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- Author or Editor: R. M. HOLMES x
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Abstract
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Abstract
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Abstract
The influence of mesoscale features (e.g., irrigation projects, desert regions, patches of forest, cities, etc.) on the atmosphere is difficult to determine unless the sensors are very numerous or highly mobile. An instrumented aircraft system permits such measurements and was used to determine the influence of lakes and reservoirs, irrigation, a group of forested hills, a small city, and an area of (dry land) nonirrigated agricultural land on the vertical and horizontal characteristics of the lowest layer of the atmosphere. Studies were conducted over portions of southern Alberta, and southern Idaho. Strong sensible heat advection was found to cause high evaporation from a small lake with the formation of a cool air layer which extended well beyond the lee side of the lake. The flux of water vapor over irrigated land was essentially double that over surrounding nonirrigated areas. A small city produced a heat island which delayed development of a temperature inversion for up to 9 h.
Abstract
The influence of mesoscale features (e.g., irrigation projects, desert regions, patches of forest, cities, etc.) on the atmosphere is difficult to determine unless the sensors are very numerous or highly mobile. An instrumented aircraft system permits such measurements and was used to determine the influence of lakes and reservoirs, irrigation, a group of forested hills, a small city, and an area of (dry land) nonirrigated agricultural land on the vertical and horizontal characteristics of the lowest layer of the atmosphere. Studies were conducted over portions of southern Alberta, and southern Idaho. Strong sensible heat advection was found to cause high evaporation from a small lake with the formation of a cool air layer which extended well beyond the lee side of the lake. The flux of water vapor over irrigated land was essentially double that over surrounding nonirrigated areas. A small city produced a heat island which delayed development of a temperature inversion for up to 9 h.
Abstract
Three chinook situations which occurred in southern Alberta during the winter of 1967–68 were studied using an instrumented aircraft. On the days of observation, local areas experienced warm air penetration toward the surface. On 29 October 1967, severe turbulence and significant warming neat Rolling Hills, Alberta, marked the occurrence. On 18 January 1968, warm air intrusion was found from three large isolated areas of melting snow near Brooks. On 3 February 1968, a shallow layer of cold air covered the southern prairies, with a marked temperature inversion at 50 m above the surface. Local wavelike intrusions of the warm air occurred near Calgary on this day, which was one day previous to the general invasion of warm air from the south.
The available data, while somewhat incomplete, were subjected to analysis according to a modified Scorer equation to test for atmospheric and/or topographic inducement of the wave motions observed. Neither method of analysis was completely successful. More detailed and accurate observations of atmospheric motions by aircraft are required.
Abstract
Three chinook situations which occurred in southern Alberta during the winter of 1967–68 were studied using an instrumented aircraft. On the days of observation, local areas experienced warm air penetration toward the surface. On 29 October 1967, severe turbulence and significant warming neat Rolling Hills, Alberta, marked the occurrence. On 18 January 1968, warm air intrusion was found from three large isolated areas of melting snow near Brooks. On 3 February 1968, a shallow layer of cold air covered the southern prairies, with a marked temperature inversion at 50 m above the surface. Local wavelike intrusions of the warm air occurred near Calgary on this day, which was one day previous to the general invasion of warm air from the south.
The available data, while somewhat incomplete, were subjected to analysis according to a modified Scorer equation to test for atmospheric and/or topographic inducement of the wave motions observed. Neither method of analysis was completely successful. More detailed and accurate observations of atmospheric motions by aircraft are required.
Abstract
Most meteorological soil moisture budgets do not account for soil moisture stress changes in the drying cycle or for changes in ground cover or expanding root system. A simple modulated technique is described which considers these factors. Soil moisture stress determined by this technique has a significantly higher correlation with wheat yield than does moisture stress determined by a common method.
Abstract
Most meteorological soil moisture budgets do not account for soil moisture stress changes in the drying cycle or for changes in ground cover or expanding root system. A simple modulated technique is described which considers these factors. Soil moisture stress determined by this technique has a significantly higher correlation with wheat yield than does moisture stress determined by a common method.
