1. OBSERVATORY, METEOROLOGY, AND DATA
Mauna Loa Observatory (MLO) continues to evolve in the scope of the measurements conducted, the way in which data are recorded and transmitted, and the number and form of the buildings on the site. With installation of the majority of the Network for the Detection of Stratospheric Change (NDSC) instrumentation completed at MLO, remote monitoring of stratospheric ozone concentrations, temperatures, and water vapor has become routine. At the surface, ultraviolet (UV) radiation is now monitored in a program that is designed and operated in a manner to set the world standard. Over the past 2 years essentially all the instruments of the core MLO continuous measurement programs, as well as the NDSC instruments, were connected to the Internet. In a number of cases these instruments are controlled and adjusted from locations other than Hawaii.
Four new structures have been added to the MLO site over the past 2 years: a 3.7 m 7.3 m building for the microwave ozone and microwave water vapor instruments, a similar building to accommodate visitors and their programs, a 3.7 m 4.9 m tank storage building appended to the main observatory, and the Global Oscillation Network Group (GONG) 2.4 m 6 m instrumented container. The GONG program, operated by the University of Arizona on space at MLO, is a study of the sun's core. The old Atomic Energy Commission (AEC) building was refurbished and a roof catchment water supply and a sink added.
A new Network for the Detection of Stratospheric Change (NDSC) building, which was to be erected on the 4-acre (16,187 m2) parcel to the east of the main MLO site, has been scaled back to a smaller structure to be erected south of the main observatory building. If all goes to plan, this 306.6 m2 building will be completed by December 1996.
At the Hilo facility, the refurbishing of the electronics shop and the addition of air conditioning to the room were major improvements as was the addition of an elevator linking the basement to the rest of the building. Installation of the FTS2000 telephone system in the Hilo offices with connections to the MLO site has reduced monthly telephone costs and expanded the number of lines available. MLO and cooperative/visitor programs now use 29 telephone lines in addition to the Internet. A note on Hilo's rain: Although Hilo has a reputation for having a lot of rain, in 1995 it had 2.5 m less than in 1994. But 1994 was a special year. On one day in August at sea level, Hilo had 45 cm of rain in 8 hours (greater amounts fell at higher elevations). In September, it had 50 cm in 7 hours.
At the Cape Kumukahi, Hawaii (KUM) site, grid electric power was added to the tower, with a distribution panel providing 110 V, 220 V and recreational vehicle (RV) circuits. A 15 m 15 m area was graded, filled, and security fenced to provide a site for mobile trailers and vans for future short-term research projects. The KUM tower now has four air sample lines running from near the top (18 m) to the base. Two of these lines are used for weekly trace gas and oxygen flask sampling and are purged continuously. No aerosol or radiation measure-ments are conducted at KUM at present.
The largest nonroutine research activity of the past 2 years was the Mauna Loa Ozone Profile Intercomparison (MLO3) program, summer 1995, in which various NDSC ozone-profiling instruments were intercompared. Preparations for the program included the construction of a building to house the University of Massachusetts Millitech microwave ozone profiler; installation of the NOAA/NIWA multispectra, UV radiometer system; and preparation of a pad area for two 16.7 m-long National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) ozone lidar trailers. The Jet Propulsion Laboratories (JPL) ozone lidar, also part of the study, had been in full operation at MLO for more than a year prior to the intercomparison. World standard Dobson no. 83, secondary standard no. 65, and the MLO station Dobson were operated prior to, and during, the intercomparison. During a 3-week intensive study period in August, daily ozonesonde launches were conducted from Hilo. Some balloons carried three ozonesondes to determine the variability between instruments.
Ancillary MLO3 measurements included aerosol/temperature profiles with the NOAA lidars, infrared multispectral measurements with the University of Denver Fourier Transform Interferometer (FTIR) spectrometer, and twice-daily measurements from radiosondes launched from Hilo. A number of passes of a satellite carrying aerosol and ozone measurement instruments occurred during the intensive study period.
