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Aerographer's Mate: Module 1

2010 July 9

Aerographer's Mate

Snippets from the US Navy’s “Aerographer’s Mate: Module 1—Surface Weather Observations” 1999 training manual.

You didn’t think there was just #4, did you?

I bumped into #4 first because I was looking for information on weather networks. But #1 has some interesting pieces to it as well.

DRY-BULB TEMPERATURE

The dry-bulb temperature (also called the ambient
air temperature, or simply the air temperature) reflects
the amount of heat present in the air. It is read directly
from a ventilated thermometer on an electric
psychrometer, sling psychrometer, rotor psychrometer,
or from automatic measuring equipment. The
temperature must be obtained to the nearest 1/10 degree
and may be read in either Fahrenheit or Celsius degrees.

WET-BULB TEMPERATURE

The wet-bulb temperature is the lowest temperature
an object may be cooled to by the process of
evaporation. It is read directly from the wet-bulb
thermometer on an electric psychrometer, sling
psychrometer, or rotor psychrometer. Water
evaporating from the moistened wick on the wet-bulb
thermometer bulb cools the thermometer bulb and
lowers the temperature reading. The cooling effect of
the evaporation from the bulb is inversely proportional
to the amount of water vapor present in the air: the more
water vapor present, the less moisture will evaporate
from the moistened wick, and the less cooling of the
thermometer bulb will occur. From the dry- and wetbulb
readings, the dew-point temperature and humidity
values may be calculated. The automatic weather
observation systems do not provide a wet-bulb
temperature, but automatically process equivalent
measurements to compute dew-point temperature.

SEA SURFACE TEMPERATURE

Another temperature reading in shipboard weather
observations is the sea surface temperature. It is
supposed to reflect the temperature of the upper few
inches of the sea surface. On some ships with OA
divisions, installed sensors automatically measure this
value. There are three other acceptable methods for
obtaining a sea-surface temperature reading: the
bucket temperature method; by expendable
bathythermograph; and by use of the seawater injection
temperature. The sea-surface temperature reading must
be accurate since it is a major input into many undersea
warfare (USW) acoustic products.

Bucket Temperature

The bucket temperature method is by far the most
accurate, yet is also the most work intensive. In this
method, a sample of seawater is obtained by casting a
lightweight bucket or coffee can with a strong line
attached over the side of the ship and retrieving a water
sample. This should be done as near to the bow of the
ship as possible, since the passage of the ship through
the water tends to mix surface water with water from the
keel level of the ship. The “bucket” should also be cast
ahead of where the observer is standing so that the
bucket fills as it drifts by the observer. As the
movement of the ship carries the bucket astern of the
observer, the bucket should be retrieved. A standard
thermometer is then inserted into the water sample, and
the water is slowly stirred with the thermometer until
the temperature reading stabilizes. The temperature is
read to the nearest 1/10 degree Fahrenheit.

Bathythermograph Temperature

The next best method is to obtain a sea surface
temperature from an expendable bathythermograph
sounding. Procedures for conducting a
bathythermograph sounding are covered in a later
module. Bucket temperatures should be conducted
occasionally to verify that the recorded
bathythermograph surface temperature is accurate.
Sound velocimeterreadings may also be used in lieu of a
bathythermograph reading.

Seawater Injection Temperature

The least accurate method is the seawater injection
temperature reading. Seawater injection temperatures
are read in the engineering spaces and are usually
readily available by shipboard phone from the “main
engine room control” watch/operator. Seawater is
constantly taken onboard for cooling the engines and
for conversion to freshwater. The seawater injection
ports are located well below the water line, sometimes
as deep as 60 feet on aircraft carriers. Therefore,
temperature readings at that point do not accurately
reflect a sea surface temperature, but rather a near
surface temperature reading.

In tropical waters, the difference between the
surface temperature and the near-surface temperature is
usually slight. But in certain regions of the mid- and
high-latitudes, a strong surface thermocline may exist,
which will cause a rapid decrease is temperature from
the surface to the injection level. This may cause the
difference between the actual surface temperature and
the injection temperature to be very large. If injection
temperatures are used, they should be routinely checked
against bucket temperatures and bathythermograph
temperatures, and adjusted if necessary.

AUTOMATIC WEATHER STATIONS

Automatic weather stations are electronic packages
that sample, record, and display or transmit weather
information to a collection site or user. In the mid-
1970’s, several systems were introduced that could
measure temperature, wind, pressure, and precipitation.
By the early 1980’s, sensors were developed that could
determine sky cover and visibility. In the mid-1980’s
remote observation sites were in use, providing full
spectrum observation data via satellite and phone lines.
In 1988, installation was started on a network of
Automatic Meteorological Observation Stations
(AMOS) in the Pacific to support the Joint Typhoon
Warning Center. In the late 1990’s, we will see more of
these automatic weather stations installed.
The automated weather stations in use by the Navy
and Marine Corps at shore stations are called
Automated Surface Observing Systems (ASOS), while
the equipment system used for shipboard observations
is called the Shipboard Meteorological and
Oceanographic Observing System (SMOOS). The
widely used meteorological buoys are also a type of
fully automated weather stations.

