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Abstract
Input data from the AYE-SESAME I experiment are utilized to describe the effects of random errors in rawinsonde data on the computation of ageostrophic winds Computer-generated random errors for wind direction and speed and temperature are introduced into the station soundings at 25 mb intervals from which isentropic data sets are created. The ageostrophic wind and its components are computed for both the 312 K and 324 K isentropic surfaces. The total form of the ageostrophic wind components consists of the local wind tendency and inertial-advective contributions. The geostrophic momentum form of the ageostrophic wind components consists of the isallobaric and inertial-geostrophic-advective contributions. All winds are computed for 2000 GMT 10 April 1979 except the isallobaric and the local wind tendency, which are calculated for the 1700–2000 GMT time period. The ageostrophic wind components were quite strong during this time.
Quantitative analyses utilizing various statistical parameters and qualitative analyses from a visual comparison of fields are discussed. Results show that the geostrophic momentum forms of the ageostrophic wind components are generally less sensitive to rawinsonde error than their total form counterparts. This is most likely due to the fact that the mass field is observed more accurately by a rawinsonde than the momentum field. Divergence fields generated from the various ageostrophic wind components are presented as they are more sensitive to rawinsonde error than the various ageostrophic wind components themselves. These divergence fields revel that the isallobaric and inertial-geostrophic-advective divergences are less affected by rawinsonde random errors then the divergence of the local wind tendency or inertial-advective winds. Finally, this study indicates that the ageostrophic wind can be reliably diagnosed from the rawinsonde data gathered during the AYE-SESAME I experiment in 1979.
Abstract
Input data from the AYE-SESAME I experiment are utilized to describe the effects of random errors in rawinsonde data on the computation of ageostrophic winds Computer-generated random errors for wind direction and speed and temperature are introduced into the station soundings at 25 mb intervals from which isentropic data sets are created. The ageostrophic wind and its components are computed for both the 312 K and 324 K isentropic surfaces. The total form of the ageostrophic wind components consists of the local wind tendency and inertial-advective contributions. The geostrophic momentum form of the ageostrophic wind components consists of the isallobaric and inertial-geostrophic-advective contributions. All winds are computed for 2000 GMT 10 April 1979 except the isallobaric and the local wind tendency, which are calculated for the 1700–2000 GMT time period. The ageostrophic wind components were quite strong during this time.
Quantitative analyses utilizing various statistical parameters and qualitative analyses from a visual comparison of fields are discussed. Results show that the geostrophic momentum forms of the ageostrophic wind components are generally less sensitive to rawinsonde error than their total form counterparts. This is most likely due to the fact that the mass field is observed more accurately by a rawinsonde than the momentum field. Divergence fields generated from the various ageostrophic wind components are presented as they are more sensitive to rawinsonde error than the various ageostrophic wind components themselves. These divergence fields revel that the isallobaric and inertial-geostrophic-advective divergences are less affected by rawinsonde random errors then the divergence of the local wind tendency or inertial-advective winds. Finally, this study indicates that the ageostrophic wind can be reliably diagnosed from the rawinsonde data gathered during the AYE-SESAME I experiment in 1979.
Abstract
An a posteriori analysis was conducted utilizing precipitation, rawinsonde and seeding generator data from seven randomized winter cloud-seeding research projects conducted in orographic settings in the Rocky Mountain West and on the Pacific Coast of the United States. Variables were developed and investigated to establish generalized seedability criteria that are applicable to a variety of meteorological and topographic conditions. The variables were divided into four general categories: time available, water available, nuclei available and mixing available. This approach established stratifications under which positive (increases) or negative (decreases) seeding effects occurred. The study showed that positive seeding effects occurred at the crest under stable or unstable conditions when a “crest” trajectory was present, moderate-to-high cloud moisture was present and the cloud-top temperature was between −10 and −30°C. Decreases occurred at the crest for unstable clouds with a “blow-over” trajectory, with low cloud moisture and cloud-top temperature colder than −30°C. The precipitation for upwind and downwind regions of a barrier was also increased or decreased depending on stability, trajectory, cloud moisture and cloud-top temperature. Other stratifications are discussed in the paper.
