Bagtasa, G., 2020. Influence of Madden-Julian Oscillation on the intraseasonal variability of summer and winter monsoon rainfall in the Philippines. Journal of Climate. Accepted Aug2020.
Abstract.The present study investigates the influence of the Madden-Julian Oscillation (MJO) on the intraseasonal variability of summer and winter monsoon rainfall in the Philippines. The monsoon wind-terrain interaction that gives rise to rainfall in the Philippines leads to a sharp contrast between west and east coast rainfall patterns during summer and winter monsoon seasons, respectively. During the summer monsoon season, the eastward propagating MJO modulates tropical cyclone (TC) activity in the western North Pacific (WNP) on MJO phases 5 to 7. TC rainfall and remote TC precipitation due to Rossby wave response to TC heating induces strong southwesterly flow that enhances moisture transport and brings anomalous rainfall to the western region of the Philippines. On the other hand, during the winter season, an induced Matsuno-Gill type pattern to the southeast of the Philippines influences the strength of the Asian winter monsoon. Active (inactive) convection in the tropical maritime continent and Western Pacific on MJO phases 4 to 6 produces the anomalous Philippine Sea cyclonic (anticyclonic) circulation. The cyclonic (anticyclonic) anomaly leads to an enhanced (weakened) northeast monsoon flow and wet (dry) rainfall anomaly along the eastern Philippines.
Ohyama, H., Morino, I., Velazco, V. A., Klausner, T., Bagtasa, G., Kiel, M., Frey, M., Hori, A., Uchino, O., Matsunaga, T., Deutscher, N., DiGangi, J. P., Choi, Y., Diskin, G. S., Pusede, S. E., Fiehn, A., Roiger, A., Lichtenstern, M., Schlager, H., Wang, P. K., Cho, C. C.-K., Andrés-Hernández, M. D., and Burrows, J. P. (2020): Validation of XCO2 and XCH4 retrieved from a portable Fourier transform spectrometer with those from in-situ profiles from aircraft borne instruments, Atmos. Meas. Tech. Accepted Aug2020.
Abstract. Column-averaged dry-air mole fractions of carbon dioxide (XCO2) and methane (XCH4) measured by a solar viewing portable Fourier transform spectrometer (FTS, EM27/SUN) have been characterized and validated by comparison using in-situ profile measurements made during the transfer flights of two aircraft campaigns: Korea-United States Air Quality Study (KORUS-AQ) and Effect of Megacities on the Transport and Transformation of Pollutants on the Regional and Global Scale (EMeRGe). The aircraft flew over two Total Carbon Column Observing Network (TCCON) sites: Rikubetsu, Japan (43.46° N, 143.77° E) for the KORUS-AQ campaign and Burgos, Philippines (18.53° N, 120.65° E) for the EMeRGe campaign. The EM27/SUN was deployed at the corresponding TCCON sites during the overflights. The mole fraction profiles obtained by the aircraft over Rikubetsu differed between the ascending and the descending flights above approximately 8 km for both CO2 and CH4. Because the spatial pattern of tropopause heights based on potential vorticity values from the ERA5 reanalysis show that the tropopause height over the Rikubetsu site was consistent with the descending profile, we used only the descending profile to compare with the EM27/SUN data. Both the XCO2 and XCH4 derived from the descending profiles over Burgos were lower than those from the ascending profiles. Output from the Weather Research and Forecast Model indicate that higher CO2 for the ascending profile originated in central Luzon, an industrialized and densely populated region about 400 km south of the Burgos TCCON site. Air masses observed with the EM27/SUN overlap better with those from the descending aircraft profiles than those from the ascending aircraft profiles with respect to their properties such as origin and atmospheric residence times. Consequently, the descending aircraft profiles were used for the comparison with the EM27/SUN data. The EM27/SUN XCO2 and XCH4 data were derived by using the GGG2014 software in which air mass independent correction factors utilized for the TCCON data (0.9898 for XCO2 and 0.9765 for XCH4) were not applied. The comparison of the EM27/SUN observations with the aircraft data revealed that on average, the EM27/SUN XCO2 data were biased low by 1.22 % and the EM27/SUN XCH4 data were biased low by 1.7 %. The resulting air mass independent correction factors of 0.9878 for XCO2 and 0.9833 for XCH4 were obtained for the portable FTS.
