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Abstract
The hypothesis that inertial instability plays a role in the upscale development of mesoscale convective systems (MCSs) is explored by sampling environments that supported the growth of MCSs in the Preliminary Regional Experiment for STORM (Stormscale Operational and Research Meteorology) (PRE-STORM) network with high quality special soundings. Secondary circulations that occurred in the presence of inertial instabilities were analyzed and documented using rawinsonde data with high spatial and temporal resolution from the PRE-STORM field program. Additional examples of MCS environments were examined using data from the Mesoscale Analysis and Prediction System. Results show strong divergence and cross-stream accelerations occurred at upper-tropospheric levels where inertial instabilities were present. These accelerations were not uniform over the domain but were focused in the regions of instability. Also, the analyses of these data showed that regions of inertial instability may be more commonplace than is typically assumed.
The Regional Atmospheric Modeling System was used to increase the understanding of the basic processes and secondary circulations that enhance MCS growth in inertially unstable environments. Model results indicate that the strength of the divergent outflow was strongly linked to the degree of inertial stability in the local environment. The results also showed a strong dependence on the magnitude of the Coriolis parameter. Finally, experiments using varying degrees of vertical stability indicated that there was also significant sensitivity to this parameter.
Abstract
The hypothesis that inertial instability plays a role in the upscale development of mesoscale convective systems (MCSs) is explored by sampling environments that supported the growth of MCSs in the Preliminary Regional Experiment for STORM (Stormscale Operational and Research Meteorology) (PRE-STORM) network with high quality special soundings. Secondary circulations that occurred in the presence of inertial instabilities were analyzed and documented using rawinsonde data with high spatial and temporal resolution from the PRE-STORM field program. Additional examples of MCS environments were examined using data from the Mesoscale Analysis and Prediction System. Results show strong divergence and cross-stream accelerations occurred at upper-tropospheric levels where inertial instabilities were present. These accelerations were not uniform over the domain but were focused in the regions of instability. Also, the analyses of these data showed that regions of inertial instability may be more commonplace than is typically assumed.
The Regional Atmospheric Modeling System was used to increase the understanding of the basic processes and secondary circulations that enhance MCS growth in inertially unstable environments. Model results indicate that the strength of the divergent outflow was strongly linked to the degree of inertial stability in the local environment. The results also showed a strong dependence on the magnitude of the Coriolis parameter. Finally, experiments using varying degrees of vertical stability indicated that there was also significant sensitivity to this parameter.
Abstract
A network of three boundary layer radar wind profilers is used to study characteristics of mountain waves and rotors and to explore the utility of such a network. The data employed were collected as part of the Terrain-Induced Rotor Experiment (T-REX), which took place in Owens Valley, California, in early 2006. The wind profilers provide a continuous time––height representation of wave and rotor structure. During intensive observing period 3 (IOP 3), the profiler network was positioned in an L-shaped configuration, capturing key features of the mountain waves and rotor, including the boundary layer vortex sheet (or shear layer), turbulence within this shear layer, the classical lower turbulence zone (LTZ), and wave motion above the LTZ. Observed features were found to be in good agreement with recent high-resolution numerical simulations. Using the wind profiler with superior time resolution (Multiple Antenna Profiler Radar), a series of updraft––downdraft couplets were observed beneath the first downwind wave crest. These are interpreted as signatures of subrotors. Such detailed observations of subrotors are rare, even though subrotors are believed to be a common feature of rotor circulations in Owens Valley. During IOP 6, the network was repositioned to form a line across the valley. A simple algorithm was used to determine the amplitude, wavelength, and phase of the primary wave over the valley and to observe their changes over time and height. In the IOP-6 case, the wavelength increased over time, the phase indicated an eastward-shifting wave crest, and the amplitude increased with height and also varied over time.
