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- Author or Editor: Robert R. Gillies x
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Abstract
Wavelet multiresolution analysis was used to examine the variation in dominant length scales determined from remotely sensed airborne- and satellite-derived surface energy flux data. The wavelet cospectra are computed between surface radiometric temperature, fractional vegetation, and derived energy fluxes at airborne (12 m) and Advanced Very High Resolution Radiometer (AVHRR) (1000 m) resolutions. Length scale analysis of high-resolution data shows that small-scale variability in temperature dominates over other effects. Analysis of coarse-resolution data shows that small-scale variations in vegetation are important, although the large-scale variation in radiometric temperature dominates the derived fluxes. This is determined to be a result of the fact that, at smaller scales, the incoming solar radiation effect is muted by the small-scale variability in vegetation, temperature, and albedo, whereas at coarser scales, the large-scale effect of incoming radiation on temperature dominates over the smaller-scale features in surface variability.
Abstract
Wavelet multiresolution analysis was used to examine the variation in dominant length scales determined from remotely sensed airborne- and satellite-derived surface energy flux data. The wavelet cospectra are computed between surface radiometric temperature, fractional vegetation, and derived energy fluxes at airborne (12 m) and Advanced Very High Resolution Radiometer (AVHRR) (1000 m) resolutions. Length scale analysis of high-resolution data shows that small-scale variability in temperature dominates over other effects. Analysis of coarse-resolution data shows that small-scale variations in vegetation are important, although the large-scale variation in radiometric temperature dominates the derived fluxes. This is determined to be a result of the fact that, at smaller scales, the incoming solar radiation effect is muted by the small-scale variability in vegetation, temperature, and albedo, whereas at coarser scales, the large-scale effect of incoming radiation on temperature dominates over the smaller-scale features in surface variability.
Abstract
This study outlines a method for the estimation of regional patterns of surface moisture availability (M 0) and fractional vegetation (Fr) in the presence of spatially variable vegetation cover. The method requires relating variations in satellite-derived (NOAA, Advanced Very High Resolution Radiometer) surface radiant temperature to a vegetation index (computed from satellite visible and near-infrared data) while coupling this association to an inverse modeling scheme. More than merely furnishing surface soil moisture values, the method constitutes a new conceptual and practical approach for combining thermal infrared and vegetation index measurements for incorporating the derived values of M 0 into hydrologic and atmospheric prediction models.
Application of the technique is demonstrated for a region in and around the city of Newcastle upon Tyne situated in the northeast of England. A regional estimate of M 0 is derived and is probably good for fractional vegetation cover up to 80% before errors in the estimated soil water content become unacceptably large. Moreover, a normalization scheme is suggested from which a nomogram, “universal triangle,” is constructed and is seen to fit the observed data well. The universal triangle also simplifies the inclusion of remotely derived M 0 in hydrology and meteorological models and is perhaps a practicable step toward integrating derived data from satellite measurements in weather forecasting.
Abstract
This study outlines a method for the estimation of regional patterns of surface moisture availability (M 0) and fractional vegetation (Fr) in the presence of spatially variable vegetation cover. The method requires relating variations in satellite-derived (NOAA, Advanced Very High Resolution Radiometer) surface radiant temperature to a vegetation index (computed from satellite visible and near-infrared data) while coupling this association to an inverse modeling scheme. More than merely furnishing surface soil moisture values, the method constitutes a new conceptual and practical approach for combining thermal infrared and vegetation index measurements for incorporating the derived values of M 0 into hydrologic and atmospheric prediction models.
Application of the technique is demonstrated for a region in and around the city of Newcastle upon Tyne situated in the northeast of England. A regional estimate of M 0 is derived and is probably good for fractional vegetation cover up to 80% before errors in the estimated soil water content become unacceptably large. Moreover, a normalization scheme is suggested from which a nomogram, “universal triangle,” is constructed and is seen to fit the observed data well. The universal triangle also simplifies the inclusion of remotely derived M 0 in hydrology and meteorological models and is perhaps a practicable step toward integrating derived data from satellite measurements in weather forecasting.
