Extended Time Observations Methodology



Data will be collected for the Extended Time Observations-Extended Area (ETO-EA) spatial area 100° latitude by 80° longitude bounded by 50°S to 50°N latitude and 60°W to 140°W longitude. This area is chosen to include a wide range of cloud types, including the Intertropical Convergence Zone, South American and California stratocumulus, Brazilian cumulonimbus, East Coast U.S. stratocumulus, and cirrus at both low and middle latitudes. While the primary focus of FIRE-I is on marine stratocumulus and continental cirrus cloud systems, the ETO data set must support the intercomparison of ISCCP cloud properties over a wide range cloud types and locations. In addition, later studies of GCM cloud of parameterizations can then be compared to observations over a wider range of atmospheric conditions. Finally, validation of bidirectional reflectance models using simultaneous GOES and AVHRR data requires a wide range of solar zenith, viewing zenith, and viewing azimuth angles with sufficient samples to ensure stable statistics.

Grided map of North and South America

Data for extended area, extended time satellite observations will be extracted from the NOAA/NESDIS archive on an as needed basis. It is expected that data for multiple-satellite, multiple-view studies of th directional properties of the cloud radiance field will focus on daytime only data and of that only conjunctions of satellite observations that allow simultaneous views of individual cloud systems.

Within each month of the year, data will be collected for 6 days on, 9 days off, and 6 days on, etc. This sampling will allow some time dependent studies of cloud evolution, while obtaining independent synoptic meteorological samples. The 6 days on and 9 days off cycle is dictated by the NOAA polar orbiter ground track repeat cycle of 9.5 days. By allowing 9 days off between the two data samples, the complete range of NOAA viewing angles will be sampled for any geographic area within one month. In order to simplify data collection planning, the two 6 day periods will be taken on the 5th to 10th days and the 20th to 25th days of each month.

The satellite data to be included in the FIRE ETO-EA archive is given below:

  1. AVHRR GAC Data, 5 spectral channels, 2 satellites, day and night, giving four samples per day. Data volume is 1.5 6250 BPI tapes/observation day.
  2. HIRS Sounder Data, 20 spectral channels, 2 satellites, day and night, giving four samples per day. Data volume is approximately 0.2 tapes/observation day.
  3. GOES VAS Imager Data, 8 km spatial resolution, 2 spectral channels, GOES East and West, every 3 hours. Data volume is 0.5 6250 BPI tapes/observation day.
  4. GOES VAS Sounder Data, 16 km spatial resolution, 2 to 4 spectral channels, GOES East and West, every four hours.
  5. ERBE broadband data, 2 channels, scanner and nonscanner, up to 3 satellites, day and night, six times per day.
  6. ISCCP B3 data, 3 hourly, GOES East and GOES West, analyzed cloud property data.


SURFACE OBSERVATIONS

The description of the downwelling radiation fields and the conventional meteorological fields will be constructed primarily from observations and analyses which are routinely available. The NOAA/NWS and northern hemisphere international rawinsonde networks (-90 sites) and the U.S. Solar Radiation Network (NOAA/ERL) will provide the extended area surface and upper air data. However, satellite derived information on standard meteorological fields (soundings and wind fields) will be incorporated into the data sets for the regions within the FIRE domain which are not well-sampled by the rawinsonde network; this is currently done operationally by the NOAA/NMC using products provided by NOAA/NESDIS. These data are operationally archived by NOAA and will be added to the FIRE archive when acquired for specific FIRE studies.

The surface observation data sets are:

  1. Full vertical resolution rawinsonde observations for all launch sites within the FIRE domain (temperature, humidity, and horizontal wind speed and direction as functions of pressure);
  2. Standard NMC "ridded analyses over the FIRE domain (fields of temperature, humidity, horizontal wind speed and direction, and vertical motion at standard pressure levels);
  3. Gridded analyses of daily total and direct solar radiation at the surface.


LIMITED AREA

The Extended Time Observations-Limited Area (ETO-LA) satellite data sets will contain data for the cirrus and stratocumulus IFO regions (recall Fig. 1) and for the two regions covering the surface lidar sites. Data will be collected for the same 6-day on 9-day off cycle used in the ETO- EA data set to give a total of 12 days per month for all 12 months of the year.