Abstract
A network of three boundary layer radar wind profilers is used to study characteristics of mountain waves and rotors and to explore the utility of such a network. The data employed were collected as part of the Terrain-Induced Rotor Experiment (T-REX), which took place in Owens Valley, California, in early 2006. The wind profilers provide a continuous time––height representation of wave and rotor structure. During intensive observing period 3 (IOP 3), the profiler network was positioned in an L-shaped configuration, capturing key features of the mountain waves and rotor, including the boundary layer vortex sheet (or shear layer), turbulence within this shear layer, the classical lower turbulence zone (LTZ), and wave motion above the LTZ. Observed features were found to be in good agreement with recent high-resolution numerical simulations. Using the wind profiler with superior time resolution (Multiple Antenna Profiler Radar), a series of updraft––downdraft couplets were observed beneath the first downwind wave crest. These are interpreted as signatures of subrotors. Such detailed observations of subrotors are rare, even though subrotors are believed to be a common feature of rotor circulations in Owens Valley. During IOP 6, the network was repositioned to form a line across the valley. A simple algorithm was used to determine the amplitude, wavelength, and phase of the primary wave over the valley and to observe their changes over time and height. In the IOP-6 case, the wavelength increased over time, the phase indicated an eastward-shifting wave crest, and the amplitude increased with height and also varied over time.
Abstract
The primary goal of this study is to explore the potential for estimating the vertical velocity (VV) of air from the surface to the stratosphere, using widely available radiosonde and dropsonde data. The rise and fall rates of radiosondes and dropsondes, respectively, are a combination of the VV of the atmosphere and still-air rise–fall rates. The still-air rise–fall rates are calculated using basic fluid dynamics and characteristics of radiosonde and dropsonde systems. This study validates the technique to derive the VV from radiosonde and dropsonde data and demonstrates its value. This technique can be easily implemented by other users for various scientific applications.
The technique has been applied to the Terrain-induced Rotor Experiment (T-REX) dropsonde and radiosonde data. Comparisons among radiosonde, dropsonde, aircraft, and profiling radar vertical velocities show that the sonde-estimated VV is able to capture and describe events with strong vertical motions (larger than ∼1 m s−1) observed during T-REX. The VV below ∼5 km above ground, however, is overestimated by the radiosonde data. The analysis of derived VVs shows interesting features of gravity waves, rotors, and turbulence. Periodic variations of vertical velocity in the stratosphere, as indicated by the radiosonde data, correspond to the horizontal wavelength of gravity waves with an averaged horizontal wavelength of ∼15 km. Two-dimensional VV structure is described in detail by successive dropsonde deployment.
Abstract
The primary goal of this study is to explore the potential for estimating the vertical velocity (VV) of air from the surface to the stratosphere, using widely available radiosonde and dropsonde data. The rise and fall rates of radiosondes and dropsondes, respectively, are a combination of the VV of the atmosphere and still-air rise–fall rates. The still-air rise–fall rates are calculated using basic fluid dynamics and characteristics of radiosonde and dropsonde systems. This study validates the technique to derive the VV from radiosonde and dropsonde data and demonstrates its value. This technique can be easily implemented by other users for various scientific applications.
The technique has been applied to the Terrain-induced Rotor Experiment (T-REX) dropsonde and radiosonde data. Comparisons among radiosonde, dropsonde, aircraft, and profiling radar vertical velocities show that the sonde-estimated VV is able to capture and describe events with strong vertical motions (larger than ∼1 m s−1) observed during T-REX. The VV below ∼5 km above ground, however, is overestimated by the radiosonde data. The analysis of derived VVs shows interesting features of gravity waves, rotors, and turbulence. Periodic variations of vertical velocity in the stratosphere, as indicated by the radiosonde data, correspond to the horizontal wavelength of gravity waves with an averaged horizontal wavelength of ∼15 km. Two-dimensional VV structure is described in detail by successive dropsonde deployment.
