The Maritime Continent (MC) of Southeast Asia, comprising the archipelago of islands from the Malay Peninsula through Indonesian New Guinea and the Philippines, hosts some of the world’s most complex aerosol, cloud, and coupled ocean–terrestrial–atmospheric systems. With its steep topography situated in the Pacific warm pool, the MC is an important contributor to Earth’s moisture, energy, and vertical transport budgets far outside its tropical latitude range (e.g., Ramage 1968; Jin and Hoskins 1995; Neale and Slingo 2003; Carminati et al. 2014). High levels of pollution and biomass burning emissions contrast with natural marine and biogenic aerosol sources. Burning for agriculture and urbanization occurs at significant rates (Miettinen et al. 2016). These burning emissions are strongly tied to precipitation anomalies associated with numerous interseasonal and intraseasonal cycles (Field and Shen 2008; Reid et al. 2012, 2013; Field et al. 2016) and a nonlinear hydrological response (Taufik et al. 2017). The region further includes significant anthropogenic emissions from heavy industry, mobile sources, and biofuel (e.g., Balasubramanian et al. 2003; Lee et al. 2019; Chen et al. 2020). The resulting regional-scale air quality events are among the worst in the world with adverse health outcomes and economic feedback (e.g., Kim et al. 2015; Crippa et al. 2016; Koplitz et al. 2016, 2017; Lee et al. 2018, 2019). Increasing emissions coincide with climatic change in temperature and rainfall within a region already vulnerable to weather extremes (e.g., Endo et al. 2009; Yusef and Francisco 2009; IPCC 2013, 2014; Deni et al. 2010; Cruz et al. 2013; Cinco et al. 2014; Villafuerte et al. 2014; Olaguera et al. 2018; Bagtasa 2020).
Clouds within the MC exist in a spectrum of pristine through highly polluted regimes and likely demonstrate aerosol particle, microphysics, precipitation, and radiation interdependencies. Observational evidence suggests higher aerosol loadings result in 1) enhanced warm cloud albedo in Southeast Asia (Sorooshian et al. 2009, 2013; Ross et al. 2018) due to reduced droplet size, through the Twomey effect (Twomey 1974, 1977); 2) indicators of aerosol-related storm invigoration have been observed through enhanced lightning (e.g., Yuan et al. 2011; Thornton et al. 2017); and 3) suppressed warm rain and enhanced deep-convection-related precipitation processes (e.g., Rosenfeld and Lensky 1998; Rosenfeld 1999). While it is unclear how aerosol impacts differ in terrestrial versus maritime environments, we expect findings from other regions and modeling studies to have some applicability to the MC. These include a host of aerosol-induced micro- and macrophysical changes in clouds (e.g., Tao et al. 2012; Dey et al. 2011), such as delays in warm rain formation (Berg et al. 2008) and congestus and overall storm invigoration (e.g., Lyons et al. 1998; Wang et al. 2009; Storer et al. 2014). Modeling studies are largely consistent in warm-phase cloud processes, but less so as ice nucleation begins to take hold (Khain et al. 2005; van den Heever et al. 2006; Saleeby et al. 2010; Cotton et al. 2012; Fan et al. 2013; Grant and van den Heever 2015; Sheffield et al. 2015; Mace and Abernathy 2016; Gryspeerdt et al. 2017). At the same time, radiation perturbations by particles feed back into atmospheric stability and cloud formation (Ackerman et al. 2000; Sokolowsky et al. 2022). In sum, aerosol particle impacts on cloud processes are coupled to aerosol life cycle, the radiative budget, and feedback to cloud microphysical and dynamical processes.
The National Aeronautics and Space Administration (NASA) Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex), conducted from Clark International Airport, Philippines, with its 25 August–5 October 2019 intensive operations period, worked to deconvolve interlaced aerosol, cloud, and radiation processes to isolate the role of aerosol particles within Southeast Asia’s southeast monsoon system. To document the mission and promote its use to a broad interdisciplinary community, this paper provides a summary of CAMP2Ex, a demonstration of some of the technology developed to meet its scientific goals, and the mission’s assets, experienced environments, and early scientific findings. To promote the use of CAMP2Ex data, extensive supplemental material is also provided for the measured environment, the instrument payloads/performances, and remote sensing and modeling components (supplemental sections S.1, S.2, and S.3, respectively). CAMP2Ex was organized around compositional, convective, and radiative focus areas with associated in situ, modeling, and remote sensing technology efforts investigating warm- and mixed-phase clouds, such as fair weather cumulus, congestus, and altocumulus, as well as their organization and proclivity to develop into deeper convection. NASA’s P-3 aircraft, Stratton Park Engineering Company’s (SPEC) Learjet 35 aircraft, a Manila Observatory ground site, and partners including the Office of Naval Research (ONR) Propagation of Intraseasonal Tropical Oscillations (PISTON; Sobel et al. 2021) R/V Sally Ride research cruise and those involved in the Years of the Maritime Continent (Yoneyama and Zhang 2020), made useful observations. CAMP2Ex promoted not only interdisciplinary observations, but new informatics technologies to fuse field observations with satellite remote sensing and modeling efforts to holistically examine the monsoon system. CAMP2Ex supports the next generation of Earth-observing systems including a host of the latest geostationary sensors such as on Himawari-8 (Bessho et al. 2016) and NASA’s developing Atmosphere Observing System (AOS).
