibal to represent the mean undisturbed wind is due to (1) inaccuracy and (2) unrepresentativeness of the pibal observation. Most of the inaccuracy arises from incorrectly prescribed heights of the balloon based on a constant rate of ascent. In the cases studied, the average error (Table I) was 4.1° in direction and 3.3 miles/hour in speed. The unrepresentativeness due to turbulence averaged 1.3° and 2.5 miles/hour. The total inaccuracy and unrepresentativeness together averaged 5.6° and 4.1 miles/hour.
Abstract
Several recent studies have utilized a Haar wavelet covariance transform to provide automated detection of the boundary layer top from lidar backscatter profiles by locating the maximum in the covariance profiles. This approach is effective where the vertical gradient in the backscatter is small within and above the boundary layer, and where the inversion is sharp and well defined. These near-ideal conditions are often not met, particularly under stable stratification where the inversion may be deep and is sometimes ill defined, and vertical gradients are common. Here the effects of vertical gradients and inversion depth on the covariance transform are examined. It is found that a significant dilation-dependent bias in the determination of the boundary layer top may result when using the published method. An alternative approach is developed utilizing multiple wavelet dilations, and is capable of identifying both the upper and lower limits of the backscatter transition zone associated with the inversion while remaining insensitive to mean vertical gradients in the background signal. This approach enables more detailed information on the small-scale structure of the inversion and entrainment zone to be retrieved than is possible using existing techniques.
Abstract
Several recent studies have utilized a Haar wavelet covariance transform to provide automated detection of the boundary layer top from lidar backscatter profiles by locating the maximum in the covariance profiles. This approach is effective where the vertical gradient in the backscatter is small within and above the boundary layer, and where the inversion is sharp and well defined. These near-ideal conditions are often not met, particularly under stable stratification where the inversion may be deep and is sometimes ill defined, and vertical gradients are common. Here the effects of vertical gradients and inversion depth on the covariance transform are examined. It is found that a significant dilation-dependent bias in the determination of the boundary layer top may result when using the published method. An alternative approach is developed utilizing multiple wavelet dilations, and is capable of identifying both the upper and lower limits of the backscatter transition zone associated with the inversion while remaining insensitive to mean vertical gradients in the background signal. This approach enables more detailed information on the small-scale structure of the inversion and entrainment zone to be retrieved than is possible using existing techniques.
Abstract
A method for determining the angular offsets between measurement axes for multiple motion sensing systems and a sonic anemometer using underway data is demonstrated. This enables a single angular rate sensor to be used with spatially separated accelerometers, collocated with sonic anemometers, for the motion correction of turbulence measurements on a mobile platform such as a ship. Effective motion correction of turbulence measurements at sea is demonstrated. The errors in instrument alignment are considered, and estimates are made of the resulting biases in wind stress estimates.
Abstract
A method for determining the angular offsets between measurement axes for multiple motion sensing systems and a sonic anemometer using underway data is demonstrated. This enables a single angular rate sensor to be used with spatially separated accelerometers, collocated with sonic anemometers, for the motion correction of turbulence measurements on a mobile platform such as a ship. Effective motion correction of turbulence measurements at sea is demonstrated. The errors in instrument alignment are considered, and estimates are made of the resulting biases in wind stress estimates.
Synopsis
The purpose of this article is to introduce a substantial short cut in finding the wind flow in an isentropic surface. This is done by utilizing the fact that, at a given level in the isentropic surface, the acceleration potential is uniquely determined by the pressure. From new tables of values for every 5000 feet, values for any level can be quickly obtained by easy interpolation.
Synopsis
The purpose of this article is to introduce a substantial short cut in finding the wind flow in an isentropic surface. This is done by utilizing the fact that, at a given level in the isentropic surface, the acceleration potential is uniquely determined by the pressure. From new tables of values for every 5000 feet, values for any level can be quickly obtained by easy interpolation.
Abstract
The time of onset of the initial electrification in a thunderstorm cell has been correlated with the appearance of the initial radar (3 cm) precipitation-echo. The results show that precipitation is a necessary, but not sufficient, condition for the onset of thunderstorm electrification. The presence of radar-detectable precipitation does not lead to thunderstorm electrification, unless the precipitation echo evidences rapid vertical development. When this condition is fulfilled, the appearance of the initial electrification is almost coincident with the appearance of the initial radar precipitation-echo. On days when no precipitation echoes were present, no electric fields significantly different from the fair-weather positive fields were observed, although the clouds noted ranged from small fair-weather cumulus to clouds of considerable depth and active convection.