Abstract
The best way to train the next wave of observational talent is through direct experience. In 2012 and again in 2014, students at St. Cloud State University (SCSU) welcomed deployments of professional atmospheric research equipment, allowing them to support and execute field projects. The Boundary Structure Experiments with Central Minnesota Profiling (BaSE CaMP) projects brought the Mobile Integrated Sounding System (MISS) from the National Center for Atmospheric Research’s (NCAR) Earth Observing Laboratory (EOL) to SCSU for a National Science Foundation–funded educational deployment. Its diverse instrumentation and ability to travel to interesting weather events and locations makes MISS extremely valuable for teaching students about both weather experiments and measurement strategies. In addition to the university project, outreach activities with MISS took place at high schools, regional conferences, and public events. MISS carries four instruments: a boundary layer wind profiler, a radio acoustic sounding system (RASS), radiosondes, and an instrumented 10-m tower. The type and time of MISS deployments were quite varied so students could participate around their class schedule, jobs, and other commitments. Each year the project had periods of fixed operations and mobile activity, where MISS was relocated to best observe current weather conditions. BaSE CaMP operations and results were incorporated into many classes in the meteorology program at SCSU. The original course request was for Radar and Satellite Meteorology, but other activities contributed to Atmospheric Dynamics, Physical Meteorology, and Meteorological Analysis Software courses.
Abstract
The best way to train the next wave of observational talent is through direct experience. In 2012 and again in 2014, students at St. Cloud State University (SCSU) welcomed deployments of professional atmospheric research equipment, allowing them to support and execute field projects. The Boundary Structure Experiments with Central Minnesota Profiling (BaSE CaMP) projects brought the Mobile Integrated Sounding System (MISS) from the National Center for Atmospheric Research’s (NCAR) Earth Observing Laboratory (EOL) to SCSU for a National Science Foundation–funded educational deployment. Its diverse instrumentation and ability to travel to interesting weather events and locations makes MISS extremely valuable for teaching students about both weather experiments and measurement strategies. In addition to the university project, outreach activities with MISS took place at high schools, regional conferences, and public events. MISS carries four instruments: a boundary layer wind profiler, a radio acoustic sounding system (RASS), radiosondes, and an instrumented 10-m tower. The type and time of MISS deployments were quite varied so students could participate around their class schedule, jobs, and other commitments. Each year the project had periods of fixed operations and mobile activity, where MISS was relocated to best observe current weather conditions. BaSE CaMP operations and results were incorporated into many classes in the meteorology program at SCSU. The original course request was for Radar and Satellite Meteorology, but other activities contributed to Atmospheric Dynamics, Physical Meteorology, and Meteorological Analysis Software courses.
The Atmospheric Emitted Radiance Interferometer (AERI) was used to measure the infrared radiative properties and the temperature of the Gulf of Mexico during a 5-day oceanographic cruise in January 1995. The ocean skin temperature was measured with an accuracy believed to be better than 0.1 °C. The surface reflectivity/emissivity was determined as a function of view angle and sea state. The radiative properties are in good theoretical consistency with in situ measurements of ocean bulk temperature and the meteorological observations made from the oceanographic vessel. The AERI and in situ measurements provide a strong basis for accurate global specifications of sea surface temperature and ocean heat flux from satellites and ships.
The Atmospheric Emitted Radiance Interferometer (AERI) was used to measure the infrared radiative properties and the temperature of the Gulf of Mexico during a 5-day oceanographic cruise in January 1995. The ocean skin temperature was measured with an accuracy believed to be better than 0.1 °C. The surface reflectivity/emissivity was determined as a function of view angle and sea state. The radiative properties are in good theoretical consistency with in situ measurements of ocean bulk temperature and the meteorological observations made from the oceanographic vessel. The AERI and in situ measurements provide a strong basis for accurate global specifications of sea surface temperature and ocean heat flux from satellites and ships.
