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Abstract
The relative contributions of locally evapotranspired (i.e., recycled) moisture versus externally advected water vapor for the growing-season precipitation of the U.S. Corn Belt and surrounding areas (1.23 × 106 km2) are estimated in this paper. Four May–August seasons with highly contrasting precipitation and crop yields (1975, 1976, 1979, and 1988) are investigated. A simple recycling equation—developed from the traditional atmospheric moisture budget and involving regional evapotranspiration and atmospheric water vapor inflow—is applied on daily, monthly, and seasonal time scales. Several atmospheric moisture budget components {moisture flux divergence [MFD], storage change [or change in precipitable water (dPW)], and inflow [IF]} are evaluated for 24-h periods using standard finite difference and line integral methods applied to objectively analyzed U.S. and Canadian rawinsonde data (50-hPa vertical resolution, surface to 300 hPa) for 0000 and 1200 UTC. Daily area-averaged precipitation (P) totals are derived from approximately 600 evenly distributed (but ungridded) recording rain gauges. Evapotranspiration (E) is estimated as the residual of the moisture budget equation for 24-h periods; values compare favorably with the few existing observations.
Traditional budget results show the following: E is weakly related to P on monthly and seasonal time scales; there is surprising interannual constancy of seasonal E cycles and averages given the large variation in resulting crop yields; and monthly and seasonal variability of the export of the E − P surplus is determined largely by the horizontal velocity divergence component of MFD. New recycling analyses suggest that the contribution of local E to P (i.e., P E/P) is relatively small and remarkably consistent (largely 0.19–0.24) for monthly and seasonal periods, despite large P and crop yield variations. However, the monthly/seasonal averaging process is found to completely mask a striking decrease of daily P E/P (from approximately 0.30 to 0.15) with increasing P from 0 to 8 mm day−1. Unique and detailed analyses of P-stratified daily moisture budget results provide key insights into apparent contradictions between daily and monthly/seasonal recycling and related results and concomitant interannual variability, especially for the very dry 1988 season. Interpretation is facilitated by the use of modeled daily global radiation values, measured (instantaneous) and modeled (monthly) soil moisture, United States Department of Agriculture (USDA) crop yield estimates, and satellite normalized difference vegetation index (NDVI) imagery. This paper shows that land–atmosphere interactions are intimately involved in pronounced seasonal climate anomalies for the world's richest agricultural region, but apparently with considerable complexity that includes plant behavior, solar radiation forcing, and challenging time-scale interrelations.
Abstract
The relative contributions of locally evapotranspired (i.e., recycled) moisture versus externally advected water vapor for the growing-season precipitation of the U.S. Corn Belt and surrounding areas (1.23 × 106 km2) are estimated in this paper. Four May–August seasons with highly contrasting precipitation and crop yields (1975, 1976, 1979, and 1988) are investigated. A simple recycling equation—developed from the traditional atmospheric moisture budget and involving regional evapotranspiration and atmospheric water vapor inflow—is applied on daily, monthly, and seasonal time scales. Several atmospheric moisture budget components {moisture flux divergence [MFD], storage change [or change in precipitable water (dPW)], and inflow [IF]} are evaluated for 24-h periods using standard finite difference and line integral methods applied to objectively analyzed U.S. and Canadian rawinsonde data (50-hPa vertical resolution, surface to 300 hPa) for 0000 and 1200 UTC. Daily area-averaged precipitation (P) totals are derived from approximately 600 evenly distributed (but ungridded) recording rain gauges. Evapotranspiration (E) is estimated as the residual of the moisture budget equation for 24-h periods; values compare favorably with the few existing observations.
Traditional budget results show the following: E is weakly related to P on monthly and seasonal time scales; there is surprising interannual constancy of seasonal E cycles and averages given the large variation in resulting crop yields; and monthly and seasonal variability of the export of the E − P surplus is determined largely by the horizontal velocity divergence component of MFD. New recycling analyses suggest that the contribution of local E to P (i.e., P E/P) is relatively small and remarkably consistent (largely 0.19–0.24) for monthly and seasonal periods, despite large P and crop yield variations. However, the monthly/seasonal averaging process is found to completely mask a striking decrease of daily P E/P (from approximately 0.30 to 0.15) with increasing P from 0 to 8 mm day−1. Unique and detailed analyses of P-stratified daily moisture budget results provide key insights into apparent contradictions between daily and monthly/seasonal recycling and related results and concomitant interannual variability, especially for the very dry 1988 season. Interpretation is facilitated by the use of modeled daily global radiation values, measured (instantaneous) and modeled (monthly) soil moisture, United States Department of Agriculture (USDA) crop yield estimates, and satellite normalized difference vegetation index (NDVI) imagery. This paper shows that land–atmosphere interactions are intimately involved in pronounced seasonal climate anomalies for the world's richest agricultural region, but apparently with considerable complexity that includes plant behavior, solar radiation forcing, and challenging time-scale interrelations.
