ACE-1 measurements will be conducted on two ship platforms. The NOAA R/V Discoverer will be devoted exclusively to the ACE-1 program. Additional measurements of DMS and size-segregated aerosol composition will be made on the CSIRO R/V Southern Surveyor.
4.1.1 R/V Discoverer
Investigators aboard the R/V Discoverer will conduct both seawater and atmo-spheric measurements to quantify the processes and local closure experiments listed above. The shiptime during the ACE-1 intensive will be used for:
2. Chemical, physical and radiative measurements of the atmospheric aerosol to address the local closure and process studies outlined in section 3, and
3. Surface support for the aircraft Lagrangian experiments and column closure experiments. The ship will release balloons for the Lagrangian experiment.
The sequence of operations aboard Discoverer during the ACE-1 intensive will depend on the synoptic meteorological conditions, the locations of the major oceanographic frontal zones, and the status of the other observational platforms and therefore must remain flexible. Several of the planned activities listed above can be carried out simultaneously as was done during the 1991 PSI-3 cruise and the 1992 IGAC/MAGE cruise. The ship will provide surface support for column closure experiments whenever meteorological conditions and aircraft/satellite schedules permit. Local closure experiments of the chemical, physical and radiative aerosol properties will be conducted continuously. A tentative ship schedule is listed below:
18-25 November Sampling north of the Subantarctic Frontal Zone and southwest of Tasmania. Provide ground support for Lagrangian experiments.
25-27 November Sampling south of the Subantarctic Frontal Zone, measurement intercomparison with Macquarie Island.
27-30 November Sampling south of the Subtropical Front and southwest of Tasmania. Provide ground support for Lagrangian experiments.
01-07 December Atmospheric sampling upwind of Cape Grim for measurement intercomparison with land, ship and aircraft platforms. Provide ground support for Lagrangian experiments.
07-14 December Sampling north of the Subtropical Front, west of Tasmania. Atmospheric sampling upwind of Cape Grim for second measurement intercomparison with land and aircraft platforms. Transit to Hobart.
The following measurements will be made aboard the ship. Leg 1 refers to the Seattle to Hobart transit and Leg 2 refers to the ACE-1 intensive:
Atmospheric Chemical Measurements
Mass size distributions of nss sulfate, MSA, ammonium, and other major ions with a six-stage hi-vol cascade impactor. Sampling times will range from 6 to 24 hours. (Quinn, PMEL for Sievering, UC)
Sub- and super-micron nss sulfate, MSA, ammonium, and other major ions with a two stage multi-jet cascade impactor. Sampling time periods will be 4 to 6 hours. (Quinn, PMEL)
The ammonium to nss sulfate molar ratio from 10 to 600 nm diameter using thermal conditioning in conjunction with a TDMA. (Heintzenberg and Wiedensohler, IfT)
Single particle analysis using SEM/EDXA to characterize aerosol morphology, chemical composition, and aerodynamics. (Anderson, ASU and Tindale, TAMU)
Single particle analysis using TEM to characterize aerosol morphology and chemical composition. (Quinn, PMEL for McInnes, UC)
Combustion analysis for sub-micron total organic and elemental carbon (Quinn & Hansen, PMEL) and total organic nitrogen and carbon. (Suzuki, SU)
Organic speciation using thermal desorption and super-critical fluid extraction and GC analysis. (Hansen, PMEL)
Gas phase measurements of SO2 (De Bruyn & Saltzman, RSMAS), NH3 (Quinn, PMEL), DMS (Bates, PMEL), CO and O3 (surface and vertical profiles) (Johnson, JISAO), Alkenes (Johnson, JISAO/UW), NMHC (Shi & Prinn, MIT), PAN and nitrogen oxides (Carsey, AOML), Rn (Bates, PMEL & Whittlestone, ANSTO), methyl halides (Moore, DU, Leg I only), CO2 (Feely, PMEL), carbon isotopes (Quay, UW), NO (Bates, PMEL & Jaffe, UAlaska).
Total number concentration of CN with Dp>15 nm and CN with Dp>3 nm using TSI 3760 and 3025 particle counters, respectively. (Kapustin, JISAO & Covert, UW)
Particle number size distribution from 3 to 10000 nm diameter using an UDMPS, standard DMPS, and TSI 3300 APS. (Kapustin, JISAO & Covert, UW)
Particle number size distribution from 200 to 20000 nm using a CSASP-200 PMS probe (Durkee, NPGS)
CCN number concentration at 0.65% supersaturation. (Kapustin, JISAO & Covert, UW)
Hygroscopic growth of aerosol particles with TDMA. (Swietlicki, LU)
Light scattering and backscattering fraction by submicron and total aerosol at wavelengths of 450, 550, and 700 nm.(Quinn and Bates, PMEL)
Total light scattering at low reference RH and at a higher RH using dual Radiance Research Corporation nephelometers. (Kapustin, JISAO & Covert, UW)
Aerosol optical depth with hand-held and sun-seeking sunphotometers. (Quinn, PMEL & Dutton, CMDL; Porter, UH; Weller, MOP)
CO oxidation rates (Zafiriou, WHOI, Leg I only)
NH4+ and pH (Quinn, PMEL & Dickson, UCSD)
DMS (Bates, PMEL)
CO (Johnson, JISAO)
Alkenes (Johnson, JISAO/UW)
NMHC (Shi & Prinn, MIT)
Methyl halides (Moore, DU, Leg I only)
pCO2 (Feely, PMEL)
POC, PON, POS, DOC, DON, DOS (Suzuki, SU)
Vertical profiles of atmospheric temperature, dew point and winds, UHF/VHF Doppler wind profiler, radio acoustic sounding system (NCAR).