Bagtasa, G. and Yuan, C.S., 2020. Influence of local meteorology on the chemical characteristics of fine particulates in Metropolitan Manila in the Philippines. Atmospheric Pollution Research.
Abstract. The chemical characteristics of fine particulates in Metropolitan Manila, capital of the Philippines, were investigated. Week-long daily PM2.5 sampling observations were done in the months of May and October of 2018 in the Manila Bay area. May and October correspond to the boreal spring and fall monsoon transition periods, respectively. The sampling periods were selected to minimize the contribution of transboundary pollutants and to determine the influence of local mesoscale weather under similar synoptic flow conditions. Results show the daily average PM2.5 mass concentration for spring and fall to be 29.07 ±4.69 and 50.06 ±8.79 μg m 3, respectively. Most PM2.5 components were also found to be higher during fall. The difference in concentration between the two seasons is mainly due to the strong land/sea-breeze in spring induced by warmer land surface temperature. In spring, strong sea-breeze disperses PM2.5 inland, and the nighttime land-breeze serves as the outflow path of fine aerosols from Metropolitan Manila. In fall, the opposing flow of the weaker sea-breeze to the prevailing easterly produces stagnant air that leads to higher accumulated particulate concentration. Moreover, the suppressed outflow during fall season resulted in higher PM2.5 contribution of aged secondary aerosol components. Overall, the largest contributors to Metropolitan Manila PM2.5 mass concentration are the primary and secondary aerosols from local vehicular emissions, followed by soil dust and seasalt.
JA Garcia, E Vallar, MC Galvez, G Bagtasa (2019) Application of the WRF/Chem v. 3.6. 1 on the reanalysis of criteria pollutants over Metro Manila. Sustainable Environment Research 29 (1), 38
YL Tseng, CS Yuan, G Bagtasa, HL Chuang, and TC Li (2019) Inter-correlation of Chemical Compositions, Transport Routes, and Source Apportionment Results of Atmospheric PM2. 5 in Southern Taiwan and the Northern Philippines. Aerosol and Air Quality Research 19, 2645-2661
Gerry Bagtasa, Mylene G Cayetano, Chung-Shin Yuan, Osamu Uchino, Tetsu Sakai, Toshiharu Izumi, Tomohiro Nagai, Isamu Morino, Ronald C Macatangay, Voltaire A Velazco (2019). Long-range transport of aerosols from East and Southeast Asia to northern Philippines and its direct radiative forcing effect. Atmospheric Environment 218, 117007
Abstract. Two elevated fine particulate mass concentration events were observed in a span of a week in northern Philippines on March of 2017. Results from chemical characterization, lidar observation, and model simulations of particulate matter show the high aerosol concentration events to be caused by long range transport (LRT) of anthropogenic pollutants from northern East Asia at the surface and biomass burning emission from Indochina aloft. In this study, we investigated the transport path of these LRT aerosols and estimated their direct radiative forcing. A strong Siberian high and a confluent flow induced by a continental high over the main Asian continent and a cyclonic circulation over the south of Japan produced a strong northerly wind that carried pollutants from northern East Asia to northern Philippines. At the same time, strong westerlies 2–4 km aloft carried biomass burning emissions from Indochina, which also had an impact on ground concentration. Mass extinction efficiency of LRT aerosols was estimated to be in the range of 2.06–6.44 m2g-1 with a mean value of 4.32±1.32 m2g-1. In addition, we calculated the direct radiative forcing effect under clear sky condition and found that the transported aerosols had a mean net negative forcing (cooling) effect of -50.80±12.38 Wm-2 and -11.98±3.96 Wm-2 on surface and at the top of the atmosphere, respectively. Such pollutant transport during wintertime cold surges had been shown to reduce local surface pollutants in northern China. Consequently, its impacts shift to downwind regions as far as the Philippines. As winter cold surge frequency increases due to the warming arctic, more LRT events may be expected as a result of climate change.
