Search

Search Results

• 11. [Article] Estimating the economic net returns of Oregon & Washington forests with regard to climate change

  Little work has been conducted regarding the net returns of forest lands. The Ricardian model is ripe with potential to estimate the effects of climate on net returns to forestry. Multiple linear regression ...

  Citation × Citation Citation Abstract Copy Title: Estimating the economic net returns of Oregon & Washington forests with regard to climate change Author: Johnson, Zoe I. Little work has been conducted regarding the net returns of forest lands. The Ricardian model is ripe with potential to estimate the effects of climate on net returns to forestry. Multiple linear regression allows each climate variable to measure its effect of net returns with the assumption of all other factors being fixed. Independent variables of average temperature (°C), average temperature squared (°C²), average precipitation (mm), average precipitation squared (mm2), maximum August temperature (°C), and minimum December temperature (°C) were scaled by year using dummy variables to output the dependent variable of real net returns (USD 2010) per county of tree species. This OLS linear regression showed annual precipitation, marginal precipitation, and maximum temperature experienced by forests to affect the net returns they produced. Increased precipitation is expected to increase net returns to forests while higher maximum temperatures will negatively impact net returns in Douglas Fir regions and positively affect pine regions. Precipitation is linearly related to forest net returns, while temperature is not linearly related. With this finding, various areas of Oregon and Washington that are expected to experience heavier precipitation due to climate change should expect more net returns from their forestlands. Title: Estimating the economic net returns of Oregon & Washington forests with regard to climate change Author: Johnson, Zoe I. Little work has been conducted regarding the net returns of forest lands. The Ricardian model is ripe with potential to estimate the effects of climate on net returns to forestry. Multiple linear regression allows each climate variable to measure its effect of net returns with the assumption of all other factors being fixed. Independent variables of average temperature (°C), average temperature squared (°C²), average precipitation (mm), average precipitation squared (mm2), maximum August temperature (°C), and minimum December temperature (°C) were scaled by year using dummy variables to output the dependent variable of real net returns (USD 2010) per county of tree species. This OLS linear regression showed annual precipitation, marginal precipitation, and maximum temperature experienced by forests to affect the net returns they produced. Increased precipitation is expected to increase net returns to forests while higher maximum temperatures will negatively impact net returns in Douglas Fir regions and positively affect pine regions. Precipitation is linearly related to forest net returns, while temperature is not linearly related. With this finding, various areas of Oregon and Washington that are expected to experience heavier precipitation due to climate change should expect more net returns from their forestlands. Close

• 12. [Article] Characterizing Rain/snow Partitioning in Mountain Watersheds for Present-day and Future Projected Climates

  Presented at The Oregon Water Conference, May 24-25, 2011, Corvallis, OR.

  Citation × Citation Citation Abstract Copy Title: Characterizing Rain/snow Partitioning in Mountain Watersheds for Present-day and Future Projected Climates Author: Sproles, Eric A., Nolin, Anne W. Presented at The Oregon Water Conference, May 24-25, 2011, Corvallis, OR. Title: Characterizing Rain/snow Partitioning in Mountain Watersheds for Present-day and Future Projected Climates Author: Sproles, Eric A., Nolin, Anne W. Presented at The Oregon Water Conference, May 24-25, 2011, Corvallis, OR. Close

• 13. [Article] Intraseasonal Variability of the West African Monsoon and Atlantic ITCZ

  Intraseasonal variability of boreal summer rainfall and winds in tropical West Africa and the east Atlantic is examined using daily Tropical Rainfall Measuring Mission (TRMM) precipitation and the NCEP–NCAR ...

