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The system for the collection and archiving of climatic data from approximately 7000 cooperative observing stations across the United States is in need of improvement. Despite the efforts of many dedicated volunteers and professionals, suspect or incomplete data continue to enter the national climate archive. Cooperative observers need further education regarding the importance of collecting complete and accurate data. The transition to the Maximum/Minimum Temperature Systems (MMTS) from the former liquid-in-glass thermometers mounted in Cotton Region shelters needs to be better coordinated, particularly with respect to the continuity of temperature data. The role of the Cooperative Program Managers in overseeing the physical well being of the network and the quality of data emanating from its needs to be strengthened. A continuation of efforts recently begun at the National Climatic Data Center (NCDC) to improve the digitization and quality-control procedures employed in data archiving is required. These improvements might be fulfilled within the present National Oceanic and Atmospheric Administration (NOAA) infrastructure. Another avenue which might be explored is the amalgamation of all aspects of the United States climate-observing system under the supervision of a new department within NOAA's National Environmental Satellite, Data, and Information Service (NESDIS). Regardless of how this is achieved, now is the time to improve the system. There has never been a greater need for a national climatic database of superlative quality, whether it be for investigations of climate change, meteorological research, agricultural planning and assessment, engineering, environmental-impact assessment, utilities planning, or litigation.
The system for the collection and archiving of climatic data from approximately 7000 cooperative observing stations across the United States is in need of improvement. Despite the efforts of many dedicated volunteers and professionals, suspect or incomplete data continue to enter the national climate archive. Cooperative observers need further education regarding the importance of collecting complete and accurate data. The transition to the Maximum/Minimum Temperature Systems (MMTS) from the former liquid-in-glass thermometers mounted in Cotton Region shelters needs to be better coordinated, particularly with respect to the continuity of temperature data. The role of the Cooperative Program Managers in overseeing the physical well being of the network and the quality of data emanating from its needs to be strengthened. A continuation of efforts recently begun at the National Climatic Data Center (NCDC) to improve the digitization and quality-control procedures employed in data archiving is required. These improvements might be fulfilled within the present National Oceanic and Atmospheric Administration (NOAA) infrastructure. Another avenue which might be explored is the amalgamation of all aspects of the United States climate-observing system under the supervision of a new department within NOAA's National Environmental Satellite, Data, and Information Service (NESDIS). Regardless of how this is achieved, now is the time to improve the system. There has never been a greater need for a national climatic database of superlative quality, whether it be for investigations of climate change, meteorological research, agricultural planning and assessment, engineering, environmental-impact assessment, utilities planning, or litigation.
Abstract
Areally weighted clear sky surface albedo of snow-covered land in the middle and high latitudes of the Northern Hemisphere was measured from satellite imagery in A 1×1° latitude-longitude cells. The study area included 87% of the land polewards of 25°N, where Dickson and Posey found the probability of the seasonal occurrence of snow cover over −2.5 cm deep to be greater than zero. Albedo is 0.60 in Eurasia and 0.56 in North America, approximately 3.5 times greater than snow-free conditions. The highest average value for a 5° latitudinal zone is 0.77 at 70–75°N. The lowest is 0.43 at 60–75°N, which includes 0.36 in Eurasia and 0.58 in North America. The low albedo is due to the masking of snow covered ground by the canopy of coniferous forests.
Data were obtained by image processor analyses of Defense Meteorological Satellite Program imagery. Scene brightness was converted to surface albedo by linear interpolation between bright and dark snow-covered surfaces with known albedo.
The resulting chart is a refinement of an earlier product. The 1 × 1° digital data set is available for use in climate modeling.
Abstract
Areally weighted clear sky surface albedo of snow-covered land in the middle and high latitudes of the Northern Hemisphere was measured from satellite imagery in A 1×1° latitude-longitude cells. The study area included 87% of the land polewards of 25°N, where Dickson and Posey found the probability of the seasonal occurrence of snow cover over −2.5 cm deep to be greater than zero. Albedo is 0.60 in Eurasia and 0.56 in North America, approximately 3.5 times greater than snow-free conditions. The highest average value for a 5° latitudinal zone is 0.77 at 70–75°N. The lowest is 0.43 at 60–75°N, which includes 0.36 in Eurasia and 0.58 in North America. The low albedo is due to the masking of snow covered ground by the canopy of coniferous forests.
Data were obtained by image processor analyses of Defense Meteorological Satellite Program imagery. Scene brightness was converted to surface albedo by linear interpolation between bright and dark snow-covered surfaces with known albedo.