Gerry Bagtasa (2019), 118‐year climate and extreme weather events of Metropolitan Manila in the Philippines. International Journal of Climatology. https://doi.org/10.1002/joc.6267
Abstract. Metropolitan Manila, the Philippines, is a megacity with a population of 12.9 million people. Unabated urbanization and disorganized infrastructure build-up, coupled with a large urban poor population have made many of its population vulnerable to climate change. This study presents the 118-year urban climate and extreme weather events of Metropolitan Manila. Daily average and minimum temperature are on the rise comparable to countrywide trends. Consequently, there are more warm and less cold nights. Total annual precipitation is also increasing at a rate of 77.99 mm/decade. Decreasing simple daily intensity index implies that higher observed precipitation is due to the increase in wet days count rather than intensity. Tropical cyclones (TCs) are critical in producing most extreme rainfall events in the metropolis. Extreme precipitation is induced either by a TC's immediate rainbands or remote precipitation effects by enhancing the prevailing summer monsoon flow. TC-induced rain modulates annual rainfall variability and is estimated to contribute 45.2% to Metropolitan Manila mean total rainfall.
Gerry Bagtasa (2019). Enhancement of Summer Monsoon Rainfall by Tropical Cyclones in Northwestern Philippines. J. Meteor. Soc. Japan, 97, https://doi.org/10.2151/jmsj.2019-052
Abstract. The influence of tropical cyclones (TC) on the western North Pacific (WNP) summer monsoon flow—as well as the impact on rainfall in the Philippines during the months of June to September from 1958 to 2017—were investigated. High precipitation event (HPE) days with measured rainfall in the upper 85th, 95th, and 99th percentiles were determined using daily rainfall averages via data acquired from eight synoptic stations in northwestern Philippines. More than 90 % of HPE days coincide with TC occurrence in the WNP, whereas landfalling TCs only account for 12.8 – 15.1 % of HPE days. The present study looks at the non-landfalling TCs that are coincident with HPEs. The result shows that these non-landfalling TCs remotely play a key role that affects almost all local HPEs in northwestern Philippines.
Analysis of the TC tracks and their influence on southwesterly summer monsoon flow in Southeast Asia during HPE days shows that most of the TCs move along a line segment connecting northern Luzon and Okinawa, Japan. The composite low-level flow of all HPE days is characterized by a zonally-oriented eastward trough at the 1005 – 1007 hPa isobar along 20°N that extends to at least 135°E longitude over the northern half of the Philippines; a deepening of the monsoon trough in northern South China Sea also occurs. The 1005 – 1007 hPa trough induces an eastward shift on the southwesterly flow causing a 1.94 – 4.69 times increase in mean zonal wind velocity and 2.67 – 6.92 times increase in water vapor flux (via moisture conveyor belt) along western Luzon. In addition, increasing trends of 6.0 % per decade in the mean annual number of HPE days per decade and 12.7% per decade in the annual total HPE precipitation are found to be significant in the upper 85th percentile of daily rainfall. These increases are attributed to the recent changes in WNP TC tracks.
Lagrosas, Nofel, Gerry Bagtasa, Naohiro Manago, and Hiroaki Kuze (2019). Influence of Ambient Relative Humidity on Seasonal Trends of the Scattering Enhancement Factor for Aerosols in Chiba, Japan. Aerosol and Air Quality Research vol. 19(8), pp.1856-1871. DOI: 10.4209/aaqr.2018.07.0267
Abstract. In this study, we used ground instruments, namely, a visibility meter, an integrating nephelometer, an aethalometer, a lidar, and a weather monitor, to measure the scattering enhancement factor, f(RH), which quantifies the effect of ambient relative humidity (RH) on aerosol light-scattering, and to generate a model of its annual variation in the city of Chiba, Japan. First, the f(RH) values were calculated with chemical analysis data. Second, visibility-meter and aethalometer data were used to model the monthly trends of f(RH) at 550 nm. The f(RH) values were higher during summer than during the other three seasons, which can be attributed to the general pattern of the regional climatology as well as the loading of different particle types into the lower troposphere. Third, the f(RH) values at 532 nm were obtained from lidar and aethalometer measurements. Low and constant f(RH) values were observed during November, whereas higher and increasing f(RH) values were observed during May. Also, dust events during March 2015 showed decreasing f(RH) with increasing RH.
