cloud water
Speciation of water‐soluble inorganic, organic, and total nitrogen in a background marine environment: Cloud water, rainwater, and aerosol particles
Thu, 07/28/2011 - 15:26 — ckassGioda, 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
Thu, 07/28/2011 - 15:09 — ckassScholl, 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
Thu, 07/28/2011 - 15:07 — ckassScholl 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.