The resulting chart is a refinement of an earlier product. The 1 × 1° digital data set is available for use in climate modeling.
Abstract
Albedos of surfaces covered with 50 cm of fresh dry snow following a major U.S. East Coast storm on 11–12 February 1983 ranged from 0.20 over a mixed coniferous forest to 0.80 over open farmland. As the snow cover dissipated, albedo decreased in a quasi-linear fashion over forests. It dropped rapidly at first, then slowly, over shrubland; while the opposite was observed over farmland.
Following the melt, the albedo of snowfree surfaces ranged from 0.07 over a predominantly wet peat field to 0.20 over a field covered with corn stubble and yellow grass. The difference between snow-covered and snowfree albedo was 0.72 over the peaty field and 0.10 over the mixed forest.
Visible band (0.28–0.69 μm) reflectivities of snow-covered fields and shrubland were higher than those in the near-infrared (0.69–2.80 μm), whereas the opposite was true over mixed coniferous forests. Visible and near-infrared reflectivities were approximately equal over deciduous forests.
Data were collected in a series of low-altitude flights between 10 February and 24 March 1984 in northern New Jersey and southeastern New York with Eppley hemispheric pyranometers mounted on the wingtip of a Cessna 172 aircraft.
Abstract
Albedos of surfaces covered with 50 cm of fresh dry snow following a major U.S. East Coast storm on 11–12 February 1983 ranged from 0.20 over a mixed coniferous forest to 0.80 over open farmland. As the snow cover dissipated, albedo decreased in a quasi-linear fashion over forests. It dropped rapidly at first, then slowly, over shrubland; while the opposite was observed over farmland.
Following the melt, the albedo of snowfree surfaces ranged from 0.07 over a predominantly wet peat field to 0.20 over a field covered with corn stubble and yellow grass. The difference between snow-covered and snowfree albedo was 0.72 over the peaty field and 0.10 over the mixed forest.
Visible band (0.28–0.69 μm) reflectivities of snow-covered fields and shrubland were higher than those in the near-infrared (0.69–2.80 μm), whereas the opposite was true over mixed coniferous forests. Visible and near-infrared reflectivities were approximately equal over deciduous forests.
Data were collected in a series of low-altitude flights between 10 February and 24 March 1984 in northern New Jersey and southeastern New York with Eppley hemispheric pyranometers mounted on the wingtip of a Cessna 172 aircraft.
Abstract
This study presents a climatology of water vapor fluxes for the eastern United States and adjacent Atlantic with particular focus on the Northeast. Pathways of moisture transport comprising this climatology were discerned using a self-organizing map methodology ingesting daily integrated vapor transport data from ECMWF ERA-Interim Reanalysis from 1979 to 2017 at a 2.5° × 2.5° spatial resolution. Sixteen spatially distinct moisture transport patterns capture the variety of water vapor transport in the region. The climatology of water vapor transport is precisely and comprehensively defined via synthesis of spatial and temporal characteristics of the fluxes. Each flux has a distinct seasonality and frequency. The fluxes containing the highest amounts of moisture transport occur less frequently than those with less moisture transport. Because the patterns showing less moisture transport are prevalent, they are major contributors to the manner in which water vapor is moved through the eastern United States. The spatial confinement of fluxes is inversely related to persistence, with strong, narrow bands of enhanced moisture transport most often moving through the region on daily time scales. Many moisture fluxes meet a threshold-based definition of atmospheric rivers, with the diversity in trajectories and moisture sources indicating that a variety of mechanisms develop these enhanced moisture transport conditions. Temporal variability in the monthly frequencies of several of the fluxes in this study aligns with changes in the regional precipitation regime, demonstrating that this water vapor flux climatology provides a precise moisture-delivery framework from which changes in precipitation can be investigated.
