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The output of effective ice nuclei from silver iodide generators can vary by at least three to four orders of magnitude as a function of the type of generator device employed and its operational efficiency. A detailed consideration of each phase of the process of calibrating silver iodide generators shows that with care meaningful calibrations to within a factor of 1.5 are possible.
The repeatability of actual calibration experiments together with space closed volume experiments support the validity of generator testing procedures.
The output of effective ice nuclei from silver iodide generators can vary by at least three to four orders of magnitude as a function of the type of generator device employed and its operational efficiency. A detailed consideration of each phase of the process of calibrating silver iodide generators shows that with care meaningful calibrations to within a factor of 1.5 are possible.
The repeatability of actual calibration experiments together with space closed volume experiments support the validity of generator testing procedures.
Abstract
The NCAR acoustical ice nucleus counter was calibrated against a Bigg-Warner Weather Bureau type chamber modified as a mixing chamber. The mixing chamber was in turn calibrated against the CSU-NSF isothermal diffusion cloud chamber. This work was carried out using a 300-liter aluminized mylar bag into which known samples of silver iodide nuclei were introduced. Nuclei were transferred from the bag to the NCAR counter in a carrier gas, at a flow rate of 10 liters min−1. It was found that the NCAR counter measured from 16–52% of the count given by the mixing chamber. An NCAR unit was modified with a velvet liner to test the feasibility of eliminating the glycol system, and measurements were made as described above. The modified unit did not count reliably.
Abstract
The NCAR acoustical ice nucleus counter was calibrated against a Bigg-Warner Weather Bureau type chamber modified as a mixing chamber. The mixing chamber was in turn calibrated against the CSU-NSF isothermal diffusion cloud chamber. This work was carried out using a 300-liter aluminized mylar bag into which known samples of silver iodide nuclei were introduced. Nuclei were transferred from the bag to the NCAR counter in a carrier gas, at a flow rate of 10 liters min−1. It was found that the NCAR counter measured from 16–52% of the count given by the mixing chamber. An NCAR unit was modified with a velvet liner to test the feasibility of eliminating the glycol system, and measurements were made as described above. The modified unit did not count reliably.
Abstract
Mountains often act as barriers to low-level flow creating regions of stagnant, decoupled flow within thermally stratified air masses. This paper addresses the question: how does a region of low-level decoupled flow affect the overlying orographic cloud?
Three different methodologies were used to examine this problem. The first method involved analysis of one and a half months of precipitation and wind data from a 24-station mesonetwork located in the Yampa River valley and surrounding mountains of northwest Colorado during the winter of 1981/1982 as part of the third Colorado Orographic Seeding Experiment (COSE III). The second method was a case study analysis of two orographic storms using data from an instrumented cloud physics aircraft to supplement the data from the mesonetwork. The third method involved two-dimensional numerical simulations using Colorado State University's Regional Atmospheric Modeling System (RAMS).
The results show that the presence of extensive low-level decoupled flow causes part of the orographic lift of the mountain barrier to be experienced upstream of the barrier. This changes the location of condensate production which in turn shifts precipitation upstream and appears to enhance the precipitation efficiency for the entire barrier.
Abstract
Mountains often act as barriers to low-level flow creating regions of stagnant, decoupled flow within thermally stratified air masses. This paper addresses the question: how does a region of low-level decoupled flow affect the overlying orographic cloud?
Three different methodologies were used to examine this problem. The first method involved analysis of one and a half months of precipitation and wind data from a 24-station mesonetwork located in the Yampa River valley and surrounding mountains of northwest Colorado during the winter of 1981/1982 as part of the third Colorado Orographic Seeding Experiment (COSE III). The second method was a case study analysis of two orographic storms using data from an instrumented cloud physics aircraft to supplement the data from the mesonetwork. The third method involved two-dimensional numerical simulations using Colorado State University's Regional Atmospheric Modeling System (RAMS).
The results show that the presence of extensive low-level decoupled flow causes part of the orographic lift of the mountain barrier to be experienced upstream of the barrier. This changes the location of condensate production which in turn shifts precipitation upstream and appears to enhance the precipitation efficiency for the entire barrier.
Abstract
No abstract available.
Abstract
No abstract available.
Arid and semiarid rangelands comprise a significant portion of the earth's land surface. Yet little is known about the effects of temporal and spatial changes in surface soil moisture on the hydrologic cycle, energy balance, and the feedbacks to the atmosphere via thermal forcing over such environments. Understanding this interrelationship is crucial for evaluating the role of the hydrologic cycle in surface–atmosphere interactions.
This study focuses on the utility of remote sensing to provide measurements of surface soil moisture, surface albedo, vegetation biomass, and temperature at different spatial and temporal scales. Remote-sensing measurements may provide the only practical means of estimating some of the more important factors controlling land surface processes over large areas. Consequently, the use of remotely sensed information in biophysical and geophysical models greatly enhances their ability to compute fluxes at catchment and regional scales on a routine basis. However, model calculations for different climates and ecosystems need verification. This requires that the remotely sensed data and model computations be evaluated with ground-truth data collected at the same areal scales.