Cloud cover using total-sky camera (PMEL).
Surface seawater temperature, salinity, chlorophyll a, and nitrate (Bates, PMEL).
Satellite observations of aerosol optical depth, aerosol number & size (Durkee, NPGS, Leg 1 only).
Smart balloon releases (R.Johnson, ARL, leg 2 only).
4.1.2 R/V Southern Surveyor
Although the primary objective of the R/V Southern Surveyor is to study ocean carbon cycling as part of the Joint Global Ocean Flux Study (JGOFS), many of the chemical and biological measurements will be a valuable addition to the ACE-1 and will be particularly important in assessing the processes controlling seawater DMS concentrations. The primary cruise objectives that relate specifically to ACE-1 include:
2. Studies to determine the processes controlling the conversion of DMS to DMSO (Jones, JCU).
3. Mass size distributions of nss sulfate, MSA, ammonium, and other major ions with a six-stage hi-vol cascade impactor (Greene & Tindale, TAMU).
4. In-situ optical measurements including spectral absorbtion and upwelling and down-welling spectral irradiance (Parslow, CSIRO).
5. Atmospheric radon measurements to characterize air mass origins (Whittlestone, ANSTO).
6. Balloon launches to determine vertical distributions of temperature, humidity and winds (NCAR).
18-20 November Mapping features of the front. Provide ground support for Lagrangian experiments.
20-21 November Process station south of the Subantarctic Frontal Zone (53S).
21-30 November Process stations at 1 intervals up 140E to 42S. Atmospheric sampling upwind of Cape Grim for measurement intercomparison with land, ship and aircraft platforms.
01-07 December Atmospheric sampling upwind of Cape Grim. Measurement intercomparison with land, ship and aircraft platforms. Provide ground support for Lagrangian experiments. Transit to Hobart.
ACE-1's coordinated airborne research component plans to conduct a comprehensive suite of chemical and physical measurements aboard NCAR's Research Aviation Facility's recently acquired C-130 aircraft. The C-130 research platform will be equipped with the capability to make measurements of boundary layer structure and fluxes; aerosol microphysical and chemical properties; cloud properties; radiation; and the concentration of gas phase aerosol precursors and tracers including oxidants, sulfur and nitrogen gases, hydrocarbons, and halocarbons. To address key aspects of ACE-1's scientific objectives, the proposed program's flight plans and sampling strategies exploit these measurement and aircraft capabilities in synergistic designs that will produce rigorous characterizations of:
2. aerosol nucleation and accretion processes;
3. the vertical distribution of aerosols, their precursors, and their effects on tropospheric chemistry and the Earth's radiation budget; and
4. the latitudinal variation of free-tropospheric aerosol concentrations and nucleation/processing rates.
Figure 4. Generic detailed vertical profile consisting of a stack of level altitude legs arranged either perpendicular of parallel to the wind, which can be folded into an “L”, Chevron, or “U” shaped pattern. Sampling time at each altitude is nominally 20 to 40 minutes to allow long integration time measurements. LIDAR mapping of the column would occur during both the low altitude under-flight and highest altitude over flight legs as well as at intermediate altitudes.
2. stratocumulus and convective cloud processing experiments aimed at assessing the effects of clouds and tropospheric aerosols on one another;
3. column closure and vertical distribution experiments aimed at assessing the tropospheric vertical distribution of aerosols and their precursors, and their effects on radiation budgets; and
4. intercomparison and survey experiments in the vicinity of Cape Grim, Macquarie Island, and the R/V Discoverer (see also section 6.3).
2. characterize the representativeness of the vertical distribution of aerosols and aerosol precursors in the clean remote marine environment.
4.2.1 Measurement and C-130 Aircraft Capabilities
A novel suite of sensors on the C-130 aircraft will provide an unprecedented capability to conduct airborne studies on the chemical and physical factors affecting the production and fate of particles and their impact on processes in the troposphere. The measurements include a unique blend of capabilities necessary to critically address ACE-1's objectives (see Table of C-130 measurements and C-130 diagram). These include the measurement of eddy correlation ozone, sensible heat, water and momentum fluxes; aerosol microphysical parameters; size segregated aerosol chemical composition; cloud properties; radiation; important atmospheric oxidants (O3, OH, H2O2); aerosol precursors (H2SO4, SO2, DMS, NH3, etc.); tracers of anthropogenic and biogenic emissions (NMHCs, CFCs, CO, etc.); and the primary parameters needed for interpretive studies using detailed photochemical models (NO, UV Flux, CO, etc.). Sampling times for these sensors vary from less than a second (e.g. the high speed flux instrumentation) to as long as 40 minutes (e.g. measurement of aerosol chemical composition). Flight profiles
Figure 5. Transit flights to and from Hobart including a nearly pole-to-pole latitudinal transect on the north-south transit. Profiling of tropospheric vertical structure (in the form of extended vertical stacks or in-progress stair-step ascents/descents) will occur at the positions indicated on both the north-south and south-north transits.
In addition, the vertical characterization of the middle to lower troposphere will employ series of 20 to 40 minute constant altitude legs arranged in vertical stacks (generically shown in Figure 4). This will enable sampling at each altitude for all measurement systems with the spatial variability along each leg being well defined by the high speed sensors, as well as a number of the intermittent or moderate speed (few minutes) measurement systems (DMS, SO2, ultra-fine aerosol distribution, etc.). The endurance of the C-130 will enable a typical flight to carry out approximately three such detailed vertical soundings (stacks) throughout designated portions of the lower 8 km of the troposphere, with high resolution continuity being obtained from both the high speed sensors and the remote LIDAR mapping of aerosol backscatter. The LIDAR sensor will also be used to produce real- time tropospheric column survey information for inflight fine- tuning of the location of vertical profiles and altitudes of the level legs. In particular, this information will be used to change the nominal altitude leg duration and number of levels in situations where longer (or shorter) sampling times may be needed and where the LIDAR profiling indicates a more (or less) homogeneous lower tropospheric column would require fewer (or more) level sampling legs.