Abstract
Atmospheric moisture budget components are evaluated for a large area (1.23 × 106 km2) in the midwestern United States for all 12-h (1200–0000, 0000–1200 UTC) and 24-h (1200–1200 UTC) periods during the contrasting summers (May–August) of 1975, 1976, 1979, and 1988. The atmospheric moisture flux divergence (MFD, separated into horizontal and vertical advection components, HA and VA) and storage change (dPW) are estimated using a standard finite-difference method applied to objectively analyzed U.S. and Canadian rawinsonde data (50-hPa vertical resolution, surface–300 hPa) for 0000 and 1200 UTC. Area-averaged precipitation (P) totals are derived from approximately 600 relatively evenly distributed (but ungridded) recording rain gauges. Evapotranspiration (E) is estimated as a residual of the moisture budget equation and compares favorably with the few existing observations, especially when totaled for periods of 1 month or longer. Relationships between the budget components are established for the daily, monthly, and seasonal timescales using stratification, correlation, and cross-spectral analyses.
On monthly and seasonal timescales, the surface is a net source of water vapor (positive E−P) and the bulk of this surplus is exported from the region, largely through HA. For the daily budget, a threshold P rate (∼4 mm day−1) separates surplus E−P budgets from deficit budgets. On all timescales, most of the P variance is reflected in the VA component of MFD, while HA explains ∼80% of the variation in dPW. For the monthly and (especially) daily budgets, E has bimodal distributions with P where the minimum E occurs at P ∼ 2.6 mm day−1 (monthly) and P ∼ 4–5 mm day−1 (daily). For drier daily P regimes, relatively high E is associated with increased (decreased) dry VA (HA). The correlation of E with P becomes substantially more positive from the daily-to-monthly timescale, confirming the importance of land–atmosphere interactions over longer periods. The above stratification and correlation results are complemented by cross-spectral analyses that identify strong associations between P–HA and P–dPW previously masked by phase differences. The cross-spectral results also prompt the development of a conceptual model that describes the temporal relationships among the budget components for eastward-moving large-scale, “wavelike” disturbances with 3–10-day timescales. The suggested sequence of interactions—moist HA is accompanied by a pronounced PW increase and then followed by a moist VA maximum; this horizontal and then vertical moisture redistribution is first associated with an E minimum and then culminates in a P maximum; after the P event, atmospheric drying occurs through increased (diminished) dry HA (moist VA), which leads to an E maximum and then P minimum.
Abstract
Atmospheric moisture budget components are evaluated for a large area (1.23 × 106 km2) in the midwestern United States for all 12-h (1200–0000, 0000–1200 UTC) and 24-h (1200–1200 UTC) periods during the contrasting summers (May–August) of 1975, 1976, 1979, and 1988. The atmospheric moisture flux divergence (MFD, separated into horizontal and vertical advection components, HA and VA) and storage change (dPW) are estimated using a standard finite-difference method applied to objectively analyzed U.S. and Canadian rawinsonde data (50-hPa vertical resolution, surface–300 hPa) for 0000 and 1200 UTC. Area-averaged precipitation (P) totals are derived from approximately 600 relatively evenly distributed (but ungridded) recording rain gauges. Evapotranspiration (E) is estimated as a residual of the moisture budget equation and compares favorably with the few existing observations, especially when totaled for periods of 1 month or longer. Relationships between the budget components are established for the daily, monthly, and seasonal timescales using stratification, correlation, and cross-spectral analyses.