In the staff arena, an MLO physical scientist spent from June to December 1994 at the Australian Baseline Station, Cape Grim, Tasmania, in an exchange with the Technical Officer from Cape Grim. All parties concerned, and their families, found the experience to be beneficial. The Technical Officer helped improve the MLO sulfate (SO2) measurement program and quickly became a valued member of the MLO mountain crew. MLO recommends similar exchanges in the future. A staff member new to MLO in January 1995 has responsibilities for managing data flow and data archiving, and has rapidly become a valued addition and a capable computer operator.
In May 1994, a motorcyclist was killed during a race on the MLO road when his brakes locked and he missed a turn in the road. This event, and the fact that the organizer of the weekly commercial bike rides down MLO was also killed in an unrelated bicycle accident in Kona, have dramatically reduced bicycle traffic on the MLO road.
MLO was host to about 960 visitors in 1994-1995. Countries represented were from Japan, China, Canada, Germany, Burkina-Faso, Switzerland, France, Togo, Australia, Brazil, Russia, Iran, England, Denmark, Samoa, Mexico, Singapore, Italy, Holland, New Zealand, Norway, and Sweden. These visitors were in addition to guests from 21 states. Most of these visitors were given a guided tour and many left with at least one color reprint of the most up-to-date CMDL data plots MLO had available.
Visitors to MLO from NOAA's higher level administrative community included the NOAA Administrator; NOAA Deputy Under Secretary; NOAA Associate Under Secretary; Director, Sustainable Development and Inter-governmental Affairs; outgoing Deputy Director, Environmental Research Laboratories (ERL); newly appointed Deputy Director, ERL; and Director, Oceans and Atmospheric Research Programs Office.
Mauna Loa Mountain is still inflating and carbon dioxide (CO2) gas releases from the summit caldera persist which means that an eruption may occur within a few years. Therefore, an escape plan and an equipment removal list have been drawn up. In essence, most equipment valued over $10,000 per item will be removed when it is predicted that lava will inundate MLO within 12 hours.
Table 1.1 summarizes the programs in operation or terminated at MLO during 1994-1995. Relevant details of note on the respective programs are as follows:
The CMDL Siemens Ultramat-3 infrared (IR) CO2 analyzer and the Scripps Institution of Oceanography (SIO) Applied Physics IR CO2 analyzer were operated in parallel without major problems throughout 1994 and 1995. Routine maintenance and calibrations were undertaken on both instruments as scheduled. An electronic engineer from SIO upgraded the SIO CO2 data acquisition system in 1994. Data are now recorded on a Brown strip chart recorder and stored on a personal computer (PC) hard disk and a floppy disk, which are mailed to SIO weekly. The CMDL CO2 data acquisition system was modified on November 28, 1995, through the replacement of the original Control and Monitoring System (CAMS) data logger with a Unix CMDL Carbon Cycle Group (CCG) system connected to the Internet. Through computers in Boulder and in Hilo operators are able to monitor operation of the CO2 analyzer and plot CO2 concentrations in near-real time. The CCG has the capability of modifying the CO2 measurement control software from Boulder. The venerable CO2 strip chart recorder is now used only for viewing the weekly standard gas calibrations and weekly maintenance procedures.
Outgassing from the volcanic vents at the Mauna Loa caldera and along the
northeast rift zone at Mauna Loa continued to cause periodic observable disturbances
in some of the CO2 data records. As in prior years, these venting
events occurred mostly between midnight and 0800 (local standard time (LST)
of the following day, during the downslope wind regime. The erratic CO2
concentration data resulting from these venting events were easily identified
by visually scanning chart records or by utilizing a computerized data screening
procedure, and thus they have been separated from the clean-air record without
difficulty. Such venting episodes were detected mainly on the basis of criteria
for CO2 concentration, variability, and wind sector. The criterion
for the CO2 standard deviation screening was 1.0 ppm which is the
value suggested by Thoning et al. .
