Weather Basics

by Paul E. Carrigan, U.S. Navy (Ret)

Here's how Paul E. Carrigan described some of what he learned in 1941 when he attended Aerographer’s school at the U.S. Naval Air Station, Lakehurst, New Jersey beginning April 1941.

The job of Navy aerographers included taking, transmitting, and recording six main kinds of weather observations:

1. Hourly (Surface) - each hour, on the hour, twenty-four times daily.
2. Synoptic (Surface) - Four times daily at designated Greenwich Meridian Time. A synoptic observation includes far more data and detail than an hourly.
3. Ship Report - This is a synoptic with additional information such as position, course, speed, swell, and sea conditions.
4. Pilot Balloon (PIBAL) (Upper-Air) - Small, unmanned, balloon sounding to determine the winds aloft. It is taken twice daily at designated Greenwich times. Soundings are also made at unscheduled times when needed.
5. Radiosonde (RAOB) (Upper-Air) - Unmanned balloon and instrument sounding to obtain pressure, temperature, and humidity aloft. They are scheduled twice daily at designated Greenwich times. Also launched at unscheduled times if weather conditions deemed it necessary.
6. Pilot Reports (PIREP) - Taken by pilots or aerographers in flight. Any time available.

Instruments

To take these observations, we worked with a variety of instruments. Some of these are:

• Thermometers obtain various temperature readings, including maximum and minimum temperatures.
• Hygrometer - an instrument for measuring the humidity of the air or a gas.
• Psychrometer—a hygrometer employing both a wet and dry bulb thermometer used to obtain the dew point temperature and relative humidity.
• Thermograph—a self-recording thermometer.
• Mercurial and Aneroid barometers for measuring atmospheric pressure in either inches of mercury or millibars.
• Barographs—a recording aneroid barometer.
• Hygrograph—an instrument that automatically records variations in humidity.
• Hygrothermographs—records both humidity and temperature changes.
• Selsyn wind direction indicator.
• Anemometer—an instrument to measure wind velocity and direction.
• Theodolite—a modified surveyor’s transit used to track a PIBAL (pilot balloon) to obtain relative azimuth angles each minute of the balloon’s flight.
• Circular plotting board—a device for showing graphically the periodic position of a moving target in relation to a stationary observer’s position. It is used to work up the PIBAL data observed through the theodolite.
• Radiosonde (RAOB)—Two instruments. First is the temperature, pressure, humidity instrument package with its battery and radio transmitter carried aloft by the large RAOB balloon. Second, the radiosonde receiver records the precise tone signals transmitted by the balloon’s instrument package during flight.
• Clinometer—a hand-held device that indicates elevation angles. Used in Aerology in conjunction with a large spotlight at night to determine the base of a cloud layer by triangulation.
• Standard rain gauge—a rainfall collecting instrument, the contents of which are periodically measured with a calibrated dipstick then emptied.
• Tipping bucket rain gauge—an instrument that collects rainwater and records the amount using a small interior bucket that trips each time it becomes full. A classy Navy weather station has a tipping bucket rain gauge.

Instructors explained how these various instruments worked, how to read them, change charts on the recording ones, how to maintain them, and in some cases, how to make minor repairs, adjustments, or recalibration.

Instruments provided approximately half of the data for each type of weather observation. Some of this data was immediately usable such as the temperature, wind direction, and velocity. Other data, such as that obtained from the PIBAL and RAOB, had to be processed through calibration, correction, or interpolation tables, plotting boards, or special charts to obtain usable values and additional data.

The remaining half of the observations were obtained by visually noting the current weather phenomena, such as establishing the visibility (the greatest distance toward the horizon that objects can be identified with the naked eye). The types of clouds had to be identified and their heights, amounts, and direction of movement. The State of the Sky—the total amount of sky covered by clouds—had to be determined and any specific weather phenomena occurring at the time of observation.

The data for each type of observation was transcribed into a precise weather code. The report was transmitted by radio or teletype so that all weather stations could share the information. Centrally-located weather offices, both civilian and military, were designated collection and dissemination centers. These stations assembled the various weather reports and placed them in “books” or schedules for rebroadcast. Specific weather codes in numerical form had been devised to handle this vast amount of twenty-four-hour-a-day radio/teletype traffic.

The Synoptic Code

The simplest weather code was the one used in the PIBAL sounding. The code identifies the station with a call number, altitude, wind direction, and velocity at each standard level. The code used for this was HDDFF, where:

H=altitude level. For example, 5,000 feet is “5”.
DD=wind direction represented by compass degrees. For example, a wind blowing from 320 degrees (Northwest) is “32”.
FF= Wind force (velocity) in mph.

A trained weatherman could glance at the numbered groups for this reporting station’s latest PIBAL sounding and determine what 53218 meant.