Abstract
Stable boundary layers are still a relatively problematic component of atmospheric modeling, despite their frequent occurrence. While general agreement exists that Monin–Obukhov similarity is not applicable in the stable boundary layer (SBL) due to the nonhomogeneous, nonstationary flow, no universal organizing theory for the surface SBL has been presented. The Stable Atmospheric Variability and Transport (SAVANT) field campaign took place in the fall of 2018 to explore under what conditions shallow drainage flow is generated. The campaign took place in an agricultural setting and covered the period of both pre- and postharvest, allowing for not only a basic exploration of the boundary layer but also a robust dataset for applied agricultural understanding of aerosol dispersion and impacts of changes in surface cover on drainage flows. This article provides a description of the field campaign. Examples of publicly available data products are presented, as well as examples of shallow drainage flow and corresponding lidar measurements of dispersion. Additionally, the field campaign was used to provide educational opportunities for students from several disciplines, and the outcomes of these joint educational ventures are discussed as models for future collaborations.
Abstract
Stable boundary layers are still a relatively problematic component of atmospheric modeling, despite their frequent occurrence. While general agreement exists that Monin–Obukhov similarity is not applicable in the stable boundary layer (SBL) due to the nonhomogeneous, nonstationary flow, no universal organizing theory for the surface SBL has been presented. The Stable Atmospheric Variability and Transport (SAVANT) field campaign took place in the fall of 2018 to explore under what conditions shallow drainage flow is generated. The campaign took place in an agricultural setting and covered the period of both pre- and postharvest, allowing for not only a basic exploration of the boundary layer but also a robust dataset for applied agricultural understanding of aerosol dispersion and impacts of changes in surface cover on drainage flows. This article provides a description of the field campaign. Examples of publicly available data products are presented, as well as examples of shallow drainage flow and corresponding lidar measurements of dispersion. Additionally, the field campaign was used to provide educational opportunities for students from several disciplines, and the outcomes of these joint educational ventures are discussed as models for future collaborations.
Abstract
High-resolution observations from scanning Doppler and aerosol lidars, wind profiler radars, as well as surface and aircraft measurements during the Terrain-induced Rotor Experiment (T-REX) provide the first comprehensive documentation of small-scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain. Although rotors are already recognized as potential hazards for aircraft, it is proposed that these small-scale vortices, or subrotors, are the most dangerous features because of strong wind shear and the transient nature of the vortices. A life cycle of a subrotor event is captured by scanning Doppler and aerosol lidars over a 5-min period. The lidars depict an amplifying vortex, with a characteristic length scale of ∼500–1000 m, that overturns and intensifies to a maximum spanwise vorticity greater than 0.2 s−1. Radar wind profiler observations document a series of vortices, characterized by updraft/downdraft couplets and regions of enhanced reversed flow, that are generated in a layer of strong vertical wind shear and subcritical Richardson number. The observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes. As the subrotors break from the vortex sheet, intensification occurs through vortex stretching and in some cases tilting processes related to three-dimensional turbulent mixing. The subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength, which illustrates the predictability challenges for the turbulent characterization of rotors.
Abstract
High-resolution observations from scanning Doppler and aerosol lidars, wind profiler radars, as well as surface and aircraft measurements during the Terrain-induced Rotor Experiment (T-REX) provide the first comprehensive documentation of small-scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain. Although rotors are already recognized as potential hazards for aircraft, it is proposed that these small-scale vortices, or subrotors, are the most dangerous features because of strong wind shear and the transient nature of the vortices. A life cycle of a subrotor event is captured by scanning Doppler and aerosol lidars over a 5-min period. The lidars depict an amplifying vortex, with a characteristic length scale of ∼500–1000 m, that overturns and intensifies to a maximum spanwise vorticity greater than 0.2 s−1. Radar wind profiler observations document a series of vortices, characterized by updraft/downdraft couplets and regions of enhanced reversed flow, that are generated in a layer of strong vertical wind shear and subcritical Richardson number. The observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes. As the subrotors break from the vortex sheet, intensification occurs through vortex stretching and in some cases tilting processes related to three-dimensional turbulent mixing. The subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength, which illustrates the predictability challenges for the turbulent characterization of rotors.
