# Critical Frequencies Codes

**UFOFS, UFOFH, UMUFH, UFMNH , and UFESH**

The data in the UFOFS, UFOFH, UFMNH, UFESH, and UMUFH codes include:

Critical frequencies of F2 region (foF2) as a function of time

Maximum and minimum values of foF2 and hour of occurrence

F-min frequencies for every 6 hours (first hours same as for first foF2 group)

Minimum o-layer component frequency

Critical frequency of sporatic E (foEs)

The codes are almost identical, except values are given for6-hour intervalsin the UFOFS (xxxxS) code and for1-hour intervalsin the UFOFH, UFMNH, UFESH, and UMUFH codes (xxxxH).

Also, the values are given for foF2 in the UFOFS and UFOFH codes and for M(3000)F2 in the UMUFH code (seefggghgroup).

The UFESH code is used to report auroral sporadic E. It is the same as the UFOFH code, except the letter h in the groupfggghis defined as 6 = F, spread echoes for auroral sporadic E.

*Example:*

*Definition of symbols:*

**UFOFS**comes from radio**FOF**2**,**code O (every**S**ix hours, Universal time)

**UFOFH**comes from**FOF**2**,**code**H**our, Universal time)

**UMUFH**comes from**M**aximum**U**sable Frequency**F**actor (3000) F2, code D (every**H**our, UT time)

**UFMNH**comes from**F**requency**M**i**N**imum (every**H**our, UT time) ???????

**UFESH**comes from**F**requency**E**-**S**poradic (every**H**our, UT time)

**I I I I I**= station indicator

**Y**= last digit of year**MM**= month of year, 01 = January, 02 = February,*etc.***DD**= UT day of month

**/**= filler**HHmm**= UT hour and minute of beginning of period

- For the xxxxS codes, use the following time indicators:
**f**= even-hour indicator, give data for 6-hour intervals, beginning with the appropriate hour after the date:- 0 = 0000 hours
- 3 = 0600
- 6 = 1200
- 9 = 1800

- For the xxxxH codes, use the following time indicators:
**f**= UT hour of data reported, beginning with the appropriate hour after the date- 0 = 0000
- 1 = 0100
- 2 = 0200
- 3 = 0300
- 4 = 0400
- 5 = 0500
- 6 = 0600
- 7 = 0700
- 8 = 0800
- 9 = 0900
- 0 = 1000
- 1 = 1100
- 2 = 1200
- 3 = 1300
- 4 = 1400
- 5 = 1500
- 6 = 1600
- 7 = 1700
- 8 = 1800
- 9 = 1900
- 0 = 2000
- 1 = 2100
- 2 = 2200
- 3 = 2300

**ggg**-
- =value of foF2 (in tenths of MHz) for UFOFS and UFOFH (report as 000 if symbols only are applicable)
- = value of M(3000)F2 (in hundredths) for UMUFH (report as 000 if symbols only are applicable)
- = minimum value (in tenths of MHz) of the o-layer component frequency (UFMNH) (report as 000 if symbols only are applicable)
- = value of foEs (in tenths of MHz) for UFESH (report as 000 if symbols only are applicable)

**h**= descriptive letter symbol (see Piggott and Rawer,*URSI Handbook of Ionogram Interpretation and Reduction,*1961, for full information)-
- X = none (use
**/**in teletype messages) - 1 = A, blanketing sporadic E
- 2 = B, complete absorption
- 3 = C, equipment trouble
- 4 = D, frequency higher than equipment limit
- 5 = E, frequency lower than equipment limit
- 6 = F, spread echoes
- 7 = G, foF2 < foF1 (report foF1 in group
**ggg**above) - 8 = I or T, interpolated or smoothed value
- 9 = R, measurement influenced by, or impossible because of attenuation in the vicinity of a critical frequency
- 0 = any other
- For code UFESH:
- 6 = F, spread echoes for auroral sproadic E

- X = none (use

**MAXMI**= key word, indicating the following groups given**MAX**imum and**MI**nimum foF2 during 24-hour period reported

**HH**= nearest hour of maximum value**ppp**= maximum value of foF2 in 24-hour period reported, in tenths of MHz

**HH**= nearest hour of minimum value**qqq**= minimum value of foF2 in 24-hour period reported, in tenths of MHz

**EFMIN**= key word, indicating f-MIN data to follow

**i i**= f-min in tenths of MHz for time of first**fgggh**- group above

**j j**= f-min in tenths of MHz for 6 hours later than**i i**

**k k**= f-min in tenths of MHz for 12 hours later than**i i**

**l l**= f-min in tenths of MHz for 18 hours later than**i i**

**/ /**= filler

*Notes: 1. In ***i i j j k*** ***k l l / / ***groups,
"99" will signify f-min > 9.9 MHz
2. If a symbol is to be used for f-min, encode as follows:
X1 = A X3 = C
X2 = B X5 = E
(The X's should be*

**/**

*in teletype messages)*

Note: **/** is to be used for data not available.