On monthly and seasonal timescales, the surface is a net source of water vapor (positive E−P) and the bulk of this surplus is exported from the region, largely through HA. For the daily budget, a threshold P rate (∼4 mm day−1) separates surplus E−P budgets from deficit budgets. On all timescales, most of the P variance is reflected in the VA component of MFD, while HA explains ∼80% of the variation in dPW. For the monthly and (especially) daily budgets, E has bimodal distributions with P where the minimum E occurs at P ∼ 2.6 mm day−1 (monthly) and P ∼ 4–5 mm day−1 (daily). For drier daily P regimes, relatively high E is associated with increased (decreased) dry VA (HA). The correlation of E with P becomes substantially more positive from the daily-to-monthly timescale, confirming the importance of land–atmosphere interactions over longer periods. The above stratification and correlation results are complemented by cross-spectral analyses that identify strong associations between P–HA and P–dPW previously masked by phase differences. The cross-spectral results also prompt the development of a conceptual model that describes the temporal relationships among the budget components for eastward-moving large-scale, “wavelike” disturbances with 3–10-day timescales. The suggested sequence of interactions—moist HA is accompanied by a pronounced PW increase and then followed by a moist VA maximum; this horizontal and then vertical moisture redistribution is first associated with an E minimum and then culminates in a P maximum; after the P event, atmospheric drying occurs through increased (diminished) dry HA (moist VA), which leads to an E maximum and then P minimum.
Abstract
Horn of Africa rainfall varies on multiple time scales, but the underlying climate system controls on this variability have not been examined comprehensively. This study therefore investigates the linkages between June–September Horn of Africa (especially Ethiopian) rainfall and regional atmospheric circulation and global sea surface temperature (SST) variations on several key time scales. Wavelet analysis of 5-day average or monthly total rainfall for 1970–99 identifies the dominant coherent modes of rainfall variability. Several regional atmospheric variables and global SST are then identically wavelet filtered, based on the rainfall frequency bands. Regression, correlation, and composite analyses are subsequently used to identify the most important rainfall–climate system time-scale relationships.
The results show that Ethiopian monsoon rainfall variation is largely linked with annual time-scale atmospheric circulation patterns involving variability in the major components of the monsoon system. Although variability on the seasonal (75–210 days), quasi-biennial (QB; 1.42–3.04 yr), and El Niño–Southern Oscillation (ENSO; 3.04–4.60 yr) time scales accounts for much less variance than the annual mode (210 days–1.42 yr), they significantly affect Ethiopian rainfall by preferentially modulating the major regional monsoon components and remote teleconnection linkages. The seasonal time scale largely acts in phase with the annual mode, by enhancing or reducing the lower-tropospheric southwesterlies from the equatorial Atlantic during wet or dry periods. The wet QB phase strengthens the Azores and Saharan high and the tropical easterly jet (TEJ) over the Arabian Sea, while the wet ENSO phase enhances the Mascarene high, the TEJ, and the monsoon trough more locally. The effects of tropical SST on Ethiopian rainfall also are prominent on the QB and ENSO time scales. While rainfall–SST correlations for both the QB and ENSO modes are strongly positive (negative) over the equatorial western (eastern) Pacific, only ENSO exhibits widespread strong negative correlations over the Indian Ocean. Opposite QB and ENSO associations tend to characterize dry Ethiopian conditions. The relationships identified on individual time scales now are being used to develop and validate statistical prediction models for Ethiopia.
Abstract
Horn of Africa rainfall varies on multiple time scales, but the underlying climate system controls on this variability have not been examined comprehensively. This study therefore investigates the linkages between June–September Horn of Africa (especially Ethiopian) rainfall and regional atmospheric circulation and global sea surface temperature (SST) variations on several key time scales. Wavelet analysis of 5-day average or monthly total rainfall for 1970–99 identifies the dominant coherent modes of rainfall variability. Several regional atmospheric variables and global SST are then identically wavelet filtered, based on the rainfall frequency bands. Regression, correlation, and composite analyses are subsequently used to identify the most important rainfall–climate system time-scale relationships.
