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Abstract
Results from a detailed three-dimensional model of the atmospheric boundary layer are compared with observational data in a case of nonprecipitating convection in a tropical boundary layer. The model is a slightly improved version of the one developed by Sommeria (1976) in collaboration with J.W. Deardorff. The experimental data come from the NCAR 1972 Puerto Rico experiment which provided a good set of aircraft turbulence measurements in the fair weather mixed layer over the tropical ocean. The comparison involves statistical properties of the turbulent field as well as some structural features in the presence of small clouds.
Abstract
Results from a detailed three-dimensional model of the atmospheric boundary layer are compared with observational data in a case of nonprecipitating convection in a tropical boundary layer. The model is a slightly improved version of the one developed by Sommeria (1976) in collaboration with J.W. Deardorff. The experimental data come from the NCAR 1972 Puerto Rico experiment which provided a good set of aircraft turbulence measurements in the fair weather mixed layer over the tropical ocean. The comparison involves statistical properties of the turbulent field as well as some structural features in the presence of small clouds.
Abstract
The structure of the convective atmospheric boundary layer and the characteristics of the associated turbulent mixing processes in undisturbed conditions over the tropical ocean are investigated using data collected during the GARP Atlantic Tropical Experiment (GATE). The data were obtained by a number of aircraft equipped with turbulence measuring instrumentation. The fluxes of momentum, sensible and latent heat throughout the subcloud layer are presented for four cases considered in detail. It is shown that the sensible and latent heat fluxes at the top of the mixed layer (and therefore the distribution of heating and moistening in the boundary layer) are strongly affected by the presence or absence of cumulus convection while the virtual heat flux remains unaffected. Features of this cloud-subcloud interaction are discussed in the light of Betts (1976) coupled cloud-subcloud layer model.
An examination of the spectra (and cospectra) of subcloud-layer variables shows that with the exception of vertical velocity, the spectra are generally dominated by low-frequency fluctuations. This behavior is attributed to the effects of entrainment which may produce relatively large, long-lived excursions from the mixed-layer average in the weakly mixed GATE boundary layer and to the existence of mesoscale (∼10 km) variability.
Wherever possible comparisons are drawn with previous measurements and corresponding situations over land, where mixing processes are usually much more energetic. Aircraft measurements of the sensible and latent heat fluxes are compared with those derived from tethered balloon probes and budget calculations which were employed concurrently during GATE. Aircraft and tethered balloon fluxes showed good agreement; however, the budget results differ, probably due to a different sampling strategy.
Abstract
The structure of the convective atmospheric boundary layer and the characteristics of the associated turbulent mixing processes in undisturbed conditions over the tropical ocean are investigated using data collected during the GARP Atlantic Tropical Experiment (GATE). The data were obtained by a number of aircraft equipped with turbulence measuring instrumentation. The fluxes of momentum, sensible and latent heat throughout the subcloud layer are presented for four cases considered in detail. It is shown that the sensible and latent heat fluxes at the top of the mixed layer (and therefore the distribution of heating and moistening in the boundary layer) are strongly affected by the presence or absence of cumulus convection while the virtual heat flux remains unaffected. Features of this cloud-subcloud interaction are discussed in the light of Betts (1976) coupled cloud-subcloud layer model.
An examination of the spectra (and cospectra) of subcloud-layer variables shows that with the exception of vertical velocity, the spectra are generally dominated by low-frequency fluctuations. This behavior is attributed to the effects of entrainment which may produce relatively large, long-lived excursions from the mixed-layer average in the weakly mixed GATE boundary layer and to the existence of mesoscale (∼10 km) variability.
Wherever possible comparisons are drawn with previous measurements and corresponding situations over land, where mixing processes are usually much more energetic. Aircraft measurements of the sensible and latent heat fluxes are compared with those derived from tethered balloon probes and budget calculations which were employed concurrently during GATE. Aircraft and tethered balloon fluxes showed good agreement; however, the budget results differ, probably due to a different sampling strategy.