Abstract
This study presents a climatology of water vapor fluxes for the eastern United States and adjacent Atlantic with particular focus on the Northeast. Pathways of moisture transport comprising this climatology were discerned using a self-organizing map methodology ingesting daily integrated vapor transport data from ECMWF ERA-Interim Reanalysis from 1979 to 2017 at a 2.5° × 2.5° spatial resolution. Sixteen spatially distinct moisture transport patterns capture the variety of water vapor transport in the region. The climatology of water vapor transport is precisely and comprehensively defined via synthesis of spatial and temporal characteristics of the fluxes. Each flux has a distinct seasonality and frequency. The fluxes containing the highest amounts of moisture transport occur less frequently than those with less moisture transport. Because the patterns showing less moisture transport are prevalent, they are major contributors to the manner in which water vapor is moved through the eastern United States. The spatial confinement of fluxes is inversely related to persistence, with strong, narrow bands of enhanced moisture transport most often moving through the region on daily time scales. Many moisture fluxes meet a threshold-based definition of atmospheric rivers, with the diversity in trajectories and moisture sources indicating that a variety of mechanisms develop these enhanced moisture transport conditions. Temporal variability in the monthly frequencies of several of the fluxes in this study aligns with changes in the regional precipitation regime, demonstrating that this water vapor flux climatology provides a precise moisture-delivery framework from which changes in precipitation can be investigated.
Abstract
Continental-scale snow cover extent has now been monitored from space for more than 20 yr in visible wavelengths. Here, the authors utilize weekly snow cover extent charts derived from such analyses to identify unusually rapid (1 week) spatially extensive snow cover accumulation and ablation events across the North American continent. Ancillary data are employed to describe the atmospheric patterns associated with the events. These episodes, which occur irregularly from year to year, bring about important changes in the total albedo of the continent.
Rapid extensive accumulation events occur during two preferred portions of the accumulation season. The early season accumulation events average 1-week snow cover increases of 3.9 × 106 km2 and begin near the end of October. Late season accumulation events occur 1 month later and lead to average increases of 3.5 × 106 km2. These rapid advances in the North American snowpack are associated with distinct and consistent atmospheric anomalies that are conducive to spatially extensive snowfalls.
Rapid ablation events also fall into two groupings based upon their timing within the annual cycle. Early season ablation episodes occur near the middle of March and account for snow cover losses averaging 2.1 × 106 km2. Early ablation events are associated with fluxes of sensible and latent heat induced by atmospheric disturbances moving along the Canadian–U.S. border. Late season events occur near the middle of May and are generally associated with anomalous high pressure at the surface and aloft over eastern Canada. This category of ablation events is not associated with large sensible heat flux to the snowpack. The loss of snow cover is more likely associated with downwelling longwave radiation fluxes from cloudy skies or shortwave radiation fluxes under clear-sky conditions.
Abstract
Continental-scale snow cover extent has now been monitored from space for more than 20 yr in visible wavelengths. Here, the authors utilize weekly snow cover extent charts derived from such analyses to identify unusually rapid (1 week) spatially extensive snow cover accumulation and ablation events across the North American continent. Ancillary data are employed to describe the atmospheric patterns associated with the events. These episodes, which occur irregularly from year to year, bring about important changes in the total albedo of the continent.
Rapid extensive accumulation events occur during two preferred portions of the accumulation season. The early season accumulation events average 1-week snow cover increases of 3.9 × 106 km2 and begin near the end of October. Late season accumulation events occur 1 month later and lead to average increases of 3.5 × 106 km2. These rapid advances in the North American snowpack are associated with distinct and consistent atmospheric anomalies that are conducive to spatially extensive snowfalls.
Rapid ablation events also fall into two groupings based upon their timing within the annual cycle. Early season ablation episodes occur near the middle of March and account for snow cover losses averaging 2.1 × 106 km2. Early ablation events are associated with fluxes of sensible and latent heat induced by atmospheric disturbances moving along the Canadian–U.S. border. Late season events occur near the middle of May and are generally associated with anomalous high pressure at the surface and aloft over eastern Canada. This category of ablation events is not associated with large sensible heat flux to the snowpack. The loss of snow cover is more likely associated with downwelling longwave radiation fluxes from cloudy skies or shortwave radiation fluxes under clear-sky conditions.
Abstract
No abstract available.
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No abstract available.
Abstract
This study presents the first evidence for the occurrence of a downslope windstorm in New Jersey. During the early morning hours of 4 January 2009, an unanticipated strong wind event was observed. Despite a zone forecast calling for winds less than 4 m s−1 issued 4 h prior to the event, winds up to 23 m s−1 were reported at High Point, New Jersey (elevation 550 m), with gusts to 30 m s−1 in its immediate lee (elevation 311 m). These winds were highly localized; a nearby Automated Surface Observing System (ASOS) station (Sussex, New Jersey, 12 km distant) reported calm winds between 0700 and 1000 UTC, just as the winds were peaking near High Point. High Point is the highest point in New Jersey, and is part of the quasi-two-dimensional Kittatinny Mountain extending from Pennsylvania into New York. This study tests the hypothesis that the topography of High Point, upon interacting with the local atmospheric stability and wind profiles, was sufficient to produce a downslope windstorm, thus causing these unusual winds. The results indicate that the presence of a sharp low-level temperature inversion in combination with a northwesterly low-level jet perpendicular to the ridge provided the key ingredients for the strong winds. Linear theory does not appear to explain the winds. Instead, prior studies incorporating nonlinearity predict a trapped lee wave or possibly a hydraulic jump, and model simulations suggest that High Point was indeed tall enough to generate such a wave along with rotors, although observations were not available to confirm this. Given sufficient model resolution, many aspects of this event were predictable. Similar windstorms have occurred before at High Point, but observations show that this event was the most amplified in recent years.