TABLE 1.1. Summary of Measurement Programs at MLO in 1994-1995
|CO2||Siemens Ultramat-3 IR analyzer||Continuous|
|0.5-L glass flasks, through analyzer||1 pair wk-1|
|CO||Trace Analytical RGA3 reduction gas analyzer no. R5||Continuous|
|CO2, CH4, CO, 13C, 18O of CO2||2.5-L glass flasks, MAKS pump unit*
3-L evacuated glass flasks
|1 pair wk-1
1 pair wk-1
|CH4||Carle automated GC no. 6 (removed 11/95)||1 sample (24 min)-1|
|HP6890GC (began 11/95)||Continuous|
|AIRKIT pump unit, 2.5-L glass flasks (began 5/95)||1 pair wk-1|
|SO2||TECO model 435 pulsed-florescence analyzer (began 6/94)||Continuous|
|Surface O3||Dasibi ozone meter||Continuous|
|Total O3||Dobson spectrophotometer no. 76||3 day-1, weekdays|
|O3 profiles||Dobson spectrophotometer no. 76 (automated Umkehr
Balloonborne ECC sonde
|N2O, CFC-11, CFC-12, CFC-113, CH3CCl3, CCl4||300-mL stainless steel flasks||1 sample wk-1|
|N2O, CFC-11, CFC-12, CFC-113, CH3CCl3, CCl4, SF6, HCFC-22, HCFC-141b, HCFC-142b, CH3Br, CH3Cl, CH2Cl2, CHCl3, C2HCl3, C2Cl4, H-1301, H-1211, H-2402, HFC-134a||850-mL stainless steel flasks||1 sample wk-1|
|CFC-11, CFC-12, CFC-113, N2O, CCl4, CH3CCl3||HP5890 automated GC||1 sample h-1|
|N2O||Shimadzu automated GC||1 sample h-1|
|Radon||Two-filter system||Continuous integrated 30-min samples|
|Condensation nuclei||Pollak CNC
|Optical properties||Four-wavelength nephelometer: 450, 550,
700, 850 nm three-wavelength nephelometer:
450, 550, 700 nm
|Aerosol light absorption (black carbon)||Aethalometer||Continuous|
|Stratospheric and upper tropospheric aerosols||Lidar: 694.3 nm, 532 nm||1 profile wk-1|
|Global irradiance||Eppley pyranometers with Q, OG1, and RG8 filters||Continuous|
|Direct irradiance||Eppley pyrheliometer with Q filter||Continuous|
|Eppley pyrheliometer with RG8 filter|
|Eppley pyrheliometer with Q, OG1,||3 day-1|
|RG2, and RG8 filters|
|Eppley/Kendall active cavity radiometer||1 mo-1|
|Diffuse irradiance||Eppley pyrgeometer with shading disk and Q filter||Continuous|
|UV solar radiation||Yankee Environmental UVB pyranometer (280-320 nm)||Continuous|
|Terrestrial (IR) radiation||Global downwelling IR pyrgeometer||Continuous|
|Turbidity||J-202 and J-314 sunphotometers with 380-, 500-, 778-,
862 nm narrowband filters
PMOD three-wavelength sunphotometer:
380, 500, 778 nm; narrowband
|3 day-1, weekdays
|Column water vapor||Two wavelength tracking sunphotometer: 860, 940 nm||Continuous|
|Air temperature||Aspirated thermistor, 2-, 9-, 37-m heights
Max.-min. thermometers, 2-m height
|Air temperature (30-70 KM)||Lidar||1 profile wk-1|
|Temperature gradient||Aspirated thermistors, 2-, 9-, 37-m heights||Continuous|
|Dewpoint temperature||Dewpoint hygrometer, 2-m height||Continuous|
|Relative humidity||TSL 2-m height||Continuous|
|Wind (speed and direction)||8.5-, 10-, and 38-m heights||Continuous|
|Precipitation||Rain gauge, 20-cm||5 wk-1|
|Rain gauge, 20-cm§||1 wk-1|
|Rain gauge, tipping bucket||Continuous|
|Total perceptible water||Foskett IR hygrometer||Continuous|
|CO2 (SIO)||Applied Physics IR analyzer||Continuous|
|CO2, 13C, N2O (SIO)||5-L evacuated glass flasks*||1 pair wk-1|
|CO2, CO, CH4, 13C/12C (CSIRO)||Pressurized glass flask sample||1 mo-1|
|CH4, CH3CC13, CH3C1, F-22, F-12, F-11, F-113, CO, CO2, N2O, CHC13, CC14 (OGIST)||Pressurized stainless steel flasks*||3 wk-1|
|O2 analyses (SIO)||5-L glass flasks through tower line and pump unit*||3 (2 mo)-1|
|O2 analyses (URI)||3-L glass flasks through tower line and pump unit||2 (2 mo)-1|
|CH4 (13C/12C) (Univ. of Washington)||35-L evacuated flask||2 mo-1|