Abstract
No Abstract Available.
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No Abstract Available.
Abstract
The diapycnal motion in the stratified ocean near a sloping bottom boundary is studied using analytical solutions from one-dimensional boundary layer theory. Bottom-intensification of the diapycnal mixing intensity ensures that in the stratified mixing layer (SML), where isopycnals are relatively flat, the diapycnal motion is downward toward denser fluid. In contrast, convergence of the diffusive buoyancy flux near the seafloor drives diapycnal upwelling in what we define as the bottom boundary layer (BBL). Much of the one-dimensional BBL is characterized by a stratification only slightly reduced from that in the SML because the maximum in the buoyancy flux at the top of the BBL, where the diapycnal velocity changes sign, must occur in well-stratified fluid. The diapycnal upwelling in the BBL is determined by variations not only in the magnitude of the buoyancy gradient but also in the curvature of isopycnals. The net diapycnal upwelling is concentrated in the bottom half of the BBL where the magnitude of the buoyancy gradient changes most rapidly. The curvature effect drives upwelling near the seafloor that only makes a significant contribution to the net upwelling for steep slopes. The structure of the diapycnal velocity in this stratified BBL differs from the case of a turbulent well-mixed BBL that has been assumed in some recent theoretical studies on bottom-intensified mixing. This work therefore extends recent theories in a way that should be more applicable to abyssal ocean observations where well-mixed BBLs are not common.
Abstract
The diapycnal motion in the stratified ocean near a sloping bottom boundary is studied using analytical solutions from one-dimensional boundary layer theory. Bottom-intensification of the diapycnal mixing intensity ensures that in the stratified mixing layer (SML), where isopycnals are relatively flat, the diapycnal motion is downward toward denser fluid. In contrast, convergence of the diffusive buoyancy flux near the seafloor drives diapycnal upwelling in what we define as the bottom boundary layer (BBL). Much of the one-dimensional BBL is characterized by a stratification only slightly reduced from that in the SML because the maximum in the buoyancy flux at the top of the BBL, where the diapycnal velocity changes sign, must occur in well-stratified fluid. The diapycnal upwelling in the BBL is determined by variations not only in the magnitude of the buoyancy gradient but also in the curvature of isopycnals. The net diapycnal upwelling is concentrated in the bottom half of the BBL where the magnitude of the buoyancy gradient changes most rapidly. The curvature effect drives upwelling near the seafloor that only makes a significant contribution to the net upwelling for steep slopes. The structure of the diapycnal velocity in this stratified BBL differs from the case of a turbulent well-mixed BBL that has been assumed in some recent theoretical studies on bottom-intensified mixing. This work therefore extends recent theories in a way that should be more applicable to abyssal ocean observations where well-mixed BBLs are not common.
Abstract
Small-scale turbulent mixing in the upper Equatorial Undercurrent (EUC) of the eastern Pacific cold tongue is a critical component of the SST budget that drives variations in SST on a range of time scales. Recent observations have shown that turbulent mixing within the EUC is modulated by tropical instability waves (TIWs). A regional ocean model is used to investigate the mechanisms through which large-scale TIW circulation modulates the small-scale shear, stratification, and shear-driven turbulence in the EUC. Eulerian analyses of time series taken from both the model and the Tropical Atmosphere Ocean (TAO) array suggest that increases in the zonal shear of the EUC drive increased mixing on the leading edge of the TIW warm phase. A Lagrangian vorticity analysis attributes this increased zonal shear to horizontal vortex stretching driven by the strain in the TIW horizontal velocity field acting on the existing EUC shear. To investigate the impact of horizontal vortex stretching on the turbulent heat flux averaged over a TIW period the effects of periodic TIW strain are included as forcing in a simple 1D mixing model of the EUC. Model runs with TIW forcing show turbulent heat fluxes up to 30% larger than runs without TIW forcing, with the magnitude of the increase being sensitive to the vertical mixing scheme used in the model. These results emphasize the importance of coupling between the large-scale circulation and small-scale turbulence in the equatorial regions, with implications for the SST budget of the equatorial Pacific.