By far, the most complex weather code was the one for the six-hourly synoptic observation. At each Greenwich synoptic time (map time), weathermen worldwide make a detailed weather report. After collection and dissemination, these observations are entered on synoptic weather maps for analysis. This simultaneous reporting, regardless of each station’s location and time zone, shows global weather at that moment.

Each primary weather station with forecasting responsibilities selects a hundred or more synoptics entered upon that station’s area map. For example: Because all weather systems in the northern hemisphere generally move from west to east, the Navy weather office at Lakehurst would be primarily interested in the weather reports from the U.S., Canada, part of the Caribbean, and the western Atlantic Ocean. The Lakehurst synoptic map would cover this area. On the other hand, the Seattle, Washington Navy weather center’s map and signals would cover the western half of the U.S. and Canada, Alaska and the Aleutian Islands, and the North Pacific Ocean.

To have room to enter the complexity of data from upwards of two hundred stations on the maps, even in condensed form, the synoptic code employed both numerals and symbols. This complicated things because the transmission was in numeral form only.

For example, there are twenty-seven basic types of clouds, nine each for low, middle, and high. Each cloud type indicates weather past, present, or future. Each of the twenty-seven clouds was assigned a one-digit numeral such as low five, middle two, high six, represented in the synoptic code arrangement as C1 , Cm, and Ch. Each number, in turn, was represented on the map by a special weather symbol. Low one, for example, is cumulus of fair weather and represented by a symbol that looks like a scoop of ice cream with a flat base. Low two is cumulus, heavy, and swelling. Its symbol is two scoops of ice cream, one on top of the other. The symbols closely resemble what the cloud actually looks like.

There are ninety-nine weather phenomena, each assigned two digits (WW) in the synoptic code and each represented by a special symbol. Zero through thirty-nine represent special phenomena such as dust devils, tornadoes, hurricanes, sand storms, water spout, heat lightning, etc. All 40s are types of fog represented on the map by horizontal bars in various combinations. The 50s are drizzles, with the comma (,) being the basic symbol. The 60s are types of rain with the dot (.) symbol. The 70s are snow represented by the asterisk (*) symbol. For example, 72 is light continuous snow represented by the symbol **. All of the 80s are showers represented by a basic triangle symbol. The 90s are thunderstorms, with capital R being the basic symbol.

There are other codes within the synoptic code, including those for the state of the sky, wind force, visibility, barometric tendency during the past three hours, amount of barometric change, past weather, amount of precipitation during past weather, cloud direction, cloud height, etc.

Two men normally did the map entering, with one man calling off the data while the other entered the information with a pen around each numbered station’s circle on the map. Let us say that number 121 on a synoptic map represents Flagstaff, AZ. Man A would say, “121...121” (giving man B a second or two to locate the station) ..“northwest five and overcast...187..36..snow shower..8 miles and 31...low three at 25 from the northwest..mid 4 and a high 1...plus 10 George..showers at 1 a trace.....129...129 (next station)”.

Man A was looking at a bunch of five group numbers arranged in the order of the synoptic code. This arrangement, reading from left to right, differs from the precise order in which he must call off the data for ease of entering. His eyes had to skip about and he had to know the codes within the synoptic code. Man B had to know the same thing, plus the symbols and the specific arrangement to place the information around the Flagstaff station circle. After calling out “121...121 ... northwest 5” in the above example, man A had to locate the numeral for the state of the sky. In this case, it was figure a. In the state of the sky code, this means overcast. Man B dutifully filled in the station circle to indicate a complete cloud cover. 187...36 represented a pressure of 1018.7 millibars and a Fahrenheit temperature of 36 degrees. This data for PPPTT was in the third five-digit numeral group of the synoptic code. There was a coded figure for the present weather of snow showers and a code figure for 8 miles visibility. 36 was the dew point. The symbols for barometric tendency closely resemble the tendency as evidenced by the trace mark on the barograph. In the above case, the figure was 4, denoted ‘George.’ George is a barometric tendency that falls then rises sharply, hence, the symbol is a checkmark.

Balloon Soundings

I’d better explain upper wind balloon soundings. A balloon, approximately six inches in diameter, uninflated, is used. A white balloon is used for contrast if the sky is clear or clouds scattered; otherwise, we use a black one. A night-sounding uses a small light bulb screwed into a tiny dry cell battery attached by a cord to the balloon’s neck.

The balloon's neck stretches over an adapter connected to the helium tank by a rubber hose. Tiny brass weights are placed in receptacles on the adapter base, and the balloon inflates until it lifts the adapter plus the weight. The balloon's neck is twisted, removed from the adapter, and sealed with a rubber band. The balloon has expanded to roughly thirty inches in diameter. When released, it rises at a known ascension rate— either 180 or 280 meters per minute, depending on the weights used.