AUTOMATED SURFACE OBSERVING SYSTEM (ASOS)

The Automated Surface Observing System (ASOS)
is a configuration of fully automated observationequipment that will replace observation equipment at
all shore stations. These automated systems are
currently being installed. The AN/GMQ-29
semiautomatic weather station, the AN/GMQ-32
transmissometer system, the AN/GMQ-13 cloud height
set, and the AN/UMQ-5 wind-measuring set will be
replaced. The ASOS automatically collects, processes,
and error checks observation data and formats. In
addition, ASOS automatically displays, archives, and
reports weather elements included in a surface weather
observation. … snip …

Sensor Package

One or more ASOS sensor packages (fig. 2-1) are
normally located at the touch-down end of main
runways. From left to right, figure 2-1 shows the
following sensors: … snip …

SHIPBOARD METEOROLOGICAL AND OCEANOGRAPHIC OBSERVING SYSTEM (SMOOS)

The Shipboard Meteorological and Oceanographic
Observing System (SMOOS) is an add-on system of
supplemental shipboard sensors for the Tactical
Environmental Support System (TESS). The
“Observer” function in TESS provides the ability to
enter local environmental observation data, construct
observation report messages, review received
messages, and correct erroneous data.
The SMOOS is a suite of environmental sensors
that provide continuous automated measurement of
meteorological and oceanographic parameters. The
sensors automatically send the data to TESS, where it is
processed, error-checked, displayed, and distributed.
The observer may supplement or override data from the
automatic sensors. SMOOS will input data from
shipboard wind speed and direction transmitters and
from the following sensors:
Atmospheric pressure sensor
Temperature/dew-point sensor
Cloud height detector
Visibility sensor
Precipitation sensor
Seawater temperature sensor
Operation and maintenance manuals are provided
with each installation. Now let’s briefly discuss the
sensors. … snip …

METEOROLOGICAL BUOYS

A third type of automatic weather station is the
meteorological buoy. Meteorological buoys may be either moored in a permanent location or drifting buoys.
Routinely deployed by aircraft since 1989, drifting
meteorological buoys (fig. 2-6) are sonobuoy-size
weather stations that provide wind, air pressure, air and
sea surface temperature, wave period, and sea
temperature/salinity depth profiles to collection points
via satellite.

As an observer, you will have little opportunity to
see a fully automatic weather station, since no observer
support is required. However, you will use
observations and data transmitted by these stations. We
discuss these products in later modules

INSTRUMENT SHELTER

The ML-41 instrument shelter, shown in figure
2-13, is still in use at many Naval and Marine Corps
stations. The shelter is used for the protection and
acclimatization of “backup” observation equipment.
The shelter is constructed of wood, which is a poor
transmitter of heat. It has a louvered door and sides, as
well as a double-layered, sloping roof. This type of
construction helps keep out water and sunlight, yet
allows a free flow of air through the structure. These
shelters are always painted white to help reflect sunlight
and infrared radiation.

MAXlMUM AND MINIMUM THERMOMETERS

Maximum and minimum thermometers are
alcohol-filled thermometers mounted on a Townsend
support inside an instrument shelter. These
thermometers are strictly backup equipment for the
maximum and minimum temperature function of
automatic and semiautomatic observation systems.
Proper use and care are detailed in NA 50-3OFR-518.
Figure 2-15 shows the instruments mounted on the
Townsend support, and figure 2-16 shows the detail of
the Townsend support.

PSYCHROMETERS

A psychrometer is any device that contains both a
dry-bulb and a wet-bulb thermometer used to measure
ambient air temperature and wet-bulb air temperature.
Currently there are three different types of
psychrometers used by the Navy and Marine Corps: the
electric psychrometer, the sling psychrometer, and the
rotor psychrometer

The World Meteorological Organization (WMO) is
an international organization located in Geneva,
Switzerland. Operating as part of the United Nations, its
purpose is to provide international exchange of
meteorological, oceanographic, and geophysical data
and to conduct research in these areas. Most members of
the United Nations are also members of the WMO, and
have agreed to an international exchange of data in code
forms specified by the WMO. These codes are used
throughout the world and are known as the WMO
International Codes. International codes have been
established for reporting surface weather conditions,
aviation weather conditions, upper atmospheric
conditions, climatic conditions, oceanographic
conditions, earthquakes, and volcanic activity. In this
chapter, we will discuss weather logs for recording
observations, the applicable reference sources, and the
four surface observation codes. Now let’s take a closer
look at the WMO regions and code forms. … snip …

Weather observers throughout the world record and
report surface weather observations in four different
international code forms. The four code forms are

METAR Code;
SPECI Code;
Land Synoptic Code; and
Ship Synoptic Code.