CAMP2Ex within the southwest monsoon environment
Despite broad knowledge of aerosol–cloud relationships, the real-world impact of these processes in the monsoon environment remains highly uncertain (IPCC 2013; National Academies of Sciences, Engineering, and Medicine 2018). Mindanao farmers, for instance, noted a climatic decline in the number of light precipitation days, leading to agricultural stress. At the same time, Philippine urbanization is thought to increase rainfall locally (Cruz et al. 2013; Bagtasa 2020). These observations resulted in a number of climate questions and subsequent studies associated with the 7 Southeast Asian Studies Program (7SEAS; Reid et al. 2013) and led to the formation of the CAMP2Ex mission. Aerosol–cloud interactions were one of the hypothesized factors causing precipitation modulation. However, isolating one component of an aerosol–cloud system is confronted by the inherently coupled nature of the aerosol life cycle within meteorological, terrestrial/maritime, cloud, and radiation processes. CAMP2Ex met this challenge by isolating biomass burning and anthropogenic emissions life cycles within MC’s southwest monsoon (SWM) system. By basing in the Philippines, CAMP2Ex observations were located between emissions sources in the MC and sinks within the northwest tropical Pacific (NWTP) monsoonal trough. This placement enabled observations of composition, cloud, and radiation within a host of tropical to subtropical meteorological phenomena in conditions ranging from highly polluted to pristine. Consideration was made for the inhomogeneous nature of the meteorology and composition. Indeed, while the “Maritime Continent” is often thought of as being maritime in nature, in reality the region out to 500 km from shore is often littoral in nature with a combination of both terrestrial and maritime influences.
Figure 1 provides examples of the aerosol and convective elements of the region. Figure 1a provides an overview chart with Fig. 1b depicting a corresponding smoke outbreak matching the overall conceptual model as observed by Suomi NPP VIIRS on 16 September 2019 (near the mission’s midway point), overlaid with filled contours of satellite-estimated precipitation and open isopleths of 550-nm smoke aerosol optical depth (AOD) from a consensus of models (Sessions et al. 2015; Xian et al. 2019). Smoke from peat fires on Borneo and Sumatra was transported by the SWM flow for over 4,000 km around Borneo, over the Sulu Sea, across the Philippines, and eventually into the mesoscale convective systems (MCSs) within the NWTP monsoonal trough. Aloft, winds reverse in direction becoming northeasterly with the lightest winds at 5 km. On 16 September, the P-3 flew to the north of Borneo in this heavy smoke where AOD at 532 nm was ∼1. The vertical profiles of aerosol backscatter shown in Fig. 1c were measured by lidar (track marked by a green line in Fig. 1b), with aerosol layers (here predominantly smoke) depicted as warmer colors with clouds as red. Visual context for this time is provided in Fig. 1d. With most of the smoke below 1-km altitude, visibility in the marine boundary layer (MBL) was only a few kilometers and mass concentrations neared 100 μg m−3 even though the location was 2,000 km downwind from the source. Most MBL clouds were only a few hundred meters deep, but congestus had tops to 3 km with sporadic altocumulus. Additional cloud-lofted aerosol layers between 2 and 5 km were also observed. The following day (17 September 2019), the P-3 sampled the smoke again, this time over the NWTP after an additional day of transport (marked as a magenta oval in Fig. 1b). Over the NWTP, convergence/confluence lines of convection developed within the smoke with cloud-top heights to 3–4 km (Fig. 1e) as well as sharp boundaries of smoke and organized deep convection and squall lines (Fig. 1f). In addition to sampling such massively polluted environments as this, CAMP2Ex sampled a host of low- to midlevel convective entities, including land–sea breeze fronts and induced deep convection with tops to 14+ km (Fig. 1g); convection developing into deep phases to 14+ km and spawning strong cold pools (Fig. 1h); significant particle removal by organized systems in the monsoonal trough (Fig. 1i); and a wide variety of fair weather cumulus, congestus, and altocumulus in both pristine and polluted conditions (Fig. 1j). Such sampling was performed in a range of pristine to Asian mainland and polluted environments. All of these features in Fig. 1 had strong relationships to the overarching thermodynamic environment. Corresponding skew-T and visible satellite imagery is provided in section S.1 of the online supplemental material.