Abstract
Small-scale turbulent mixing in the upper Equatorial Undercurrent (EUC) of the eastern Pacific cold tongue is a critical component of the SST budget that drives variations in SST on a range of time scales. Recent observations have shown that turbulent mixing within the EUC is modulated by tropical instability waves (TIWs). A regional ocean model is used to investigate the mechanisms through which large-scale TIW circulation modulates the small-scale shear, stratification, and shear-driven turbulence in the EUC. Eulerian analyses of time series taken from both the model and the Tropical Atmosphere Ocean (TAO) array suggest that increases in the zonal shear of the EUC drive increased mixing on the leading edge of the TIW warm phase. A Lagrangian vorticity analysis attributes this increased zonal shear to horizontal vortex stretching driven by the strain in the TIW horizontal velocity field acting on the existing EUC shear. To investigate the impact of horizontal vortex stretching on the turbulent heat flux averaged over a TIW period the effects of periodic TIW strain are included as forcing in a simple 1D mixing model of the EUC. Model runs with TIW forcing show turbulent heat fluxes up to 30% larger than runs without TIW forcing, with the magnitude of the increase being sensitive to the vertical mixing scheme used in the model. These results emphasize the importance of coupling between the large-scale circulation and small-scale turbulence in the equatorial regions, with implications for the SST budget of the equatorial Pacific.
Abstract
Tropical instability waves (TIWs) and equatorial Kelvin waves are dominant sources of intraseasonal variability in the equatorial Pacific Ocean, and both play important roles in the heat and momentum budgets of the large-scale flow. While individually they have been well studied, little is known about how these two features interact, although satellite observations suggest that TIW propagation speed and amplitude are modulated by Kelvin waves. Here, the influence of Kelvin waves on TIW kinetic energy (TIWKE) is examined using an ensemble set of 1/4° ocean model simulations of the equatorial Pacific Ocean. The results suggest that TIWKE can be significantly modified by 60-day Kelvin waves. To leading order, TIWs derive kinetic energy from the meridional shear and available potential energy of the background zonal currents, while losing TIWKE to friction and the radiation of waves. The passage of Kelvin waves disrupts this balance. Downwelling (upwelling) Kelvin waves induce decay (growth) in TIWKE through modifications to the background currents and the TIWs’ Reynolds stresses. These modulations in TIWKE affect eddy heat fluxes and the downward radiation of waves, with implications for the variability of SST and the energetics of abyssal flows in the eastern equatorial Pacific.
Abstract
Tropical instability waves (TIWs) and equatorial Kelvin waves are dominant sources of intraseasonal variability in the equatorial Pacific Ocean, and both play important roles in the heat and momentum budgets of the large-scale flow. While individually they have been well studied, little is known about how these two features interact, although satellite observations suggest that TIW propagation speed and amplitude are modulated by Kelvin waves. Here, the influence of Kelvin waves on TIW kinetic energy (TIWKE) is examined using an ensemble set of 1/4° ocean model simulations of the equatorial Pacific Ocean. The results suggest that TIWKE can be significantly modified by 60-day Kelvin waves. To leading order, TIWs derive kinetic energy from the meridional shear and available potential energy of the background zonal currents, while losing TIWKE to friction and the radiation of waves. The passage of Kelvin waves disrupts this balance. Downwelling (upwelling) Kelvin waves induce decay (growth) in TIWKE through modifications to the background currents and the TIWs’ Reynolds stresses. These modulations in TIWKE affect eddy heat fluxes and the downward radiation of waves, with implications for the variability of SST and the energetics of abyssal flows in the eastern equatorial Pacific.
Abstract
A vertical anemometer of the propeller type is described. The instrument is sensitive and economical and output is acceptable to most zero-center millivolt recorders. The voltage output reverses in polarity when the direction of rotation reverses (updrafts or downdrafts).
Abstract
A vertical anemometer of the propeller type is described. The instrument is sensitive and economical and output is acceptable to most zero-center millivolt recorders. The voltage output reverses in polarity when the direction of rotation reverses (updrafts or downdrafts).