Abstract
Persistent winter inversions result in poor air quality in the Intermountain West of the United States. Although the onset of an inversion is relatively easy to predict, the duration and the subsequent breakup of a persistent inversion event remains a forecasting challenge. For this reason and for this region, historic soundings were analyzed for Salt Lake City, Utah, with reanalysis and station data to investigate how persistent inversion events are modulated by synoptic and intraseasonal variabilities. The results point to a close linkage between persistent inversions and the dominant intraseasonal (30 day) mode that characterizes the winter circulation regime over the Pacific Northwest. Meteorological variables and pollution (e.g., particulate matter of ≤2.5-μm diameter, PM2.5) revealed coherent variations with this intraseasonal mode. The intraseasonal mode also modulates the characteristics of the synoptic (6 day) variability and further influences the duration of persistent inversions in the Intermountain West. The interaction between modes suggests that a complete forecast of persistent inversions is more involved and technically beyond numerical weather prediction models intended for the medium range (∼10 day). Therefore, to predict persistent inversions, the results point to the adoption of standard medium-range forecasts with a longer-term climate diagnostic approach.
Abstract
Persistent winter inversions result in poor air quality in the Intermountain West of the United States. Although the onset of an inversion is relatively easy to predict, the duration and the subsequent breakup of a persistent inversion event remains a forecasting challenge. For this reason and for this region, historic soundings were analyzed for Salt Lake City, Utah, with reanalysis and station data to investigate how persistent inversion events are modulated by synoptic and intraseasonal variabilities. The results point to a close linkage between persistent inversions and the dominant intraseasonal (30 day) mode that characterizes the winter circulation regime over the Pacific Northwest. Meteorological variables and pollution (e.g., particulate matter of ≤2.5-μm diameter, PM2.5) revealed coherent variations with this intraseasonal mode. The intraseasonal mode also modulates the characteristics of the synoptic (6 day) variability and further influences the duration of persistent inversions in the Intermountain West. The interaction between modes suggests that a complete forecast of persistent inversions is more involved and technically beyond numerical weather prediction models intended for the medium range (∼10 day). Therefore, to predict persistent inversions, the results point to the adoption of standard medium-range forecasts with a longer-term climate diagnostic approach.
Abstract
Previous studies have indicated a widespread decline in snowpack over Utah accompanied by a decline in the snow–precipitation ratio while anecdotal evidence claims have been put forward that measured changes in Utah’s snowpack are spurious and do not reflect actual change. Using two distinct lines of investigation, this paper further analyzes the winter precipitation regime in the state of Utah. First, by means of observation-based, gridded daily temperature, precipitation, and remotely sensed data, as well as utilizing a climatological rain–snow threshold (RST) temperature method, the precipitation regime of Utah was scrutinized. Second, a comprehensive synoptic analysis was conducted as an alternate means that is independent from surface observations. It was found that the proportion of winter (January–March) precipitation falling as snow has decreased by 9% during the last half century, a combined result from a significant increase in rainfall and a minor decrease in snowfall. Meanwhile, observed snow depth across Utah has decreased and is accompanied by consistent decreases in snow cover and surface albedo. Weather systems with the potential to produce precipitation in Utah have decreased in number with those producing snowfall decreasing at a considerably greater rate. Further circulation analysis showed that an anomalous anticyclone has developed over western North America, which acts to reduce the frequency of cyclone waves impacting Utah. Combined with the increased precipitation, this feature suggests that the average precipitation per event has intensified with more of it falling as rain than as snow. Trends in the hydroclimate such as these have implications for present and future regional water policy in the state of Utah.
Abstract
Previous studies have indicated a widespread decline in snowpack over Utah accompanied by a decline in the snow–precipitation ratio while anecdotal evidence claims have been put forward that measured changes in Utah’s snowpack are spurious and do not reflect actual change. Using two distinct lines of investigation, this paper further analyzes the winter precipitation regime in the state of Utah. First, by means of observation-based, gridded daily temperature, precipitation, and remotely sensed data, as well as utilizing a climatological rain–snow threshold (RST) temperature method, the precipitation regime of Utah was scrutinized. Second, a comprehensive synoptic analysis was conducted as an alternate means that is independent from surface observations. It was found that the proportion of winter (January–March) precipitation falling as snow has decreased by 9% during the last half century, a combined result from a significant increase in rainfall and a minor decrease in snowfall. Meanwhile, observed snow depth across Utah has decreased and is accompanied by consistent decreases in snow cover and surface albedo. Weather systems with the potential to produce precipitation in Utah have decreased in number with those producing snowfall decreasing at a considerably greater rate. Further circulation analysis showed that an anomalous anticyclone has developed over western North America, which acts to reduce the frequency of cyclone waves impacting Utah. Combined with the increased precipitation, this feature suggests that the average precipitation per event has intensified with more of it falling as rain than as snow. Trends in the hydroclimate such as these have implications for present and future regional water policy in the state of Utah.