Aerosol and cloud phenomena of the southwest monsoon system. (a) Overview of the monsoonal system from the Maritime Continent through the Philippines to the western Pacific monsoonal trough. (b) A corresponding SNPP VIIRS image to (a) of a typical smoke event (16 Sep 2019) with overlaid Integrated Multi-satellitE Retrievals for GPM-IMERG satellite precipitation rates (Tan et al. 2019; Huffman et al. 2020) and open isopleths of 550-nm smoke aerosol optical depth (AOD) from the Navy Aerosol Analysis and Precision System Reanalysis (NAAPS; Lynch et al. 2016) showing transport of smoke 4,000 km from Borneo into mesoscale convective systems in the monsoonal trough. (c) High Spectral Resolution Lidar 2 (HSRL-2; Burton et al. 2016) aerosol backscatter over the Sulu Sea on this day along the track marked in green on (b); (d) eastward view from cockpit at the southernmost point of (c); (e) convergence line of convection from the same plume over the NWTP the following day (17 Sep 2019); and (f) edge of a nearby MCS terminating the plume (17 Sep 2019). Other aerosol convective feature interactions included (g) coastal convection spawned by a morning land breeze, (h) isolated convective cell with forming cold pool, and (i) congestus in pristine conditions on the very last flight of the mission.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1
Aerosol and cloud phenomena of the southwest monsoon system. (a) Overview of the monsoonal system from the Maritime Continent through the Philippines to the western Pacific monsoonal trough. (b) A corresponding SNPP VIIRS image to (a) of a typical smoke event (16 Sep 2019) with overlaid Integrated Multi-satellitE Retrievals for GPM-IMERG satellite precipitation rates (Tan et al. 2019; Huffman et al. 2020) and open isopleths of 550-nm smoke aerosol optical depth (AOD) from the Navy Aerosol Analysis and Precision System Reanalysis (NAAPS; Lynch et al. 2016) showing transport of smoke 4,000 km from Borneo into mesoscale convective systems in the monsoonal trough. (c) High Spectral Resolution Lidar 2 (HSRL-2; Burton et al. 2016) aerosol backscatter over the Sulu Sea on this day along the track marked in green on (b); (d) eastward view from cockpit at the southernmost point of (c); (e) convergence line of convection from the same plume over the NWTP the following day (17 Sep 2019); and (f) edge of a nearby MCS terminating the plume (17 Sep 2019). Other aerosol convective feature interactions included (g) coastal convection spawned by a morning land breeze, (h) isolated convective cell with forming cold pool, and (i) congestus in pristine conditions on the very last flight of the mission.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1
Aerosol and cloud phenomena of the southwest monsoon system. (a) Overview of the monsoonal system from the Maritime Continent through the Philippines to the western Pacific monsoonal trough. (b) A corresponding SNPP VIIRS image to (a) of a typical smoke event (16 Sep 2019) with overlaid Integrated Multi-satellitE Retrievals for GPM-IMERG satellite precipitation rates (Tan et al. 2019; Huffman et al. 2020) and open isopleths of 550-nm smoke aerosol optical depth (AOD) from the Navy Aerosol Analysis and Precision System Reanalysis (NAAPS; Lynch et al. 2016) showing transport of smoke 4,000 km from Borneo into mesoscale convective systems in the monsoonal trough. (c) High Spectral Resolution Lidar 2 (HSRL-2; Burton et al. 2016) aerosol backscatter over the Sulu Sea on this day along the track marked in green on (b); (d) eastward view from cockpit at the southernmost point of (c); (e) convergence line of convection from the same plume over the NWTP the following day (17 Sep 2019); and (f) edge of a nearby MCS terminating the plume (17 Sep 2019). Other aerosol convective feature interactions included (g) coastal convection spawned by a morning land breeze, (h) isolated convective cell with forming cold pool, and (i) congestus in pristine conditions on the very last flight of the mission.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1
Notable in Fig. 1 are complex trilevel cloud formations (Johnson et al. 1999) including near ever-present cirrus (including subvisible cirrus) and altocumulus (e.g., Sassen and Wang 2012) that impact both solar and terrestrial radiation budgets. Further, embedded in the coupled system is a daunting number of multiscale drumbeats of the interseasonal oscillations such as El Niño–Southern Oscillation (ENSO), the monsoon (Chang et al. 2005), and the Madden–Julian oscillation (MJO)/boreal summer intraseasonal oscillation (BSISO; Jiang et al. 2004; Zhang 2005; Reid et al. 2012) down to various convective entities such as tropical cyclones and MCSs (supplemental section S.1). At the finest scales are diurnal radiation and air–sea–land contrasts that influence air–sea fluxes (e.g., Fairall et al. 1996a,b; Clayson and Bogdanoff 2013), the MBL (e.g., de Szoeke et al. 2021), and the sea–land breeze (Qian 2008; Qian et al. 2010; Wang et al. 2013). Indeed, these in turn modulate low clouds, congestus, and deep convection (Matsui et al. 2006; Ruppert 2016) with feedbacks to precipitation (e.g., Li et al. 2010; Yang and Smith 2008; Ruppert and Johnson 2015; Minobe et al. 2020). Such phenomena are tightly intertwined with aerosol emissions and life cycle (Nichol 1998; Reid et al. 2012, 2015, 2016b,a; Wang et al. 2013), aerosol transformations (Atwood et al. 2017), and aerosol scavenging (Xian et al. 2013). Aerosol–cloud interactions may also feed back into measurement assumptions and biases in the very same instruments used to monitor them (e.g., rationale for Saleeby et al. 2010).