  Citation × Citation Citation Abstract Copy Title: Intraseasonal Variability of the West African Monsoon and Atlantic ITCZ Author: Maloney, Eric D., Shaman, Jeffrey Intraseasonal variability of boreal summer rainfall and winds in tropical West Africa and the east Atlantic is examined using daily Tropical Rainfall Measuring Mission (TRMM) precipitation and the NCEP–NCAR reanalysis during 1998–2006. Intraseasonal precipitation variability is dominated by two significant spectral peaks at time scales near 15 and 50 days, accompanied by corresponding peaks in eddy kinetic energy (EKE) and eddy enstrophy. Regional precipitation variability on 30–90-day time scales is significantly correlated (+0.6) with a global Madden–Julian oscillation time series based on equatorial zonal winds, supporting the results of A. J. Matthews. The overall amplitude of the 30–90-day West African monsoon precipitation variability during a given summer, however, does not appear to be strongly regulated by interannual variability in MJO amplitude. Composite analysis and complex empirical orthogonal function analysis shows that 30–90-day precipitation anomalies are generally zonally elongated, grow and decay in place, and have maximum amplitude near the Gulf of Guinea and in the Atlantic ITCZ. Composite 30–90-day enhanced precipitation events are accompanied by a significant suppression of eastern North Atlantic trade winds. Suppressed 30–90-day precipitation events are associated with an enhancement of the Atlantic trade winds. Enhanced (suppressed) EKE occurs just to the north of the east Atlantic ITCZ during positive (negative) 30–90-day precipitation events, with the maximum EKE magnitude lagging precipitation events by about 5 days. East Atlantic tropical cyclone activity is significantly modulated on intraseasonal time scales. The number of tropical cyclones that occur in the Atlantic’s main development region to the east of 60°W is suppressed about 5–10 days before maxima in a regional intraseasonal precipitation time series, and enhanced about 5–10 days after time series maxima. An analysis of east Atlantic tropical cyclone activity based on an equatorial MJO index produces similar results. Consistent with the results of K. C. Mo, variations in vertical shear may help explain this modulation of tropical cyclone activity. Title: Intraseasonal Variability of the West African Monsoon and Atlantic ITCZ Author: Maloney, Eric D., Shaman, Jeffrey Intraseasonal variability of boreal summer rainfall and winds in tropical West Africa and the east Atlantic is examined using daily Tropical Rainfall Measuring Mission (TRMM) precipitation and the NCEP–NCAR reanalysis during 1998–2006. Intraseasonal precipitation variability is dominated by two significant spectral peaks at time scales near 15 and 50 days, accompanied by corresponding peaks in eddy kinetic energy (EKE) and eddy enstrophy. Regional precipitation variability on 30–90-day time scales is significantly correlated (+0.6) with a global Madden–Julian oscillation time series based on equatorial zonal winds, supporting the results of A. J. Matthews. The overall amplitude of the 30–90-day West African monsoon precipitation variability during a given summer, however, does not appear to be strongly regulated by interannual variability in MJO amplitude. Composite analysis and complex empirical orthogonal function analysis shows that 30–90-day precipitation anomalies are generally zonally elongated, grow and decay in place, and have maximum amplitude near the Gulf of Guinea and in the Atlantic ITCZ. Composite 30–90-day enhanced precipitation events are accompanied by a significant suppression of eastern North Atlantic trade winds. Suppressed 30–90-day precipitation events are associated with an enhancement of the Atlantic trade winds. Enhanced (suppressed) EKE occurs just to the north of the east Atlantic ITCZ during positive (negative) 30–90-day precipitation events, with the maximum EKE magnitude lagging precipitation events by about 5 days. East Atlantic tropical cyclone activity is significantly modulated on intraseasonal time scales. The number of tropical cyclones that occur in the Atlantic’s main development region to the east of 60°W is suppressed about 5–10 days before maxima in a regional intraseasonal precipitation time series, and enhanced about 5–10 days after time series maxima. An analysis of east Atlantic tropical cyclone activity based on an equatorial MJO index produces similar results. Consistent with the results of K. C. Mo, variations in vertical shear may help explain this modulation of tropical cyclone activity. Close

• 14. [Article] The relationship of precipitation in the western United States to variations in the outgoing long-wave radiation field over the tropical Pacific : the role of the mid-latitude circulation

  The relationship between the outgoing long-wave radiation (OLR) field over the tropical Pacific and wintertime monthly precipitation for the western U. S. is investigated, using the mid-latitude upper-air ...