Abstract
This study investigates the meteorological conditions associated with multidecadal drought cycles as revealed by lake level fluctuation of the Great Salt Lake (GSL). The analysis combined instrumental, proxy, and simulation datasets, including the Twentieth Century Reanalysis version 2, the North American Drought Atlas, and a 2000-yr control simulation of the GFDL Coupled Model, version 2.1 (CM2.1). Statistical evidence from the spectral coherence analysis points to a phase shift amounting to 6–9 yr between the wet–dry cycles in the Great Basin and the warm–cool phases of the interdecadal Pacific oscillation (IPO). Diagnoses of the sea surface temperature and atmospheric circulation anomalies attribute such a phase shift to a distinctive teleconnection wave train that develops during the transition points between the IPO’s warm and cool phases. This teleconnection wave train forms recurrent circulation anomalies centered over the southeastern Gulf of Alaska; this directs moisture flux across the Great Basin and subsequently drives wet–dry conditions over the Great Basin and the GSL watershed. The IPO life cycle therefore modulates local droughts–pluvials in a quarter-phase manner.
Abstract
This study investigates the meteorological conditions associated with multidecadal drought cycles as revealed by lake level fluctuation of the Great Salt Lake (GSL). The analysis combined instrumental, proxy, and simulation datasets, including the Twentieth Century Reanalysis version 2, the North American Drought Atlas, and a 2000-yr control simulation of the GFDL Coupled Model, version 2.1 (CM2.1). Statistical evidence from the spectral coherence analysis points to a phase shift amounting to 6–9 yr between the wet–dry cycles in the Great Basin and the warm–cool phases of the interdecadal Pacific oscillation (IPO). Diagnoses of the sea surface temperature and atmospheric circulation anomalies attribute such a phase shift to a distinctive teleconnection wave train that develops during the transition points between the IPO’s warm and cool phases. This teleconnection wave train forms recurrent circulation anomalies centered over the southeastern Gulf of Alaska; this directs moisture flux across the Great Basin and subsequently drives wet–dry conditions over the Great Basin and the GSL watershed. The IPO life cycle therefore modulates local droughts–pluvials in a quarter-phase manner.
Abstract
A 10-yr record of PM2.5 (particulate matter of aerodynamic diameter ≤ 2.5 μm), collected in Cache Valley near downtown Logan, Utah, reveals a strong peak in the PM2.5 concentration climatology that is tightly localized in mid-January. The cause of this subseasonal variation in the PM2.5 climatology is investigated through dynamical downscaling and large-scale diagnostics. Climatological analysis of the U.S. winter mean ridge reveals a mid-January subseasonal shift in the zonal direction, likely in response to variations in the Rossby wave source over the central North Pacific Ocean. This displacement of the winter mean ridge, in turn, has an impact on regional-scale atmospheric conditions—specifically, subsidence with local leeside enhancements and midlevel warming over Cache Valley. The analyses of this study indicate that the subseasonal peak of long-term mean PM2.5 concentrations in Cache Valley is linked to the large-scale circulations’ subseasonal evolution, which involves remote forcing in the circumpolar circulations as well as possible tropical–midlatitude interactions. This subseasonal evolution of the winter mean circulation also affects precipitation along the West Coast.
Abstract
A 10-yr record of PM2.5 (particulate matter of aerodynamic diameter ≤ 2.5 μm), collected in Cache Valley near downtown Logan, Utah, reveals a strong peak in the PM2.5 concentration climatology that is tightly localized in mid-January. The cause of this subseasonal variation in the PM2.5 climatology is investigated through dynamical downscaling and large-scale diagnostics. Climatological analysis of the U.S. winter mean ridge reveals a mid-January subseasonal shift in the zonal direction, likely in response to variations in the Rossby wave source over the central North Pacific Ocean. This displacement of the winter mean ridge, in turn, has an impact on regional-scale atmospheric conditions—specifically, subsidence with local leeside enhancements and midlevel warming over Cache Valley. The analyses of this study indicate that the subseasonal peak of long-term mean PM2.5 concentrations in Cache Valley is linked to the large-scale circulations’ subseasonal evolution, which involves remote forcing in the circumpolar circulations as well as possible tropical–midlatitude interactions. This subseasonal evolution of the winter mean circulation also affects precipitation along the West Coast.