CAMP2Ex focus areas
CAMP2Ex was organized around the focus areas of composition, clouds, and radiation that contributed to Philippine air quality and convection priorities. Integrating these components was an overarching technology effort to provide context to the observations as well as supporting a series of ongoing cross-disciplinary studies, including refinement of remote sensing retrievals, modeling, and informatics technologies.
Composition.
This focus area quantified airmass composition, aerosol optical and microphysical properties [e.g., size, hygroscopicity, cloud condensation nuclei (CCN) efficiency, absorption], and the overall aerosol life cycle of sources, transport, transformation, nucleation, and sinks. The community needs to know which particles activate as cloud droplets or remain as interstitial particles; we also need to know which processes affect particle transformation, detrainment aloft, and removal by precipitation. Investigations focused on particle evolution including scavenging, cloud processing, and nucleation feedbacks onto CCN budgets. To improve aerosol monitoring and modeling, and to investigate fundamental particle observability, a significant effort is being made to infer aerosol microphysical properties from remote sensing observations, in particular, polarimeters, lidars, and imagers. CAMP2Ex continues to assess and advance remote sensing retrieval algorithms that quantify important geophysical aerosol parameters such as CCN concentration, aerosol “type,” or “chemical speciation” from remote sensing.
Cloud physics.
The cloud physics focus area tested specific hypotheses about aerosol impacts on cloud microphysics and precipitation. More polluted conditions are thought to increase cloud droplet number and reduce cloud droplet size, but reduce raindrop number and increase mean raindrop size (Altaratz et al. 2008; Saleeby et al. 2010; May et al. 2011; Sheffield et al. 2015), with corresponding increases in overall congestus height (Konwar et al. 2012; Li et al. 2013; Sheffield et al. 2015). The strength of this impact may be modulated by environmental factors such as wind shear, relative humidity, and convective available potential energy (CAPE; e.g., Lee et al. 2008; Khain et al. 2008; Storer et al. 2010, 2014; S. Freeman et al. 2023, unpublished manuscript). Dynamical feedbacks between aerosol and cloud processes are also being examined such as whether increases in CCN weaken cold pools (e.g., supporting studies of Saleeby et al. 2010; Storer et al. 2010; Grant and van den Heever, 2015; dissenting studies of Tao et al. 2007; Cotton et al. 2012). Finally, this focus area also worked to evaluate detrainment processes of aerosol particles and water vapor (Leung and van den Heever 2022), as well as their precursors into the free troposphere and their association with altocumulus cloud life cycle.
Radiation and energy budget.
The cloud and aerosol system is also forced by diurnally varying radiation. Atmospheric radiation is not only a strong forcing agent for the system, but also a primary means for monitoring aerosol and cloud properties by remote sensing. Objectives include the quantification of the diurnal radiation budget in complex maritime tropical cloud fields, including the role of cirrus and altocumulus in convective cloud development. From a remote sensing perspective, resolved and unresolved cloud heterogeneities were investigated to characterize their impact on cloud property retrievals. Technology developments for advancing the remote sensing of cloud properties include cloud stereography, tomography, convolutional neural network (CNN) retrievals, along with methods to constrain 3D radiation fields and cirrus properties above the aircraft or at surface sites.
Within these focus areas, the Manila Observatory (MO) led further Philippine efforts focused on local and long-range transport of pollutants (e.g., Cruz et al. 2019; Braun et al. 2020; Hilario et al. 2020) and on the confounding relationships between aerosol emissions and land use change on convection. Monitoring at MO allows studies in these focus areas to occur within highly urbanized environments, including investigating how diurnal urban boundary layer characteristics are related to cloud and radiation environments, and ultimately to air quality.