  Citation × Citation Citation Abstract Copy Title: The relationship of precipitation in the western United States to variations in the outgoing long-wave radiation field over the tropical Pacific : the role of the mid-latitude circulation Author: Twining, David S. The relationship between the outgoing long-wave radiation (OLR) field over the tropical Pacific and wintertime monthly precipitation for the western U. S. is investigated, using the mid-latitude upper-air circulation as an intermediary. Principal components (PC's) of the 500mb monthly averaged height field over the NE Pacific and western North America are compared with those of the monthly tropical Pacific OLR field. It is found that, of the first 6 PC's of the height field, five are correlated significantly with the first 3 OLR field PC's at lags of between two and six months. Canonical correlations between the two sets of PC's are greatest at a lag of four months and are highly significant. When stratified by different levels of the OLR field PC's, the separations between means of the height field PC's are highly significant as well. Differing distributions of the height field PC ensemble are also found to be associated with different OLR field PC levels. The relationship between the 500mb height field and concurrent western district precipitation is examined. Using a hybrid model including both linear statistical and non-linear physical components it is found that considerably more of the variance in the precipitation can be explained by that of the height field alone than when the precipitation is inferred directly from a linear statistical model. A set of reconstructed height field PC's is predicted from OLR values based on the height field/OLR stratification associations compiled for a period separate from that of the forecast. Applied to the precipitation model, this results in predicted western district precipitation which is better correlated with the observations than is the equivalent precipitation forecast from the linear statistical relationship of precipitation to the Southern Oscillation Index. Title: The relationship of precipitation in the western United States to variations in the outgoing long-wave radiation field over the tropical Pacific : the role of the mid-latitude circulation Author: Twining, David S. The relationship between the outgoing long-wave radiation (OLR) field over the tropical Pacific and wintertime monthly precipitation for the western U. S. is investigated, using the mid-latitude upper-air circulation as an intermediary. Principal components (PC's) of the 500mb monthly averaged height field over the NE Pacific and western North America are compared with those of the monthly tropical Pacific OLR field. It is found that, of the first 6 PC's of the height field, five are correlated significantly with the first 3 OLR field PC's at lags of between two and six months. Canonical correlations between the two sets of PC's are greatest at a lag of four months and are highly significant. When stratified by different levels of the OLR field PC's, the separations between means of the height field PC's are highly significant as well. Differing distributions of the height field PC ensemble are also found to be associated with different OLR field PC levels. The relationship between the 500mb height field and concurrent western district precipitation is examined. Using a hybrid model including both linear statistical and non-linear physical components it is found that considerably more of the variance in the precipitation can be explained by that of the height field alone than when the precipitation is inferred directly from a linear statistical model. A set of reconstructed height field PC's is predicted from OLR values based on the height field/OLR stratification associations compiled for a period separate from that of the forecast. Applied to the precipitation model, this results in predicted western district precipitation which is better correlated with the observations than is the equivalent precipitation forecast from the linear statistical relationship of precipitation to the Southern Oscillation Index. Close

• 15. [Article] Construction of a model organism for performing calcium carbonate precipitation in a porous media reactor

  Aquifers are an important storage location and source of fresh groundwater. They may become polluted by a number of contaminants including mobile divalent radionuclides such as strontium-90 which is a ...