Abstract
The relationship of satellite-derived cloud motions to actual convective systems within a convectively active phase of the intraseasonal oscillation is examined by using both cloud-scale properties produced by a cloud-resolving model and field observations to clarify what is going on at shorter time- and space scales. Each convective system has a life cycle of up to 1–2 days. Described in terms of active convection, the system consists of successive precipitation cells generated ahead of the gust front. Described in terms of its cloud shield, the system is more continuous. When easterly winds prevail above 2 km, both precipitating clouds and upper-tropospheric anvil clouds move westward with about the same phase speed (∼10 m s−1). However, during the westerly wind period, precipitating clouds move eastward with a phase speed of ∼10 m s−1, which is better represented by the radar observations and surface precipitation. The westward movement of cloud patterns viewed from the satellite images is mostly due to the horizontal advection of the anvil by the mean flow and the creation of new convective cells to the west of the old convective clouds.
Abstract
The relationship of satellite-derived cloud motions to actual convective systems within a convectively active phase of the intraseasonal oscillation is examined by using both cloud-scale properties produced by a cloud-resolving model and field observations to clarify what is going on at shorter time- and space scales. Each convective system has a life cycle of up to 1–2 days. Described in terms of active convection, the system consists of successive precipitation cells generated ahead of the gust front. Described in terms of its cloud shield, the system is more continuous. When easterly winds prevail above 2 km, both precipitating clouds and upper-tropospheric anvil clouds move westward with about the same phase speed (∼10 m s−1). However, during the westerly wind period, precipitating clouds move eastward with a phase speed of ∼10 m s−1, which is better represented by the radar observations and surface precipitation. The westward movement of cloud patterns viewed from the satellite images is mostly due to the horizontal advection of the anvil by the mean flow and the creation of new convective cells to the west of the old convective clouds.
Abstract
A definite relationship between cloud distribution and sub-cloud layer structure and fluxes in fair weather is documented using measurements of wind, temperature, humidity and overhead cloud occurrence from the NCAR DeHasvilland aircraft. Three cases are used. These were extracted from data taken to the north of Puerto Rico on 14 and 15 December 1972 in mesoscale regions of reasonably uniform convection ranging from suppressed with very little shallow cloudiness to slightly enhanced with active (but non-precipitating) trade cumulus having tops to 2000 m. On both days synoptic conditions were suppressed and the surface winds were from the cast at 10 to 15 m s−1.
In the highly suppressed cases, there is evidence that cloud distribution was determined by subcloud layer circulations—roll vortices which persisted throughout the flight patterns. In the more enhanced case, the predominant coupling was by well-defined cloud scale updrafts which were traceable to at least 100 m below cloud base.
As a consequence of these interactions, the fluxes of moisture and momentum in the upper subcloud layer were found to be strongly coupled to cloud distribution. A comparison of direct measurements from the aircraft and the results of budget computations by other workers for several suppressed situations in the trades suggests that almost all of the fluxes out of the mixed layer are concentrated in mesoscale cloud patches and that a large function of the transport is due to motions on the scale of the individual cumulus.
Abstract
A definite relationship between cloud distribution and sub-cloud layer structure and fluxes in fair weather is documented using measurements of wind, temperature, humidity and overhead cloud occurrence from the NCAR DeHasvilland aircraft. Three cases are used. These were extracted from data taken to the north of Puerto Rico on 14 and 15 December 1972 in mesoscale regions of reasonably uniform convection ranging from suppressed with very little shallow cloudiness to slightly enhanced with active (but non-precipitating) trade cumulus having tops to 2000 m. On both days synoptic conditions were suppressed and the surface winds were from the cast at 10 to 15 m s−1.
In the highly suppressed cases, there is evidence that cloud distribution was determined by subcloud layer circulations—roll vortices which persisted throughout the flight patterns. In the more enhanced case, the predominant coupling was by well-defined cloud scale updrafts which were traceable to at least 100 m below cloud base.
As a consequence of these interactions, the fluxes of moisture and momentum in the upper subcloud layer were found to be strongly coupled to cloud distribution. A comparison of direct measurements from the aircraft and the results of budget computations by other workers for several suppressed situations in the trades suggests that almost all of the fluxes out of the mixed layer are concentrated in mesoscale cloud patches and that a large function of the transport is due to motions on the scale of the individual cumulus.
