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• 1. [Article] Frequency Modes of Monsoon Precipitation in Arizona and New Mexico

  The interannual and intraseasonal variability of the North American monsoon is of great interest because a large proportion of the annual precipitation for Arizona and New Mexico arrives during the summer ...

  Citation × Citation Citation Abstract Copy Title: Frequency Modes of Monsoon Precipitation in Arizona and New Mexico Author: Hall-McKim, Eileen A., Nolin, Anne W. The interannual and intraseasonal variability of the North American monsoon is of great interest because a large proportion of the annual precipitation for Arizona and New Mexico arrives during the summer monsoon. Forty-one years of daily monsoon season precipitation data for Arizona and New Mexico were studied using wavelet analysis. This time-localized spectral analysis method reveals that periodicities of less than 8 days are positively correlated with mean daily precipitation during the 1 July–15 September monsoon period. Roughly 17% of the years indicate no significant periodicity during the monsoon period for either region and are associated with low monsoon precipitation. High- and low-frequency modes explain an equivalent percentage of the variance in monsoon precipitation in both Arizona and New Mexico, and in many years concurrent multiple periodicities occur. Wavelet analysis was effective in identifying the contribution of high-frequency modes that had not been discerned in previous studies. These results suggest that precipitation processes during the monsoon season are modulated by phenomena operating at synoptic (2–8 days) and longer (>8 days) time scales and point to the need for further studies to better understand the associated atmospheric processes. Title: Frequency Modes of Monsoon Precipitation in Arizona and New Mexico Author: Hall-McKim, Eileen A., Nolin, Anne W. The interannual and intraseasonal variability of the North American monsoon is of great interest because a large proportion of the annual precipitation for Arizona and New Mexico arrives during the summer monsoon. Forty-one years of daily monsoon season precipitation data for Arizona and New Mexico were studied using wavelet analysis. This time-localized spectral analysis method reveals that periodicities of less than 8 days are positively correlated with mean daily precipitation during the 1 July–15 September monsoon period. Roughly 17% of the years indicate no significant periodicity during the monsoon period for either region and are associated with low monsoon precipitation. High- and low-frequency modes explain an equivalent percentage of the variance in monsoon precipitation in both Arizona and New Mexico, and in many years concurrent multiple periodicities occur. Wavelet analysis was effective in identifying the contribution of high-frequency modes that had not been discerned in previous studies. These results suggest that precipitation processes during the monsoon season are modulated by phenomena operating at synoptic (2–8 days) and longer (>8 days) time scales and point to the need for further studies to better understand the associated atmospheric processes. Close

• 2. [Article] An Atmospheric Teleconnection Linking ENSO and Southwestern European Precipitation

  Numerous studies have demonstrated statistical associations between the El Niño–Southern Oscillation (ENSO) and precipitation in the Mediterranean basin. The dynamical bases for these teleconnections have ...