  Citation × Citation Citation Abstract Copy Title: Construction of a model organism for performing calcium carbonate precipitation in a porous media reactor Author: Kaufman, Megan J. Aquifers are an important storage location and source of fresh groundwater. They may become polluted by a number of contaminants including mobile divalent radionuclides such as strontium-90 which is a byproduct of uranium fission. A method for remediating such divalent radionuclides is sequestration through co-precipitation into calcium carbonate. Calcium carbonate precipitation occurs naturally but can be enhanced by the use of ureolytic microorganisms living within the aquifer. The microbial enzyme urease cleaves ammonia from urea (added as a stimulant to the aquifer) increasing the pH and subsequently pushing the bicarbonate equilibrium towards precipitation. Laboratory experimentation is necessary to better predict field scale outcomes of remediation that is driven by ureolytic calcium carbonate co-precipitation. To aid in such laboratory experiments, I constructed two ureolytic organisms which contain green fluorescent protein (GFP) so that the location of the microbes in relation to media flow paths and precipitation can be viewed by microscopy in a 2- dimensional porous medium flow cell reactor. The reactor was operated with a parallel flow regime where the two influent media would not promote microbially induced calcium carbonate precipitation until they were mixed in the flow cell. A demonstration study compared the results of parallel flow and mixing in the reactor operated with and without one of the GFP-containing ureolytic organisms. The growth and precipitation of calcium carbonate within the reactor pore space altered flow paths to promote a wider mixing zone and a more widely distributed overall calcium carbonate precipitation pattern. This study will allow optimization of remediation efforts of contaminants such as strontium-90 in aquifers. Title: Construction of a model organism for performing calcium carbonate precipitation in a porous media reactor Author: Kaufman, Megan J. Aquifers are an important storage location and source of fresh groundwater. They may become polluted by a number of contaminants including mobile divalent radionuclides such as strontium-90 which is a byproduct of uranium fission. A method for remediating such divalent radionuclides is sequestration through co-precipitation into calcium carbonate. Calcium carbonate precipitation occurs naturally but can be enhanced by the use of ureolytic microorganisms living within the aquifer. The microbial enzyme urease cleaves ammonia from urea (added as a stimulant to the aquifer) increasing the pH and subsequently pushing the bicarbonate equilibrium towards precipitation. Laboratory experimentation is necessary to better predict field scale outcomes of remediation that is driven by ureolytic calcium carbonate co-precipitation. To aid in such laboratory experiments, I constructed two ureolytic organisms which contain green fluorescent protein (GFP) so that the location of the microbes in relation to media flow paths and precipitation can be viewed by microscopy in a 2- dimensional porous medium flow cell reactor. The reactor was operated with a parallel flow regime where the two influent media would not promote microbially induced calcium carbonate precipitation until they were mixed in the flow cell. A demonstration study compared the results of parallel flow and mixing in the reactor operated with and without one of the GFP-containing ureolytic organisms. The growth and precipitation of calcium carbonate within the reactor pore space altered flow paths to promote a wider mixing zone and a more widely distributed overall calcium carbonate precipitation pattern. This study will allow optimization of remediation efforts of contaminants such as strontium-90 in aquifers. Close

• 16. [Article] Precipitation efficiency derived from isotope ratios in water vapor distinguishes dynamical and microphysical influences on subtropical atmospheric constituents

  This is the publisher’s final pdf. The article is copyrighted by American Geophysical Union and published by John Wiley & Sons, Inc. It can be found at: http://agupubs.onlinelibrary.wiley.com/agu/jgr/j...

  Citation × Citation Citation Abstract Copy Title: Precipitation efficiency derived from isotope ratios in water vapor distinguishes dynamical and microphysical influences on subtropical atmospheric constituents Author: Bailey, A., Nusbaumer, J., Noone, D. This is the publisher’s final pdf. The article is copyrighted by American Geophysical Union and published by John Wiley & Sons, Inc. It can be found at: http://agupubs.onlinelibrary.wiley.com/agu/jgr/journal/10.1002/%28ISSN%292169-8996/ Title: Precipitation efficiency derived from isotope ratios in water vapor distinguishes dynamical and microphysical influences on subtropical atmospheric constituents Author: Bailey, A., Nusbaumer, J., Noone, D. This is the publisher’s final pdf. The article is copyrighted by American Geophysical Union and published by John Wiley & Sons, Inc. It can be found at: http://agupubs.onlinelibrary.wiley.com/agu/jgr/journal/10.1002/%28ISSN%292169-8996/ Close

• 17. [Article] Evaluation of a probabilistic quantitative precipitation forecasting experiment

  Forecasts of the likelihood of occurrence of various amounts of precipitation are very important, since excessive precipitation amounts over relatively short time periods can have adverse effects on public ...