The basic approach to vertical profiling (or "stacks") can also be applied to detailed studies of the marine boundary layer, as in the case of the Lagrangian experiments (section 4.2.4), or the Cape Grim and R/V Discoverer intercomparisons (section 4.2.8). Alternatively, extended vertical stacks can be used to profile the entire tropospheric column below 8 km, as in profiles planned for the column closure experiments (section 4.2.7) or the vertical distribution surveys (section 4.2.9). These basic stack-type profiles, or slight modification of them, can be used to satisfy more than one scientific goal in any one particular flight.
Figure 6. Kilauea plume chemistry/aerosol evolution experiment. The plume, which is trapped within the boundary layer’s inversion will be sampled at three downwind positions with incrementally more or less dilute precursors. At extended series of figure-8’s with zig zag patterns in the plume will be used to sample the plume and adjacent regions just before dawn and approximately 2.5 hours thereafter for 2 additional cycles.
Atmospheric Chemical Measurements
Gas phase H2SO4, MSA, OH by API-MS (Eisele, GIT/NCAR).
Mass size distributions of nss sulfate, MSA, ammonium, and other major ions with a two-stage impactor (Huebert & Wylie, UH).
Mass size distributions of organic and elemental carbon with a two-stage impactor (Huebert & Wylie, UH).
Ammonia and nitrogen oxide by LIF (Bradshaw, GIT).
Single particle analysis using SEM/EDXA to characterize aerosol morphology, chemical composition, and aerodynamics. (Anderson, ASU).
Inferred aerosol composition as a function of size using thermally conditioned OPCs (Clarke, UH).
Ozone by Teco UV and NO Chemiluminesence (Kok, NCAR).
H2O2 by peroxidase (Kok, NCAR).
CO by HgO detector (Kok, NCAR & Bandy, DU).
HNO3 with nylon filters (Huebert & Wylie, UH).
CFCs and NMHC using canisters and laboratory GC-MS analysis (Blake & Rowland, UC Irvine).
Particle number size distribution from 3 to 500 nm diameter using a radial DMPS (Seinfeld, Flagan and Russell, CIT).
Particle number size distribution from 3 to 12 nm diameter in four size bins using tuned ultrafine CN counters (McMurry, UM).
CCN size spectra (Hudson, DRI).
Total light scattering and the backscattered fraction using nephelometry at wavelengths of 450, 550, and 700 nm at low and high RH (Clarke, UH).
Index of refraction using MASP (Baumgardner, NCAR).
Aerosol hygroscopic growth using mass and RH (Huebert & Wylie, UH).
Up- and Down-welling radiation (Valero, UCSD).
Aerosol backscatter profiles with an aerosol lidar (Radke & Morley, NCAR).
Total particles > 300 nm and > 100 nm with FSSP-300 and ASASP, respectively (Baumgardner, NCAR).
Cloud droplets using various PMS probes (RAF, NCAR).
Optical depth at 3 wavelengths (Porter, UH).
Balloon location (Businger, UH).
In order to make maximum scientific use of the flight hours required to ferry the C-130 to Tasmania, measurements will be made on a long latitudinal transect (Figure 5). This transect will produce a nearly pole-to-pole free-tropospheric survey of aerosol and aerosol precursor distributions along the middle of the Pacific Basin. During the 67 hours requested for this activity, the C-130 will fly first to Anchorage, Alaska, from which it will fly a loop as far north as possible, conduct a vertical profile, then return to Anchorage. It will then step down the central Pacific, stopping at Hawaii, Christmas Island, American Samoa, and Christchurch, New Zealand. From Christchurch it will make another loop, this time as far south as possible, conduct a vertical profile, and return to Christchurch. This will be followed by a ferry flight from Christchurch to Hobart. A mini-intensive study of the Kilauea volcano's plume is also planned (section 4.2.3) during the brief stay-over in Hawaii. Detailed vertical profiles (in the form of extended vertical stacks or in progress stair-step descents/ascents) of the remote marine troposphere are planned wherever point-to-point flight times are sufficiently short to allow for the additional time and safety constraints needed (approximately 3.5 to 4 hours for vertical stacks or 1.5 to 2 hours for vertical stair-steps). Detailed vertical profiles are planned (section 4.2.9) off the coasts of Christmas Island and American Samoa (vertical stacks), and the region just north of New Zealand (in progress stair-step). These locations were selected to provide additional clean marine comparisons of vertical structures in the equatorial and southern mid-Pacific. This latitudinal survey will provide the first measurements of the large scale free-tropospheric distribution of a number of important parameters including: aerosol precursors (e.g. H2SO4 and NH3); size segregated aerosol chemical composition; and ultra-fine particle size distributions and number density.
4.2.3 Kilauea Plume Experiments
The Kilauea volcano's plume offers an exceptional opportunity to study sulfur oxidation chemistry, new particle production, and particle growth on an accelerated scale. As such, 19 flight hours are requested to conduct a mini-intensive study. This plume, which consists primarily of enhanced SO2 (but not enhanced NOx, soot, or other anthropogenic compounds), provides a unique "natural- laboratory" capable of producing rapid increases in H2SO4 concentrations under clean marine boundary layer conditions (between one to two orders of magnitude enhancements were measured on occasion during MLOPEX II). Thus, this plume offers the possibility of measuring exceptionally high, and therefore more easily measured, rates of new particle production under marine boundary layer conditions, which is thought to be rate limited by H2SO4 levels. We will therefore examine sulfur oxidation and particle growth that is abruptly turned on by the rising of the sun and, due to enhanced rates, can be tracked over periods of hours instead of days. The flight profile for this study (Figure 6) will be largely confined to the boundary layer and consists of a series of plume characterization legs occurring at three
Figure 8. Profile view of the Lagrangian experiments. Balloons will be released by R/V Discoverer at the start of the experiment.