  Citation × Citation Citation Abstract Copy Title: An Atmospheric Teleconnection Linking ENSO and Southwestern European Precipitation Author: Tziperman, Eli, Shaman, Jeffrey Numerous studies have demonstrated statistical associations between the El Niño–Southern Oscillation (ENSO) and precipitation in the Mediterranean basin. The dynamical bases for these teleconnections have yet to be fully identified. Here, observational analyses and model simulations are used to show how ENSO variability affects rainfall over southwestern Europe (Iberia, Southern France, and Italy). A precipitation index for the region, named southwestern European Precipitation (SWEP), is used. The observational analyses show that ENSO modulates SWEP during the September–December wet season. These precipitation anomalies are associated with changes in large-scale atmospheric fields to the west of Iberia that alter low-level westerly winds and onshore moisture advection from the Atlantic. The vorticity anomalies associated with SWEP variability are linked to ENSO through a stationary barotropic Rossby wave train that emanates from the eastern equatorial Pacific and propagates eastward to the Atlantic and Mediterranean. Solutions of the linearized barotropic vorticity equation produce such eastward-propagating Rossby waves with trajectories that traverse the region of observed ENSO-related anomalies. In addition, these linearized barotropic vorticity equation solutions produce a dipole of positive and negative vorticity anomalies to the west of Iberia that matches observations and is consistent with the onshore advection of moisture. Thus, interannual variability of fall and early winter precipitation over southwestern Europe is linked to ENSO variability in the eastern Pacific via an eastward-propagating atmospheric stationary barotropic Rossby wave train. Title: An Atmospheric Teleconnection Linking ENSO and Southwestern European Precipitation Author: Tziperman, Eli, Shaman, Jeffrey Numerous studies have demonstrated statistical associations between the El Niño–Southern Oscillation (ENSO) and precipitation in the Mediterranean basin. The dynamical bases for these teleconnections have yet to be fully identified. Here, observational analyses and model simulations are used to show how ENSO variability affects rainfall over southwestern Europe (Iberia, Southern France, and Italy). A precipitation index for the region, named southwestern European Precipitation (SWEP), is used. The observational analyses show that ENSO modulates SWEP during the September–December wet season. These precipitation anomalies are associated with changes in large-scale atmospheric fields to the west of Iberia that alter low-level westerly winds and onshore moisture advection from the Atlantic. The vorticity anomalies associated with SWEP variability are linked to ENSO through a stationary barotropic Rossby wave train that emanates from the eastern equatorial Pacific and propagates eastward to the Atlantic and Mediterranean. Solutions of the linearized barotropic vorticity equation produce such eastward-propagating Rossby waves with trajectories that traverse the region of observed ENSO-related anomalies. In addition, these linearized barotropic vorticity equation solutions produce a dipole of positive and negative vorticity anomalies to the west of Iberia that matches observations and is consistent with the onshore advection of moisture. Thus, interannual variability of fall and early winter precipitation over southwestern Europe is linked to ENSO variability in the eastern Pacific via an eastward-propagating atmospheric stationary barotropic Rossby wave train. Close

• 3. [Article] Climate-Driven Variability and Trends in Mountain Snowpack in Western North America

  Records of 1 April snow water equivalent (SWE) are examined here using multiple linear regression against reference time series of temperature and precipitation. This method permits 1) an examination of ...

  Citation × Citation Citation Abstract Copy Title: Climate-Driven Variability and Trends in Mountain Snowpack in Western North America Author: Mote, Philip W. Records of 1 April snow water equivalent (SWE) are examined here using multiple linear regression against reference time series of temperature and precipitation. This method permits 1) an examination of the separate roles of temperature and precipitation in determining the trends in SWE; 2) an estimation of the sensitivity of SWE to warming trends, and its distribution across western North America and as a function of elevation; and 3) inferences about responses of SWE to future warming. These results emphasize the sensitivity to warming of the mountains of northern California and the Cascades of Oregon and Washington. In addition, the contribution of modes of Pacific climate variability is examined and found to be responsible for about 10%–60% of the trends in SWE, depending on the period of record and climate index. Title: Climate-Driven Variability and Trends in Mountain Snowpack in Western North America Author: Mote, Philip W. Records of 1 April snow water equivalent (SWE) are examined here using multiple linear regression against reference time series of temperature and precipitation. This method permits 1) an examination of the separate roles of temperature and precipitation in determining the trends in SWE; 2) an estimation of the sensitivity of SWE to warming trends, and its distribution across western North America and as a function of elevation; and 3) inferences about responses of SWE to future warming. These results emphasize the sensitivity to warming of the mountains of northern California and the Cascades of Oregon and Washington. In addition, the contribution of modes of Pacific climate variability is examined and found to be responsible for about 10%–60% of the trends in SWE, depending on the period of record and climate index. Close

• 4. [Article] The Central American Midsummer Drought: Regional Aspects and Large-Scale Forcing

  The midsummer drought (MSD) is a diminution in rainfall experienced during the middle of the rainy season in southern Mexico and Central America, as well as in the adjacent Caribbean, Gulf of Mexico, and ...