The present study (MONSOON 90) attempts to address this issue for semiarid rangelands. The experimental plan included remotely sensed data in the visible, near-infrared, thermal, and microwave wavelengths from ground and aircraft platforms and, when available, from satellites. Collected concurrently were ground measurements of soil moisture and temperature, energy and water fluxes, and profile data in the atmospheric boundary layer in a hydrologically instrumented semiarid rangeland watershed. Field experiments were conducted in 1990 during the dry and wet or “monsoon season” for the southwestern United States. A detailed description of the field campaigns, including measurements and some preliminary results are given.
Arid and semiarid rangelands comprise a significant portion of the earth's land surface. Yet little is known about the effects of temporal and spatial changes in surface soil moisture on the hydrologic cycle, energy balance, and the feedbacks to the atmosphere via thermal forcing over such environments. Understanding this interrelationship is crucial for evaluating the role of the hydrologic cycle in surface–atmosphere interactions.
This study focuses on the utility of remote sensing to provide measurements of surface soil moisture, surface albedo, vegetation biomass, and temperature at different spatial and temporal scales. Remote-sensing measurements may provide the only practical means of estimating some of the more important factors controlling land surface processes over large areas. Consequently, the use of remotely sensed information in biophysical and geophysical models greatly enhances their ability to compute fluxes at catchment and regional scales on a routine basis. However, model calculations for different climates and ecosystems need verification. This requires that the remotely sensed data and model computations be evaluated with ground-truth data collected at the same areal scales.
The present study (MONSOON 90) attempts to address this issue for semiarid rangelands. The experimental plan included remotely sensed data in the visible, near-infrared, thermal, and microwave wavelengths from ground and aircraft platforms and, when available, from satellites. Collected concurrently were ground measurements of soil moisture and temperature, energy and water fluxes, and profile data in the atmospheric boundary layer in a hydrologically instrumented semiarid rangeland watershed. Field experiments were conducted in 1990 during the dry and wet or “monsoon season” for the southwestern United States. A detailed description of the field campaigns, including measurements and some preliminary results are given.
Abstract
The Chequamegon Heterogeneous Ecosystem Energy-Balance Study Enabled by a High-Density Extensive Array of Detectors 2019 (CHEESEHEAD19) is an ongoing National Science Foundation project based on an intensive field campaign that occurred from June to October 2019. The purpose of the study is to examine how the atmospheric boundary layer (ABL) responds to spatial heterogeneity in surface energy fluxes. One of the main objectives is to test whether lack of energy balance closure measured by eddy covariance (EC) towers is related to mesoscale atmospheric processes. Finally, the project evaluates data-driven methods for scaling surface energy fluxes, with the aim to improve model–data comparison and integration. To address these questions, an extensive suite of ground, tower, profiling, and airborne instrumentation was deployed over a 10 km × 10 km domain of a heterogeneous forest ecosystem in the Chequamegon–Nicolet National Forest in northern Wisconsin, United States, centered on an existing 447-m tower that anchors an AmeriFlux/NOAA supersite (US-PFa/WLEF). The project deployed one of the world’s highest-density networks of above-canopy EC measurements of surface energy fluxes. This tower EC network was coupled with spatial measurements of EC fluxes from aircraft; maps of leaf and canopy properties derived from airborne spectroscopy, ground-based measurements of plant productivity, phenology, and physiology; and atmospheric profiles of wind, water vapor, and temperature using radar, sodar, lidar, microwave radiometers, infrared interferometers, and radiosondes. These observations are being used with large-eddy simulation and scaling experiments to better understand submesoscale processes and improve formulations of subgrid-scale processes in numerical weather and climate models.
Abstract
The Chequamegon Heterogeneous Ecosystem Energy-Balance Study Enabled by a High-Density Extensive Array of Detectors 2019 (CHEESEHEAD19) is an ongoing National Science Foundation project based on an intensive field campaign that occurred from June to October 2019. The purpose of the study is to examine how the atmospheric boundary layer (ABL) responds to spatial heterogeneity in surface energy fluxes. One of the main objectives is to test whether lack of energy balance closure measured by eddy covariance (EC) towers is related to mesoscale atmospheric processes. Finally, the project evaluates data-driven methods for scaling surface energy fluxes, with the aim to improve model–data comparison and integration. To address these questions, an extensive suite of ground, tower, profiling, and airborne instrumentation was deployed over a 10 km × 10 km domain of a heterogeneous forest ecosystem in the Chequamegon–Nicolet National Forest in northern Wisconsin, United States, centered on an existing 447-m tower that anchors an AmeriFlux/NOAA supersite (US-PFa/WLEF). The project deployed one of the world’s highest-density networks of above-canopy EC measurements of surface energy fluxes. This tower EC network was coupled with spatial measurements of EC fluxes from aircraft; maps of leaf and canopy properties derived from airborne spectroscopy, ground-based measurements of plant productivity, phenology, and physiology; and atmospheric profiles of wind, water vapor, and temperature using radar, sodar, lidar, microwave radiometers, infrared interferometers, and radiosondes. These observations are being used with large-eddy simulation and scaling experiments to better understand submesoscale processes and improve formulations of subgrid-scale processes in numerical weather and climate models.