Abstract
Evidence indicates that fair-weather to towering cumulus clouds over the East Atlantic Ocean during GATE were frequently organized into mesoscale structures. Three examples of such structures are examined, using gust-probe aircraft data collected in parallel straight-and-level flight tracks at 150 m, and covering an area greater than 30×30 km. The aircraft (two cases) or rawinsonde (one case) data provide vertical profiles of mean wind, temperature and mixing ratio. Cloud patterns are revealed from an upward-looking infrared sensor on the aircraft and radar and satellite pictures.
The data show that the cumulus were organized into bands with horizontal wavelengths of 15–25 km. The circulations appear to extend through the subcloud layer, with all the fields at 150 m well related to the cloudiness overhead. Since the circulations are aligned with the subcloud-layer shear and travel in a direction parallel to the subcloud-layer wind (in the two cases for which band movement is documented), it is believed that they are primarily subcloud-layer phenomena. The subcloud-layer depth is about 600 m, giving aspect ratios of the bands from 25 to 50, in the range of mesoscale cellular convection observed in midlatitudes.
Several physical mechanisms which might explain the bands are discussed.
Abstract
Evidence indicates that fair-weather to towering cumulus clouds over the East Atlantic Ocean during GATE were frequently organized into mesoscale structures. Three examples of such structures are examined, using gust-probe aircraft data collected in parallel straight-and-level flight tracks at 150 m, and covering an area greater than 30×30 km. The aircraft (two cases) or rawinsonde (one case) data provide vertical profiles of mean wind, temperature and mixing ratio. Cloud patterns are revealed from an upward-looking infrared sensor on the aircraft and radar and satellite pictures.
The data show that the cumulus were organized into bands with horizontal wavelengths of 15–25 km. The circulations appear to extend through the subcloud layer, with all the fields at 150 m well related to the cloudiness overhead. Since the circulations are aligned with the subcloud-layer shear and travel in a direction parallel to the subcloud-layer wind (in the two cases for which band movement is documented), it is believed that they are primarily subcloud-layer phenomena. The subcloud-layer depth is about 600 m, giving aspect ratios of the bands from 25 to 50, in the range of mesoscale cellular convection observed in midlatitudes.
Several physical mechanisms which might explain the bands are discussed.
The names of 927 women who are or have been active in meteorology or closely related fields have been obtained from various sources. Of these women, at least 500 are presently active. An estimated 4–5% of the total number of Ph.D.s in meteorology are awarded to women. About 10% of those receiving B.S. and M.S. degrees are women.
The work patterns, accomplishments, and salaries of employed women meteorologists have been summarized from 330 responses to questionnaires, as functions of age, family status, part- or full-time working status, and employing institutions. It was found that women meteorologists holding Ph.D.s are more likely than their male counterparts to be employed by universities. As increasing number of women were employed in operational meteorology, although few of them were married and fewer still responsible for children. Several women were employed by private industry and some had advanced into managerial positions, although at the present time, such positions remain out of the reach of most women.
The subjective and objective effects of several gender-related factors have been summarized from the comments and responses to the questionnaires. The primary obstacles to advancement were found to be part-time work and the responsibility for children. Part-time work was found to have a clearly negative effect on salary increase as a function of age. Prejudiced discrimination and rules negatively affecting women remain important, especially to the older women, and affirmative action programs are generally seen as beneficial.
Surprisingly, in contrast to the experience of women in other fields of science, women Ph.D.s in meteorology earn salaries comparable to those of their male counterparts. It is suggested that this is a result of their employment in government or large corporations and universities where there are strong affirmative action programs and above-average salaries. Based on the responses to the questionnaire, the small size of the meteorological community is also a factor, enabling women to become recognized quickly as individuals. It also may be partially attributed to the relative youth of the women involved. They are too young to have encountered the severe discrimination others experienced in the past, and too young to have reached the barriers that have traditionally prevented women from advancing to higher positions. No figures are available that would allow comparison between salaries of male and female holders of bachelor's and master's degrees.