  Citation × Citation Citation Abstract Copy Title: The Central American Midsummer Drought: Regional Aspects and Large-Scale Forcing Author: de Szoeke, Simon P., Small, Richard Justin O., Xie, Shang-Ping The midsummer drought (MSD) is a diminution in rainfall experienced during the middle of the rainy season in southern Mexico and Central America, as well as in the adjacent Caribbean, Gulf of Mexico, and eastern Pacific seas. The aim of this paper is to describe the regional characteristics of the MSD and to propose some possible forcing mechanisms. Satellite and in situ data are used to form a composite of the evolution of a typical MSD, which highlights its coincidence with a low-level anticyclone centered over the Gulf of Mexico and associated easterly flow across Central America. The diurnal cycle of precipitation over the region is reduced in amplitude during midsummer. The MSD is also coincident with heavy precipitation over the Sierra Madre Occidental (part of the North American monsoon). Reanalysis data are used to show that the divergence of the anomalous low-level flow during the MSD is the main factor governing the variations in precipitation. A linear baroclinic model is used to show that the seasonal progression of the Pacific intertropical convergence zone (ITCZ), which moves northward following warm sea surface temperature (SST) during the early summer, and of the Atlantic subtropical high, which moves westward, are the most important remote factors that contribute toward the low-level easterly flow and divergence during the MSD. The circulation associated with the MSD precipitation deficit helps to maintain the deficit by reinforcing the low-level anticyclonic flow over the Gulf of Mexico. Surface heating over land also plays a role: a large thermal low over the northern United States in early summer is accompanied by enhanced subsidence over the North Atlantic. This thermal low is seen to decrease considerably in midsummer, allowing the high pressure anomalies in the Atlantic and Pacific Oceans to extend into the Gulf of Mexico. These anomalies are maintained until late summer, when an increase in rainfall from the surge in Atlantic tropical depressions induces anomalous surface cyclonic flow with westerlies fluxing moisture from the Pacific ITCZ toward Central America. Title: The Central American Midsummer Drought: Regional Aspects and Large-Scale Forcing Author: de Szoeke, Simon P., Small, Richard Justin O., Xie, Shang-Ping The midsummer drought (MSD) is a diminution in rainfall experienced during the middle of the rainy season in southern Mexico and Central America, as well as in the adjacent Caribbean, Gulf of Mexico, and eastern Pacific seas. The aim of this paper is to describe the regional characteristics of the MSD and to propose some possible forcing mechanisms. Satellite and in situ data are used to form a composite of the evolution of a typical MSD, which highlights its coincidence with a low-level anticyclone centered over the Gulf of Mexico and associated easterly flow across Central America. The diurnal cycle of precipitation over the region is reduced in amplitude during midsummer. The MSD is also coincident with heavy precipitation over the Sierra Madre Occidental (part of the North American monsoon). Reanalysis data are used to show that the divergence of the anomalous low-level flow during the MSD is the main factor governing the variations in precipitation. A linear baroclinic model is used to show that the seasonal progression of the Pacific intertropical convergence zone (ITCZ), which moves northward following warm sea surface temperature (SST) during the early summer, and of the Atlantic subtropical high, which moves westward, are the most important remote factors that contribute toward the low-level easterly flow and divergence during the MSD. The circulation associated with the MSD precipitation deficit helps to maintain the deficit by reinforcing the low-level anticyclonic flow over the Gulf of Mexico. Surface heating over land also plays a role: a large thermal low over the northern United States in early summer is accompanied by enhanced subsidence over the North Atlantic. This thermal low is seen to decrease considerably in midsummer, allowing the high pressure anomalies in the Atlantic and Pacific Oceans to extend into the Gulf of Mexico. These anomalies are maintained until late summer, when an increase in rainfall from the surge in Atlantic tropical depressions induces anomalous surface cyclonic flow with westerlies fluxing moisture from the Pacific ITCZ toward Central America. Close