Mission design and assets
CAMP2Ex planning accounted for the many scales associated with the monsoonal system. During the June–September SWM, low-level winds advect aerosol emissions from Indonesia, Malaysia, and Singapore, in their climatological dry and fire-prone period, toward the NWTP (e.g., Fig. 1a; Xian et al. 2013). After the late September–October SWM transition, the reverse flow occurs to form the northeast monsoon (NEM); a monsoon trough develops over the Indian Ocean, Sumatra, and Borneo, and the NWTP transforms into a drier phase. Figure 2 provides an overview of the regional monsoonal environment divided into late SWM 24 August–22 September 2019 (Fig. 2a) and early NEM 23 September–5 October 2019 (Fig. 2b) mission sampled study periods. During the SWM period, MC emissions were carried by the low-level southwest winds through the Celebes, Sulu, and South China Seas, and eventually into the larger convective elements associated with the NTWP monsoon trough. Throughout this period, the BSISO constantly marched across the region while a steady stream of tropical disturbances and cyclones formed in the NWTP and propagated to the northwest over and to the north of Luzon. These multiscale convective processes resulted in a series of monsoon enhancements and aerosol transport events from Borneo (supplemental section S.1). After an abrupt change from the SWM to the NEM on 21–23 September 2019, regional transport became less organized, the region hosted considerably less cirrus, and a variety of Asian pollution sources interspersed with NWTP air. Thus, conditions ranged from pristine to long-lasting emissions originally advected during the SWM. While considerably drier than earlier periods, tropical cyclones were still active in the region, as evidenced by the precipitation maximum in Fig. 2b east of Taiwan owing to the life cycle of Typhoon (TY) Mitag.
An overview of the regional monsoonal environment during the CAMP2Ex airborne operations period into (a) late SWM during 24 Aug–22 Sep 2019 and (b) early NEM sampled 23 Sep–5 Oct 2019. Included are mean 925-hPa winds from the ECMWF Reanalysis v5 (ERA5; Hersbach et al. 2020), satellite precipitation from IMERG, and fine-mode AOD from the International Cooperative for Aerosol Prediction consensus of the world’s operational global aerosol models (ICAP-MME; Xian et al. 2019). Monsoonal troughs, marked by heavy dashed lines, were analyzed by their surface pressure minimums. Also noted in (b) is the location of the period precipitation maximums over the NWTP due to the propagations of Typhoon Mitag.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1
An overview of the regional monsoonal environment during the CAMP2Ex airborne operations period into (a) late SWM during 24 Aug–22 Sep 2019 and (b) early NEM sampled 23 Sep–5 Oct 2019. Included are mean 925-hPa winds from the ECMWF Reanalysis v5 (ERA5; Hersbach et al. 2020), satellite precipitation from IMERG, and fine-mode AOD from the International Cooperative for Aerosol Prediction consensus of the world’s operational global aerosol models (ICAP-MME; Xian et al. 2019). Monsoonal troughs, marked by heavy dashed lines, were analyzed by their surface pressure minimums. Also noted in (b) is the location of the period precipitation maximums over the NWTP due to the propagations of Typhoon Mitag.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1
An overview of the regional monsoonal environment during the CAMP2Ex airborne operations period into (a) late SWM during 24 Aug–22 Sep 2019 and (b) early NEM sampled 23 Sep–5 Oct 2019. Included are mean 925-hPa winds from the ECMWF Reanalysis v5 (ERA5; Hersbach et al. 2020), satellite precipitation from IMERG, and fine-mode AOD from the International Cooperative for Aerosol Prediction consensus of the world’s operational global aerosol models (ICAP-MME; Xian et al. 2019). Monsoonal troughs, marked by heavy dashed lines, were analyzed by their surface pressure minimums. Also noted in (b) is the location of the period precipitation maximums over the NWTP due to the propagations of Typhoon Mitag.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1
Flight operations and mission instrumentation.
Given the complexity and spatial inhomogeneity of the MCs meteorology, the overall mission strategy was to rely heavily on airborne and space-based remote sensing for cloud and aerosol characterization, with in situ observations informing the skill and improvements of retrievals, and models providing large-scale context. The NASA P-3 conducted 12 SWM and 7 NEM flights for a total of 148 h over a host of meteorological conditions that can project back onto remote sensing. The SPEC Learjet 35 focused on deeper convection—especially in conjunction with P-3 and R/V Sally Ride remote sensors, with 10 SWM and 3 NEM flights for 37 h. P-3 flight tracks and key site locations are provided in Fig. 3a with a mission calendar and instrumentation provided in supplemental sections S.1 and S.2, respectively. With the P-3’s endurance of ∼9 h and ceiling of ∼6–8 km (depending on fuel load), the operations area ranged from the southern Sulu Sea to sample the air as it exited Borneo, to the NNE of Luzon to sample pristine NWTP environments. The PISTON R/V Sally Ride was stationed ∼700 km to the east of Manila from 5 to 25 September and marked the approximate eastern operations extent. The SPEC Learjet 35, with a 4-h endurance but greater airspeed and maximum altitude of 13 km, was tasked to provide more measurements of active convection already being sampled by the P-3, or monitored from the R/V Sally Ride.
