cloud water

Speciation of water‐soluble inorganic, organic, and total nitrogen in a background marine environment: Cloud water, rainwater, and aerosol particles

Gioda, A., G. J. Reyes‐Rodríguez, G. Santos‐Figueroa, J. L. Collett Jr., S. Decesari, M. d. C. K. V. Ramos, H. J. C.
Bezerra Netto, F. R. de Aquino Neto, and O. L. Mayol‐Bracero (2011), Speciation of water‐soluble inorganic, organic, and total
nitrogen in a background marine environment: Cloud water, rainwater, and aerosol particles, J. Geophys. Res., 116, D05203,
doi:10.1029/2010JD015010.

Abstract: 
Cloud water, rainwater, and aerosol particles were collected in Puerto Rico from December 2004 to March 2007 in order to investigate their chemical composition, relation to sources, and removal processes. The species analyzed were inorganic ions, metals, total and dissolved organic carbon (TOC, DOC), total nitrogen (TN), and organic acids. For all samples, the dominant species were marine (Na+, Cl−), representing about 50%–65% of total content. Non‐sea‐salt fraction was dominated by SO42− (17%–25%), followed by water‐soluble organic (2%–8%) and total nitrogen (2% –6%) compounds. Organic acids represented contributions to the organic fraction in cloud water of 20% and 6% for aerosol particles. Inorganic species were predominant in total nitrogen portion. The chemical composition of cloud water, rainwater, and aerosol particles were observed to be sensitive to transport patterns. Air masses from northwest Africa showed the highest concentrations of nss‐Ca2+, Fe, and Al, suggesting a crustal origin. The pH values for cloud water and rainwater observed under this transport pattern were higher than background conditions, probably due to the alkalinity associated with nss‐Ca2+. The highest concentrations of Cl− and SO42−, with lower pH, were measured during periods of influence from Soufriere Hills volcano eruptions, most likely due to emitted SO2 and HCl. Air masses from North America had an anthropogenic influence, where levels of nss‐SO42−, TOC, and TN were higher (∼4 times) than in clean air masses. These results suggest that long‐range transport could be an extra source of metals and organic/nitrogen species to the Caribbean region ecosystems.

Cloud water in windward and leeward mountain forests: The stable isotope signature of orographic cloud water

Scholl, M. A., T. W. Giambelluca, S. B. Gingerich, M. A. Nullet, and L. L. Loope (2007), Cloud water in windward
and leeward mountain forests: The stable isotope signature of orographic cloud water, Water Resour. Res., 43, W12411,
doi:10.1029/2007WR006011.

Abstract: 
Cloud water can be a significant hydrologic input to mountain forests. Because it is a precipitation source that is vulnerable to climate change, it is important to quantify amounts of cloud water input at watershed and regional scales. During this study, cloud water and rain samples were collected monthly for 2 years at sites on windward and leeward East Maui. The difference in isotopic composition between volume-weighted average cloud water and rain samples was 1.4% d18O and 12% d2H for the windward site and 2.8% d18O and 25% d2H for the leeward site, with the cloud water samples enriched in 18O and 2H relative to the rain samples. A summary of previous literature shows that fog and/or cloud water is enriched in 18O and 2H compared to rain at many locations around the world; this study documents cloud water and rain isotopic composition resulting from weather patterns common to montane environments in the trade wind latitudes. An end-member isotopic composition for cloud water was identified for each site and was used in an isotopic mixing model to estimate the proportion of precipitation input from orographic clouds. Orographic cloud water input was 37% of the total precipitation at the windward site and 46% at the leeward site. This represents an estimate of water input to the forest that could be altered by changes in cloud base altitude resulting from global climate change or deforestation.

The stable isotope amount effect: New insights from NEXRAD echo tops, Luquillo Mountains, Puerto Rico

Scholl MA, Shanley JB, Zegarra JP, Coplen TB. 2009. The stable isotope
amount effect: new insights from NEXRAD echo tops, Luquillo
Mountains, Puerto Rico. Water Resources Research 45: W12407, DOI:
10.1029/2008WR007515.

Abstract: 
The stable isotope amount effect has often been invoked to explain patterns of isotopic composition of rainfall in the tropics. This paper describes a new approach, correlating the isotopic composition of precipitation with cloud height and atmospheric temperature using NEXRAD radar echo tops, which are a measure of the maximum altitude of rainfall within the clouds. The seasonal differences in echo top altitudes and their corresponding temperatures are correlated with the isotopic composition of rainfall. These results offer another factor to consider in interpretation of the seasonal variation in isotopic composition of tropical rainfall, which has previously been linked to amount or rainout effects and not to temperature effects. Rain and cloud water isotope collectors in the Luquillo Mountains in northeastern Puerto Rico were sampled monthly for three years and precipitation was analyzed for δ18O and δ2H. Precipitation enriched in 18O and 2H occurred during the winter dry season (approximately December-May) and was associated with a weather pattern of trade-wind showers and frontal systems. During the summer rainy season (approximately June-November), precipitation was depleted in 18O and 2H and originated in low pressure systems and convection associated with waves embedded in the prevailing easterly airflow. Rain substantially depleted in 18O and 2H compared to the aforementioned weather patterns occurred during large low pressure systems. Weather analysis showed that 29 % of rain input to the Luquillo Mountains was trade-wind orographic rainfall, and 30 % of rainfall could be attributed to easterly waves and low pressure systems. Isotopic signatures associated with these major climate patterns can be used to determine their influence on streamflow and groundwater recharge and to monitor possible effects of climate change on regional water resources.
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