Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 7245-7259, 2017
https://doi.org/10.5194/acp-17-7245-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
16 Jun 2017
Analyzing cloud base at local and regional scales to understand tropical montane cloud forest vulnerability to climate change
Ashley E. Van Beusekom1, Grizelle González1, and Martha A. Scholl2 1USDA Forest Service International Institute of Tropical Forestry, Jardín Botánico Sur, 1201 Calle Ceiba, Río Piedras, Puerto Rico 00926, USA
2US Geological Survey National Research Program, 12201 Sunrise Valley Drive, Reston, VA 20192, USA
Abstract. The degree to which cloud immersion provides water in addition to rainfall, suppresses transpiration, and sustains tropical montane cloud forests (TMCFs) during rainless periods is not well understood. Climate and land use changes represent a threat to these forests if cloud base altitude rises as a result of regional warming or deforestation. To establish a baseline for quantifying future changes in cloud base, we installed a ceilometer at 100 m altitude in the forest upwind of the TMCF that occupies an altitude range from ∼ 600 m to the peaks at 1100 m in the Luquillo Mountains of eastern Puerto Rico. Airport Automated Surface Observing System (ASOS) ceilometer data, radiosonde data, and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite data were obtained to investigate seasonal cloud base dynamics, altitude of the trade-wind inversion (TWI), and typical cloud thickness for the surrounding Caribbean region. Cloud base is rarely quantified near mountains, so these results represent a first look at seasonal and diurnal cloud base dynamics for the TMCF. From May 2013 to August 2016, cloud base was lowest during the midsummer dry season, and cloud bases were lower than the mountaintops as often in the winter dry season as in the wet seasons. The lowest cloud bases most frequently occurred at higher elevation than 600 m, from 740 to 964 m. The Luquillo forest low cloud base altitudes were higher than six other sites in the Caribbean by ∼ 200–600 m, highlighting the importance of site selection to measure topographic influence on cloud height. Proximity to the oceanic cloud system where shallow cumulus clouds are seasonally invariant in altitude and cover, along with local trade-wind orographic lifting and cloud formation, may explain the dry season low clouds. The results indicate that climate change threats to low-elevation TMCFs are not limited to the dry season; changes in synoptic-scale weather patterns that increase frequency of drought periods during the wet seasons (periods of higher cloud base) may also impact ecosystem health.

Citation: Van Beusekom, A. E., González, G., and Scholl, M. A.: Analyzing cloud base at local and regional scales to understand tropical montane cloud forest vulnerability to climate change, Atmos. Chem. Phys., 17, 7245-7259, https://doi.org/10.5194/acp-17-7245-2017, 2017.
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Short summary
For three years of data in the Luquillo Mountains of Puerto Rico, cloud base was lowest during the mid-summer dry season, and cloud bases were lower than the mountaintops as often in the winter dry season as in the wet seasons. The results indicate climate change threats to cloud forests are not limited to the dry season; changes in synoptic-scale weather patterns that increase frequency of drought periods during the wet seasons (periods of higher cloud base) may also impact ecosystem health.
For three years of data in the Luquillo Mountains of Puerto Rico, cloud base was lowest during...
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