Abstract
An a posteriori analysis was conducted utilizing precipitation, rawinsonde and seeding generator data from seven randomized winter cloud-seeding research projects conducted in orographic settings in the Rocky Mountain West and on the Pacific Coast of the United States. Variables were developed and investigated to establish generalized seedability criteria that are applicable to a variety of meteorological and topographic conditions. The variables were divided into four general categories: time available, water available, nuclei available and mixing available. This approach established stratifications under which positive (increases) or negative (decreases) seeding effects occurred. The study showed that positive seeding effects occurred at the crest under stable or unstable conditions when a “crest” trajectory was present, moderate-to-high cloud moisture was present and the cloud-top temperature was between −10 and −30°C. Decreases occurred at the crest for unstable clouds with a “blow-over” trajectory, with low cloud moisture and cloud-top temperature colder than −30°C. The precipitation for upwind and downwind regions of a barrier was also increased or decreased depending on stability, trajectory, cloud moisture and cloud-top temperature. Other stratifications are discussed in the paper.
Abstract
Understanding and predicting Earth’s environment requires information and knowledge of detailed physical, chemical, and biological processes directly from observations. Well-organized and properly conducted field campaigns are powerful ways to make such observations. Major international field campaigns with participation from multiple countries bring together expertise and resources to address complex scientific issues that are difficult or impossible to be tackled by a few scientists in a single nation. This article describes the essential elements of international field campaigns, the necessary steps of planning and execution that need to be taken for their success, and other considerations that make international field campaigns successful. The intention of this article is to encourage early career professionals to participate in and learn to organize field campaigns in this exciting time of rapidly evolving technological observing capabilities and increasing efforts to seek global diversity, equity, and inclusion in science.
Abstract
Understanding and predicting Earth’s environment requires information and knowledge of detailed physical, chemical, and biological processes directly from observations. Well-organized and properly conducted field campaigns are powerful ways to make such observations. Major international field campaigns with participation from multiple countries bring together expertise and resources to address complex scientific issues that are difficult or impossible to be tackled by a few scientists in a single nation. This article describes the essential elements of international field campaigns, the necessary steps of planning and execution that need to be taken for their success, and other considerations that make international field campaigns successful. The intention of this article is to encourage early career professionals to participate in and learn to organize field campaigns in this exciting time of rapidly evolving technological observing capabilities and increasing efforts to seek global diversity, equity, and inclusion in science.
Abstract
The composition of canister hydrocarbon data collected at four surface sites and from aircraft during a 1985 field experiment in California's south-central coast air basin was analyzed to determine the source. Statistical routines from a commonly used software package (SAS) were used to perform a principal component extraction on a 15-variable vector space containing the most important hydrocarbons (as well as CO) in the air quality samples. The ratios of each of the 15 hydrocarbon species to total nonmethane hydrocarbon (NMHC) were plotted as a function of the ethane-to-acetylene (E/A) ratio. The plots serve as an estimator of the source profile and were consistent with the source profiles obtained by the principal component analysis.
The source reconciliation analysis identified two principal sources. One appears to be rich in acetylene, carbon monoxide (CO), and some unique hydrocarbons. This source corresponds closely to accepted hydrocarbon profiles for automobile emissions. The second major source is high in methane, ethane, and propane, but also contains reasonable amounts of butane and pentane. This type of composition suggests a geogenic source. In addition to these two major sources, clean oceanic air was identified as a third component. The biogenic compound isoprene also occurred in some samples.
Canister data from three of four sites were dominated by a profile of trace gases associated with a geogenic source. The reactivity of the geogenic air mass is about 50% that of urban air. The dominance of such a low-reactive emission source affects the amount of ozone predicted by photochemical modeling of the region.
Abstract
The composition of canister hydrocarbon data collected at four surface sites and from aircraft during a 1985 field experiment in California's south-central coast air basin was analyzed to determine the source. Statistical routines from a commonly used software package (SAS) were used to perform a principal component extraction on a 15-variable vector space containing the most important hydrocarbons (as well as CO) in the air quality samples. The ratios of each of the 15 hydrocarbon species to total nonmethane hydrocarbon (NMHC) were plotted as a function of the ethane-to-acetylene (E/A) ratio. The plots serve as an estimator of the source profile and were consistent with the source profiles obtained by the principal component analysis.