Flight tracks and instrumentation. (a) Flight tracks for 19 NASA P-3 flights conducted between 25 Aug and 5 Oct 2019. Also noted is the Clark airborne base of operations and the operations area of PISTON’s R/V Sally Ride collection; (b)–(e) Key P-3, SPEC Learjet 35, Manila Observatory, and R/V Sally Ride instrumentation, respectively. AERONET = Aerosol Robotic Network; AMPR = Advanced Microwave Precipitation Radiometer; APR3 = Airborne Precipitation Radar 3rd generation; DLH = Diode Laser Hygrometer; HSRL = High Spectral Resolution Lidar; RSP = Research Scanning Polarimeter.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1
Flight tracks and instrumentation. (a) Flight tracks for 19 NASA P-3 flights conducted between 25 Aug and 5 Oct 2019. Also noted is the Clark airborne base of operations and the operations area of PISTON’s R/V Sally Ride collection; (b)–(e) Key P-3, SPEC Learjet 35, Manila Observatory, and R/V Sally Ride instrumentation, respectively. AERONET = Aerosol Robotic Network; AMPR = Advanced Microwave Precipitation Radiometer; APR3 = Airborne Precipitation Radar 3rd generation; DLH = Diode Laser Hygrometer; HSRL = High Spectral Resolution Lidar; RSP = Research Scanning Polarimeter.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1
Flight tracks and instrumentation. (a) Flight tracks for 19 NASA P-3 flights conducted between 25 Aug and 5 Oct 2019. Also noted is the Clark airborne base of operations and the operations area of PISTON’s R/V Sally Ride collection; (b)–(e) Key P-3, SPEC Learjet 35, Manila Observatory, and R/V Sally Ride instrumentation, respectively. AERONET = Aerosol Robotic Network; AMPR = Advanced Microwave Precipitation Radiometer; APR3 = Airborne Precipitation Radar 3rd generation; DLH = Diode Laser Hygrometer; HSRL = High Spectral Resolution Lidar; RSP = Research Scanning Polarimeter.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1
An accounting of atmospheric instruments deployed on the P-3, Learjet 35, and at the Manila Observatory along with the location of key instruments of PISTON’s R/V Sally Ride are shown in Figs. 3b–e, respectively. CAMP2Ex depended heavily on the P-3’s remote sensing and profiling observations for monitoring the evolution of aerosol and cloud structure (supplemental Table S.2.1). Typically, the P-3 would arrive to survey a target region at maximum altitude (∼6–8 km). The active two-wavelength extinction (355 and 532 nm) and three-wavelength backscatter (adding 1,064 nm) “2α-3β” High Spectral Resolution lidar (HSRL-2; Fig. 1b) on the P-3 provided below-aircraft profiles of spectral light extinction, backscatter, lidar ratio (the ratio of particle extinction to backscatter), and depolarization. These quantities can be further related to aerosol type and particle size, cloud-top heights, and boundary layer structure. The passive Research Scanning Polarimeter (RSP) retrieved cloud optical thickness, cloud-top height, droplet and aerosol particle size distributions, aerosol optical depth, aerosol absorption, and aerosol refractive index. Its multiangle polarimetric observations that use parallax and cloud bow structure are resistant to the influences of the ubiquitous thin cirrus above (Alexandrov et al. 2012a). The Airborne Third Generation Precipitation Radar (APR3) Doppler Ka-, Ku-, and W-band radar and the four-band Advanced Microwave Precipitation Radiometer (AMPR) provided profile and integrated information on cloud liquid/ice water, precipitation rates, and drop size. Full-frame broadband mid- and longwave imagery, as well zenith and nadir all-sky cameras, provided parallax information on cloud topography. Finally, dropsondes provided state profiles to combine with profiling remote sensors, thereby providing environmental context of these measurements.
P-3 remote sensing was supported by in situ measurements including measurements of meteorological state and 20-Hz turbulence and water vapor (supplemental Table S.2.2). Radiation measurements included upwelling and downwelling total solar, total longwave, and hyperspectral solar, in conjunction with downwelling direct and diffuse broadband (400–2,700 nm) and spectral (350–1,000 nm at 1-nm resolution) solar radiation. These helped constrain the radiative budget and assess heating rates, and also allowed for estimation of cirrus and aerosol optical depth. Aerosol particle, droplet, and ice size measurements spanned 10 nm to millimeters, with internal (from NASA/Washington University) and wing-mounted (from SPEC Inc.) probes. A comprehensive NASA Langley Aerosol Research Group Experiment (LARGE) and gas chemistry package was installed for particle microphysics, optical properties, and chemistry. A particularly unique capability of the P-3’s in situ package was the measurement of cloud droplet chemistry.