• 5. [Article] JonesJuliaCEOASChangingForestWater.pdf

  Citation × Citation Citation Abstract Copy Title: JonesJuliaCEOASChangingForestWater.pdf Author: Creed, Irena F., Jones, Julia A., et al., Spargo, Adam T. Title: JonesJuliaCEOASChangingForestWater.pdf Author: Creed, Irena F., Jones, Julia A., et al., Spargo, Adam T. Close

• 6. [Article] JonesJuliaCEOASChangingForestWater_TableS1.pdf

  Citation × Citation Citation Abstract Copy Title: JonesJuliaCEOASChangingForestWater_TableS1.pdf Author: Creed, Irena F., Jones, Julia A., et al., Spargo, Adam T. Title: JonesJuliaCEOASChangingForestWater_TableS1.pdf Author: Creed, Irena F., Jones, Julia A., et al., Spargo, Adam T. Close

• 7. [Article] Vegetation dynamics and rainfall sensitivity of the Amazon

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the National ...

  Citation × Citation Citation Abstract Copy Title: Vegetation dynamics and rainfall sensitivity of the Amazon Author: Tucker, Compton J., Hilker, Thomas, et al., Lyapustin, Alexei I. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the National Academy of Sciences and can be found at: http://www.pnas.org/. Title: Vegetation dynamics and rainfall sensitivity of the Amazon Author: Tucker, Compton J., Hilker, Thomas, et al., Lyapustin, Alexei I. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the National Academy of Sciences and can be found at: http://www.pnas.org/. Close

• 8. [Article] Specific consensus statement on the likely impacts of climate change on the Pacific Northwest

  The signatories of this statement seek to describe the state of scientific knowledge regarding likely impacts of climate change to the Pacific Northwest region. The intent is to assist Governor Kulongoski’s ...

  Citation × Citation Citation Abstract Copy Title: Specific consensus statement on the likely impacts of climate change on the Pacific Northwest The signatories of this statement seek to describe the state of scientific knowledge regarding likely impacts of climate change to the Pacific Northwest region. The intent is to assist Governor Kulongoski’s Advisory Group on Global Warming in its task of developing a greenhouse gas emission reduction strategy for Oregon. The signatories agree that climate change is underway and that it is having global effects as well as impacts in the Pacific Northwest region. Title: Specific consensus statement on the likely impacts of climate change on the Pacific Northwest The signatories of this statement seek to describe the state of scientific knowledge regarding likely impacts of climate change to the Pacific Northwest region. The intent is to assist Governor Kulongoski’s Advisory Group on Global Warming in its task of developing a greenhouse gas emission reduction strategy for Oregon. The signatories agree that climate change is underway and that it is having global effects as well as impacts in the Pacific Northwest region. Close

• 9. [Article] Changing forest water yields in response to climate warming: results from long-term experimental watershed sites across North America

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) ...

  Citation × Citation Citation Abstract Copy Title: Changing forest water yields in response to climate warming: results from long-term experimental watershed sites across North America Author: Creed, Irena F., Jones, Julia A., et al., Spargo, Adam T. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by John Wiley & Sons Ltd. The published article can be found at: http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291365-2486. Title: Changing forest water yields in response to climate warming: results from long-term experimental watershed sites across North America Author: Creed, Irena F., Jones, Julia A., et al., Spargo, Adam T. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by John Wiley & Sons Ltd. The published article can be found at: http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291365-2486. Close

• 10. [Article] The Tropical Eastern Pacific Seasonal Cycle: Assessment of Errors and Mechanisms in IPCC AR4 Coupled Ocean–Atmosphere General Circulation Models

  Warmer SST and more rain in the Northern Hemisphere are observed year-round in the tropical eastern Pacific with southerly wind crossing the equator toward the atmospheric heating. The southerlies are ...