The results show that Ethiopian monsoon rainfall variation is largely linked with annual time-scale atmospheric circulation patterns involving variability in the major components of the monsoon system. Although variability on the seasonal (75–210 days), quasi-biennial (QB; 1.42–3.04 yr), and El Niño–Southern Oscillation (ENSO; 3.04–4.60 yr) time scales accounts for much less variance than the annual mode (210 days–1.42 yr), they significantly affect Ethiopian rainfall by preferentially modulating the major regional monsoon components and remote teleconnection linkages. The seasonal time scale largely acts in phase with the annual mode, by enhancing or reducing the lower-tropospheric southwesterlies from the equatorial Atlantic during wet or dry periods. The wet QB phase strengthens the Azores and Saharan high and the tropical easterly jet (TEJ) over the Arabian Sea, while the wet ENSO phase enhances the Mascarene high, the TEJ, and the monsoon trough more locally. The effects of tropical SST on Ethiopian rainfall also are prominent on the QB and ENSO time scales. While rainfall–SST correlations for both the QB and ENSO modes are strongly positive (negative) over the equatorial western (eastern) Pacific, only ENSO exhibits widespread strong negative correlations over the Indian Ocean. Opposite QB and ENSO associations tend to characterize dry Ethiopian conditions. The relationships identified on individual time scales now are being used to develop and validate statistical prediction models for Ethiopia.
Abstract
Monthly multi-annual mean heat budgets are calculated for the Caribbean Sea; previous results from the Gulf of Mexico are included to portray fields for the combined Central American seas. Oceanic heat storage rates (QT ) for the upper 200 meters in the Caribbean are calculated directly from vertical subsurface temperature data for the decade 1967–76; spatial distribution of QT are contoured on maps for February, May, August and November. In the Gulf of Mexico, QT was found to be determined principally by the surface heat exchange. In the Caribbean Sea, QT is related primarily to convergence and divergence of heat transport; QT patterns in the southern Caribbean can be associated with Ekman pumping and heat advection due to currents. The monthly mean surface heat exchanges are defined by the averages of Bunker's unpublished data and the atlas data of Hastenrath and Lamb. Comparisons are also made with the results of both Budyko and Coló in the Caribbean Sea for historical perspective. Monthly mean oceanic heat transport divergences are then derived as residuals in the heat budget equation. Partial verification is obtained by directly computing the horizontal component of heat advection using estimates of water transport in the Central American seas.
Estimates of the seasonal freshwater budgets in the Central American seas are calculated using the oceanic precipitation rates (P) of Dorman and Bourke and the averaged evaporation rates (E) obtained from Bunker and from Hastenrath and Lamb. Annual mean E – P values of 104 and 112 cm are obtained for the Caribbean Sea and Central American seas, respectively. The freshwater continuity is examined by including estimates of river discharge rates; it is shown that river discharge does not compensate for the net water loss caused by an excess of evaporation over precipitation. An analysis of the freshwater flux in the Central American seas, using typical salinity data, indicates a convergence of freshwater over the region consistent with the earlier observation of excessive evaporation.
Abstract
Monthly multi-annual mean heat budgets are calculated for the Caribbean Sea; previous results from the Gulf of Mexico are included to portray fields for the combined Central American seas. Oceanic heat storage rates (QT ) for the upper 200 meters in the Caribbean are calculated directly from vertical subsurface temperature data for the decade 1967–76; spatial distribution of QT are contoured on maps for February, May, August and November. In the Gulf of Mexico, QT was found to be determined principally by the surface heat exchange. In the Caribbean Sea, QT is related primarily to convergence and divergence of heat transport; QT patterns in the southern Caribbean can be associated with Ekman pumping and heat advection due to currents. The monthly mean surface heat exchanges are defined by the averages of Bunker's unpublished data and the atlas data of Hastenrath and Lamb. Comparisons are also made with the results of both Budyko and Coló in the Caribbean Sea for historical perspective. Monthly mean oceanic heat transport divergences are then derived as residuals in the heat budget equation. Partial verification is obtained by directly computing the horizontal component of heat advection using estimates of water transport in the Central American seas.
Estimates of the seasonal freshwater budgets in the Central American seas are calculated using the oceanic precipitation rates (P) of Dorman and Bourke and the averaged evaporation rates (E) obtained from Bunker and from Hastenrath and Lamb. Annual mean E – P values of 104 and 112 cm are obtained for the Caribbean Sea and Central American seas, respectively. The freshwater continuity is examined by including estimates of river discharge rates; it is shown that river discharge does not compensate for the net water loss caused by an excess of evaporation over precipitation. An analysis of the freshwater flux in the Central American seas, using typical salinity data, indicates a convergence of freshwater over the region consistent with the earlier observation of excessive evaporation.