  Citation × Citation Citation Abstract Copy Title: Evaluation of a probabilistic quantitative precipitation forecasting experiment Author: Hsu, Wu-ron Forecasts of the likelihood of occurrence of various amounts of precipitation are very important, since excessive precipitation amounts over relatively short time periods can have adverse effects on public safety and economic efficiency, As a result, forecasters at the National Weather Service Forecast Office in San Antonio, Texas were asked to formulate subjective probabilistic quantitative precipitation forecasts on an experimental basis beginning in February 1981. This study describes methods of evaluating probability forecasts of this ordinal variable and presents some results of the first year of the experiment. Scalar and vector evaluation procedures are described. In the case of scalar evaluation, the inclusion of a no-skill line and a no-correlation line on reliability diagrams is helpful in representing the skill, reliability, and resolution qeometrically in two-state situations. Geometrical interpretations of attributes of forecasts can also be accomplished in three-state situations based on vector evaluation procedures. A skill score for subsample forecasts is shown to be useful in identifying systematic errors made by forecasters or forecast systems. A beta model is developed to obtain a forecaster's predictive distributions (i.e., the distribution of use of probability values). The experimental results show that the skill of the subjective forecasts is generally higher than the skill of objective guidance forecasts for measurable precipitation (i.e., precipitation amounts exceeding a threshold of 0.01 inches), but that the opposite is true for threshold associated with larger precipitation amounts. This result is due primarily to the forecaster's tendency to over forecast for the events associated with higher precipitation thresholds. The tendency to over forecast is most pronounced in the nighttime forecasts and in the forecasts for drier stations. The MCS objective guidance forecasts, on the other hand, are quite reliable for both periods and all stations. The vector evaluation approach indicates that the degree of overforecasting is quite high for bimodal forecasts and that the skill contribution from bimodal forecasts is negative in many cases. Title: Evaluation of a probabilistic quantitative precipitation forecasting experiment Author: Hsu, Wu-ron Forecasts of the likelihood of occurrence of various amounts of precipitation are very important, since excessive precipitation amounts over relatively short time periods can have adverse effects on public safety and economic efficiency, As a result, forecasters at the National Weather Service Forecast Office in San Antonio, Texas were asked to formulate subjective probabilistic quantitative precipitation forecasts on an experimental basis beginning in February 1981. This study describes methods of evaluating probability forecasts of this ordinal variable and presents some results of the first year of the experiment. Scalar and vector evaluation procedures are described. In the case of scalar evaluation, the inclusion of a no-skill line and a no-correlation line on reliability diagrams is helpful in representing the skill, reliability, and resolution qeometrically in two-state situations. Geometrical interpretations of attributes of forecasts can also be accomplished in three-state situations based on vector evaluation procedures. A skill score for subsample forecasts is shown to be useful in identifying systematic errors made by forecasters or forecast systems. A beta model is developed to obtain a forecaster's predictive distributions (i.e., the distribution of use of probability values). The experimental results show that the skill of the subjective forecasts is generally higher than the skill of objective guidance forecasts for measurable precipitation (i.e., precipitation amounts exceeding a threshold of 0.01 inches), but that the opposite is true for threshold associated with larger precipitation amounts. This result is due primarily to the forecaster's tendency to over forecast for the events associated with higher precipitation thresholds. The tendency to over forecast is most pronounced in the nighttime forecasts and in the forecasts for drier stations. The MCS objective guidance forecasts, on the other hand, are quite reliable for both periods and all stations. The vector evaluation approach indicates that the degree of overforecasting is quite high for bimodal forecasts and that the skill contribution from bimodal forecasts is negative in many cases. Close

• 18. [Article] Projected temperature and precipitation changes for Corvallis and Los Angeles for the 2030-2059 period using the Hadley Center's regional climate model (HadRM3P).