We hope to be able to deploy one of the "smart" constant-altitude balloons (which were designed for use in the Lagrangian experiments near Hobart) during this experiment, to test the balloon system and to serve as a tag for us to follow as we observe the chemical evolution. The major uncertainty in this plan is the fact that with no launch vehicle, the balloon will have to be launched from the south coast of the island of Hawaii. From that location, there is a possibility that the balloon may become trapped in one of the island's lee-vortices, rather than following the bulk of the plume downwind. If successful, this will also permit us to practice our balloon-following procedures prior to the Hobart Lagrangian experiments.
In addition to the aerosol-evolution study, the Kilauea plume also offers a unique opportunity to test vertical-column radiative closure (section 4.2.7) and to assess measurement uncertainties under conditions where scattering is greatly enhanced by a point source of fine particle sulfate under (otherwise) clean marine conditions. This will also serve as a primary calibration and test of the column-closure methodology under conditions where the signal-to-noise ratio will not contribute appreciably to the uncertainty. The flight profile for this experiment will consist of three vertical stacks (section 4.2.7) in areas identified by lidar profiling as low, medium, and high optical depth regions. The timing of one stack will coincide with a satellite overpass (e.g. AVHRR). Each stack will be preceded by a horizontal lidar leg designed to characterize inhomogeneities in aerosol backscatter and optical depth. The lidar data will help in the selection of the starting point for the "stack," and will help us avoid altitudes where steep gradients in the aerosol might be evident. Legs will be flown at the surface and two other altitudes below the inversion (Figure 12). Two additional legs will be flown above the inversion as suggested by the lidar data.
These measurements will provide an opportunity for column closure under ideal measurement conditions where the effects of sulfate aerosol can be isolated and compared to the marine background into which it was introduced. In addition, the Kilauea plume column- closure flight will be used as a plume mapping expedition for what will be the subsequent day's plume chemistry/aerosol evolution experiment. By obtaining a first glimpse of what to expect, this staging will provide valuable information and the insight needed to refine detailed flight plans for the chemistry/aerosol growth experiment.
Figure 9. Detailed boundary layer profile for the Lagrangian experiments. Each flight will consist of a ferry and two or three stacks of the type shown here.
Approximately 80 flight hours will be needed to conduct the two Lagrangian experiments that are planned for the clean mid-latitude marine boundary layer south of Tasmania. This major component of the ACE-1 experimental plan is aimed at elucidating the factors controlling the development and growth of remote marine boundary layer aerosols. Satellite observations will be used to identify relatively homogeneous air masses for the starting positions of the Lagrangian experiments. The R/V Discoverer will be positioned to launch balloons into the identified air masses. At least one Lagrangian experiment will be flown in clear air (to the extent possible), in order to observe photochemical changes in DMS and other sulfur species.
The flight plan sequence for the C-130 (depicted in plan and profile views in Figures 7 and 8) will start a flight every 12-13 hours from Hobart. Each flight will consist of a ferry and two or three vertical stacks of the type shown in Figure 9. All flight personnel (including both the aircrew and scientific observers) will be double-crewed to maintain RAF safety standards and high data quality through four sequential flights. Each flight will be directed first toward the location being transmitted by the balloons, after which a survey profile will be used to fine-tune the location. Flight legs will largely be confined to the boundary layer, with special emphasis on the surface mixed layer, if decoupling has isolated a part of the boundary layer from the surface. After the completion of a Lagrangian experiment there will be 2-3 aircraft down-days to process data and use the experience gained to improve the subsequent flights.
Although Figures 7 & 8 show L-shaped flight legs, we are evaluating a plan to use circular legs of roughly 60 km diameter at each altitude. These legs would greatly improve the accuracy with which entrainment could be measured, thereby improving the most uncertain term in our chemical budgets. Depending on the impact of a 1-2 degree roll angle on the measurement systems, we may use this approach for one or both Lagrangian experiments.
4.2.5 Marine Stratocumulus Cloud Processing Experiments
The Hobart intensive offers a unique opportunity to examine marine stratocumulus clouds in a nearly pristine environment. Eighteen hours of flight time are requested to conduct two dedicated flights aimed at better understanding marine stratocumulus, which 1) contribute more to radiative forcing than any other cloud type and 2) with its associated highly turbulent boundary layer, processes enormous amounts of boundary layer air through cloud. The Dynamics and Chemistry of Marine Stratocumulus program (1985) and portions of the FIRE program (Fire, 1988; and ASTEX/FIRE, 1992) clearly point out that additional data are needed. Acquisition of data on the sparsely studied Southern Hemisphere stratocumulus, using the here-to-fore unprecedented array of aerosol and gas phase (i.e. H2SO4,
Figure 10. Vertical profiling design for stratocumulus cloud experiments will sample below, in and above cloud. Sampling profiles will be repeated three times during a given flight.
The flight plan for this experiment (Figure 10) consists of a ferry and three vertical stacks that profile the marine boundary layer, the stratocumulus cloud layer, and the adjacent free- troposphere above. Three vertical stacks are needed to help insure representativeness of sampling over a sufficiently broad region of a marine stratocumulus system and to obtain sufficient statistics to evaluate boundary fluxes and entrainment rates (including H2O, O3, and possibly NH3). In particular, levels above cloud will be examined for signs of H2O/O3 anticorrelation and O3/ultra-fine particle correlation. The second flight is required in order to further test representativeness of the findings, but more importantly to refine sampling strategies based on the data and learning experience gained from the first flight.