The SPEC Learjet 35 was equipped with in situ probes to characterize active convection from cloud base to top, especially for clouds penetrating above the P-3’s ceiling (Fig. 2c; supplemental Table S.2.5). Included were state, liquid/ice water, and microphysics probes to characterize cloud cores, precipitation, and ice formation. These included overlapping ranges of sampling sizes from aerosol condensation nuclei (CN) and fine-mode size to small cloud droplets and precipitation, as well as droplet and ice crystal imaging. Identical instruments were included on the P-3 when possible. For airborne coordination, early in the mission the Learjet 35 operated in the same region as the P-3. By the mission midpoint, the Learjet 35 flew below the P-3, providing in situ observations that corresponded to the P-3’s remote sensors.
To provide context to the airborne mission, a 2018 through early 2020 CAMP2Ex Weather and Composition Monitoring (CHECSM) effort was initiated, centered on sensors located at the Manila Observatory that monitored aerosol, cloud, and radiation properties within the Metro Manila megacity. CHECSM provides a framework to evaluate satellite and model products, assess regional weather and climate, and evaluate local, maritime, and long-range transport contributions to the Manila region. In this way, CHECSM afforded an avenue to engage local agencies and students in a manner that projected both onto CAMP2Ex science requirements and applications important to the Philippine people—notably air quality and precipitation. The Manila Observatory supported long-term aerosol and radiation monitoring at a megacity with a regional population of over 20 million. At the center were a ground-based HSRL to monitor aerosol and cloud layers, and radiometers to close the radiative budget at the surface, including solar, IR, and direct/diffuse radiation. Extensive surface sampling of aerosol properties was conducted including size-resolved aerosol chemistry and black carbon to support air quality studies (e.g., Cruz et al. 2019; Braun et al. 2020; Stahl et al. 2020; Hilario et al. 2020).
PISTON’s 2019 R/V Sally Ride cruise provided continuous measurements of the troposphere, ocean, and air–sea transition zone including a bulk and direct flux measurement package and a comprehensive set of atmospheric and oceanographic profiling sensors (Sobel et al. 2021; data access and full data description: https://www-air.larc.nasa.gov/cgi-bin/ArcView/camp2ex?RV-SALLY-RIDE=1). PISTON also included a nearly equivalent ship cruise in 2018 on R/V Thomas G. Thompson, an array of profiling ocean floats, and two full-depth ocean moorings (data at aforementioned website under different tabs). Atmospheric remote sensing of clouds and air motion that support collaboration with CAMP2Ex include the SEA-POL C-band (Rutledge et al. 2019) and NOAA W-band radars (Moran et al. 2012), wind and HSRL lidars, and 3-hourly radiosondes. The P-3 and Learjet 35 had three and five flights, respectively, characterizing the environment around the Sally Ride.
Remote sensing, modeling, and environmental informatics.
Mission operations and analysis required the integration of a multitude of product types (see supplemental section S.3 for more remote sensing, modeling, and informatics details). CAMP2Ex makes full use of and supports the global meteorological constellation of optical, radar, microwave, and scatterometer products. Of paramount importance was the cooperation of the Japan Meteorological Agency (JMA) for expedited Advanced Himawari Imager (AHI) data access, as well as the acquisition of 2.5-min rapid scan data. The Japan Amazon Web Services node provided imagery and products at 15-min latency for integrating into real-time flight operations. Cloud and aerosol products were derived from this dataset by porting algorithms from NASA MODIS.
CAMP2Ex supports the development of next-generation satellite products, including new geostationary algorithms, optical flow algorithms, aerosol and cloud polarimetric remote sensing for NASA’s upcoming Plankton, Aerosol, Cloud, Ocean Ecosystem (PACE) and AOS missions, and the ESA Aeolus wind lidar (supplemental section S.3.1). Of great value to CAMP2Ex was its application of high-resolution imagery, typically only acquired over land, to study maritime cloud properties and evaluate issues due to the relatively coarse resolution of existing satellite-based instruments typically used for atmospheric remote sensing. CAMP2Ex was granted large acquisitions of ASTER, Landsat-8, and Sentinel-2 within ∼800 km of the Philippine coasts. Multiview digital globe high-resolution imagery was also ordered, including stereographic views.
Modeling efforts in support of CAMP2Ex were also diverse. CAMP2Ex forecasting relied heavily on the Met Office; Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA); European Centre for Medium-Range Weather Forecasts (ECMWF); and Joint Typhoon Warning Center (JTWC) forecasting and data, as well as aerosol predictions from the U.S. Naval Research Laboratory (NRL), NASA’s Global Modeling and Assimilation Office (GMAO), and other International Cooperative for Aerosol Prediction ICAP consensus members (Sessions et al. 2015; Xian et al. 2019). The rapid evolution of convection around the Philippines, and at the airfield in particular, required monitoring of PAGASA’s radar network. Post-mission analysis has spanned a range of scales and models. Of particular use are a series of basin-scale mesoscale-resolution simulations of the entire Maritime Continent, flight-specific mesoscale-resolution, and large-eddy simulations (LES) all using the Regional Atmospheric Modeling System (RAMS; Cotton et al. 2003; Saleeby and van den Heever 2013) at Colorado State University, as well as global reanalyses at GMAO and NRL. Each modeling effort focuses on different problems, ranging from interactions within the large-scale meteorological system to aerosol, microphysical, and dynamical processes within individual clouds.