  Average monthly temperatures (maximum and minimum) and precipitation patterns are expected to change as a direct consequence of anthropogenic climate change. Temperatures are expected to be warmer in the ...

  Citation × Citation Citation Abstract Copy Title: Projected temperature and precipitation changes for Corvallis and Los Angeles for the 2030-2059 period using the Hadley Center's regional climate model (HadRM3P). Author: Cheema, Karandeep Singh Average monthly temperatures (maximum and minimum) and precipitation patterns are expected to change as a direct consequence of anthropogenic climate change. Temperatures are expected to be warmer in the future but precise estimates vary depending on factors like number of ensembles and emission scenario. For this study, we used 100 ensembles to simulate a recent historical period (Dec. 1985-Nov 2014) and a future climate scenario (Dec. 2030-Nov. 2059) for two cities: Corvallis, OR and Los Angeles, CA. Atmospheric forcings followed the RCP 4.5 scenario. We used results from the simulations to compare temperature and precipitation changes between the two periods for both cities. Average monthly temperatures (maximum and minimum) increased for both cities. Both cities would experience an increase in number of days above 90 °F (14 for Corvallis and 18 more days for Los Angeles). For Corvallis, average annual temperature increased from 12.8 ± 0.3°? to 14.4 ± 0.3 °?. Average annual precipitation increased from 942.0 mm to 994.0 mm (p-value: 10−23). Likewise, for Los Angeles, average annual temperature increased from 18.1 ± 0.3°? to 19.5 ± 0.3 °? and average annual precipitation changed from 265.0 mm to 260.0 mm (p-value: 0.32). We further analyzed changes in precipitation in terms of changes in frequency and intensity. Frequency and intensity of precipitation increased in winter months for Corvallis while non-uniform patterns were seen for Los Angeles. Summer precipitation decreased in terms of frequency and intensity of precipitation events for both cities. Title: Projected temperature and precipitation changes for Corvallis and Los Angeles for the 2030-2059 period using the Hadley Center's regional climate model (HadRM3P). Author: Cheema, Karandeep Singh Average monthly temperatures (maximum and minimum) and precipitation patterns are expected to change as a direct consequence of anthropogenic climate change. Temperatures are expected to be warmer in the future but precise estimates vary depending on factors like number of ensembles and emission scenario. For this study, we used 100 ensembles to simulate a recent historical period (Dec. 1985-Nov 2014) and a future climate scenario (Dec. 2030-Nov. 2059) for two cities: Corvallis, OR and Los Angeles, CA. Atmospheric forcings followed the RCP 4.5 scenario. We used results from the simulations to compare temperature and precipitation changes between the two periods for both cities. Average monthly temperatures (maximum and minimum) increased for both cities. Both cities would experience an increase in number of days above 90 °F (14 for Corvallis and 18 more days for Los Angeles). For Corvallis, average annual temperature increased from 12.8 ± 0.3°? to 14.4 ± 0.3 °?. Average annual precipitation increased from 942.0 mm to 994.0 mm (p-value: 10−23). Likewise, for Los Angeles, average annual temperature increased from 18.1 ± 0.3°? to 19.5 ± 0.3 °? and average annual precipitation changed from 265.0 mm to 260.0 mm (p-value: 0.32). We further analyzed changes in precipitation in terms of changes in frequency and intensity. Frequency and intensity of precipitation increased in winter months for Corvallis while non-uniform patterns were seen for Los Angeles. Summer precipitation decreased in terms of frequency and intensity of precipitation events for both cities. Close

• 19. [Article] Statistical relationships between the mesoscale organization of convection, precipitation and the large-scale wind fields during the GATE

  Data from the GARP Atlantic Tropical Experiment (GATE) was analysed in an exploratory manner to discover the characteristics of mesoscale organization of convection and it's relationship to large-scale ...