Abstract
This study presents the first evidence for the occurrence of a downslope windstorm in New Jersey. During the early morning hours of 4 January 2009, an unanticipated strong wind event was observed. Despite a zone forecast calling for winds less than 4 m s−1 issued 4 h prior to the event, winds up to 23 m s−1 were reported at High Point, New Jersey (elevation 550 m), with gusts to 30 m s−1 in its immediate lee (elevation 311 m). These winds were highly localized; a nearby Automated Surface Observing System (ASOS) station (Sussex, New Jersey, 12 km distant) reported calm winds between 0700 and 1000 UTC, just as the winds were peaking near High Point. High Point is the highest point in New Jersey, and is part of the quasi-two-dimensional Kittatinny Mountain extending from Pennsylvania into New York. This study tests the hypothesis that the topography of High Point, upon interacting with the local atmospheric stability and wind profiles, was sufficient to produce a downslope windstorm, thus causing these unusual winds. The results indicate that the presence of a sharp low-level temperature inversion in combination with a northwesterly low-level jet perpendicular to the ridge provided the key ingredients for the strong winds. Linear theory does not appear to explain the winds. Instead, prior studies incorporating nonlinearity predict a trapped lee wave or possibly a hydraulic jump, and model simulations suggest that High Point was indeed tall enough to generate such a wave along with rotors, although observations were not available to confirm this. Given sufficient model resolution, many aspects of this event were predictable. Similar windstorms have occurred before at High Point, but observations show that this event was the most amplified in recent years.
Abstract
Spatial and temporal patterns in the onset, offset, and length of the snow season across Northern Hemisphere continents are examined for the period from 1967 to 2008. Full snow seasons (FSS) and core snow seasons (CSS) are defined based on the consistency of snow cover within a location over the course of the cold season. Climatologically, the seasonal onsets of FSS and CSS progress more rapidly across the continents than the slower spring northward offset. Average Northern Hemisphere FSS duration has decreased at a rate of 0.8 week decade−1 (5.3 days decade−1) between the winters of 1972/73 and 2007/08, while there is no significant hemispheric change in CSS duration. Changes in the FSS duration are attributed primarily to a progressively earlier offset, which has advanced poleward at a rate of 5.5 days decade−1. A major change in the trends of FSS offset and duration occurred in the late 1980s. Earlier FSS offsets, ranging from 5 to 25 days, and resultant abbreviated durations are observed in western Europe, central and East Asia, and the mountainous western United States. Where regional changes in CSS were observed, most commonly there were shifts in both onset and offset dates toward earlier dates. Results indicate that it is important to pay close attention to spring snowmelt as an indicator of hemispheric climate variability and change.
Abstract
Spatial and temporal patterns in the onset, offset, and length of the snow season across Northern Hemisphere continents are examined for the period from 1967 to 2008. Full snow seasons (FSS) and core snow seasons (CSS) are defined based on the consistency of snow cover within a location over the course of the cold season. Climatologically, the seasonal onsets of FSS and CSS progress more rapidly across the continents than the slower spring northward offset. Average Northern Hemisphere FSS duration has decreased at a rate of 0.8 week decade−1 (5.3 days decade−1) between the winters of 1972/73 and 2007/08, while there is no significant hemispheric change in CSS duration. Changes in the FSS duration are attributed primarily to a progressively earlier offset, which has advanced poleward at a rate of 5.5 days decade−1. A major change in the trends of FSS offset and duration occurred in the late 1980s. Earlier FSS offsets, ranging from 5 to 25 days, and resultant abbreviated durations are observed in western Europe, central and East Asia, and the mountainous western United States. Where regional changes in CSS were observed, most commonly there were shifts in both onset and offset dates toward earlier dates. Results indicate that it is important to pay close attention to spring snowmelt as an indicator of hemispheric climate variability and change.