|Total suspended particulates (DOE)||High-volume sampler||Continuous (1 filter wk-1)|
|Ultraviolet radiation (Smithsonian)||Eight-wavelength UV radiometer: 290-325 nm; narrowband||Continuous|
|Ultraviolet radiation (Univ. of Hawaii)||Robertson-Berger UV radiometer (erythema)||Continuous|
|Solar aureole intensity (CSU)||Multi-aperture tracking photometer:
2, 5, 10, 20, 30° fields of view (discontinued 9/94)
|Precipitation collection (DOE)||Exposed collection pails||Integrated monthly
|Aerosol chemistry (Univ. of Calif.-Davis)||Programmed filter sampler||Integrated 3-day sample,|
|1 continuous and
1 downslope sample (3 days)-1
|Sulfate, nitrate, aerosols (Univ. of Hawaii)||Filter system||Daily, 2000-0600 LST|
|Radon (ANSTO)||Aerosol scavenging of Rn daughters
(2-filter system after 4/95)
|Continuous; integrated 30-min samples|
|Network for Detection of Stratospheric Change (NDSC)|
|Ultraviolet radiation (NOAA and NIWA, New Zealand)||UV spectrometer (290-450 nm), 1 nm resolution||Continuous|
|Stratospheric ozone profile, 20-70 km (Univ. of Mass., Amherst)||Microwave spectroscopy, Millitech Corp., 110.8 GH||3 profiles h-1|
|Stratospheric ozone profiles (15-55 km), temperature (15-80 km), aerosol profiles (15-40 km) (JPL)||UV lidar||3-4 profiles/wk-1|
|Solar spectra (Univ. of Denver)||FTIR spectrometer, automated||5 wk-1|
All instruments are at MLO unless indicated.
*MLO and Kumukahi.
Data from this instrument recorded and processed by microcomputers.
The monthly occurrences of observable outgassing from volcanic vents on Mauna Loa for 1994 and 1995 are listed in Table 1.2, and the annual number of events for the past years are listed in Table 1.3. A paper was published in the American Geophysical Union (AGU) Monograph No. 92 concerning the outgassing history of Mauna Loa volcano as recorded in the MLO data record [Ryan, 1995]. In early 1993, the CO2 emissions from the summit, as measured at MLO, began to increase after undergoing a steady exponential decline since the last eruption in 1984. The distribution of volcanic CO2 with wind direction suggests that there is a new CO2 source just outside the summit caldera, high on the southwest rift. The average plume CO2 concentration continued to increase through the end of 1995. Condensation nuclei and SO2 in the volcanic plume also began to increase during this period. These changes may be an early precursor to the next eruption of Mauna Loa, which continues to inflate and which has produced a slightly greater frequency of shallow summit earthquakes since 1993.
The weekly CO2, methane (CH4), and other gas sampling programs, using flasks at MLO and at KUM, were carried out according to schedule throughout the year, without major problems. An AIRKIT sampling pump unit upgraded from the MAKS pump unit began its weekly operation on May 8, 1995, at KUM only. The flask types used and sampling procedure were the same as for the MAKS method.
A Trace Analytical RGA3 reduction gas analyzer for the continuous measurement of carbon monoxide (CO) mixing ratios was installed in May 1992 and continued to work well throughout 1995. The analyzer was replaced with a new, but essentially identical, unit on November 28, 1995, in an upgrade program. On the same date, system operations and chromatographic data logging were switched to a Hewlett Packard (HP) 35900E analog-digital converter system. This new installation is connected to the MLO-site Unix workstation. The system operates without using chart paper. Chromatograms stored on the workstation hard disk may be displayed on the computer monitor.