Abstract
Winter storms in the southern United States can significantly impact infrastructure and the economy. In this study, National Centers for Environmental Information Storm Event Database and local climate summaries, are used to develop a spatial climatology of freezing precipitation (freezing rain and ice pellets) and snow over the southern Great Plains, 1993–2011. Principal component analysis is performed on the 500-hPa height field, at the approximate onset time of precipitation, for 33 freezing precipitation and 42 snow case studies, to differentiate common synoptic flow fields associated with precipitation type. The five leading patterns for each precipitation type are retained. Composites of temperature, moisture, pressure, and wind fields are constructed and extended 24 h before and after precipitation initiation to track the storm system evolution. Many 500-hPa flow fields are similar for both precipitation types. However, snow-dominant events have stronger and/or more frequent surface cyclone development. Freezing precipitation is associated with the southward propagation of an Arctic anticyclone well ahead of precipitation, weak or absent surface cyclone formation, and a more western trough axis. High-impact ice storms in the region often have slow-moving upper-level flow, persistent isentropic ascent over a surface quasi-stationary front with strongly positive moisture anomalies, and warm layer airmass trajectories originating over the Gulf of Mexico. The results here are based on a relatively small sample size. However, this work is intended to be useful for forecasters, in particular as a pattern recognition aid in predicting the evolution of precipitation within southern Great Plains winter storms.
Abstract
Winter storms in the southern United States can significantly impact infrastructure and the economy. In this study, National Centers for Environmental Information Storm Event Database and local climate summaries, are used to develop a spatial climatology of freezing precipitation (freezing rain and ice pellets) and snow over the southern Great Plains, 1993–2011. Principal component analysis is performed on the 500-hPa height field, at the approximate onset time of precipitation, for 33 freezing precipitation and 42 snow case studies, to differentiate common synoptic flow fields associated with precipitation type. The five leading patterns for each precipitation type are retained. Composites of temperature, moisture, pressure, and wind fields are constructed and extended 24 h before and after precipitation initiation to track the storm system evolution. Many 500-hPa flow fields are similar for both precipitation types. However, snow-dominant events have stronger and/or more frequent surface cyclone development. Freezing precipitation is associated with the southward propagation of an Arctic anticyclone well ahead of precipitation, weak or absent surface cyclone formation, and a more western trough axis. High-impact ice storms in the region often have slow-moving upper-level flow, persistent isentropic ascent over a surface quasi-stationary front with strongly positive moisture anomalies, and warm layer airmass trajectories originating over the Gulf of Mexico. The results here are based on a relatively small sample size. However, this work is intended to be useful for forecasters, in particular as a pattern recognition aid in predicting the evolution of precipitation within southern Great Plains winter storms.
Abstract
The possible contribution of jet aircraft condensation trails (contrails) to recent observed increases in high cloudiness constitutes a potentially important human effect on climate that has received relatively little attention. Very high resolution (0.6 km) thermal-infrared imagery from the Defense Meteorological Satellite Program polar orbiters, concentrated in the nighttime and morning hours, is interpreted to derive a climatic description of contrails over the United States and adjacent areas for the midseason months (April, July, October, and January) of 1977–79. A manual technique of identifying contrails on the imagery is validated by comparison with more recent ground-based observations. Contrail spatial distributions are mapped at a 1° lat × 1° long resolution for monthly and multimonth time periods.
Contrail incidence is widespread over the United States and adjacent areas, with highest frequencies occurring over the following regions: the extreme Southwest (particularly southern California), the Southeast (especially southeast Georgia and northeast Florida), the west coast of British Columbia and Vancouver Island, and the eastern Midwest centered on southeast Indiana and western Kentucky. Contrails are most frequent during the transition-season months (April and October), and are least frequent in July. Latitudinally, contrail incidence peaks over the northern (southern) regions in July (January), suggesting a first-order association with the seasonal variation of upper-tropospheric westerly winds. Analysis of synoptic-scale midtropospheric circulation patterns confirms that the highest contrail frequencies occur in association with baroclinic phenomena, particularly cyclone waves and jet streams. Moreover, contrails tend frequently to occur in conjunction with other clouds, including the cirrus associated with jet-stream and frontal systems.
Analyses of rawinsonde data for three representative contrail “outbreak” (multiple occurrence) events during the study months confirm some earlier studies that suggest contrails form below a cold, elevated tropopause (i.e., around ridgelines in the geopotential height field), in contrast with noncontrail days. Accordingly, the temperature advection in the troposphere accompanying the contrail outbreaks is positive, or warm, and relatively weak. This contrail climatic description provides a context within which recent surface climate changes at regional and subregional scales may be cast.