The names of 927 women who are or have been active in meteorology or closely related fields have been obtained from various sources. Of these women, at least 500 are presently active. An estimated 4–5% of the total number of Ph.D.s in meteorology are awarded to women. About 10% of those receiving B.S. and M.S. degrees are women.
The work patterns, accomplishments, and salaries of employed women meteorologists have been summarized from 330 responses to questionnaires, as functions of age, family status, part- or full-time working status, and employing institutions. It was found that women meteorologists holding Ph.D.s are more likely than their male counterparts to be employed by universities. As increasing number of women were employed in operational meteorology, although few of them were married and fewer still responsible for children. Several women were employed by private industry and some had advanced into managerial positions, although at the present time, such positions remain out of the reach of most women.
The subjective and objective effects of several gender-related factors have been summarized from the comments and responses to the questionnaires. The primary obstacles to advancement were found to be part-time work and the responsibility for children. Part-time work was found to have a clearly negative effect on salary increase as a function of age. Prejudiced discrimination and rules negatively affecting women remain important, especially to the older women, and affirmative action programs are generally seen as beneficial.
Surprisingly, in contrast to the experience of women in other fields of science, women Ph.D.s in meteorology earn salaries comparable to those of their male counterparts. It is suggested that this is a result of their employment in government or large corporations and universities where there are strong affirmative action programs and above-average salaries. Based on the responses to the questionnaire, the small size of the meteorological community is also a factor, enabling women to become recognized quickly as individuals. It also may be partially attributed to the relative youth of the women involved. They are too young to have encountered the severe discrimination others experienced in the past, and too young to have reached the barriers that have traditionally prevented women from advancing to higher positions. No figures are available that would allow comparison between salaries of male and female holders of bachelor's and master's degrees.
Abstract
A performance analysis of the three turbulence-measuring aircraft which participated in the GATE is presented. These aircraft were a Lockheed C-130 operated by the Meteorological Research Flight Centre of the U.K. Meteorological Office, a Douglas DC-6 operated by the Research Flight Facility of the National Oceanographic and Atmospheric Administration, and a Lockheed L-188 operated by the Research Aviation Facility of the National Center for Atmospheric Research.
The results are based on formal intercomparison flights and analysis of fair weather days on which two or more of the aircraft were flying. In the formal intercomparison flights, two or more of the aircraft flew side by side in the fair weather atmospheric mixed layer. In both cases, the aircraft flew L-shaped patterns, consisting of 30 km legs along and normal to the mixed layer wind direction.
Quantities compared include the variances of three wind components, potential temperature, moisture, and the vertical fluxes of horizontal momentum, temperature, and moisture. The analysis shows that when all components of the gust probe system are working properly, interaircraft biases are less than the expected atmospheric variability. Quirks of the three data sets are pointed out for the benefit of future GATE data users.
Abstract
A performance analysis of the three turbulence-measuring aircraft which participated in the GATE is presented. These aircraft were a Lockheed C-130 operated by the Meteorological Research Flight Centre of the U.K. Meteorological Office, a Douglas DC-6 operated by the Research Flight Facility of the National Oceanographic and Atmospheric Administration, and a Lockheed L-188 operated by the Research Aviation Facility of the National Center for Atmospheric Research.
The results are based on formal intercomparison flights and analysis of fair weather days on which two or more of the aircraft were flying. In the formal intercomparison flights, two or more of the aircraft flew side by side in the fair weather atmospheric mixed layer. In both cases, the aircraft flew L-shaped patterns, consisting of 30 km legs along and normal to the mixed layer wind direction.
Quantities compared include the variances of three wind components, potential temperature, moisture, and the vertical fluxes of horizontal momentum, temperature, and moisture. The analysis shows that when all components of the gust probe system are working properly, interaircraft biases are less than the expected atmospheric variability. Quirks of the three data sets are pointed out for the benefit of future GATE data users.