Integrating observations, satellite, and modeling data has been a series of informatics efforts. Data are made available to the public not only through the CAMP2Ex project DOI landing page (https://doi.org/10.5067/Suborbital/CAMP2EX2018/DATA001) hosted at NASA Atmospheric Science Data Center, but also via two visualization websites. JPL applied the Hurricane Watch Package to the CAMP2Ex domain where, to provide regional environmental context, satellite, model, and a subset of aircraft observations can be overlaid and downloaded (https://camp2ex.jpl.nasa.gov/; last accessed: March 2022; Hristova-Veleva et al. 2020). The University of Wisconsin ported NASA Worldview to focus on even higher-temporal-resolution geostationary applications to the aircraft and Sally Ride (http://geoworldview.ssec.wisc.edu; last accessed: March 2022). To help introduce data users to the CAMP2Ex P-3 dataset, the University of Illinois created a full flight data fusion dashboard for a single flight (16 September 2019) where all instruments can be monitored (Di Girolamo et al. 2021; https://virdir.ncsa.illinois.edu/NCSAvis/camp2ex/public/deliverables_6-15-21/). All of these tools are designed to allow the broader community to engage with CAMP2Ex and PISTON science.
Observations of the coupled system
The 2019 season provided excellent conditions with above-average biomass burning emissions, the frequent influence of tropical disturbances, and an early monsoon transition (supplemental section S.1). These led to a wide dynamic range of environments being sampled for all focus areas.
The compositional environment.
While much can be learned from remote sensing and modeling of aerosol life cycle, large uncertainties remain in fine vertical features, airmass histories, evolving aerosol properties, and ultimately small-scale processes. While curtain data such as those in Fig. 1b provide excellent detail on layers and some information on aerosol size, they must nevertheless be combined with other information to address science and monitoring needs, including: What is the dominant particle source on average or in a particular air mass? How are particle optical properties that are the basis for remote sensing related to their physical, thermodynamic, and cloud nucleating properties? And how do evolutionary processes change these relationships?
Along flight tracks, CAMP2Ex utilized a combination of back-trajectory modeling and trace-gas analysis to classify aerosol sources. Trajectory modeling along every point throughout a flight track was a crucial first step as directional wind shear often resulted in different source regions along the vertical profile within the operations area (e.g., Fig. 4a; Hilario et al. 2021). Because the CAMP2Ex domain was so large and CO2 varied due to biological activity, excess CO and CH4 (Fig. 4b) were the best in situ tracers for aerosol sources. While both species are products of biomass burning and industrial emissions (Helfter et al. 2016; Nara et al. 2017) and have lifetimes from months to years, low excess CH4 to CO ratio indicates biomass burning sources (e.g., Akagi et al. 2011). Higher CH4:CO ratios were predominantly from anthropogenic sources ranging from peninsular Southeast Asia to East Asia, with local urban sources and Metro Manila among the highest CH4 values—perhaps due to propane leaks and fuel evaporation. Low CO mixing ratios (<100 ppb) were representative of cleaner marine environments. More reactive gasses and their reaction products, such as SO2, NO, NO2, NOy, and O3 enable further assessment of sources and photochemical activity.
Airmass compositional characteristics measured during CAMP2Ex. (a) Back trajectories at 500, 3,000, and 5,000 m from the first day of the campaign for four operations quadrants. (b) Airmass typing during CAMP2Ex using in situ observations of methane (CH4) and carbon monoxide (CO). Inset pie charts show the percentage of observations for low- and high-altitude measurements (i.e., GPS altitude less than and greater than 2.0 km, respectively, excluding observations during takeoffs and landings). (c) Particle mobility derived particle number distributions normalized to total count for some example regimes. (d) Scatterplot light scattering hygroscopicity (the ratio of 80% RH light scattering to dry light scattering from two nephelometers) vs optical-particle-counter-derived effective radius, color coded by single scattering albedo. Evaluating the entire figure, biomass burning smoke from the Maritime Continent was largely from peat fires, leading to very large sizes but higher single scattering albedo and lower hygroscopicity. Pollution particles from East Asia were also large but with higher hygroscopicity owing to increased sulfate fractions. Clean marine particles were smaller, due to a lack of anthropogenic sources and particle scavenging. Smallest particle sizes were associated with new particle formation (NPF) events. Note in all cases, particle distributions deviate from idealized lognormal behavior—a likely outcome from particle production and scavenging mechanisms.
Citation: Bulletin of the American Meteorological Society 104, 6; 10.1175/BAMS-D-21-0285.1