  Citation × Citation Citation Abstract Copy Title: The Tropical Eastern Pacific Seasonal Cycle: Assessment of Errors and Mechanisms in IPCC AR4 Coupled Ocean–Atmosphere General Circulation Models Author: Xie, Shang-Ping, de Szoeke, Simon P. Warmer SST and more rain in the Northern Hemisphere are observed year-round in the tropical eastern Pacific with southerly wind crossing the equator toward the atmospheric heating. The southerlies are minimal during boreal spring, when two precipitation maxima straddle the equator. Fourteen atmosphere–ocean coupled GCMs from the Coupled Model Intercomparison Project (CMIP3) and one coupled regional model are evaluated against observations with simple metrics that diagnose the seasonal cycle and meridional migration of warm SST and rain. Intermodel correlations of the metrics elucidate common coupled physics. These models variously simulate the climatology of SST and ITCZ rain. In 8 out of 15 models the ITCZ alternates symmetrically between the hemispheres with the seasons. This seasonally alternating ITCZ error generates two wind speed maxima per year—one northerly and one southerly—resulting in spurious cooling in March and a cool SST error of the equatorial ocean. Most models have too much rain in the Southern Hemisphere so that SST and rain are too symmetric about the equator in the annual mean. Weak meridional wind on the equator near the South American coast (2°S–2°N, 80°–90°W) explains the warm SST error there. Northeasterly wind jets blow over the Central American isthmus in winter and cool the SST in the eastern Pacific warm pool. In some models the strength of these winds contributes to the early demise of their northern ITCZ relative to observations. The February–April northerly wind bias on the equator is correlated to the antecedent December–February Central American Pacific wind speed at −0.88. The representation of southern-tropical stratus clouds affects the underlying SST through solar radiation, but its effect on the meridional atmospheric circulation is difficult to discern from the multimodel ensemble, indicating that errors other than the simulation of stratus clouds are also important for accurate simulation of the meridional asymmetry. This study identifies several features to be improved in atmospheric and coupled GCMs, including the northeasterly cross–Central American wind in winter and meridional wind on the equator. Improved simulation of the seasonal cycle of meridional wind could alleviate biases in equatorial SST and improve simulation of ENSO and its teleconnections. Title: The Tropical Eastern Pacific Seasonal Cycle: Assessment of Errors and Mechanisms in IPCC AR4 Coupled Ocean–Atmosphere General Circulation Models Author: Xie, Shang-Ping, de Szoeke, Simon P. Warmer SST and more rain in the Northern Hemisphere are observed year-round in the tropical eastern Pacific with southerly wind crossing the equator toward the atmospheric heating. The southerlies are minimal during boreal spring, when two precipitation maxima straddle the equator. Fourteen atmosphere–ocean coupled GCMs from the Coupled Model Intercomparison Project (CMIP3) and one coupled regional model are evaluated against observations with simple metrics that diagnose the seasonal cycle and meridional migration of warm SST and rain. Intermodel correlations of the metrics elucidate common coupled physics. These models variously simulate the climatology of SST and ITCZ rain. In 8 out of 15 models the ITCZ alternates symmetrically between the hemispheres with the seasons. This seasonally alternating ITCZ error generates two wind speed maxima per year—one northerly and one southerly—resulting in spurious cooling in March and a cool SST error of the equatorial ocean. Most models have too much rain in the Southern Hemisphere so that SST and rain are too symmetric about the equator in the annual mean. Weak meridional wind on the equator near the South American coast (2°S–2°N, 80°–90°W) explains the warm SST error there. Northeasterly wind jets blow over the Central American isthmus in winter and cool the SST in the eastern Pacific warm pool. In some models the strength of these winds contributes to the early demise of their northern ITCZ relative to observations. The February–April northerly wind bias on the equator is correlated to the antecedent December–February Central American Pacific wind speed at −0.88. The representation of southern-tropical stratus clouds affects the underlying SST through solar radiation, but its effect on the meridional atmospheric circulation is difficult to discern from the multimodel ensemble, indicating that errors other than the simulation of stratus clouds are also important for accurate simulation of the meridional asymmetry. This study identifies several features to be improved in atmospheric and coupled GCMs, including the northeasterly cross–Central American wind in winter and meridional wind on the equator. Improved simulation of the seasonal cycle of meridional wind could alleviate biases in equatorial SST and improve simulation of ENSO and its teleconnections. Close