Satellite Observations

The ETO-LA satellite data sets will contain data for the cirrus and stratocumulus IFO regions and for the two regions covering the surface lidar- sites. Data will be collected for the same 6-day on 9-day off cycle used in the ETO-EA data set to give a total of 12 days per month for all 12 months of the year. Data to be included in these data sets in addition to that listed for ETO-EA include:

  1. AVHRR LAC data, I hen resolution, 5 channels, afternoon polar orbit only, day and night 2 samples per day. Data volume is 0.75 6250 BPI tapes per day.
  2. GOES VAS imager data, 1 km visible channel and 8 km infrared channel data, hourly data for both GOES East and GOES West taken on the hour and 15 minutes after the hour. Data volume is 0.5 tapes per day.
  3. Sage II and Landsat/5 data, as available.

Note that HIPS-2, VAS Sounder, ERBE, AVHRR-GAC, and ISCCP data can be obtained for the same times using a subset of the ETO-EA data set.

While the limited area extended time observations represent a sizable archive (-200 6250 BPI tapes/year), it is recognized that intensive analyses will be limited to a 10-20% subset of this data; over a four year period this subset will contain approximately 100 statistically independent samples of appropriate cirrus and stratocumulus cloud systems.

Surface Observations

Ground-based measurements from a limited number of locations offer a variety of advantages for the study of the radiative behavior of clouds. They can be made in a nearly continuous manner as the overhead atmosphere's properties change, and they can represent a time averaged measurement at a point in space as well. The measurements are usually inexpensive compared to aircraft and balloon methods, although the ground-based measurements by no means replace in situ measurements.

CIRRUS Studies

The approximate locations of the three proposed Class I observing sites are located at the University of Utah, Salt Lake City, Utah; NASA Langley Research Center, Hampton, Virginia; and NOAA ERL, Boulder, Colorado. These sites will be operated throughout the duration of FIRE (4 years). Observations will be taken when cirrus clouds are present and generally unobstructed by extensive underlying cloud layers. At each site, observations will be taken at one second intervals during at least one continuous three hour time period on at least three days of most weeks subject to the occurrence of suitable conditions. Observing times should be coordinated with the 6-day on phase of the satellite observing schedules when possible in order to maximize the acquisition of coincident satellite and surface based observations.

Details of the additional site-specific instrumentation are given below for each site.

Salt Lake City, Utah Site:
  1. scanning ruby (694 nm) lidar with dual polarization receiver
  2. scanning narrow beam infrared (10 - 12 m) radiometer
  3. all-sky, 35 mm fisheye camera
  4. Ka -band (0.8 cm) radar (occasionally).

Hampton, VA Site:

  1. scanning ruby, doubled ruby and doubled Nd YAG lidar (694, 347, 532 nm) with dual polarization receiver.
  2. scanning, narrow beam, visible (0.4 - 0.75 m) radiometer
  3. scanning, narrow beam, near infrared (1.04 - 2.2 m) radiometer
  4. precision spectral pyranometers
  5. cloud imaging cameras

Boulder, Colorado Site

  1. scanning ruby, doubled ruby and doubled Nd lidar (694, 347, 532 nm) with dual polarization receiver
  2. scanning C02 Doppler lidar (9 - 11 nm)
  3. vertically pointing, narrow beam, infrared (10-12 nm) radiometer
  4. narrow beam, visible, sun photometer (solar tracking)
  5. PROFS mesoscale solar radiation network (23 stations with pyranometers).

STRATOCUMULUS STUDIES

The Naval Postgraduate School and the Naval Research Laboratory are planning to cooperate with several universities in a multi-year field program of nearly continuous Cloud Top Boundary Layer (CTBL) studies at San Nicholas Island (SNI), California, involving the installation of a three wind component Doppler Sodar, and augmentation of the tower with a full suite of longwave and shortwave surface radiation measurements. An existing network of radiosonde stations (two island, four coastal) will be used to define horizontal variability and lower tropospheric thermodynamics.

NOAA/ERL is planning to make extended-time surface radiometry measurements at SNI. Automated pyranometers and pyrheliometers will be located at the vertices and at the center of a 5point square network occupying approximately a two square mile area. More complex and some manually-operated instruments will also be located at the center of the network to make additional measurements for giving more detailed spectral information. Portable, independent, and weatherproof data acquisition systems will be located at each vertex. Spectral measurements of solar transmission will also be made. An automated scanning radiometer with three spectral channels will be used. Also, pyrogeometer measurements of the downwelling longwave flux will be made. Depending on the success of testing now in progress, solar radiometersondes may be periodically flown vertically through the stratus deck to obtain the vertical upwelling and downwelling flux profiles for comparison with model calculations.



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