Abstract
Because of the geography of a narrow valley and surrounding tall mountains, Cache Valley (located in northern Utah and southern Idaho) experiences frequent shallow temperature inversions that are both intense and persistent. Such temperature inversions have resulted in the worst air quality in the nation. In this paper, the historical properties of Cache Valley’s winter inversions are examined by using two meteorological stations with a difference in elevation of approximately 100 m and a horizontal distance apart of ~4.5 km. Differences in daily maximum air temperature between two stations were used to define the frequency and intensity of inversions. Despite the lack of a long-term trend in inversion intensity from 1956 to present, the inversion frequency increased in the early 1980s and extending into the early 1990s but thereafter decreased by about 30% through 2013. Daily mean air temperatures and inversion intensity were categorized further using a mosaic plot. Of relevance was the discovery that after 1990 there was an increase in the probability of inversions during cold days and that under conditions in which the daily mean air temperature was below −15°C an inversion became a certainty. A regression model was developed to estimate the concentration of past particulate matter of aerodynamic diameter ≤ 2.5 μm (PM2.5). The model indicated past episodes of increased PM2.5 concentrations that went into decline after 1990; this was especially so in the coldest of climate conditions.
Abstract
Because of the geography of a narrow valley and surrounding tall mountains, Cache Valley (located in northern Utah and southern Idaho) experiences frequent shallow temperature inversions that are both intense and persistent. Such temperature inversions have resulted in the worst air quality in the nation. In this paper, the historical properties of Cache Valley’s winter inversions are examined by using two meteorological stations with a difference in elevation of approximately 100 m and a horizontal distance apart of ~4.5 km. Differences in daily maximum air temperature between two stations were used to define the frequency and intensity of inversions. Despite the lack of a long-term trend in inversion intensity from 1956 to present, the inversion frequency increased in the early 1980s and extending into the early 1990s but thereafter decreased by about 30% through 2013. Daily mean air temperatures and inversion intensity were categorized further using a mosaic plot. Of relevance was the discovery that after 1990 there was an increase in the probability of inversions during cold days and that under conditions in which the daily mean air temperature was below −15°C an inversion became a certainty. A regression model was developed to estimate the concentration of past particulate matter of aerodynamic diameter ≤ 2.5 μm (PM2.5). The model indicated past episodes of increased PM2.5 concentrations that went into decline after 1990; this was especially so in the coldest of climate conditions.
Abstract
The lake level elevation of the Great Salt Lake (GSL), a large closed basin lake in the arid western United States, is characterized by a pronounced quasi-decadal oscillation (QDO). The variation of the GSL elevation is very coherent with the QDO of sea surface temperature anomalies in the tropical central Pacific (also known as the Pacific QDO). However, such coherence denies any direct association between the precipitation in the GSL watershed and the Pacific QDO because, in a given frequency, the precipitation variation always leads the GSL elevation variation. Therefore, the precipitation variation is phase shifted from the Pacific QDO. This study investigates the physical mechanism forming the coherence between the GSL elevation and the Pacific QDO. Pronounced and coherent quasi-decadal signals in precipitation, streamflow, water vapor flux, and drought conditions are found throughout the Great Basin. Recurrent atmospheric circulation patterns develop over the Gulf of Alaska during the warm-to-cool and cool-to-warm transition phases of the Pacific QDO. These circulation patterns modulate the water vapor flux associated with synoptic transient activities over the western United States and, in turn, lead to the QDO in the hydrological cycle of the Great Basin. As the GSL integrates the hydrological responses in the Great Basin, the hydrological QDO is then transferred to the GSL elevation. Because the GSL elevation consistently lags the precipitation by a quarter-phase (about 3 yr in the quasi-decadal time scale), these processes take an average of 6 yr for the GSL elevation to eventually respond to the Pacific QDO. This creates a half-phase delay of the GSL elevation from the Pacific QDO, thereby forming the inverse, yet coherent, relationship between them. Tree-ring reconstructed precipitation records confirm that the quasi-decadal signal in precipitation is a prominent feature in this region.