Like a surveyor’s transit, a theodolite tracks the balloon's flight. This instrument has a telescope mounted on a base plate marked with 360 degrees of the compass or azimuth. The telescope also pivots for elevation, marked by a scale with degrees from o to 90. There are two knobs for control and adjustment of the vernier scales, one for azimuth and one for elevation. The knobs move in slow, clicking increments or can freewheel for fast-tracking.

Two men usually take this sounding. One man observes, and the second records. A stopwatch starts when the balloon is released. At fifty seconds, the recorder with the stopwatch says, “Stand by.” The observer centers the fleeing, rising, bobbing balloon in the crosshairs. When the sweep second-hand reaches one minute, the recorder says, “Mark.” The observer reads the elevation and azimuth degrees to tenths. He then attempts to locate the balloon again. This process repeats each minute until clouds obscure the balloon or it’s otherwise lost from view.

Under ideal conditions, it is possible to track a PIBAL for well over an hour and to altitudes approaching 50,000 feet. In four and one-half years of Alaskan duty, I can recall taking only a half dozen such soundings, all on cold, clear winter days. A ten or twelve-minute sounding average for this same period would be an optimistic estimate. We did not even attempt a PIBAL for long periods in the Aleutians because of low ceilings or extreme winds.

Upon completion of the tracking phase, the information is taken inside and worked up on a large plotting board to determine the wind direction and velocity aloft at any given level. This data, combined with pressure, temperature, and humidity, are taken through a set of tables to determine ballistic density.

There are considerable differences between taking a balloon sounding from a land station and a ship’s deck. At a shore station, the theodolite mounts on a level, solid stand with the azimuth plate locked on true north at a shore station. Additionally, the theodolite has a protective, four-sided windscreen.

Aboard ship, the portable theodolite has three adjustable, telescoping legs. The instrument sits on the exposed deck. It also has to be set up perfectly level each sounding, or the data will be useless. Two sets of carpenter’s, bubble-type levels built into the base plate for port and starboard, and fore and aft leveling. It is difficult to level a theodolite on the shaking deck of a speeding, rolling, pitching ship.

In addition, the instrument’s base plate must exactly parallel the ship's fore and aft line and lock on the ship’s heading. We record the ship’s course and speed each minute for reference corrections. The plotting board calculations consider all this data, but it becomes more complicated if the ship changes course and speed during an evasive, anti-submarine zig or zag.

Ciphers

The Japanese attack on Pearl Harbor on December 7, 1941, and the Declaration of War added one further step to our weather code work. It became necessary to encipher our weather numbers into the day’s secret radio transmission code. Each month, we were furnished with code books containing five-digit groups pages. The following example of a message sent from Kodiak to Adak will explain how this worked.

Note: The above encryption technique is called a one-time pad in which the sender and receiver are using the same codebook of ciphers or keys.

This final ciphering had to be done with every group of every report and added hours of eye-straining work to our office watch routine. It is a small wonder that many aerographer’s mates ended up wearing glasses. To accomplish our work under the pressure of limited time, we had to memorize all of the codes.

I’m hoping that the foregoing hasn’t led to utter confusion. It is only necessary to realize the great detail and problems connected with weather work. With practice, all of the various codes became a comfortable second language.

Teletypes

The hourly weather report differed markedly from the synoptic in both arrangement and code. These reports incorporated some abbreviations in addition to numbers and symbols. Some weather offices had teletype machines with special hourly weather symbols on their keyboards, while others had standard teletypes. For example, you’d typed ‘ovc’ on a regular keyboard for overcast, while a special keyboard’s overcast symbol was a cross inside a circle.

Some Teletype machines had eight symbols (arrows) for wind direction and four symbols for cloud cover.

Pilot Reports (PIREPs) used the Aircraft Meteorological Code (AirMetCo). This combination of the synoptic, hourly, and ship code contained provisions for reporting the aircraft’s position, altitude, speed, cloud bases and tops, turbulence, icing conditions, etc.

Weather reports from commercial ships ceased with the outbreak of war. No ship captain would give away his ship’s position to enemy submarines by using his radio transmitter. The result was that the vast expanses of ocean were blank on our weather maps, adding yet another problem to weather forecasting.

There were manuals to cover every phase of our weather work. Our primary ‘Bible’ was the hardcover Aerographer’s Manual, a thick volume that went into great detail. Smaller, special manuals such as the Radiosonde Manual went into the taking of this complex observation. We used a small, blue cover Circular S publication for our Cloud Atlas. This manual contained representative photographs of the different basic clouds and their variations to help identify clouds. It also explained how each type forms and the weather associated with it.