Abstract
The possible contribution of jet aircraft condensation trails (contrails) to recent observed increases in high cloudiness constitutes a potentially important human effect on climate that has received relatively little attention. Very high resolution (0.6 km) thermal-infrared imagery from the Defense Meteorological Satellite Program polar orbiters, concentrated in the nighttime and morning hours, is interpreted to derive a climatic description of contrails over the United States and adjacent areas for the midseason months (April, July, October, and January) of 1977–79. A manual technique of identifying contrails on the imagery is validated by comparison with more recent ground-based observations. Contrail spatial distributions are mapped at a 1° lat × 1° long resolution for monthly and multimonth time periods.
Contrail incidence is widespread over the United States and adjacent areas, with highest frequencies occurring over the following regions: the extreme Southwest (particularly southern California), the Southeast (especially southeast Georgia and northeast Florida), the west coast of British Columbia and Vancouver Island, and the eastern Midwest centered on southeast Indiana and western Kentucky. Contrails are most frequent during the transition-season months (April and October), and are least frequent in July. Latitudinally, contrail incidence peaks over the northern (southern) regions in July (January), suggesting a first-order association with the seasonal variation of upper-tropospheric westerly winds. Analysis of synoptic-scale midtropospheric circulation patterns confirms that the highest contrail frequencies occur in association with baroclinic phenomena, particularly cyclone waves and jet streams. Moreover, contrails tend frequently to occur in conjunction with other clouds, including the cirrus associated with jet-stream and frontal systems.
Analyses of rawinsonde data for three representative contrail “outbreak” (multiple occurrence) events during the study months confirm some earlier studies that suggest contrails form below a cold, elevated tropopause (i.e., around ridgelines in the geopotential height field), in contrast with noncontrail days. Accordingly, the temperature advection in the troposphere accompanying the contrail outbreaks is positive, or warm, and relatively weak. This contrail climatic description provides a context within which recent surface climate changes at regional and subregional scales may be cast.
Abstract
Economic decision models incorporating biophysical simulation models are used to examine the impact of the use of Southern Oscillation (SO) information on sorghum production in Texas. Production for 18 sites is aggregated to examine the impact of the use of SO information on the aggregate supply curve and other production and economic variables. Two information scenarios are examined. For all expected prices, the use of SO information increased producers’ net returns over the scenario in which SO information is not used. Depending on price, the expected Texas aggregate sorghum supply curve using SO information shifted both left and right of the without SO information supply curve. Changes in nitrogen use based on the SO information is a major factor causing the shift in the supply curves. Further, the use of SO information decreased aggregate expected costs per metric ton of production. Changes associated with the use of SO information can be summarized as follows: the use of SO information provides producers a method to use inputs more efficiently. This more efficient use has implications for both the environment and for the agricultural sector.
Abstract
Economic decision models incorporating biophysical simulation models are used to examine the impact of the use of Southern Oscillation (SO) information on sorghum production in Texas. Production for 18 sites is aggregated to examine the impact of the use of SO information on the aggregate supply curve and other production and economic variables. Two information scenarios are examined. For all expected prices, the use of SO information increased producers’ net returns over the scenario in which SO information is not used. Depending on price, the expected Texas aggregate sorghum supply curve using SO information shifted both left and right of the without SO information supply curve. Changes in nitrogen use based on the SO information is a major factor causing the shift in the supply curves. Further, the use of SO information decreased aggregate expected costs per metric ton of production. Changes associated with the use of SO information can be summarized as follows: the use of SO information provides producers a method to use inputs more efficiently. This more efficient use has implications for both the environment and for the agricultural sector.
Abstract
The article describes research opportunities associated with evaluating the characteristics of climate forecasts in settings where sequential decisions are made. Illustrative results are provided for corn production in east central Illinois. These results indicate that the production process examined has sufficient flexibility to utilize climate forecasts for specific production seasons but the value of those forecasts is sensitive to economic parameters as well as forecasts characteristics. Forecasts periods of greatest importance, as well as the relationships between forecast value, accuracy, and lead time, are evaluated.
Abstract
The article describes research opportunities associated with evaluating the characteristics of climate forecasts in settings where sequential decisions are made. Illustrative results are provided for corn production in east central Illinois. These results indicate that the production process examined has sufficient flexibility to utilize climate forecasts for specific production seasons but the value of those forecasts is sensitive to economic parameters as well as forecasts characteristics. Forecasts periods of greatest importance, as well as the relationships between forecast value, accuracy, and lead time, are evaluated.