4.2.6 Convective Cumulus Processing Experiments
The Hobart intensive also offers a unique opportunity to study the production of small particles that have been reported to occur near the top of convective cumulus clouds. If confirmed, these processes could be an important source of cloud condensation nuclei to the lower altitudes. The region south of Tasmania is ideally suited to study this process in a nearly pristine environment. Here, high pressure systems are replaced by frontal systems which in turn are displaced by a region containing few clouds. This clear region is itself replaced with a convective area containing the cumulus clouds that can grow to 4-6 km in height.
This study requires 18 dedicated flight hours to conduct two flights that will use a combination of two basic profiling methods. One profile type focuses on characterizing the convective cloud processing of air and its associated cloud top outflow (Figure 11), and a second type attempts to address the representativeness or ensemble average effect of a number of clouds (Figure 11). Two flights are required in order that refinements of the sampling strategy can be affected based on the data and learning experience gained on the first flight. The high speed sensors that will be capable of accurately defining the cloud and its plume include H2O, O3, and temperature and wind ( < 0.1 second resolution) as well as CN, H2SO4, NH3, and NO (» 10 second resolution). These measurements will be used in real-time to coordinate sampling by the longer integration time or intermittent measurement systems (e.g. SO2, DMS and NMHC). This strategy will also allow long integration time measurements (e.g. aerosol chemical composition) to integrate a number of events and obtain ensemble averages. In addition, the speed of the rapid response sensors will enable the cloud to be profiled from the
Figure 11. Cumulus cloud processing experiment profile type I will first pass over top of cloud (+200m) then pass through cloud profile from top down. This pattern will be repeated on as many clouds as possible within a given flight. Type II is a variant of type I that will measure the ensemble effect of cumulus clouds.
4.2.7 Column Closure Experiments
The clear-sky column radiative closure experiments will attempt to establish a quantitative link between aerosol microphysics, chemistry and optical properties measured in the troposphere. Specific objectives include the role of aerosol sulfate in radiative forcing and aerosol radiative properties for the clean marine boundary layer. These include so-called local closure that link these properties through measurements over a limited time and space and column closure that integrates these properties over the vertical aerosol column (which is generally dominated by the lower troposphere). This closure will be attempted between measurements made aboard the C-130 and also with satellite derived radiances and upwelling radiances obtained from shipboard. Two dedicated flights (10 hour Hawaii and 7 hour Hobart flights) will be used for the radiative closure experiments. We will use at least another 9 flight hours for column closure studies, but on flights where this is compatible with other science objectives (such as the Cape Grim intercomparison flights). Apart from the need for clear air (real- time satellite retrievals will be used for flight planning), the two dedicated flights will be coordinated with satellite overpasses, to permit comparisons between in situ and remotely sensed column-integrated radiative properties.
A procedure similar to that in the Kilauea plume (but with longer and fewer sample legs) will be employed during the Hobart closure studies. The extended sampling periods are required to increase the sensitivity of those instruments for which the lower concentrations south of Hobart would otherwise be problematic. Additional vertical stacks to assess representativeness of the sampling will be carried out in co-ordination with other planned profiling activities during the Hobart intensive and on the transit flights. These studies will establish:
2. the spectral optical depth of this sulfate aerosol throughout the column and its relationship to aerosol microphysical and chemical measurements;
3. an evaluation/calibration of satellite retrieved aerosol optical properties for a wide range of conditions at and above the concentrations expected for most of ACE-1.
Figure 12. Clear-air column closure experiment flight plan consisting of a series of three extended vertical stacks. Flights will be arranged to coincide with AVHRR overpasses and surface measurements of water leaving radiance from the R/V Discoverer, Southern Surveyor, or NASA’s buoy near Maui.
4.2.9 Survey of Tropospheric Vertical Structure
The ACE-1 program offers a unique opportunity to test, under a variety of remote marine conditions, the hypothesis that new particles are produced in the upper troposphere where aerosol surface area is sufficiently small to favor new particle formation over growth of pre-existing aerosols. These new particles would then slowly grow by coagulation while subsiding and would eventually be entrained into the boundary layer where they would rapidly grow to cloud condensation nuclei by accreting H2SO4 vapor. In the mid-latitudes south of Hobart, at least six detailed vertical profiles of the lower 8 km tropospheric/column will be obtained during the column closure experiments. Additional southern mid-latitude profiles of vertical structure may also be obtained from the cloud processing and Cape Grim intercomparison flights.
To expand this data base to a broader region of the southern/mid- Pacific, we will use 16 flight hours and stop-overs at Christmas Island and Brisbane to make vertical profiles during the transit flight sequences to and from the Hobart intensive site. Four of these profiles will consist of extended vertical stacks (Figure 15), and two will be in the form of in-progress stair-step profiles with long (30 minute) sampling legs (Figure 16). During the north-south latitudinal survey one vertical stack will be made off the coast of Christmas Island at the northern edge of the Southern Equatorial Current, and a second will be made at the southern edge of the Southern Equatorial Current just east of American Samoa. These points were chosen based on their scientific importance (e.g. closeness to the ITCZ, northern and southern boundaries of the South Equatorial Current, and coupling to ground-based measurements e.g. CMDL site at Samoa), and from a safety/flight planning perspective (i.e. point-to-point flight time short enough to enable the addition of the
Figure 13. Macquarie Island survey/intercomparison flight plan with boundary layer survey off the coast.