Abstract
Eighteen global atmospheric general circulation models (AGCMs) participating in the second phase of the Atmospheric Model Intercomparison Project (AMIP-2) are evaluated for their ability to simulate the observed spatial and temporal variability in snow mass, or water equivalent (SWE), over North America during the AMIP-2 period (1979–95). The evaluation is based on a new gridded SWE dataset developed from objective analysis of daily snow depth observations from Canada and the United States with snow density estimated from a simple snowpack model. Most AMIP-2 models simulate the seasonal timing and the relative spatial patterns of continental-scale SWE fairly well. However, there is a tendency to overestimate the rate of ablation during spring, and significant between-model variability is found in every aspect of the simulations, and at every spatial scale analyzed. For example, on the continental scale, the peak monthly SWE integrated over the North American continent in AMIP-2 models varies between ±50% of the observed value of ∼1500 km3. The volume of water in the snowpack, and the magnitudes of model errors, are significant in comparison to major fluxes in the continental water balance. It also appears that the median result from the suite of models tends to do a better job of estimating climatological mean features than any individual model. Year-to-year variations in large-scale SWE are only weakly correlated to observed variations, indicating that sea surface temperatures (specified from observations as boundary conditions) do not drive interannual variations of SWE in these models. These results have implications for simulations of the large-scale hydrologic cycle and for climate change impact assessments.
Abstract
Eighteen global atmospheric general circulation models (AGCMs) participating in the second phase of the Atmospheric Model Intercomparison Project (AMIP-2) are evaluated for their ability to simulate the observed spatial and temporal variability in snow mass, or water equivalent (SWE), over North America during the AMIP-2 period (1979–95). The evaluation is based on a new gridded SWE dataset developed from objective analysis of daily snow depth observations from Canada and the United States with snow density estimated from a simple snowpack model. Most AMIP-2 models simulate the seasonal timing and the relative spatial patterns of continental-scale SWE fairly well. However, there is a tendency to overestimate the rate of ablation during spring, and significant between-model variability is found in every aspect of the simulations, and at every spatial scale analyzed. For example, on the continental scale, the peak monthly SWE integrated over the North American continent in AMIP-2 models varies between ±50% of the observed value of ∼1500 km3. The volume of water in the snowpack, and the magnitudes of model errors, are significant in comparison to major fluxes in the continental water balance. It also appears that the median result from the suite of models tends to do a better job of estimating climatological mean features than any individual model. Year-to-year variations in large-scale SWE are only weakly correlated to observed variations, indicating that sea surface temperatures (specified from observations as boundary conditions) do not drive interannual variations of SWE in these models. These results have implications for simulations of the large-scale hydrologic cycle and for climate change impact assessments.
Abstract
Significant declines in spring Northern Hemisphere (NH) snow cover extent (SCE) have been observed over the last five decades. As one step toward understanding the causes of this decline, an optimal fingerprinting technique is used to look for consistency in the temporal pattern of spring NH SCE between observations and simulations from 15 global climate models (GCMs) that form part of phase 5 of the Coupled Model Intercomparison Project. The authors examined simulations from 15 GCMs that included both natural and anthropogenic forcing and simulations from 7 GCMs that included only natural forcing. The decline in observed NH SCE could be largely explained by the combined natural and anthropogenic forcing but not by natural forcing alone. However, the 15 GCMs, taken as a whole, underpredicted the combined forcing response by a factor of 2. How much of this underprediction was due to underrepresentation of the sensitivity to external forcing of the GCMs or to their underrepresentation of internal variability has yet to be determined.
Abstract
Significant declines in spring Northern Hemisphere (NH) snow cover extent (SCE) have been observed over the last five decades. As one step toward understanding the causes of this decline, an optimal fingerprinting technique is used to look for consistency in the temporal pattern of spring NH SCE between observations and simulations from 15 global climate models (GCMs) that form part of phase 5 of the Coupled Model Intercomparison Project. The authors examined simulations from 15 GCMs that included both natural and anthropogenic forcing and simulations from 7 GCMs that included only natural forcing. The decline in observed NH SCE could be largely explained by the combined natural and anthropogenic forcing but not by natural forcing alone. However, the 15 GCMs, taken as a whole, underpredicted the combined forcing response by a factor of 2. How much of this underprediction was due to underrepresentation of the sensitivity to external forcing of the GCMs or to their underrepresentation of internal variability has yet to be determined.