The Carle automated gas chromatograph (GC) system, Carle 6, was in continuous operation throughout the period providing CH4 data from a grab air sample taken every 24 minutes. On November 28, 1995, the Carle 6 was replaced with the HP6890 GC, which is considered the best commercial GC available in the market. The system uses nitrogen carrier gas instead of helium, which has improved sensitivity in the measurement. A new analog-digital converter, HP35900E, which has the capacity of obtaining better precision, has replaced the original HP3393 integrator. The new CH4 GC system is paperless; the chromatograms are stored in the CCG hard disk and can be displayed on the CH4 computer monitor at the observatory.
The CH4 data continued to show clearly defined cycles of varying frequencies. The typical diurnal cycle was well correlated with upslope and downslope winds, with the marine boundary layer air having the higher CH4 concentrations. Multiday or synoptic-scale CH4 cycles were also observed, which apparently relate to different air mass source regions.
An SO2 monitoring program was developed in house during the spring of 1994, with measurements beginning at MLO on June 1, 1994. The measurement system is built around a TECO 435 pulsed-florescence analyzer with a PC controlling flows, monitoring temperatures and humidities, and acquiring data. The system runs on hourly cycles consisting of a 20-minute sample of ambient air through a Teflon line at 4 m, followed by a 10-minute zero-air sample, a 20-minute sample of air from a high-volume polyvinyl chloride (PVC) line at 34 m, and another 10-minute zero-air sample. A one-point, 1.2-ppb calibration is performed for 10 minutes every 12 hours by injecting a 10-ppm SO2-in-air standard into the 1000 L min-1 high-volume flow. A six-point calibration is automatically run every 10 days over a range of concentrations between 125 ppt and 5 ppb. Injecting the calibration gas into the ambient air sample allows us to measure the effect of humidity on the loss of SO2 in the sampling system. It also allows the use of a stable ppm-level calibration gas to perform sub-ppb calibrations.
The system had a 95% data recovery rate in 1994-1995, with most of the downtime
caused by an intermittent failure of the computer hard drive. Several system
modifications were made, including the addition of humidity and temperature
sensors in January and February of 1995. Data graphs are available over the
Internet in Hilo in near-real time.
TABLE 1.2. Estimated Mauna Loa Venting Episodes (Total Time in Hours) at MLO in 1994 and 1995
*Criteria: CO2 SD 1.0 ppm; wind direction sector 135°-225°; wind speed 1.35 m s-1.
No data due to new system installation.
TABLE 1.3. CO2 Venting Events From 1988 Through 1995
*No data for December due to new system installation.
One-minute-average measurements of zero air had a standard deviation of 35 ppt, yielding a 1-hour detection limit of about 10 ppt. The nightly average clean-air baseline concentration of SO2 at MLO as measured through the 4-m Teflon intake varied between 10 and 30 ppt. The high-volume PVC intake lost 5 to 10 ppt of SO2 through dry deposition, and began to experience hygroscopic losses at relative humidities above 40%. During "Asian dust" events, which bring high concentrations of radon and anthropogenic gases, the SO2 concentration increased to as much as 100 ppt. The volcanic plume from Mauna Loa (detected by high variability in the CO2 concentration) contained up to 500 ppt SO2 and had an SO2 to CO2 ratio of about 10-4. The largest source of SO2 was Kilauea volcano located 1 km above sea level on the south slope of Mauna Loa. Traces of its eruptive plume were frequently transported to MLO in the daytime upslope winds, producing SO2 concentrations that occasionally exceed 50 ppb. On 15% of the nights in 1995, SO2 from Kilauea was detected at concentrations between 100 ppt and 25 ppb in the downslope winds between midnight and 0700 LST.
The 1994-1995 MLO ozone monitoring program consisted of three measurement foci: continuous MLO surface ozone monitoring using a Dasibi model 1003-AH UV-absorption ozone monitor; total ozone three times a day and Umkehr ozone profile measurements two times a day using a computer-based automated Dobson instrument (Dobson no. 76); and ozone profile measurements based on weekly ascents of balloonborne electrochemical concentration cell (ECC) ozonesondes released from the National Weather Service (NWS) station at the Hilo airport.
