Characteristics of aerosol and cloud particle size distributions in the tropical tropopause layer measured with optical particle counter and lidar

International audienceAn optical particle counter (OPC) is used in conjunction with lidar measurements to examine the characteristics of the particle size distribution in cirrus cloud in the tropical tropopause layer (TTL) over Thailand where the TTL is defined as the height at which temperature is lower than ?75°C in this paper. Of 11 OPC launches, cirrus cloud was detected at 10?15 km high on 7 occasions, cirrus was detected in the TTL in 6 cases, and simultaneous OPC and lidar measurements were made on two occasions. Comparison of lidar and OPC measurements reveal that the cloud heights of cirrus in the TTL varies by several hundred meters over distances of tens kilometers; hence the height is not always horizontally uniform. The mode radii of particles constituting the clouds are estimated by lidar and OPC measurements to be less than approximately 10 ?m. The regression lines of the particle size distribution with and without cirrus cloud exhibit similar features at equivalent radii of <0.8 ?m. Enhancement in the integrated number concentration at radii greater than 0.8 ?m indicates that liquid particles tend to be frozen at a radius of 0.8 ?m, with cirrus clouds above 10 km exhibiting similar features. On the other hand, enhancement in the particle size distribution at radii greater than 0.9 ?m and a peak at around 0.8 ?m in the ratio of the standard deviation of count values to that of the Poisson distribution of the averaged count values are common features of cirrus clouds in the TTL, where the ratio shows the vertical homogeneity of the particle number. These typical features suggest that the transition from liquid, sulfuric acid aerosol, to ice is more observable in the TTL and the timing of freezing may vary with height in the TTL

Characteristics of particle size distributions in the tropical tropopause based on optical particle counter and lidar measurements

International audienceAn optical particle counter (OPC) is used in conjunction with lidar measurements to examine the characteristics of the particle size distribution in cirrus cloud at the tropical tropopause (TT) over Thailand. Of 11 OPC launches, cirrus cloud was detected at 10?15 km high on 7 occasions, cirrus was detected at the TT in 6 cases, and simultaneous OPC and lidar measurements were made on two occasions. Comparison of lidar and OPC measurements reveal that the cloud height of cirrus in the TT varies by several hundred meters over distances of tens kilometers; hence the height is not horizontally uniform. The mode radii of particles constituting the clouds are estimated by lidar and OPC measurements to be less than approximately 10 ?m. The regression lines of the particle size distribution with and without cirrus cloud exhibit similar features at equivalent radii of <0.7 ?m. Enhancement in the integrated number concentration at radii greater than 0.7 ?m indicates that liquid particles tend to be frozen at a radius of 0.7 ?m, with cirrus clouds above 10 km exhibiting similar features. In addition, common features of cirrus clouds at the TT include a local maximum in the particle size distribution at 2.0 ?m and a peak between 0.5 ?m and 1.7 ?m in the ratio of the standard deviation of count values to that of the Poisson distribution of the averaged count values. Each feature implies that all ice particles in the clouds may be nucleated by the same mechanism and particles in this size range are actively frozen at the TT. These parameters are thus good indicators for checking the results of cirrus cloud models in the TT

Lake Kumphawapi — An archive of Holocene paleoenvironmental and paleoclimatic changes in northeast Thailand

The long-term climatic and environmental history of Southeast Asia, and of Thailand in particular, is still fragmentary. Here we present a new 14C-dated, multi-proxy sediment record (TOC, C/N, CNS isotopes, Si, Zr, K, Ti, Rb, Ca elemental data, biogenic silica) for Lake Kumphawapi, the second largest natural lake in northeast Thailand. The data set provides a reconstruction of changes in lake status, groundwater fluctuations, and catchment run-off during the Holocene. A comparison of multiple sediment sequences and their proxies suggests that the summer monsoon was stronger between c. 9800 and 7000 cal yr BP. Lake status and water level changes around 7000 cal yr BP signify a shift to lower effective moisture. By c. 6500 cal yr BP parts of the lake had been transformed into a peatland, while areas of shallow water still occupied the deeper part of the basin until c. 5400–5200 cal yr BP. The driest interval in Kumphawapi’s history occurred between c. 5200 and 3200 cal yr BP, when peat extended over large parts of the basin. After 3200 cal yr BP, the deepest part of the lake again turned into a wetland, which existed until c. 1600 cal yr BP. The observed lake-level rise after 1600 cal yr BP could have been caused by higher moisture availability, although increased human influence in the catchment cannot be ruled out. The present study highlights the use of multiple sediment sequences and proxies to study large lakes, such as Lake Kumphawapi in order to correctly assess the time transgressive response to past changes in hydroclimate conditions. Our new data set from northeast Thailand adds important paleoclimatic information for a region in Southeast Asia and allows discussing Holocene monsoon variability and ITCZ movement in greater detail

A 150-year record of phytoplankton community succession controlled by hydroclimatic variability in a tropical lake

Climate and human-induced environmental change promote biological regime shifts between alternate stable states, with implications for ecosystem resilience, function, and services. While these effects have been shown for present-day ecosystems, the long-term response of microbial communities has not been investigated in detail. This study assessed the decadal variations in phytoplankton communities in a ca. 150 year long sedimentary archive of Lake Nong Thale Prong (NTP), southern Thailand using a combination of bulk geochemical analysis, quantitative polymerase chain reaction (qPCR) and lipid biomarkers techniques including compound-specific hydrogen isotope analysis as a proxy for precipitation. Relatively drier and by inference warmer conditions from ca. 1857 to 1916 Common Era (CE) coincided with a dominance of the green algae <i>Botryococcus braunii</i>, indicating lower nutrient levels in the oxic lake surface waters, possibly related to lake water stratification. A change to higher silica (Si) input around 1916 CE was linked to increased rainfall and concurs with an abrupt takeover by diatom blooms lasting for 50 years. These were increasingly outcompeted by cyanobacteria from the 1970s onwards, most likely because of increased levels of anthropogenic phosphate and a reduction in rainfall. Our results showcase that the multi-proxy approach applied here provides an efficient way to track centennial-scale limnological, geochemical and microbial change, as influenced by hydroclimatic and anthropogenic forcing