Gerry Bagtasa, Mylene G. Cayetano, and Chung-Shin Yuan (2018). Seasonal variation and chemical characterization of PM2.5 in northwestern Philippines. Atmos. Chem. Phys., 18, 4965-4980. https://doi.org/10.5194/acp-18-4965-2018
Abstract. The seasonal and chemical characteristics of fine particulate matter (PM2.5) were investigated in Burgos, Ilocos Norte, located at the northwestern edge of the Philippines. Each 24h sample of fine aerosol was collected for four seasons. Fine particulate in the region shows strong seasonal variation in both concentration and composition. Highest mass concentration was seen during the boreal spring season with a mean mass concentration of 21.6±6.6µg m−3, and lowest was in fall with a mean concentration of 8.4±2.3µg m−3. Three-day wind back trajectory analysis of air mass reveals the influence of the northwestern Pacific monsoon regimes on PM2.5 concentration. During southwest monsoon, sea salt was the dominant component of fine aerosols carried by moist air from the South China Sea. During northeast monsoon, on the other hand, both wind and receptor model analysis showed that higher particulate concentration was due to the long-range transport (LRT) of anthropogenic emissions from northern East Asia. Overall, sea salt and soil comprise 33% of total PM2.5 concentration, while local biomass burning makes up 33%. LRT of industrial emission, solid waste burning and secondary sulfate from East Asia have a mean contribution of 34% to the total fine particulate for the whole sampling period.
Gerry Bagtasa (2017). Contribution of Tropical Cyclones to Rainfall in the Philippines. Journal of Climate. Vol 30. pp. 3621-3633. http://dx.doi.org/10.1175/JCLI-D-16-0150.1
Tropical cyclone (TC)-induced rainfall (TC rain) in the Philippines was investigated using a combination of ground and satellite observations to produce a blended 64-yr precipitation dataset. A total of 1673 TCs were examined using best track data from the Japan Meteorological Agency. Rainfall from 100 (~1110 km) of the TC center was considered as TC-induced rainfall. TC rain contribution is highest in the northern Philippines, particularly along the western coast of Luzon (up to 54%), and lowest in the southern islands of Mindanao (6%). The high TC rain contribution is attributed to the enhancement of the Asian southwest monsoon by TCs located to the northeast of the Philippines. An unsupervised clustering method, k-means clustering, was used to divide the archipelago into four climate subtypes according to monthly rainfall variation. Interannual variability of rainfall from climate clusters with high TC rain contribution generally follows the variability of TC rain. On the other hand, the variability of low TC rain clusters is mainly influenced by El Niño–Southern Oscillation (ENSO). All clusters show increasing trends of 16.9%–19.3% decade−1 in TC rain percentage contribution since 2000. This study hypothesizes that this increasing trend is due to changes in the characteristics of TC steering mechanisms and thermodynamic properties east of the Philippines in the past one and a half decades.
Rhonalyn L. Vergara, Ernest P. Macalalad, Gerry Bagtasa, Edgar A. Vallar, Maria Cecilia D. Galvez, and Raquel V. Francisco (2017). Correlation of Aerosol Optical Properties with Surface Meteorological Parameters Over Manila. Adv. Sci. Lett. 23, 1448–1451
Aerosol optical properties such as aerosol optical depth (AOD) at 500 nm together with wavelength exponent (α) and Ångstrom turbidity coefficient (β) obtained from a sunphotometer over Manila were used to analyze their response to the changes in temperature, relative humidity (RH) and zonal wind. Data retrieved for a one year period of measurements (August 2009–July 2010) were used to describe the variations of the aerosol optical properties. Temperature showed weak correlations with the aerosol optical properties. Surface RH confirmed evidence for its influence on aerosols size distribution and dominant aerosol type. Zonal wind demonstrated influences on the prevailing aerosol present at a certain area and caused alteration the amount of its loading.
BA Racoma, CP David, IA Crisologo and G Bagtasa (2016). The Change in Rainfall from Tropical Cyclones due to Orographic Effect of the Sierra Madre Mountain Range in Luzon, Philippines. Phil. Journal of Science. in press.