Ozonesondes were launched weekly whenever supplies were available from Boulder. In 1994 there were 45 ozonesonde flights. In 1995 there were 52 ozonesonde flights, which included an intensive period in August when daily flights were launched during an NDSC intercomparison with the Dobson ozone spectro-photometer, two ozone lidar systems, a microwave ozone profiler, and a variety of related instruments operated at MLO.
Halocarbons and Nitrous Oxide
The Radiatively Important Trace Species (RITS) system for measuring halocarbons and nitrous oxide had its semiannual maintenance in March 1994 and August 1994. Besides the normal checks, precision checks and round-robin tank measurements were undertaken. System software was upgraded in August and a watchdog timer installed to cut down on computer lockups.
In May 1995 a new computer system was installed. At that time the watchdog timer was removed because it never worked well, and Channel A was connected to P5 (AR/CH4) to curb the CO2 effect. In October 1995, new file transfer protocol (FTP) 4.0 software was installed and a more extensive hardware check of the GCs was carried out. During both of these major maintenance undertakings, round-robin tank measurements were made and precision checks completed. In general, the operation of the RITS computer has improved over the previous years with the installation of the new unit.
By the end of 1995, the CMDL Department of Energy (DOE) radon program had collected 5 complete years of data. The radon instrument has performed reliably, the only problems being a broken drive belt and periodic replacement of the filter paper roll. A radon calibration source was purchased in 1995, and the instrument calibration was found to be within 5% of the source value. Daily average radon between 0000 and 0700 LST is shown in Figure 1.1, along with a 90-day running mean. The principal source of radon is soil. Radon has a half-life of 3.8 days. The amount of atmospheric radon reaching Mauna Loa during baseline conditions is a function of both the amount of continental radon injected into the free troposphere and its travel time across the Pacific Ocean. The yearly radon cycles seen in Figure 1.1 are similar to those measured for dust particles and anthropogenic gases and aerosols at MLO. There is a late-winter/spring maximum that is caused by the fast transport of air coming from Asia, and a late-summer/autumn minimum that occurs when air has spent long periods over the tropical Pacific. The 5-year record is beginning to show interannual variability. The average radon concentrations in the spring of 1991 and 1992 were higher than those of later years.
Fig. 1.1. Daily average radon at MLO measured by the CMDL-DOE radon instrument between 0000 and 0700 LST (downslope air) with a 90-point running mean (darker line). The annual peaks in the mean define the spring Asian dust season when fast air transport brings continental air and Gobi Desert dust to the observatory.
The mean annual cycle of radon varied from a high of 270 mBq m-3 in March to a low of 70 mBq m-3 in August. This is a factor of 4, which is two radon half-lives or about 7.5 days. If the seasonal variation in radon is entirely due to variations in air mass transport time across the Pacific, it follows that the average transit time of continental air to MLO is 1 week less in the spring than in late summer.
Condensation nucleus counter. The Thermo Systems Incorporated (TSI) unit is a continuous-expansion condensation nucleus counter (CNC) in which condensation occurs in butyl alcohol vapor in a chamber and single-particle counting statistics are used as a basis for calculating condensation nuclei (CN) concentrations. The instrument has continued to display higher counts than the Pollak CNC since its return from the manufacturer in 1991.
Nephelometer. The four-wavelength nephelometer continues to run without too much downtime. A three-wavelength nephelometer with much better resolution was installed and activated in April 1994. These two units will operate in parallel for a couple of years sampling the same air stream before the older instrument will be retired.
Aethalometer. The aethalometer performed satisfactorily during 1994-1995. A new computer and program was set up in September 1994. A dual-head pump was installed in November 1994 to increase the air sample flow rate.