Abstract
This is the first part of a two-part paper defining the nature of the vertical air motion in and around GATE cumulonimbus clouds. The statistics are from a total of 104 km of flight legs, flown on six days in GATE, at altitudes from near the surface to 8100 m. The basic data sets analyzed are time series of vertical velocity at a frequency of 1 Hz. For the purpose of study, convective events are divided into two categories: drafts, requiring only that vertical velocity be continuously positive (negative) for 500 m and exceed an absolute value of 0.5 m s−1 for 1 s; and cores, the stronger portions of the stronger drafts, requiring that upward (downward) vertical velocity be continuously greater than an absolute value of 1 m s−1 for 500 m. The distributions of average vertical velocity, maximum vertical velocity, diameter and mass flux are given for drafts and cores at five altitude intervals between 150 m and 8 km. In all cases, the distributions are approximately log-normal.
Above cloud base, updrafts tend to be smaller but more intense than downdrafts. Updrafts and down-drafts near cloud base are comparable in size and intensity. Downdraft cores are smaller than updraft cores at all attitudes. They also are weaker, except near cloud base, where updraft and downdraft cores have comparable intensity. In the middle troposphere, only 10% of the updraft cores have mean vertical velocities greater than 5 m s−1, and only 10% have diameters in excess of 2 km.
Abstract
This is the first part of a two-part paper defining the nature of the vertical air motion in and around GATE cumulonimbus clouds. The statistics are from a total of 104 km of flight legs, flown on six days in GATE, at altitudes from near the surface to 8100 m. The basic data sets analyzed are time series of vertical velocity at a frequency of 1 Hz. For the purpose of study, convective events are divided into two categories: drafts, requiring only that vertical velocity be continuously positive (negative) for 500 m and exceed an absolute value of 0.5 m s−1 for 1 s; and cores, the stronger portions of the stronger drafts, requiring that upward (downward) vertical velocity be continuously greater than an absolute value of 1 m s−1 for 500 m. The distributions of average vertical velocity, maximum vertical velocity, diameter and mass flux are given for drafts and cores at five altitude intervals between 150 m and 8 km. In all cases, the distributions are approximately log-normal.
Above cloud base, updrafts tend to be smaller but more intense than downdrafts. Updrafts and down-drafts near cloud base are comparable in size and intensity. Downdraft cores are smaller than updraft cores at all attitudes. They also are weaker, except near cloud base, where updraft and downdraft cores have comparable intensity. In the middle troposphere, only 10% of the updraft cores have mean vertical velocities greater than 5 m s−1, and only 10% have diameters in excess of 2 km.
Abstract
Pressure perturbations are measured from an aircraft by subtracting its pressure altitude from its actual altitude. The pressure perturbation is equal to the resulting “D-value” multiplied by the acceleration of gravity and density of air. Normally, the actual altitude is measured using a radar altimeter, but this becomes increasingly difficult over increasingly complex terrain.
Here, we document a technique in which inertial altitude is used instead of radar altitude, eliminating the need for extremely accurate navigation or simple terrain, and apply it to document the pressure field at the base of an evolving cumulus congestus in CCOPE. Analysis of both this case study and aircraft self-calibration maneuvers in clear, undisturbed air suggests that a D-value (pressure) accuracy of 2 m (20 Pa) is achievable at cumulus-congestus scales. This accuracy is degraded, however, if the phenomenon of interest is large compared to the flight track.
Abstract
Pressure perturbations are measured from an aircraft by subtracting its pressure altitude from its actual altitude. The pressure perturbation is equal to the resulting “D-value” multiplied by the acceleration of gravity and density of air. Normally, the actual altitude is measured using a radar altimeter, but this becomes increasingly difficult over increasingly complex terrain.
Here, we document a technique in which inertial altitude is used instead of radar altitude, eliminating the need for extremely accurate navigation or simple terrain, and apply it to document the pressure field at the base of an evolving cumulus congestus in CCOPE. Analysis of both this case study and aircraft self-calibration maneuvers in clear, undisturbed air suggests that a D-value (pressure) accuracy of 2 m (20 Pa) is achievable at cumulus-congestus scales. This accuracy is degraded, however, if the phenomenon of interest is large compared to the flight track.
Abstract
No Abstract available.
Abstract
No Abstract available.