  Citation × Citation Citation Abstract Copy Title: Statistical relationships between the mesoscale organization of convection, precipitation and the large-scale wind fields during the GATE Author: De Silva, Sirilath J. Data from the GARP Atlantic Tropical Experiment (GATE) was analysed in an exploratory manner to discover the characteristics of mesoscale organization of convection and it's relationship to large-scale wind profiles. Automated methods were developed to identify the convective cells and their linear organization. These automated methods use a median high-pass filter to identify enhanced cells and a simple pattern recognition technique to ascertain the linear organization between them. Due to the simplified nature of the algorithm, the whole data set of the 21 day period from the phase 3 of GATE was processed in an economical manner obtaining a large data base which was used in the investigation of clusters and other associated phenomena. The mesoscale organization of convective cells and the widespread areas of lighter precipitation associated with them showed expected characteristics and compared satisfactorily with previous results. A large fraction of the rainfall (64%) fell from the widespread area. The total precipitation had a correlation of 0.94 with the fractional area of the widespread and a correlation of 0.89 with the fractional area of the clusters. The widespread precipitation had a correlation index of 0.97 with it's fractional area and the cluster precipitation had a strong linear relationship to it's area with a correlation of 0.99. These factors argue well for the parameterization of rainfall rate in tropical regions to a high accuracy by the area covered by organized convective cells and widespread areas. It was also seen that there was a good correlation with the number of clusters and number of cores with the total precipitation rate in a given area. These factors create a strong argument for identifying mesoscale systems consisting of convective cells and widespread precipitation as basic units of precipitation in tropical regions, having a characteristic life cycle of their own. The widespread and total precipitation showed very good correlation with upper-level vertical motion. Clusters tended to align parallel with the horizontal low-level wind shear and the degree of alignment appears to depend on the strength of the wind shear. Title: Statistical relationships between the mesoscale organization of convection, precipitation and the large-scale wind fields during the GATE Author: De Silva, Sirilath J. Data from the GARP Atlantic Tropical Experiment (GATE) was analysed in an exploratory manner to discover the characteristics of mesoscale organization of convection and it's relationship to large-scale wind profiles. Automated methods were developed to identify the convective cells and their linear organization. These automated methods use a median high-pass filter to identify enhanced cells and a simple pattern recognition technique to ascertain the linear organization between them. Due to the simplified nature of the algorithm, the whole data set of the 21 day period from the phase 3 of GATE was processed in an economical manner obtaining a large data base which was used in the investigation of clusters and other associated phenomena. The mesoscale organization of convective cells and the widespread areas of lighter precipitation associated with them showed expected characteristics and compared satisfactorily with previous results. A large fraction of the rainfall (64%) fell from the widespread area. The total precipitation had a correlation of 0.94 with the fractional area of the widespread and a correlation of 0.89 with the fractional area of the clusters. The widespread precipitation had a correlation index of 0.97 with it's fractional area and the cluster precipitation had a strong linear relationship to it's area with a correlation of 0.99. These factors argue well for the parameterization of rainfall rate in tropical regions to a high accuracy by the area covered by organized convective cells and widespread areas. It was also seen that there was a good correlation with the number of clusters and number of cores with the total precipitation rate in a given area. These factors create a strong argument for identifying mesoscale systems consisting of convective cells and widespread precipitation as basic units of precipitation in tropical regions, having a characteristic life cycle of their own. The widespread and total precipitation showed very good correlation with upper-level vertical motion. Clusters tended to align parallel with the horizontal low-level wind shear and the degree of alignment appears to depend on the strength of the wind shear. Close

• 20. [Article] Long-term effects of changes in vegetation condition, precipitation and watershed parameters on summer low-flows in the semi-arid Pacific Northwest

  Summer low-flow behavior in the semi-arid areas of the Pacific Northwest was studied. Long-term data from thirty-eight streams/rivers and thirty-six precipitation stations was exploited. The study area ...