Lidar. Ruby lidar (694 nm) observations of stratospheric aerosols were continued throughout 1994-1995, adding to the MLO lidar database extending back to late 1974. The only significant modification to the instrument, following the major changes in 1993 (486 computer for data acquisition and automatic control of the laser), was rotating the entire lidar 90 in the building in April 1995. This was undertaken to provide more room for the new YAG lidar described below in this section. The lidar reorientation resulted in the ruby lidar telescope being positioned closer to the outgoing beam (from 122 cm to 79 cm), thereby increasing the low-altitude signal strength. The data are still being acquired with the 10-MHz, 8-bit Biomation unit and the operating conditions (PMT voltages, data-taking delays, number of shots) are unchanged.
Data analysis was improved to better account for signal-induced noise generated by the strong signal at low altitudes. A nonlinear fit of the signal background improved the aerosol profile between 30 and 45 km where it should converge to zero (backscatter ratio of one). The same extinction-to-backscatter ratio (50) and standard atmosphere that have been used in the past were maintained. The entire record of aerosol profiles is not currently available in a database, although the integrated backscatter is. Reanalysis of raw signals from 1984 to 1990 to add to the overall database was started in 1995 and has continued to the present.
In March 1994 the first aerosol profiles were taken with the new Nd:YAG laser-based lidar. The laser (Spectra Physics GCR-6, 30 Hz) emits 39 W at 1064 nm and has frequency doubling and tripling to produce 532 nm and 355 nm wavelengths. The 532 nm wavelength is the only wavelength used for measurements. A single mirror (61-cm diameter) focuses light onto a liquid light guide that carries the illumination to three PMT detectors. The detectors are electronically gated at low altitudes to reduce signal-induced noise. All channels are photon counted and have dynamical ranges of 10 MHz. Channel one detects the full signal for stratospheric and mesospheric altitudes and channel two detects a few percent of the signal for the troposphere. A third channel detects a Raman-shifted wavelength from nitrogen to obtain molecular density in the presence of aerosols. Besides producing a much better measurement than the ruby lidar, the new system is largely built with equipment that is readily available and serviceable. A second 61-cm mirror was installed for detection of the 1064 nm wavelength in the future.
The aerosol analysis for the new system is quite similar to the ruby lidar procedures (with changes in Rayleigh scattering cross sections) but simpler because of the much larger dynamic range of the electronics. A significant difference in the systems is that the Nd:YAG lidar obtains accurate data above the aerosol layer (35-45 km), which may then be used as an aerosol-free altitude. The ruby lidar analysis assumes an aerosol-free reference altitude below that altitude (around 15 km), which is not always a valid assumption. The Nd:YAG measurement is now used to correct the reference for the ruby lidar. The 532 nm signal is also used to measure atmospheric temperatures from 33 to 70 km by assuming the ideal gas law, hydrostatic equilibrium, and pure Rayleigh scattering. The temperature is initialized at 80 km using a MAP85 model calculated for 19.5N with seasonal dependence.
See sections 3.1.2-3.1.7 for results of the observations.
The set of solar radiation instruments at MLO remained unchanged from previous years. In March 1994 the Physikalisch-Meteorologisches Observatorium Davos (PMOD) (World Radiation Center) sunphotometer filters were exchanged and their spectral characteristics measured in Boulder. Hand-held sunphotometers continued to be calibrated at MLO, with 34 calibrations performed in 1994 and 38 made in 1995.
In September 1995, a new data acquisition and control system was installed in the solar dome. The system is based on an HP data acquisition unit and a personal computer, and is tied to the Internet. It automatically operates the dome shutter and adjusts the azimuthal position of the dome based on calculations of the sun position and feedback from a shaft encoder on the dome drive motor. After overcoming a few initial problems, the system has performed well.
UV Radiation Monitoring
In July 1995 a spectral UV monitor was installed at MLO. The instrument was originally developed and operated at the National Institute for Water and Atmosphere (NIWA) in Lauder, New Zealand, and then moved to MLO when a newer instrument was built to replace it. The monitor measures the global UV spectrum between 290 and 450 nm in 0.2 nm steps with a bandpass of 1.15 nm. It is calibrated with mercury and standard lamps every week. An absolute standard lamp calibration is made several times per year. Early results from this program are presented in section 3 of this Summary Report.