Three detailed vertical profiles are also planned during the return transit from Hobart (Figure 5). The first profile will be an extended vertical stack over the western edge of the Tasman Sea that will profile clean extra-tropical marine inflow to the Australian continent near 30°S. A second vertical stack is planned just north of Nadi, Fiji, at a more westward point along the southern edge of the Southern Equatorial Current, and the third vertical profile will be an in-progress stair-step into Christmas Island. In addition, the profiling activities at Christmas Island should give unique new insights to the recent ground-based sulfur chemistry/aerosol production studies that have indicated a strong coupling between the diurnal cycles of DMS and SO2.
These profiles of the extra-tropical to equatorial mid-Pacific troposphere will provide the first ever vertical distributions for a number of important parameters within this data sparse region (e.g. H2SO4, MSA, NH3, ultra-fine size distribution, and size segregated chemical composition). In addition, these profiles will provide perhaps the only opportunity this decade to assess a number of scientific questions, such as whether NH3 distribution and levels in the troposphere are sufficient to affect particle formation and growth or to act as the missing source of the ozone precursor NO. An accurate knowledge of the distribution of all of these parameters within the tropospheric column is essential to furthering our understanding of both homogeneous and heterogeneous atmospheric processes. Thus, these additional vertical soundings of aerosol and aerosol precursor distribution will greatly add to the knowledge of tropospheric structure of data sparse parameters in extremely data sparse regions of the world.
4.2.10 Flight Program Compatibility/Mission Readiness
Mission go/no-go criteria will be established for each type of investigation. While it is most desirable to fly with all instruments functioning perfectly, this may not always be possible, due to unavoidable instrument failures. Therefore, in addition to aircraft readiness, we will define a minimum compliment of sensors necessary to achieve a basic subset of scientific goals of each experiment. This matrix of measurements and goals will be used, in conjunction with each day's meteorological context, to define the best mission for a given operational scenario. In this regard, the missions planned for Hobart lend themselves well to contingency planning.
Figure 14. Cape Grim intercomparison flight profiles consisting of a stack of chevrons in the upwind boundary layer off Cape Grim. Profiles will be made to characterize several air mass types including clear sector air and continental air (for continental “plume” signature identifications).
Time constraints will allow us very little latitude to take unscheduled down-days during the transects. The existing lack of data on most of the parameters being measured suggests that if even only just a few instruments were operational (e.g. H2SO4, MSA, SO2, and DMS, or ultra-fine aerosol composition and size distribution, or H2SO4, and NH3 and aerosol composition), the transects would be scientifically successful. This assurance of success, coupled with the transit nature of these missions, limits the go/no-go criterion to aircraft readiness. Instrument spares will be sent airfreight from RAF to Honolulu to allow for instrument maintenance during the Hawaii stopover, but very little repair work will be possible during the remainder of the transects.
The test flights will be conducted from Denver, CO. Due to complexity of the payload, and the fact that ACE-1 represents the first time integration for most sensors aboard the C-130 aircraft, 3 test flights will be required. These are planned for 2.5, 3.5, and 5 hour duration. The first two flights will be primarily focused on testing new inlets and general instrument "shake-down" with the third test flight and the transit to Anchorage planned to provide a complete operational test of the entire integrated payload. A last CAINE community aerosol inlet evaluation test flight will also be flown near the beginning of October.
Figure 15. Extended vertical stack profile to be used on transit flights. Profiles consist of an in progress overflight in which the LIDAR system helps define the location of the profile and choice of altitudes for each of four level 45 minute “U” folded legs. The last leg is flown in the marine boundary layer and provides a return flight path in-progress LIDAR under-flight of the column.
A. Test Flights (NCAR/RAF LOCAL FLIGHTS)
10/13 1. Test Flight #1 (Equip. Shakedown, Flow Test, etc.) 2.5 hours
10/20 2. Test Flight #2 (Equip. Shakedown) 3.5 hours
10/26 3. Test Flight #3 (Full-Up Operational Tests) 5.0 hours
3 flights Sub-Total 11.0 hours
B. North-South Transect
10/29 1. Denver - Anchorage Ferry 8.0 hours
(4th Test Flight) (one day rest)
10/31 2. Anchorage - North-Anchorage 10.0 hours
(local flight with spiral descent at northern end)
11/1 3. Anchorage - Hawaii 10.0 hours
(in progress descent profile near Hawaii)
11/7 4. Hawaii - Christmas 8.0 hours
(with extend vertical stack near Christmas approx. 155°W 2°N)
11/8 5. Christmas - Samoa 8.0 hours
(with extended vertical tack near 165°W 12°S)
11/9 6. Samoa - Christchurch 9.0 hours
(with in progress vertical stair-step near 178°W 32°S)
(one day rest)
11/12 7. Christchurch - South-Christchurch 10.0 hours
(with spiral profile at southern end and in progress
vertical stair-step return) (one day rest)
11/14 8. Christchurch - Hobart 4.0 hours
8 flights, 13 days Sub-Total 67.0 hours
C. Kilauea Plume Intensive
11/4 1. Column Closure 10.0 hours
(three vertical stacks at low, medium, and high plume loading)
11/5 2. Aerosol Growth Experiment 9.0 hours
(three horizontal profiles as a function of solar exposure time)
(one rest day)
2 flights, 3 days Sub-Total 19.0 hours
D. Lagrangian Experiments
1. Two sequences of 4 flights each (10 hours/flight) 80.0 hours
8 flights Sub-Total 80.0 hours
1. Convective Cloud Processing 18.0 hours
(two flights dedicated 9 hours each)
2. Stratus Cloud Processing 18.0 hours
(two flights dedicated 9 hours each)
3. Column Closure Experiment 10.0 hours
(one dedicated flight 3 vertical stacks @7 hours
with one Cape Grim comparison @3 hours)
4. Macquarie Island Survey (one dedicated flight) 10.0 hours
5. Vertical Profiling/Regional Survey Flights with
the Following Overlapping Goals
(a) Testing Representativeness of Vertical Stacks
in Column Closure Experiment (3 vertical stacks)
(b) Cape Grim Intercomparison under varied conditions
(clean air, continental plume, etc.) (3 vertical stacks)
(c) Characterizing Continental Plume Signatures (over-
lapping portions of (a) and (b))
two flights dedicated to (a)-(c) @10 hours each 20.0 hours
8 flights Sub-Total 76.0 hours
F. South-North Return Transect
12/15 1. Hobart - Brisbane 8.5 hours
(with vertical stack near 160°E 32°S)
12/16 2. Brisbane - Nadi 9.0 hours
(with vertical stack near 175°E 15°N)
12/18 3. Nadi - Christmas 5 hours
(with in progress vertical stair-step into Christmas)
12/20 4. Christmas - Hilo, Hawaii 5.5 hours
(with in progress vertical stair-step out of Christmas)
(one day rest)
12/22 5. Hawaii - Moffett 7.5 hours
12/23 6. Moffett - RAF 3.0 hours
6 flights, 7 days Sub-Total 42.0 hours
Program Total 295 hours
Land-based measurements at the regional base-line stations are an important component of ACE-1 because their long-term record provides a means by which the intensive experiment can be extrapolated in a broader climatological context. During the intensive experiment, the land-based measurements will provide an opportunity to conduct closure experiments over a range of conditions and for extended periods. They also will provide a ground base for column closure experiments made in conjunction with the aircraft.