  Citation × Citation Citation Abstract Copy Title: Long-term effects of changes in vegetation condition, precipitation and watershed parameters on summer low-flows in the semi-arid Pacific Northwest Author: Zeb, Aurang Summer low-flow behavior in the semi-arid areas of the Pacific Northwest was studied. Long-term data from thirty-eight streams/rivers and thirty-six precipitation stations was exploited. The study area was divided into five zones based on annual average precipitation. Trends and patterns in summer low-flows and precipitation were identified. Different zones showed different trends and patterns in precipitation over the period of record but significant similarities within each zone. Most of the summer low-flow and precipitation records showed that the 1930's and the late 1980's to early 1990's experienced major droughts. A possible return interval of 50-60 years appeared reasonable for similar major droughts in the study area. Spring, summer and fall precipitation, on average, were found insignificantly related to the summer low-flows, except for northern Idaho and southeastern Oregon where summer precipitation was significant in explaining the summer low-flow trends. Winter and annual precipitation were found significantly related to summer low-flows. But the zonal equations constructed to predict summer low-flows using precipitation alone were considered unsuitable for practical use. Zonal and regional recession models to forecast summer stream flows with significant accuracies were constructed successfully. Extreme summer low-flows were not significantly related to different watershed cover types in eastern Oregon. However, percentage of rangelands appeared to be more related to the extreme summer low-flow than other cover types. An extreme summer low-flow prediction model was constructed using several watershed and precipitation variables. Many of these variables were found to be significantly related to extreme summer low-flow. Watershed average width and annual minimum precipitation explained 71% of the variations in the extreme summer low-flow. The model finally selected, with the inclusion of watershed end point elevation, was able to explain 79% of the variability in the extreme summer low-flow. Stream and precipitation gauges need to be carefully maintained during dry periods. Also, generalization of climatic trends based on a few observations in a large region can be misleading. Title: Long-term effects of changes in vegetation condition, precipitation and watershed parameters on summer low-flows in the semi-arid Pacific Northwest Author: Zeb, Aurang Summer low-flow behavior in the semi-arid areas of the Pacific Northwest was studied. Long-term data from thirty-eight streams/rivers and thirty-six precipitation stations was exploited. The study area was divided into five zones based on annual average precipitation. Trends and patterns in summer low-flows and precipitation were identified. Different zones showed different trends and patterns in precipitation over the period of record but significant similarities within each zone. Most of the summer low-flow and precipitation records showed that the 1930's and the late 1980's to early 1990's experienced major droughts. A possible return interval of 50-60 years appeared reasonable for similar major droughts in the study area. Spring, summer and fall precipitation, on average, were found insignificantly related to the summer low-flows, except for northern Idaho and southeastern Oregon where summer precipitation was significant in explaining the summer low-flow trends. Winter and annual precipitation were found significantly related to summer low-flows. But the zonal equations constructed to predict summer low-flows using precipitation alone were considered unsuitable for practical use. Zonal and regional recession models to forecast summer stream flows with significant accuracies were constructed successfully. Extreme summer low-flows were not significantly related to different watershed cover types in eastern Oregon. However, percentage of rangelands appeared to be more related to the extreme summer low-flow than other cover types. An extreme summer low-flow prediction model was constructed using several watershed and precipitation variables. Many of these variables were found to be significantly related to extreme summer low-flow. Watershed average width and annual minimum precipitation explained 71% of the variations in the extreme summer low-flow. The model finally selected, with the inclusion of watershed end point elevation, was able to explain 79% of the variability in the extreme summer low-flow. Stream and precipitation gauges need to be carefully maintained during dry periods. Also, generalization of climatic trends based on a few observations in a large region can be misleading. Close