Abstract
A three-step process is proposed to be most efficient for generating skillful climate forecasts which could reduce the adverse socioeconomic effects of climatic variability. These steps involve identifying weather-sensitive economic sectors, documenting the flexibility of these sectors with respect to likely forecast information, and the development of accordingly focused forecast capabilities. An illustration of the types of information needed to identify sector flexibility is provided for Midwest crop production. Finally, a pilot study using actual farmer data for east central Illinois suggests that increased corn yields could have resulted if producers had been forewarned of the benign weather conditions experienced during the 1979 growing season. This implies that skillful, properly structured climate forecasts may be useful to Midwest crop producers.
Abstract
A three-step process is proposed to be most efficient for generating skillful climate forecasts which could reduce the adverse socioeconomic effects of climatic variability. These steps involve identifying weather-sensitive economic sectors, documenting the flexibility of these sectors with respect to likely forecast information, and the development of accordingly focused forecast capabilities. An illustration of the types of information needed to identify sector flexibility is provided for Midwest crop production. Finally, a pilot study using actual farmer data for east central Illinois suggests that increased corn yields could have resulted if producers had been forewarned of the benign weather conditions experienced during the 1979 growing season. This implies that skillful, properly structured climate forecasts may be useful to Midwest crop producers.
Abstract
This study investigates the role of large-scale environmental factors, notably sea surface temperature (SST), low-level relative vorticity, and deep-tropospheric vertical wind shear, in the interannual variability of November–April tropical cyclone (TC) activity in the Australian region. Extensive correlation analyses were carried out between TC frequency and intensity and the aforementioned large-scale parameters, using TC data for 1970–2006 from the official Australian TC dataset. Large correlations were found between the seasonal number of TCs and SST in the Niño-3.4 and Niño-4 regions. These correlations were greatest (−0.73) during August–October, immediately preceding the Australian TC season. The correlations remain almost unchanged for the July–September period and therefore can be viewed as potential seasonal predictors of the forthcoming TC season. In contrast, only weak correlations (<+0.37) were found with the local SST in the region north of Australia where many TCs originate; these were reduced almost to zero when the ENSO component of the SST was removed by partial correlation analysis. The annual frequency of TCs was found to be strongly correlated with 850-hPa relative vorticity and vertical shear of the zonal wind over the main genesis areas of the Australian region. Furthermore, correlations between the Niño SST and these two atmospheric parameters exhibited a strong link between the Australian region and the Niño-3.4 SST. A principal component analysis of the SST dataset revealed two main modes of Pacific Ocean SST variability that match very closely with the basinwide patterns of correlations between SST and TC frequencies. Finally, it is shown that the correlations can be increased markedly (e.g., from −0.73 to −0.80 for the August–October period) by a weighted combination of SST time series from weakly correlated regions.
Abstract
This study investigates the role of large-scale environmental factors, notably sea surface temperature (SST), low-level relative vorticity, and deep-tropospheric vertical wind shear, in the interannual variability of November–April tropical cyclone (TC) activity in the Australian region. Extensive correlation analyses were carried out between TC frequency and intensity and the aforementioned large-scale parameters, using TC data for 1970–2006 from the official Australian TC dataset. Large correlations were found between the seasonal number of TCs and SST in the Niño-3.4 and Niño-4 regions. These correlations were greatest (−0.73) during August–October, immediately preceding the Australian TC season. The correlations remain almost unchanged for the July–September period and therefore can be viewed as potential seasonal predictors of the forthcoming TC season. In contrast, only weak correlations (<+0.37) were found with the local SST in the region north of Australia where many TCs originate; these were reduced almost to zero when the ENSO component of the SST was removed by partial correlation analysis. The annual frequency of TCs was found to be strongly correlated with 850-hPa relative vorticity and vertical shear of the zonal wind over the main genesis areas of the Australian region. Furthermore, correlations between the Niño SST and these two atmospheric parameters exhibited a strong link between the Australian region and the Niño-3.4 SST. A principal component analysis of the SST dataset revealed two main modes of Pacific Ocean SST variability that match very closely with the basinwide patterns of correlations between SST and TC frequencies. Finally, it is shown that the correlations can be increased markedly (e.g., from −0.73 to −0.80 for the August–October period) by a weighted combination of SST time series from weakly correlated regions.
