Spatial and temporal variations in precipitation and cloud interception in the Sierra Nevada of central California

Spatial and temporal variations in patterns of precipitation and cloud interception were studied for a period of 14 months in the Sierra Nevada of central California. 14 fully automated sampling stations, located at elevations from 800 to 2400 m, were utilized in the study. Both precipitation and cloud interception were observed to increase with elevation. Cloudwater deposition increased at higher elevations due both to a greater frequency of cloud interception and higher wind speeds. Cloudwater deposition, caused primarily by the interception of clouds associated with cold fronts approaching from the north or north-west, is most important at elevations above 1500 m; however, the interception of highly polluted winter “Tule” fogs, lifting above the floor of the San Joaquin Valley, appears to be an important mechanism for cloudwater deposition at lower elevation sites. Observed and estimated hydrological and chemical inputs to the passive cloudwater collectors used in the study were substantial, suggesting that cloud interception may contribute significantly to the same inputs for exposed conifers in the region

Cloud water chemistry in Sequoia National Park

Interception of cloudwater by forests in the Sierra Nevada Mountains may contribute significantly to acidic deposition in the region. Cloudwater sampled in Sequoia National Park had pH values ranging from 4.4 to 5.7. The advance of cold fronts into the Park appears to lead to higher aerosol and gas phase concentrations than are seen under normal mountain-valley circulations, producing higher cloud-water concentrations than might otherwise be expected. Estimates of annual deposition rates of NO_3^−, SO_4^(2−), NH_4^+ and H^+ due to cloudwater impaction are comparable to those measured in precipitation

Automated rainwater collector

An automated rain water collector is disclosed to collect a plurality of successive rain water samples, comprised of a reservoir into which rain water is collected and discharged, and a motor-driven turntable which holds a plurality of sample bottles. When the reservoir is filled to a predetermined volume, means, such as a liquid level sensor, actuates a valve to open same and discharge the liquid sample from the reservoir into one of the bottles at a filling station on the turntable. The valve then closes and the turntable rotates to index the next bottle beneath the reservoir at the filling station, and the operation is repeated to fill the latter bottle. When all of the bottles on the turntable have been filled, the indexing means is deactivated and liquid accumulating in the reservoir is diverted to an overflow bottle

Active cloudwater collector

A cloud water collector is disclosed comprised of a sampler duct having a plurality of spaced Teflon strands, in the form of screens, mounted across the conduit at an acute angle facing the open inlet of the conduit. Droplets in a cloud sample are drawn into the conduit by a fan located at the back end of the conduit, impact upon the Teflon strands and are drawn down to the lower ends of the strands, where they drop and the accumulated droplets are diverted to a sample bottle for collection. The cloud water collector can be automated to collect a plurality of successive cloud water samples by an automated sampler containing a reservoir into which cloud water obtained in the cloud water collector is discharged. A motor-driven turntable is provided which holds a plurality of sample bottles. When the reservoir is filled to a predetermined volume, apparatus, such as a liquid level sensor, actuates a valve to open same and discharge the liquid sample from the reservoir into one of the bottles at a filling station on the turntable. The valve then closes and the turntable rotates to index the next bottle beneath the reservoir at the filling station, and the operation is repeated to fill the latter bottle. When all of the bottles on the turntable have been filled, the indexing mechanism is deactivated and liquid accumulating in the reservoir is diverted to an overflow bottle

Vertical Transport Rates in the Stratosphere in 1993 from Observations of CO2, N2O and CH4

Measurements of CO2, N2O and CH4 are analyzed to define hemispheric average vertical exchange rates in the lower stratosphere from November 1992 to October 1993. Effective vertical diffusion coefficients were small in summer, less than or equal to 1 m(exp 2)/sec at altitudes below 25 km; values were similar near the tropopause in winter, but increased markedly with altitude. The analysis suggests possibly longer residence times for exhaust from stratospheric aircraft, and more efficient transport from 20 km to the middle stratosphere, than predicted by many current models. Seasonally-resolved measurements of stratospheric CO2 and N2O provide significant new constraints on rates for global-scale vertical transport

Evaluation of single-footprint AIRS CH4 profile retrieval uncertainties using aircraft profile measurements

We evaluate the uncertainties of methane optimal estimation retrievals from single-footprint thermal infrared observations from the Atmospheric Infrared Sounder (AIRS). These retrievals are primarily sensitive to atmospheric methane in the mid-troposphere through the lower stratosphere (&sim;2 to &sim;17&thinsp;km). We compare them to in situ observations made from aircraft during the HIAPER Pole to Pole Observations (HIPPO) and Atmospheric Tomography Mission (ATom) campaigns, and from the NOAA GML aircraft network, between the surface and 5&ndash;13&thinsp;km, across a range of years, latitudes between 60∘&thinsp;S to 80∘&thinsp;N, and over land and ocean. After a global, pressure-dependent bias correction, we find that the land and ocean have similar biases and that the reported observation error (combined measurement and interference errors) of &sim;27&thinsp;ppb is consistent with the SD between aircraft and individual AIRS observations. A single observation has measurement (noise related) uncertainty of &sim;17&thinsp;ppb, a &sim;20&thinsp;ppb uncertainty from radiative interferences (e.g., from water or temperature), and &sim;30&thinsp;ppb due to &ldquo;smoothing error&rdquo;, which is partially removed when making comparisons to in situ measurements or models in a way that accounts for this regularization. We estimate a 10&thinsp;ppb validation uncertainty because the aircraft typically did not measure methane at altitudes where the AIRS measurements have some sensitivity, e.g., the stratosphere, and there is uncertainty in the truth that we validate against. Daily averaging only partly reduces the difference between aircraft and satellite observation, likely because of correlated errors introduced into the retrieval from temperature and water vapor. For example, averaging nine observations only reduces the aircraft&ndash;model difference to &sim;17&thinsp;ppb vs. the expected &sim;10&thinsp;ppb. Seasonal averages can reduce this &sim;17&thinsp;ppb uncertainty further to &sim;10&thinsp;ppb, as determined through comparison with NOAA aircraft, likely because uncertainties related to radiative effects of temperature and water vapor are reduced when averaged over a season. &nbsp;</p