The Persistent Cold-Air Pool Study (PCAPS) was conducted in Utah's Salt Lake valley from 1 December 2010 to 7 February 2011. The field campaign's primary goal was to improve understanding of the physical processes governing the evolution of multiday cold-air pools (CAPs) that are common in mountain basins during the winter. Meteorological instrumentation deployed throughout the Salt Lake valley provided observations of the processes contributing to the formation, maintenance, and destruction of 10 persistent CAP episodes. The close proximity of PCAPS field sites to residences and the University of Utah campus allowed many undergraduate and graduate students to participate in the study.
Ongoing research, supported by the National Science Foundation, is using the PCAPS dataset to examine CAP evolution. Preliminary analyses reveal that variations in CAP thermodynamic structure are attributable to a multitude of physical processes affecting local static stability: for example, synoptic-scale processes impact changes in temperatures and cloudiness aloft while variations in boundary layer forcing modulate the lower levels of CAPs. During episodes of strong winds, complex interactions between the synoptic and mesoscale f lows, local thermodynamic structure, and terrain lead to both partial and complete removal of CAPs. In addition, the strength and duration of CAP events affect the local concentrations of pollutants such as PM2.5.
The Persistent Cold-Air Pool Study (PCAPS) was conducted in Utah's Salt Lake valley from 1 December 2010 to 7 February 2011. The field campaign's primary goal was to improve understanding of the physical processes governing the evolution of multiday cold-air pools (CAPs) that are common in mountain basins during the winter. Meteorological instrumentation deployed throughout the Salt Lake valley provided observations of the processes contributing to the formation, maintenance, and destruction of 10 persistent CAP episodes. The close proximity of PCAPS field sites to residences and the University of Utah campus allowed many undergraduate and graduate students to participate in the study.
Ongoing research, supported by the National Science Foundation, is using the PCAPS dataset to examine CAP evolution. Preliminary analyses reveal that variations in CAP thermodynamic structure are attributable to a multitude of physical processes affecting local static stability: for example, synoptic-scale processes impact changes in temperatures and cloudiness aloft while variations in boundary layer forcing modulate the lower levels of CAPs. During episodes of strong winds, complex interactions between the synoptic and mesoscale f lows, local thermodynamic structure, and terrain lead to both partial and complete removal of CAPs. In addition, the strength and duration of CAP events affect the local concentrations of pollutants such as PM2.5.
Metcrax 2006
Meteorological Experiments in Arizona's Meteor Crater
The Meteor Crater Experiment (METCRAX 2006) was conducted in October 2006 at Arizona's Meteor Crater to investigate stable boundary layer evolution in a topographically uncomplicated basin surrounded by the nearly homogeneous plain of the Colorado Plateau. The two goals of the experiment were 1) to investigate the microscale and mesoscale structure and evolution of the stable boundary layer in the crater and its surroundings and 2) to determine whether atmospheric seiches or standing waves are produced inside the crater. This article provides an overview of the scientific goals of the experiment; summarizes the research measurements, the crater topography, and the synoptic meteorology of the study period; and presents initial analysis results. Analyses show that nighttime temperature inversions form frequently in the crater and that they are often perturbed by internal wave motions. Nighttime cooling produces a shallow (15–30 m deep) surface-based inversion that is surmounted by a horizontally homogeneous near-isothermal layer that extends all the way to the rim, where a second inversion extends above rim level. Seiches are sometimes present on the crater floor. The diurnal propagation of shadows from the crater rim produces important spatial differences in the surface radiation budget and thus the timing of the slope flow transition, and the crater atmosphere is often perturbed during nighttime by a southwesterly mesoscale drainage flow.