A modified version of the METAR and SPECI code
is used by federal agencies in the United States. Surface
Weather Observations and Reports, Federal
Meteorological Handbook No. 1 (FMH-1) is a
publication developed by the National Oceanic and
Atmospheric Administration (NOAA) for use by the
National Weather Service. It contains detailed
instructions for the METAR and SPECI codes as used in
the United States. Other federal agencies may develop
their own observing handbooks. However, they must
comply with the basic standards set forth in FMH-1. … snip …

SURFACE AVIATION WEATHER – METAR/SPECI CODE

The METAR code is an International Observation
code used to record and disseminate routine surface
aviation weather observations. The SPECI code is a
related International code used to record and
disseminate selected surface aviation weather
observations marking significant changes in the
weather conditions. It is used to supplement the hourly
observations in the METAR code.

The METAR and SPECI codes discussed in this
section are used by all Navy and Marine Corps activities
worldwide and are a modified version of the WMO
METAR and SPECI codes used by most of the other
countries in the world.

As previously mentioned, the primary reference
manuals for Navy and Marine Corps activities are
NAVMETOCCOMINST 3141.2 and NAVMETOCCOMINST
3144.1. You, as an observer, must be
thoroughly familiar with these instructions. We will
now discuss the encoding of the individual elements of a
METAR observation.

TYPES OF OBSERVATIONS

In METAR, there are only two types of
observations:

Routine observations (METAR)—routine
observations, taken each hour on the hour. The
observation time is noted when the last element was
3-5 observed and must be within 5 minutes before the
scheduled observation hour.

Special observations (SPECI)—observations
taken to note any significant change in the weather as
defined by NAVMETOCCOMINST 3141.2 and
NAVMETOCCOMINST 3144.1. The observation
time is the time that the significant weather element is
observed. SPECI observations are also used in the
event of an aircraft mishap, volcanic eruptions, and any
other phenomena designated by local authority.
While METAR observations contain complete
observation data, SPECI observations usually contain
data pertinent only to the significant event or local
requirement. Table II-1-1 of NAVMETOCCOMINST
3141.2 and table 2-1 of NAVMETOCCOMINST
3144.1 list which elements are reported for each type of
observation.

SYNOPTIC CODES

Where the METAR/SPECI codes are designed to
report aviation weather, the Synoptic code is
specifically designed to include data for use in
analyzing the current overall weather situation. It is a
numerical code that consists mostly of groups of five
digits, specifically designed. to permit automatic
loading of computer data bases.

The Synoptic reports are transmitted by selected
stations worldwide at 0000Z, 0600Z, 1200Z, and
1800Z—the “Synoptic Hours”—with the reports
generally called “Main Synoptic” reports. Significant
reports called “Intermediate Synoptic” reports may be
transmitted at the “Intermediate Synoptic” hours:
0300Z, 0900Z, 1500Z, and 2100Z.

Although the Synoptic code transmitted by land
stations and by ships report many of the same weather
elements by using the same symbolic groups, there are
some differences in the way the station is identified.
There are also different types of data that are only
reported by land stations, just as there is some data that
is only reported by ships.

There’s lots more stuff, but that is what caught my eye on my first pass. For those who would like to read more in this or other volumes of the whole series:

Online:
http://www.tpub.com/content/aerographer/index.htm

PDF:

AEROGRAPHER’S MATE, MODULE 01–SURFACE WEATHER OBSERVATIONS
http://www.hnsa.org/doc/pdf/aerographer1.pdf

AEROGRAPHER’S MATE, MODULE 02–MISCELLANEOUS OBSERVATIONS AND CODES
http://www.hnsa.org/doc/pdf/aerographer2.pdf

AEROGRAPHER’S MATE, MODULE 03–ENVIRONMENTAL SATELLITES AND WEATHER RADAR
http://www.hnsa.org/doc/pdf/aerographer3.pdf

AEROGRAPHER’S MATE, MODULE 04–ENVIRONMENTAL COMMUNICATIONS AND ADMINISTRATION
http://www.hnsa.org/doc/pdf/aerographer4.pdf

AEROGRAPHER’S MATE, MODULE 05–BASIC METEOROLOGY
http://www.hnsa.org/doc/pdf/aerographer5.pdf

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