Many changes to the MLO network/computer systems have occurred during the 1994-1995 period, both in the number of computers in the network and the sophistication of the operation. The "nerves" of the mountain system were expanded with the installation of fiber optic lines connecting the main building to the Radon Building, Solar Dome, University of Denver FTIR and NOAA/NIWA UV Building, Microwave Ozone Building, National Center for Atmospheric Research/High Altitude Observatory (NCAR/HAO) Facility, GONG Observatory site, and the new Visitor Building. At the Hilo site, fiber optic lines were installed to link NCAR/HAO's Hilo office and the Smithsonian Institution Observatory to MLO's Internet server.
To control the overall network, two Windows NT servers were installed as nodes, one at the Hilo office and the other at the MLO mountain site. "Trusts" were created with the NT server in CMDL, Boulder, which in effect allows the MLO and CMDL network administrators access to some of each other's network control software. This facilitates data transfer for the ozonesonde, surface ozone, and solar dome programs.
CMDL measurement programs and projects connected to the network in 1994-1995 include the aethalometer, SO2, radon, RITS, carbon cycle species, and the NOAA/NIWA UV systems. NDSC programs added were the University of Denver FTIR and the University of Massachusetts microwave ozone system. The JPL lidar group, already on the network from the previous year, added six more computers to the network.
Other groups affiliated with the MLO facility also enhanced their network utilization as NCAR/HAO added six computers at the mountain site and one at Hilo, GONG added two computers, and the Smithsonian Observatory added two computers and a printserver.
MLO computers for the staff have all been upgraded to 486s and Pentiums (six 486s and four Pentiums), and two 486 computers were installed at the observatory, one for staff and one for visitor programs. Surge protection devices and UPSs were installed at all locations to protect servers, computers, and other network devices.
New telephone and data lines were installed in 1995 giving MLO access to the Centernet and FTS2000. This resulted in an increase of eight voice and data lines split between MLO and Hilo at no increase in monthly expenses.
An MLO home page located at http://mloserv.mlo.hawaii.gov has been set up on the Internet. This page contains some information on the observatory, staff, and a few data plots.
Software upgrades were numerous and varied; some of interest to users of MLO data and the MLO network: the VAX was upgraded with a newer operating system and other software, a server was set up for remote prints, and an anonymous FTP set up for public file transfers. Excursion software has been upgraded for use with Windows 95.
The operating system for client machines is slowly being converted from Windows For Workgroups to Windows 95. Eudora is now being used for e-mail by the entire staff because it is much easier to use than the VAX mailer. The Time and Attendance program has been upgraded twice over the past 2 years. A network monitoring program has been implemented to aid in troubleshooting the network. PCanywhere is being used for testing the remote control of a test computer with the view of developing methods of controlling more routine MLO functions from a keyboard in Hilo.
MLO receives trajectory plots and meteorological data on a daily basis from Boulder automatically over the Internet. Radiosonde data from NWS are being archived weekly on our VAX. A small electronic database has been created for MLO publications, which includes scanned abstracts.
The old meteorological system and the planetary boundary layer (PBL) Met system were deactivated and removed in October 1993. They were replaced with a computer-based system, the "New Met System," which measures temperatures at the 2-, 9-, and 37-m levels, dewpoint at the 2-m level, and wind speeds and directions at the 8.5-, 10-, and 38-m levels. This new system has operated unaltered and with high reliability to date.
The MLO modified program of precipitation chemistry collection and analyses was continued throughout 1994-1995 within the basic MLO operational routine. This program consists of collection of a weekly integrated precipitation sample from the Hilo NWS station and collection of precipitation event samples at MLO. Analyses of these samples are undertaken in the Hilo laboratory for pH and conductivity.
MLO Cooperative Programs are listed in Table 1.1. In September 1994 the Colorado
State University (CSU) sunphotometer program was discontinued. The Australian
Nuclear Science and Technology Organization (ANSTO) radon monitor underwent
a major upgrade in April 1995 which resulted in an increase in sensitivity,
a decrease in the response time, simpler operation, and more reliable performance.