The Meteor Crater Experiment (METCRAX 2006) was conducted in October 2006 at Arizona's Meteor Crater to investigate stable boundary layer evolution in a topographically uncomplicated basin surrounded by the nearly homogeneous plain of the Colorado Plateau. The two goals of the experiment were 1) to investigate the microscale and mesoscale structure and evolution of the stable boundary layer in the crater and its surroundings and 2) to determine whether atmospheric seiches or standing waves are produced inside the crater. This article provides an overview of the scientific goals of the experiment; summarizes the research measurements, the crater topography, and the synoptic meteorology of the study period; and presents initial analysis results. Analyses show that nighttime temperature inversions form frequently in the crater and that they are often perturbed by internal wave motions. Nighttime cooling produces a shallow (15–30 m deep) surface-based inversion that is surmounted by a horizontally homogeneous near-isothermal layer that extends all the way to the rim, where a second inversion extends above rim level. Seiches are sometimes present on the crater floor. The diurnal propagation of shadows from the crater rim produces important spatial differences in the surface radiation budget and thus the timing of the slope flow transition, and the crater atmosphere is often perturbed during nighttime by a southwesterly mesoscale drainage flow.
Testing Atmospheric Oxidation in an Alabama ForestAbstract
The chemical species emitted by forests create complex atmospheric oxidation chemistry and influence global atmospheric oxidation capacity and climate. The Southern Oxidant and Aerosol Study (SOAS) provided an opportunity to test the oxidation chemistry in a forest where isoprene is the dominant biogenic volatile organic compound. Hydroxyl (OH) and hydroperoxyl (HO2) radicals were two of the hundreds of atmospheric chemical species measured, as was OH reactivity (the inverse of the OH lifetime). OH was measured by laser-induced fluorescence (LIF) and by taking the difference in signals without and with an OH scavenger that was added just outside the instrument’s pinhole inlet. To test whether the chemistry at SOAS can be simulated by current model mechanisms, OH and HO2 were evaluated with a box model using two chemical mechanisms: Master Chemical Mechanism, version 3.2 (MCMv3.2), augmented with explicit isoprene chemistry and MCMv3.3.1. Measured and modeled OH peak at about 106 cm−3 and agree well within combined uncertainties. Measured and modeled HO2 peak at about 27 pptv and also agree well within combined uncertainties. Median OH reactivity cycled between about 11 s−1 at dawn and about 26 s−1 during midafternoon. A good test of the oxidation chemistry is the balance between OH production and loss rates using measurements; this balance was observed to within uncertainties. These SOAS results provide strong evidence that the current isoprene mechanisms are consistent with measured OH and HO2 and, thus, capture significant aspects of the atmospheric oxidation chemistry in this isoprene-rich forest.
Abstract
The chemical species emitted by forests create complex atmospheric oxidation chemistry and influence global atmospheric oxidation capacity and climate. The Southern Oxidant and Aerosol Study (SOAS) provided an opportunity to test the oxidation chemistry in a forest where isoprene is the dominant biogenic volatile organic compound. Hydroxyl (OH) and hydroperoxyl (HO2) radicals were two of the hundreds of atmospheric chemical species measured, as was OH reactivity (the inverse of the OH lifetime). OH was measured by laser-induced fluorescence (LIF) and by taking the difference in signals without and with an OH scavenger that was added just outside the instrument’s pinhole inlet. To test whether the chemistry at SOAS can be simulated by current model mechanisms, OH and HO2 were evaluated with a box model using two chemical mechanisms: Master Chemical Mechanism, version 3.2 (MCMv3.2), augmented with explicit isoprene chemistry and MCMv3.3.1. Measured and modeled OH peak at about 106 cm−3 and agree well within combined uncertainties. Measured and modeled HO2 peak at about 27 pptv and also agree well within combined uncertainties. Median OH reactivity cycled between about 11 s−1 at dawn and about 26 s−1 during midafternoon. A good test of the oxidation chemistry is the balance between OH production and loss rates using measurements; this balance was observed to within uncertainties. These SOAS results provide strong evidence that the current isoprene mechanisms are consistent with measured OH and HO2 and, thus, capture significant aspects of the atmospheric oxidation chemistry in this isoprene-rich forest.