This paper discusses the Sierra Madre Mountain Range of the Philippines and its associated influence on the intensity and distribution of rainfall during tropical cyclones. Based on Weather and Research Forecasting model simulations, a shift in rainfall was observed in different portions of the country, due to the reduction of the topography of the mountain. Besides increasing the rainfall along the mountain range, a shift in precipitation was observed during Tropical Storm Ondoy, Typhoon Labuyo, and Tropical Storm Mario. It was also observed that the presence of the Sierra Madre Mountain Range slows down the movement of a tropical cyclones, and as such allowing more time for precipitation to form over the country. Wind profiles also suggest that the windward and leeward sides of mountain ranges during Tropical Cyclones changes depending on the storm path. It has been suggested that in predicting the distribution of rainfall, the direction of movement of a tropical cyclone as well as its adjacent areas be taken into great consideration. While the study shows high amounts of variation in the characteristics of different tropical cyclones with respect of the Sierra Madre Mountain Range, the results of this study can provide insights to pre-disaster operations before tropical cyclones approaches land. The decrease in tropical cyclones speed introduced by the Sierra Madre Mountain Range can be used to identify the possible areas that can experience prolonged rains due to the mountain range. Disaster management authorities can also prepare in advance by identifying which locations can experience orographic enhanced precipitation. However, due to the lack of available data and resources, further studies are recommended due to the study presenting limited cases.
Lagmay AMF, Bagtasa G, Crisologo IA, Racoma BAB and David CPC (2015) Volcanoes magnify Metro Manila’s southwest monsoon rains and lethal floods. Front. Earth Sci. 2:36. doi: 10.3389/feart.2014.00036
Many volcanoes worldwide are located near populated cities that experience monsoon seasons, characterized by shifting winds each year. Because of the severity of flood impact to large populations, it is worthy of investigation in the Philippines and elsewhere to better understand the phenomenon for possible hazard mitigating solutions, if any. During the monsoon season, the change in flow direction of winds brings moist warm air to cross the mountains and volcanoes in western Philippines and cause lift into the atmosphere, which normally leads to heavy rains and floods. Heavy southwest monsoon rains from 18–21 August 2013 flooded Metro Manila (population of 12 million) and its suburbs paralyzing the nation's capital for an entire week. Called the 2013 Habagat event, it was a repeat of the 2012 Habagat or extreme southwest monsoon weather from 6–9 August, which delivered record rains in the mega city. In both the 2012 and 2013 Habagat events, cyclones, the usual suspects for the delivery of heavy rains, were passing northeast of the Philippine archipelago, respectively, and enhanced the southwest monsoon. Analysis of Doppler data, rainfall measurements, and Weather Research and Forecasting (WRF) model simulations show that two large stratovolcanoes, Natib and Mariveles, across from Manila Bay and approximately 70 km west of Metro Manila, played a substantial role in delivering extreme rains and consequent floods to Metro Manila. The study highlights how volcanoes, with their shape and height create an orographic effect and dispersive tail of rain clouds which constitutes a significant flood hazard to large communities like Metro Manila..
- Lidar (atmospheric lidar) analysis of TCCON Burgos
- PM2.5 transport from East Asia and South East Asia haze transport observation and modeling
- aerosol – cloud – climate interaction modeling using WRF-Chem
- Tropical cyclone climatology in the Philippines
- Influence of weather on ambient pollutant concentration
- Mesoscale weather modeling in the Philippines
- PM concentration around power plants in Luzon
- Personal pollutant exposure from Metro Manila traffic.
- “Tempospatial Distribution and Transboundary Transport of Atmospheric Fine Particles across Bashi Channel, Taiwan Strait, and South China Sea” funded by DOST under the Meco-Teco program.
- “Creating cost-effective sensors for IR applications: High Resolution Simulation and Verification of Local CO 2 Flux in the Philippines” funded by the OVPAA Emerging Inter-Disciplinary Research (EIDR) program.
- Inter-decadal and interannual variability of Tropical cyclone wind energy exposure in the Philippines.
- Climatic changes in Metro Manila