The chemical composition of intercepted cloudwater in the Sierra Nevada

The chemical composition of cloudwater in the Sierra Nevada is dominated by NO_3^−, SO_4^(2−), and NH_4^+. Cloudwater pH is determined largely by the balance between the concentrations of these three species, although inputs of formic and acetic acid also are believed to be important, particularly when anthropogenic inputs are small. Cloudwater samples collected in Sequoia National Park (SNP) exhibited pH values ranging from 3.9 to 6.5; Yosemite National Park (YNP) cloudwater samples had pH values ranging from 3.8 to 5.2. Samples collected at YNP were more acidic than those collected at SNP. The difference in pH between the two regions appears to be due to relatively small differences in inputs of NO_3^−, SO_4^(2−), and NH_4^+. In the absence of inputs of NH_3, cloudwater pH values in the Sierra may fall below 3. Over 250 h of cloud interception were observed during a 12 month period at a cloud monitoring site at 1856 m elevation in SNP. Estimates of cloudwater deposition of NO_3^−, SO^4^(2−), and NH^4^+ indicate that cloud interception contributes significantly to regional acid deposition for closed forest canopies. Cloud interception may be the dominant deposition mechanism for isolated conifers and ridgetop canopies, where wind speeds are higher and cloudy air parcels can impact directly on foliar surfaces

Chemical composition of coastal stratus clouds: Dependence on droplet size and distance from the coast

The aerosol at elevated sites in the South Coast Air Basin in California is a mixture of sea salt and pollution-derived secondary aerosol. The influence of sea salt declines with increasing distance from the coast. Nitric acid appears to react with the NaCl in sea salt aerosol to release HCl_(g) and form NaNO_3 in the aerosol. At inland sites, aerosol concentrations differ during periods of onshore and offshore flow. The highest concentrations were observed during the day when the onshore flow transported pollutants to the sites, while lower concentrations were observed at night when drainage flows from nearby mountains influenced the sites. Variations, in liquid water content are a major influence on cloudwater ion concentrations. Comparisons of the ionic concentrations in two size-segregated fractions of cloudwater collected during several sampling intervals suggest that there is a large difference between the average composition of the smaller droplets and that of the larger droplets. The concentrations of Na^+, Ca^(2+) and Mg^(2+) in the large-droplet fraction were observed to be higher than in the small-droplet fraction, while the concentrations of SO_4^(2−), NO_3^−, NH_4^+ and H^+ were higher in the small-droplet fraction. Chloride concentrations were nearly equal in both fractions. Differences in the composition of size-fractionated cloudwater samples suggest that large droplets are formed on sea salt and soil dust, which are large aerosol, and small droplets are formed on small secondary aerosol composed primarily of (NH_4)_2SO_4 and NH_4NO_3. The concentrations of several components that exist partly in the gas phase (e.g. Cl^−, HCOOH and CH_3COOH) appear to be independent of droplet size

Fogwater chemistry at Riverside, California

Fog, aerosol, and gas samples were collected during the winter of 1986 at Riverside, California. The dominant components of the aerosol were NH_4^+, NO_3^−, and SO_(42−). Gaseous NH_3 was frequently present at levels equal to or exceeding the aerosol NH_4^+. Maximum level were 3800, 3100, 690 and 4540 neq m^(−3) for NH_4^+, NO_3^(2−) and NH_(3(g)), respectively. The fogwater collected at Riverside had very high concentrations, particularly of the major aerosol components. Maximum concentrations were 26,000 29,000 and 6200 μM for NH_4^+, NO_3^− and SO_4^(2−), respectively. pH values in fogwater ranged from 2.3 to 5.7. Formate and acetate concentrations as high as 1500 and 580 μM, respectively, were measured. The maximum CH_2O concentration was 380 μM. Glyoxal and methylglyoxal were found in all the samples; their maximum concentrations were 280 and 120 μM, respectively. Comparison of fogwater and aerosol concentrations indicates that scavenging of precursor aerosol by fog droplets under the conditions at Riverside is less than 100% efficient. The chemistry at Riverside is controlled by the balance between HNO_3 production from NO_x emitted throughout the Los Angeles basin and NH3 emitted from dairy cattle feedlots just west of Riverside. The balance is controlled by local mixing. Acid fogs result at Riverside when drainage flows from the surrounding mountains isolate the site from the NH_3 source. Continued formation of HNO_(3(g)) in this air mass eventually depletes the residual NH_(3(g)). A simple box model that includes deposition, fog scavenging, and dilution is used to assess the effect of curtailing the dairy cattle feedlot operations. The calculations suggest that the resulting reduction of NH_3 levels would decrease the total NO_3^− in the atmosphere, but nearly all remaining NO_3^− would exist as HNO_3. Fogwater in the basin would be uniformly acidic