Abstract
The lake level elevation of the Great Salt Lake (GSL), a large closed basin lake in the arid western United States, is characterized by a pronounced quasi-decadal oscillation (QDO). The variation of the GSL elevation is very coherent with the QDO of sea surface temperature anomalies in the tropical central Pacific (also known as the Pacific QDO). However, such coherence denies any direct association between the precipitation in the GSL watershed and the Pacific QDO because, in a given frequency, the precipitation variation always leads the GSL elevation variation. Therefore, the precipitation variation is phase shifted from the Pacific QDO. This study investigates the physical mechanism forming the coherence between the GSL elevation and the Pacific QDO. Pronounced and coherent quasi-decadal signals in precipitation, streamflow, water vapor flux, and drought conditions are found throughout the Great Basin. Recurrent atmospheric circulation patterns develop over the Gulf of Alaska during the warm-to-cool and cool-to-warm transition phases of the Pacific QDO. These circulation patterns modulate the water vapor flux associated with synoptic transient activities over the western United States and, in turn, lead to the QDO in the hydrological cycle of the Great Basin. As the GSL integrates the hydrological responses in the Great Basin, the hydrological QDO is then transferred to the GSL elevation. Because the GSL elevation consistently lags the precipitation by a quarter-phase (about 3 yr in the quasi-decadal time scale), these processes take an average of 6 yr for the GSL elevation to eventually respond to the Pacific QDO. This creates a half-phase delay of the GSL elevation from the Pacific QDO, thereby forming the inverse, yet coherent, relationship between them. Tree-ring reconstructed precipitation records confirm that the quasi-decadal signal in precipitation is a prominent feature in this region.
Abstract
A recent study identified a pronounced lagged relationship between the Great Salt Lake’s (GSL) elevation and the central tropical Pacific sea surface temperatures (SST) at the 10–15-year time scale. Using this relationship, a principal component analysis of historical time series of SST and local precipitation (P) was used in the construction of a lagged regression model to predict first the GSL elevation tendency and, from there, the GSL elevation. The combined principal component–lagged regression model was able to replicate and forecast turnarounds in the GSL elevation—that is, where prolonged increasing trends were followed by persistent decreases and vice versa. The coupling of the two time series is somewhat different from previous nonparametric, nonlinear time series methods developed for shorter-term (1–2 year) forecasts of the GSL volume. Moreover, by not accounting for interannual variability in the model, a forecast out to 6 years was feasible and was shown to intersect the 2009 and 2010 observations of the GSL elevation.
Abstract
A recent study identified a pronounced lagged relationship between the Great Salt Lake’s (GSL) elevation and the central tropical Pacific sea surface temperatures (SST) at the 10–15-year time scale. Using this relationship, a principal component analysis of historical time series of SST and local precipitation (P) was used in the construction of a lagged regression model to predict first the GSL elevation tendency and, from there, the GSL elevation. The combined principal component–lagged regression model was able to replicate and forecast turnarounds in the GSL elevation—that is, where prolonged increasing trends were followed by persistent decreases and vice versa. The coupling of the two time series is somewhat different from previous nonparametric, nonlinear time series methods developed for shorter-term (1–2 year) forecasts of the GSL volume. Moreover, by not accounting for interannual variability in the model, a forecast out to 6 years was feasible and was shown to intersect the 2009 and 2010 observations of the GSL elevation.
Abstract
The 2013 federal Colorado River Basin Water Supply and Demand Study projected the water imbalance between future supply and demand to increase. The Colorado water supply (WS) exemplifies a pronounced quasi-decadal oscillation (QDO) of 10–20 years throughout its historical record; however, this QDO feature is unaccounted for in the climate models used to project the future WS. Adjacent to the Colorado River, the large watershed of the Great Salt Lake (GSL) in Utah records the hydrologic QDO signal in its water surface, leading previous studies to explore the cause of decadal fluctuations in the lake elevation and assess predictability. This study reports a remarkable coherence between the Colorado WS and the GSL elevation at the 10–20-yr time scale. Analysis of precipitation and terrestrial water storage anomalies suggests a cross-basin connection in the climate and hydrometeorological variations of the Colorado WS and the GSL. The 160-yr-long and well-kept GSL elevation record makes it an effective indicator for the Colorado WS.
Abstract
The 2013 federal Colorado River Basin Water Supply and Demand Study projected the water imbalance between future supply and demand to increase. The Colorado water supply (WS) exemplifies a pronounced quasi-decadal oscillation (QDO) of 10–20 years throughout its historical record; however, this QDO feature is unaccounted for in the climate models used to project the future WS. Adjacent to the Colorado River, the large watershed of the Great Salt Lake (GSL) in Utah records the hydrologic QDO signal in its water surface, leading previous studies to explore the cause of decadal fluctuations in the lake elevation and assess predictability. This study reports a remarkable coherence between the Colorado WS and the GSL elevation at the 10–20-yr time scale. Analysis of precipitation and terrestrial water storage anomalies suggests a cross-basin connection in the climate and hydrometeorological variations of the Colorado WS and the GSL. The 160-yr-long and well-kept GSL elevation record makes it an effective indicator for the Colorado WS.