The source reconciliation analysis identified two principal sources. One appears to be rich in acetylene, carbon monoxide (CO), and some unique hydrocarbons. This source corresponds closely to accepted hydrocarbon profiles for automobile emissions. The second major source is high in methane, ethane, and propane, but also contains reasonable amounts of butane and pentane. This type of composition suggests a geogenic source. In addition to these two major sources, clean oceanic air was identified as a third component. The biogenic compound isoprene also occurred in some samples.
Canister data from three of four sites were dominated by a profile of trace gases associated with a geogenic source. The reactivity of the geogenic air mass is about 50% that of urban air. The dominance of such a low-reactive emission source affects the amount of ozone predicted by photochemical modeling of the region.
Fields of divergence, vertical motion, stability, and surface pressure tendency are examined at 3 h intervals for the first regional scale AVE-SESAME '79 (Atmospheric Variability Experiment—Severe Environmental Storms and Mesoscale Experiment) day. Two areas of severe storms formed during the period from 1200 GMT 10 April through 1200 GMT 11 April. The Red River Valley outbreak began during the afternoon of 10 April, while a second area formed in southwestern Texas during the early evening hours. Results show the rapid changes in environmental conditions associated with these two storm areas.
The propagation of an upper level jet streak into the region was a major factor in producing the Red River Valley outbreak. This streak was associated with the formation of a strong low-level jet and a small-scale surface pressure perturbation. The sudden development of a strong upper tropospheric wind maximum over Oklahoma and Kansas corresponded with major changes in kinematic parameters at that level. Instability over the Red River Valley was released by strong upward motion producing intense convection.
Similar features were responsible for the storms in southwestern Texas. Although this area was quite unstable, forcing mechanisms appear somewhat weaker than in the earlier outbreak.
Fields of divergence, vertical motion, stability, and surface pressure tendency are examined at 3 h intervals for the first regional scale AVE-SESAME '79 (Atmospheric Variability Experiment—Severe Environmental Storms and Mesoscale Experiment) day. Two areas of severe storms formed during the period from 1200 GMT 10 April through 1200 GMT 11 April. The Red River Valley outbreak began during the afternoon of 10 April, while a second area formed in southwestern Texas during the early evening hours. Results show the rapid changes in environmental conditions associated with these two storm areas.
The propagation of an upper level jet streak into the region was a major factor in producing the Red River Valley outbreak. This streak was associated with the formation of a strong low-level jet and a small-scale surface pressure perturbation. The sudden development of a strong upper tropospheric wind maximum over Oklahoma and Kansas corresponded with major changes in kinematic parameters at that level. Instability over the Red River Valley was released by strong upward motion producing intense convection.
Similar features were responsible for the storms in southwestern Texas. Although this area was quite unstable, forcing mechanisms appear somewhat weaker than in the earlier outbreak.
Abstract
A diagnostic study of a continental occluding extratropical cyclone (ETC) during 1–2 November 1992 is presented using initializations from the Mesoscale Atmospheric Prediction System (MAPS), a hybrid sigma–isentropic coordinate model. Whereas recent studies have concentrated on maritime ETCs and have used numerical model simulations, this study employs diagnostic, observational data and model initializations to develop an occlusion model. In addition, isentropic parcel trajectories from a diabatic trajectory model are examined to trace the origin and termination of air parcels associated with the development of the occluded front. The chosen storm was a moderately deepening (i.e., typical) ETC over a data-rich continental region. This storm developed over the central United States, where commercial aircraft and a network of wind profilers provided copious asynoptic data aloft, which was ingested by the MAPS. Analyses of this well-defined occluded cyclone tend to verify that the advancing cold front overtakes the retreating warm front, though it does not “ride up” the warm front, and that warm-sector parcels are lifted upward in the vicinity of the occluded front, thereby confirming that some of the parcels aloft over the surface occluded front do originate near the surface prior to occlusion. Discussion is also provided on the nature of the occluded front as a true frontal boundary.
