A 42 year inference of cloud base height trends in the Luquillo Mountains of northeastern Puerto Rico

TitleA 42 year inference of cloud base height trends in the Luquillo Mountains of northeastern Puerto Rico
Publication TypeJournal Article
Year of Publication2018
AuthorsMiller, PW, Mote, TL, Ramseyer, CA, Van Beusekom, AE, Scholl, MA, Gonzalez, G
JournalClimate Research
KeywordsCaribbean, Cloud base height, cloud forest, Lifted condensation level, Luquillo Mountains, Tropical Rainforest
AbstractThe Luquillo Mountains of eastern Puerto Rico are home to the only tropical rainfor- est managed by the United States Forest Service, with cloud-immersed forests historically occupy- ing the highest elevations. However, within the past 50 yr, studies of the Luquillo cloud forest have suggested an increase in cloud base heights (CBH), although the CBH in the area was not quan- tified until recently. The present work uses radiosonde observations from nearby San Juan, Puerto Rico, to contextualize the present-day CBH within a 42 yr (1975−2016) proxy record and deter- mine evidence for rising cloud base. Two key questions are addressed: (1) Can theoretical CBH calculations from San Juan provide a reasonable proxy for CBHs in the Luquillo Mountains? (2) Does a significant trend accompany the CBH lifting inferred from recent work in the region? The mean-layer lifted condensation level (MLLCL), a thermodynamic parameter expressing the alti- tude at which a rising air parcel reaches 100% relative humidity, serves as the proxy. The 42 yr MLLCL time series corroborates both the low CBHs claimed in the 1980s and the higher CBHs documented by recent work. When considering all available radiosonde data, statistically signifi- cant increasing CBH trends are detected for all seasons. However, when the record is standard- ized to correct for progressive vertical resolution improvements to radiosonde observations, recent CBH increases are more modest than initially indicated, and statistically significant increases are only apparent in the late rainfall season.