129 research outputs found
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Trends in snow water equivalent in the Pacific Northwest and their climatic causes
Observations of snow water equivalent (SWE) in the Pacific Northwest are examined and compared with variability and trends in temperature and precipitation at nearby climate stations. At most locations, especially below about 1800 m, substantial declines in SWE coincide with significant increases in temperature, and occur in spite of increases in precipitation
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The annual cycle of stratospheric water vapor in a general circulation model
The application of general circulation models (GCMs) to stratospheric chemistry and transport both permits and requires a thorough investigation of stratospheric water vapor. The National Center for Atmospheric Research has redesigned its GCM, the Community Climate Model (CCM2), to enable studies of the chemistry and transport of tracers including water vapor; the importance of water vapor to the climate and chemistry of the stratosphere requires that it be better understood in the atmosphere and well represented in the model. In this study, methane is carried as a tracer and converted to water; this simple chemistry provides an adequate representation of the upper stratospheric water vapor source. The cold temperature bias in the winter polar stratosphere, which the CCM2 shares with other GCMs, produces excessive dehydration in the southern hemisphere, but this dry bias can be ameliorated by setting a minimum vapor pressure. The CCM2's water vapor distribution and seasonality compare favorably with observations in many respects, though seasonal variations including the upper stratospheric semiannual oscillation are generally too small. Southern polar dehydration affects midlatitude water vapor mixing ratios by a few tenths of a part per million, mostly after the demise of the vortex. The annual cycle of water vapor in the tropical and northern midlatitude lower stratosphere is dominated by drying at the tropical tropopause. Water vapor has a longer adjustment time than methane and had not reached equilibrium at the end of the 9 years simulated here
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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 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.Keywords: Hydrology, Temperature, Snowmelt, Precipitation, Sno
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Reconsideration of the cause of dry air in the southern middle latitude stratosphere
A previous comparison of data from the Halogen Occultation Experiment (HALOE) and of output from the NCAR Community Climate Model (CCM2) in austral spring overstated the effect of dehydration in the southern polar vortex on lower strato spheric water vapor in part due to shortcomings in the HALOE retrieval algorithm and in part to remnants of the initially dry stratosphere in the CCM2 run. A new HALOE retrieval and a longer CCM2 run both show more water vapor than previously, but HALOE still shows less in the southern hemisphere than in the northern in September-October 1992. A "dried-air" tracer iri the CCM2 suggests that polar dehydration influences middle latitudes only below about 100 hPa, and seasonal variations of HALOE H2O imply no influence north of 50°S
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Snow White and the Six Dwarves Run Climate Models in Italy
No Abstract Available
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Variability of clouds and water vapor in low latitudes: view from Moderate Resolution Imaging Spectroradiometer (MODIS)
This paper shows a small sampling of the atmospheric fields provided by the
Moderate Resolution Imaging Spectroradiometer (MODIS), which is installed on both the
Terra and Aqua satellites of the Earth Observing System. These fields include macroscale
fields like cloud fraction, cloud top pressure, cloud optical depth, and column water vapor,
and microscale fields like cloud particle effective radius. Most of the atmospheric fields
resemble, in spatial pattern and temporal evolution, the cloud top temperature field;
several, however, including effective radius and clear-sky water vapor, have markedly
different spatial patterns and temporal evolution, suggesting that large-scale controls on
tropical water vapor are more complicated than a simple connection with large-scale
convergence and convection would suggest. As with several previous studies, the cloud
top temperature or pressure has a bimodal distribution with peaks in both the lower
and upper troposphere. Our analysis also reveals a dependence of cloud effective particle
size on sea surface temperature
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Three Recent Flavors of Drought in the Pacific Northwest