The ACE-1 study area (Figure 1) contains a number of operational stations with historical records of aerosol properties. These are Cape Grim (40.7S, 144.7E) on Tasmania, Macquarie Island (53S, 158E), and Baring Head (41.6S, 175.1E) at the southern end of the North Island of New Zealand. Together these stations form the apices of a regional triangle that encompasses the study region.
4.3.1 Cape Grim
Facilities at Cape Grim include a large observatory with an on-going observational program of aerosol, trace gas, passive radiation and meteorological measurements. During the ACE-1 intensive the station will also operate an NCAR Integrated Sounding System similar to that which will be on Discoverer (see section 4.1 for description of the system).
The following measurement program will be in place at Cape Grim during ACE-1:
Static thermal gradient CCN counter, 5 supersaturations from 0.23% to 1.2%, once daily set of 3 CCN spectra (can be increased) (Gras, CSIRO).
Continuous record of CCN at 0.5% at approximately 2 min. frequency (Gras, CSIRO).
PMS ASASP-X particle size spectrometer 100 - 3000 nm Dp, automatic, 4 distributions per day (can be increased to 48) (Gras, CSIRO).
TSI 3071 Electrostatic classifier with TSI 3760 CN counter for size distribution, 40 < Dp < 400 nm, one distribution daily (can be increased to 48) (Gras, CSIRO).
Particle number size distribution from 3 to 10000 nm Dp using an UDMPS, regular DMPS, and TSI 3300 APS (Covert, UW and Heintzenberg and Wiedensohler, ITR).
TDMA measurements of hygroscopic growth in the CCN size range (Covert, UW and Swietliki, LU).
Light scattering and backscattering fraction at wavelengths of 450, 550, and 700 nm. Measurements will be made with two nephelometers, one at an RH (40%) and one at a higher RH (Ogren, CMDL and Rood, UI).
Ammonium to nss sulfate molar ratio from 10 to 600 nm Dp using thermal con-ditioning in conjunction with a TDMA and an ultra-fine CN counter (Covert, UW and Heintzenberg and Wiedensohler, ITR).
Magee Scientific Aethalometer, optical absorption, interpreted as elemental carbon, 30 min. sample rate (Gras, CSIRO).
TSI 3760 CN counter (Gras, CSIRO).
Hivol, PM10 for sea-salt, nss SO4, MSA - baseline only - weekly (Prospero, RSMAS).
Size selected filter stack, (Dp < 2, and 2 < Dp < 16 mm), for sea-salt, MSA, nss SO4 - baseline only - weekly integrated (Ayers, CSIRO).
SO2 (Saltzman, RSMAS and Cainey, CSIRO).
NH3 (Whung, AOML).
DMS, automated gas chromatography, 24-48 samples per day (Ivey, AGAL).
Radon (222), delay tank system, approximately 30 min delay time and radon daughters, continuous (Whittlestone, ANSTO).
Spectral optical depth (Forgan, BoM).
Aerosol chemical composition using mass spectrometry (Murphy & Thomson, NOAA/AL).
Inorganic ions and elemental and organic carbon vs size, daily MOUDI samples (Gras, CSIRO and Huebert, UH).
Mass size distributions of nss sulfate, MSA, ammonium, and other major ions with a six-stage hi-vol cascade impactor. Sampling times will range from 2 to 6 hours (Sievering, UC).
Sub- and super-micron concentrations of nss sulfate, MSA, ammonium, and other major ions every 3 hours (Huebert, UH).
NOx, NMHC, O3 (Galbally, CSIRO).
Peroxides and aldehydes (Ayers, CSIRO).
Stable sulfur isotopes for determination of natural and anthropogenic sulfur sources (Liss, UEA).
Single particle analysis using SEM/EDXA to characterize aerosol morphology, chemical composition, and aerodynamics (Anderson, ASU and Tindale, TAMU).
Single particle analysis using TEM to characterize aerosol morphology and chemical composition (Anderson, ASU and Tindale, TAMU).