Abstract
A diagnostic study of a continental occluding extratropical cyclone (ETC) during 1–2 November 1992 is presented using initializations from the Mesoscale Atmospheric Prediction System (MAPS), a hybrid sigma–isentropic coordinate model. Whereas recent studies have concentrated on maritime ETCs and have used numerical model simulations, this study employs diagnostic, observational data and model initializations to develop an occlusion model. In addition, isentropic parcel trajectories from a diabatic trajectory model are examined to trace the origin and termination of air parcels associated with the development of the occluded front. The chosen storm was a moderately deepening (i.e., typical) ETC over a data-rich continental region. This storm developed over the central United States, where commercial aircraft and a network of wind profilers provided copious asynoptic data aloft, which was ingested by the MAPS. Analyses of this well-defined occluded cyclone tend to verify that the advancing cold front overtakes the retreating warm front, though it does not “ride up” the warm front, and that warm-sector parcels are lifted upward in the vicinity of the occluded front, thereby confirming that some of the parcels aloft over the surface occluded front do originate near the surface prior to occlusion. Discussion is also provided on the nature of the occluded front as a true frontal boundary.
Abstract
Terms of the balance equation were calculated at 300 mb to diagnose unbalanced flow in the upper troposphere both prior to and during a period of strong convection which took place during the AVE-SESAME I period. The sum of the balance equation terms displayed large imbalances(>50×10−10s−2)over the Red River Valley as early as 2100 UTC. This region grew in magnitude, expanding over Oklahoma during the next 3–6 hours. The vorticity and Laplacian terms in the balance equation dominated this imbalance.
An examination of ageostrophic, geostrophic and actual 300 mb winds at 2100 UTC revealed that the ageostrophic winds over Oklahoma were directed towards lower geopotential heights, indicating that the flow was neither in geostrophic balance nor merely responding to curved flow as described by the gradient wind equation. Such imbalance led to substantial increases in divergence and midlevel upward vertical motion.
The remaining terms of the divergence equation were computed and summed. These terms partially compensated for the strong divergence tendencies created from the balance equation. In this way, the divergence and vertical motion terms of the divergence equation checked the growth of divergence in upper levels.
Finally, an error assessment was conducted on the terms of the divergence equation. Although balance equation terms are susceptible to substantial error due to random errors in wind and height data, the patterns of these terms are more reliable, thereby permitting the conclusions of this case study.
Abstract
Terms of the balance equation were calculated at 300 mb to diagnose unbalanced flow in the upper troposphere both prior to and during a period of strong convection which took place during the AVE-SESAME I period. The sum of the balance equation terms displayed large imbalances(>50×10−10s−2)over the Red River Valley as early as 2100 UTC. This region grew in magnitude, expanding over Oklahoma during the next 3–6 hours. The vorticity and Laplacian terms in the balance equation dominated this imbalance.
An examination of ageostrophic, geostrophic and actual 300 mb winds at 2100 UTC revealed that the ageostrophic winds over Oklahoma were directed towards lower geopotential heights, indicating that the flow was neither in geostrophic balance nor merely responding to curved flow as described by the gradient wind equation. Such imbalance led to substantial increases in divergence and midlevel upward vertical motion.
The remaining terms of the divergence equation were computed and summed. These terms partially compensated for the strong divergence tendencies created from the balance equation. In this way, the divergence and vertical motion terms of the divergence equation checked the growth of divergence in upper levels.
Finally, an error assessment was conducted on the terms of the divergence equation. Although balance equation terms are susceptible to substantial error due to random errors in wind and height data, the patterns of these terms are more reliable, thereby permitting the conclusions of this case study.
Abstract
A serious systematic bias of the data set used in the original Vardiman and Moore (1978) work was detected while performing a continuing investigation of seeding “windows.” This bias occurred because a large number of no-seed cases were used in the Climax I and Climax II data sets that were not within the original strict randomization. Removal of this systematic bias produced a significant change in both the overall and stratified results. The nature of the bias and its impact on the original results are discussed.
Abstract
A serious systematic bias of the data set used in the original Vardiman and Moore (1978) work was detected while performing a continuing investigation of seeding “windows.” This bias occurred because a large number of no-seed cases were used in the Climax I and Climax II data sets that were not within the original strict randomization. Removal of this systematic bias produced a significant change in both the overall and stratified results. The nature of the bias and its impact on the original results are discussed.