Abstract
The time of onset of the initial electrification in a thunderstorm cell has been correlated with the appearance of the initial radar (3 cm) precipitation-echo. The results show that precipitation is a necessary, but not sufficient, condition for the onset of thunderstorm electrification. The presence of radar-detectable precipitation does not lead to thunderstorm electrification, unless the precipitation echo evidences rapid vertical development. When this condition is fulfilled, the appearance of the initial electrification is almost coincident with the appearance of the initial radar precipitation-echo. On days when no precipitation echoes were present, no electric fields significantly different from the fair-weather positive fields were observed, although the clouds noted ranged from small fair-weather cumulus to clouds of considerable depth and active convection.
Abstract
The Met Office unified forecast–climate model is used to compare the properties of simulated climatological cloud regimes with those produced in short-range forecasts initialized from operational analyses. The regimes are defined as principal clusters of joint cloud-top pressure–optical depth histograms. In general, the cloud regime properties are found to be similar at all forecast times, including the climatological mean. This suggests that weaknesses in the representation of fast local processes are responsible for errors in the simulation of the cloud regimes. The increased horizontal resolution of the model used for numerical weather prediction generally has little impact on the cloud regimes, although the simulation of tropical shallow cumulus is improved, while the relative frequency of tropical deep convection and cirrus compare less favorably with observations. Analysis of the initial temperature tendency profiles for each cloud regime indicates that some of the initial temperature tendency, which leads to a systematic bias in the model climatology, is associated with a particular cloud regime.
Abstract
The Met Office unified forecast–climate model is used to compare the properties of simulated climatological cloud regimes with those produced in short-range forecasts initialized from operational analyses. The regimes are defined as principal clusters of joint cloud-top pressure–optical depth histograms. In general, the cloud regime properties are found to be similar at all forecast times, including the climatological mean. This suggests that weaknesses in the representation of fast local processes are responsible for errors in the simulation of the cloud regimes. The increased horizontal resolution of the model used for numerical weather prediction generally has little impact on the cloud regimes, although the simulation of tropical shallow cumulus is improved, while the relative frequency of tropical deep convection and cirrus compare less favorably with observations. Analysis of the initial temperature tendency profiles for each cloud regime indicates that some of the initial temperature tendency, which leads to a systematic bias in the model climatology, is associated with a particular cloud regime.
Abstract
No Abstract Available.
Abstract
No Abstract Available.
Abstract
Over 50 cases of TIROS-viewed cloud vortices associated with extratropical cyclones over North America, Europe and Asia between April 1962 and November 1963 were examined to determine what meteorological information could be derived from the satellite pictures. Radiosonde stations were grouped in five principal classes according to their time-adjusted positions with reference to the vortex center and the major cloud bands. Meteorological parameters were statistically related to the age of the vortex, season, and geographical location as Well as to the principal sounding class for the position of the station.
The thermal results indicated that the means of the dew-point depression for each principal class were significantly different from the overall mean of the sample, according to the analysis of variance test. Relative tropopause heights were estimated from the means and variances of the vertical temperature differences. These results will be of value as input parameters for numerical prediction over data-silent areas.
The wind results showed that the wind directions within 333 km ahead of the major cloud band aids averaged 16° clockwise from the nearest band orientation, and behind the bands, 25° clockwise. The mean vertical wind shears within the major cloud bands and in the dry zones behind the bands were about 60° and 20°, respectively, clockwise from the band orientation. Most of the cloud bands were characterized by a speed convergence of the normal components and by a cyclonic shear and vorticity of the parallel components of the mean winds on the two sides of the bands.
Abstract
Over 50 cases of TIROS-viewed cloud vortices associated with extratropical cyclones over North America, Europe and Asia between April 1962 and November 1963 were examined to determine what meteorological information could be derived from the satellite pictures. Radiosonde stations were grouped in five principal classes according to their time-adjusted positions with reference to the vortex center and the major cloud bands. Meteorological parameters were statistically related to the age of the vortex, season, and geographical location as Well as to the principal sounding class for the position of the station.
The thermal results indicated that the means of the dew-point depression for each principal class were significantly different from the overall mean of the sample, according to the analysis of variance test. Relative tropopause heights were estimated from the means and variances of the vertical temperature differences. These results will be of value as input parameters for numerical prediction over data-silent areas.
The wind results showed that the wind directions within 333 km ahead of the major cloud band aids averaged 16° clockwise from the nearest band orientation, and behind the bands, 25° clockwise. The mean vertical wind shears within the major cloud bands and in the dry zones behind the bands were about 60° and 20°, respectively, clockwise from the band orientation. Most of the cloud bands were characterized by a speed convergence of the normal components and by a cyclonic shear and vorticity of the parallel components of the mean winds on the two sides of the bands.