Spectral optical depth measurements will be carried out close to Hobart to take advantage of the C-130 vertical profiles that will be available during each departure and arrival of the aircraft (Forgan, BoM)
4.3.3 Macquarie Island
The Macquarie Island research station has a small clean air laboratory at which a limited aerosol observational program has been carried out since 1986. A 20 m tower will be installed for the ACE-1 intensive. This station experiences clean Southern Ocean air for a large fraction of the time and provides an excellent base for a number of local closure experiments. The Macquarie Island measurements will be particularly important for expanding the scale of the experiment into the very different biogeochemical regime near the Subantarctic Frontal Zone. Regional models will benefit from having this point for comparison with the more northerly sites. Both the C-130 and the R/V Discoverer will conduct measurements near Macquarie Island to tie its smaller suite of measurements to their more comprehensive ones. Although facilities on the island are limited, it will be possible to run a small number of additional experiments during the ACE-1 intensive. Logistical support is by ship with travel time to and from Hobart of 4 to 5 days. Some ACE personnel will travel to Macquarie Island on the supply ship in September. Additional ACE personnel will be transported to the island aboard Discoverer at the beginning of the intensive. ACE personnel will depart the island at the end of December aboard the supply ship.
The following measurement program is currently at place on Macquarie Island:
Size selected filter stack, (Dp < 2, and 2 < Dp < 16 mm), for sea-salt, MSA, nss SO4 - weekly integrated (Dick, BoM BAPS; Ayers, CSIRO).
Radon (222), delay tank system, approximately 60 min delay time, continuous (Whittlestone, ANSTO).
Particle number size distributions using a DMPS (Kreidenweis, CSU).
Total number concentration of CN with Dp>15 nm and CN with Dp>3 nm using TSI 3760 and 3025 particle counters, respectively (Kreidenweis, CSU).
Daily filter samples for major ions and trace metals using a high volume cascade impactor (Tindale, TAMU).
CCN spectra (Harvey & Sturrock, NIWA).
PMS ASASP-X size distributions from 1200-3000 nm (Harvey & Sturrock, NIWA).
The Lagrangian experiments will extend to the eastern end of the ACE-1 study area, close to New Zealand. The Baring Head research station on the south end of the North Island of New Zealand provides another excellent opportunity to collect regional background measurements and to conduct local closure experiments incorporating the existing expertise at NIWA possibly augmented by other measurements. The region receives clean air from the southerly sector, usually when the air has passed around and to the east of the South Island.
Facilities at Baring Head include a 10m tower and 3 small laboratory buildings. The following measurement program is currently in place:
Aerosol sizing using PMS probes (Harvey, NIWA).
Weekly flask samples for CO2, CO, CH4
Daily filter samples for major ions and trace metals using a high volume cascade impactor (Harvey, NIWA; Tindale, TAMU).
Major ions and trace metals in precipitation (Tindale, TAMU).
Observations from satellite platforms will provide valuable inputs to mission planning as well as post-experiment analysis. Real-time receipt of satellite imagery can provide the regional characteristics of aerosol and cloud properties as well as sea surface temperature and basic meteorological information. In post-experiment studies, analysis of satellite observations are very important to place in-situ measurements in the context of the regional environment.
Current analysis of NOAA Advanced Very High Resolution Radiometer (AVHRR) measurements can provide estimates of aerosol optical depth, aerosol size characteristics, cloud reflectance at visible (0.63 mm) and near-infrared (3.7 mm) wavelengths, cloud amount, cloud top temperature, and sea surface temperature. Geostationary imagery from the Japanese GMS satellite will provide important temporal information about cloud motion and synoptic systems for forecasting and mission planning. The ATSR (Along-Track Scanning Radiometer) on ERS-2 will provide a well-calibrated, multi-wavelength view of the ACE study area. The swath width is only 512 km however so each point in the ACE area will be viewed only every three days.
Satellite Coverage During ACE-1
NOAA Polar Orbiters (N-9, N-10, N-12, N-14)
AVHRR 0.63 m 1.1 km aerosol optical depth, cloud coverage
0.86 m 1.1 km particle size index (with Ch1)
3.7 m 1.1 km cloud droplet size
11 m 1.1 km cloud top temperature
12 m 1.1 km SST (corrected for water vapor w/Ch4)
TOVS IR & MW 17 km temperature and water vapor profiles
VISSR 0.62 m 1.25 km cloud coverage
11.5 m 5 km cloud top temperature
6.7 m 5 km mid-trop. water vapor
11 m 5 km cloud top temperature
12 m 5 km SST (corrected for water vapor w/11 m)
ATSR-2 0.65 m 1 km aerosol optical depth, cloud coverage
0.87 m 1 km aerosol optical depth
1.6 m 1 km aerosol optical depth
3.7 m 1 km cloud droplet size
11 m 1 km cloud top temperature
12 m 1 km SST (corrected for water vapor w/11 m)
GOME UV & visible ozone, aerosol optical depth
SSM/I 19 GHz 40 km column water vapor
22 GHz 40 km column water vapor w/ 22 GHz
37 GHz 25 km precipitation, wind speed
85 GHz 20 km precipitation, wind speed
Currently NOAA AVHRR imagery is collected and archived at Hobart by CSIRO. The Naval Postgraduate School’s (P. Durkee) transportable satellite receiver, which is capable of collecting AVHRR and GMS data, will be set up at the mission operations center to support mission planning and assessment. Figure 17 shows the predicted frequency distribution of NOAA AVHRR overpasses from 15 November - 15 December 1995. The AVHRR sensor on NOAA-10 is significantly degraded so NOAA-12 will be given priority when passes of the two satellites overlap in time. Figure 18 shows the distribution of passes during 16 November 1995. The pattern of coverage provides views of at least part of the ACE area roughly every two hours. Any given point in the ACE area will be observed at least every four hours.