In common with much of the western United States, the Pacific Northwest (defined in this paper as Washington and Oregon) has experienced an unusual number of droughts in the past decade. This paper describes three of these droughts in terms of the precipitation, temperature, and soil moisture anomalies, and discusses different drought impacts experienced in the Pacific Northwest (PNW). For the first drought, in 2001, low winter precipitation in the PNW produced very low streamflow that primarily affected farmers and hydropower generation. For the second, in 2003, low summer precipitation in Washington (WA), and low summer precipitation and a warm winter in Oregon (OR) primarily affected streamflow and forests. For the last, in 2005, a lack of snowpack due to warm temperatures during significant winter precipitation events in WA, and low winter precipitation in OR, had a variety of different agricultural and hydrologic impacts. Although the proximal causes of droughts are easily quantified, the ultimate causes are not as clear. Better precipitation observations in the PNW are required to provide timely monitoring of conditions leading to droughts to improve prediction in the futur
Landscape-Scale Conservation And Management Of Montane Wildlife: Contemporary Climate May Be Changing The Rules
Both paleontological and contemporary results have suggested that montane ecosystems to be systems of relatively rapid faunal change compared to many valley-bottom counterparts. In addition to experiencing greater magnitudes of contemporary change in climatic parameters than species in other ecosystems, mountain-dwelling wildlife must also accommodate often greater intra-annual swings in temperature and wind speeds, poorly developed soils, and generally harsher conditions. Research on a mountain-dwelling mammal species across 15 yrs of contemporary data and historical records from 1898-1956 suggest that pace of local extinctions and rate of upslope retraction have been markedly more rapid and governed by markedly different dynamics in the last decade than during the 20th century. This may mean that understanding past dynamics of species losses may not always help predict patterns of future loss. Given the importance of clinal variability and ecotypic variation, phenotypic plasticity, behavioral plasticity, and variation in climatic conditions, for widely-distributed species’ geographic ranges to be determined by different factors in different portions of their range is not uncommon. Consequently, greatest progress in understanding distributionalchange phenomena will occur with coordinated, landscape-scale research and monitoring. Landscape Conservation Cooperatives and Climate Science Centers are newly emerging efforts that may contribute greatly to such broad-scale investigations, e.g., climate-wildlife relationships. Based on our empirical findings and our review of related literature, we propose tenets that may serve as foundational starting points for mechanism-based research at broad scales to inform management and conservation of diverse montane wildlife and the ecosystem components with which they interact
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Sub-seasonal variations in lower stratospheric water vapor
Observations of water vapor with high temporal and spatial resolution and good horizontal coverage just above the tropical tropopause have been scarce, but a preliminary version of such data has been developed using radiance measurements of the Microwave Limb Sounder. These data reveal distinct variations with periods in the ranges 10-25 days and 30-70 days, consistent with (respectively) slow Kelvin waves and the tropical intraseasonal oscillation
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Simulation of the Pinatubo aerosol cloud in general circulation model
A high resolution stratospheric version of the NCAR Community Climate Model (CCM2) with an annual cycle was used to simulate the global transport and dispersion of the Pinatuboa aerosol cloud. A passive tracer was injected into the model stratosphere over the Philippines Islands on model day June15, and the transport was simulated for 180 days using an accurate semi-Lagrangian advection scheme.
The simulated volcanic aerosol cloud initially drifted westward and expanded in longitude and latitude. The bulk of the aerosol cloud dispersed zonally to form a continuous belt in longitude and remained confined to the tropics (30°N- 25°S) centered near the 20 mb level for the entire 180 day model run, although a small amount was transported episodically into the upper troposphere in association with convective disturbances. Aerosol transported to the troposphere was dispersed within a few weeks into the Northern Hemisphere extratropics. In the Southern Hemisphere the aerosol was mixed into the region equatorward of the core of the polar night jet during the first 50 days, but penetration into Southern Polar latitudes was delayed until the final warming in November. These results, which are generally consistent with observed behavior of the El Chichon aerosol, will be compared with observations of the Pinatubo cloud in the course of the next several months
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