Abstract
Anthropogenically induced radiative imbalances in the climate system lead to a slow accumulation of heat in the ocean. This warming is often obscured by natural modes of climate variability such as El Niño–Southern Oscillation (ENSO), which drive substantial ocean temperature changes as a function of depth and latitude. The use of watermass coordinates has been proposed to help isolate forced signals and filter out fast adiabatic processes associated with modes of variability. However, how much natural modes of variability project into these different coordinate systems has not been quantified. Here we apply a rigorous framework to quantify ocean temperature variability using both a quasi-Lagrangian, watermass-based temperature coordinate and Eulerian depth and latitude coordinates in a free-running climate model under preindustrial conditions. The temperature-based coordinate removes the adiabatic component of ENSO-dominated interannual variability by definition, but a substantial diabatic signal remains. At slower (decadal to centennial) frequencies, variability in the temperature- and depth-based coordinates is comparable. Spectral analysis of temperature tendencies reveals the dominance of advective processes in latitude and depth coordinates while the variability in temperature coordinates is related closely to the surface forcing. Diabatic mixing processes play an important role at slower frequencies where quasi-steady-state balances emerge between forcing and mixing in temperature, advection and mixing in depth, and forcing and advection in latitude. While watermass-based analyses highlight diabatic effects by removing adiabatic variability, our work shows that natural variability has a strong diabatic component and cannot be ignored in the analysis of long-term trends.
Significance Statement
Quantifying the ocean warming associated with anthropogenically induced radiative imbalances in the climate system can be challenging due to the superposition with modes of internal climate variability such as El Niño. One method proposed to address this issue is the analysis of temperature changes in fluid-following (or “watermass”) coordinates that filter out fast adiabatic processes associated with these modes of variability. In this study we compare a watermass-based analysis with more traditional analyses of temperature changes at fixed depth and latitude to show that even natural modes of climate variability exhibit a substantial signal in watermass coordinates, particularly at decadal and slower frequencies. This natural variability must be taken into account when analyzing long-term temperature trends in the ocean.
Abstract
Anthropogenically induced radiative imbalances in the climate system lead to a slow accumulation of heat in the ocean. This warming is often obscured by natural modes of climate variability such as El Niño–Southern Oscillation (ENSO), which drive substantial ocean temperature changes as a function of depth and latitude. The use of watermass coordinates has been proposed to help isolate forced signals and filter out fast adiabatic processes associated with modes of variability. However, how much natural modes of variability project into these different coordinate systems has not been quantified. Here we apply a rigorous framework to quantify ocean temperature variability using both a quasi-Lagrangian, watermass-based temperature coordinate and Eulerian depth and latitude coordinates in a free-running climate model under preindustrial conditions. The temperature-based coordinate removes the adiabatic component of ENSO-dominated interannual variability by definition, but a substantial diabatic signal remains. At slower (decadal to centennial) frequencies, variability in the temperature- and depth-based coordinates is comparable. Spectral analysis of temperature tendencies reveals the dominance of advective processes in latitude and depth coordinates while the variability in temperature coordinates is related closely to the surface forcing. Diabatic mixing processes play an important role at slower frequencies where quasi-steady-state balances emerge between forcing and mixing in temperature, advection and mixing in depth, and forcing and advection in latitude. While watermass-based analyses highlight diabatic effects by removing adiabatic variability, our work shows that natural variability has a strong diabatic component and cannot be ignored in the analysis of long-term trends.
Significance Statement
Quantifying the ocean warming associated with anthropogenically induced radiative imbalances in the climate system can be challenging due to the superposition with modes of internal climate variability such as El Niño. One method proposed to address this issue is the analysis of temperature changes in fluid-following (or “watermass”) coordinates that filter out fast adiabatic processes associated with these modes of variability. In this study we compare a watermass-based analysis with more traditional analyses of temperature changes at fixed depth and latitude to show that even natural modes of climate variability exhibit a substantial signal in watermass coordinates, particularly at decadal and slower frequencies. This natural variability must be taken into account when analyzing long-term temperature trends in the ocean.
