IPS Ionospheric Medians Data Format and Data File Name Convention

One median data file contains all available yearly data for the specified station and median parameter. Downloaded medians data file name from IPS website has convention as below:

SSSS.PP

where:
SSSS - IPS Station Number, listed in following table.
PP - URSI parameter code, listed in following table.

Data Format for each record in the data file:

fields 1-4:	IPS Station Number
fields 5-6:	URSI parameter code
fields 7-8:	month
fields 9-10:	year
fields 11-12:	"40"
fields 13-168:	24*hourly values and count (QVVVDCC)

where Q=qualifier,
         VVV=value,
         D=descriptor,
         CC=count (hourly values with counts less than 5 are not included)

Data in universal time (UT). First hour of each record is 0000UT.
Note: Macquarie Island data 1950to 1958 in local time (157.5 EMT or 10.5 hours ahead of 00UT); first hour of each record for this period is 0000LT (midnight).

The URSI parameter codes are:

Code	Parameter	Units	Ref. UAG23	Definition
00	foF2	0.1 MHz	1.11	Ordinary wave critical frequency of the highest stratification in the F region.
03	M(3000)F2	0.05	1.50	Maximum usable frequency at a defined distance divided by the critical frequency of that layer.

Below are two lists of the stations. In the first list, stations are sorted by their IPS station numbers. In the second list, the stations are sorted alphabetically. Geographic co-ordinates are given; southern latitudes are negative.

Stations sorted by IPS station number:

IPS STATION NUMBER	STATION NAME	LATITUDE	LONGITUDE
0019	GREAT BADDOW	51.43	0.29
0022	POITIERS	46.35	0.20
0025	TORTOSA	40.48	0.31
0040	DAPANGO	10.52	0.12
0090	POLE STATION	-89.99	346.68
0119	DE BILT	52.06	5.10
0120	DOURBES	50.24	3.47
0121	PARIS/BAGNEUX	48.48	5.88
0122	GARCHY	47.30	3.10
0134	TAMANRASSET	22.79	5.53
0141	IBADAN	7.43	3.90
0218	ST PETER-ORDING	54.18	8.37
0221	FREIBURG/KOCHEL	47.59	7.51
0222	SOTTENS/SCHWARZENBERG	46.49	7.21
0223	MONTE CAPELLINO	44.55	8.96
0315	KJELLER	60.00	11.10
0318	JULIUSRUH/RUGEN	54.60	13.40
0319	LINDAU/HARZ	52.58	11.10
0324	ROME	41.54	12.29
0326	GIBILMANNA	37.59	14.01
0406	LONGYEARBYEN	78.12	15.40
0415	UPPSALA	50.90	17.35
0420	PRUHONICE	49.99	14.55
0421	GRAZ	47.05	15.27
0447	KINSHASA-BINZA/LEOPOLDVILLE	-4.18	15.18
0455	TSUMEB	-19.13	17.42
0510	TROMSO	69.66	18.94
0511	KIRUNA	67.83	20.42
0513	LYCKSELE	64.36	18.40
0518	KALININGRAD	54.43	20.30
0519	MIEDZESZYN	52.15	20.40
0521	BUDAPEST	47.30	19.05
0523	BEOGRAD	44.50	20.30
0524	BEKESCSABA	46.41	21.06
0543	BANGUI	4.22	18.35
0562	CAPE TOWN/HERMANUS	-33.55	18.22
0612	LULEA	65.34	22.10
0615	NURMIJARVI	60.28	24.48
0624	SOFIA	42.41	23.19
0626	ATHENS	37.58	23.43
0662	GRAHAMSTOWN	-33.28	26.48
0711	SODANKYLA	67.29	26.32
0746	LWIRO	-2.30	28.80
0751	ELIZABETHVILLE	-11.40	27.28
0758	JOHANNESBURG	-26.15	28.10
0810	MURMANSK	68.63	33.25
0815	ST PETERSBURG/LENINGRAD	59.55	30.15
0820	KIEV	50.72	30.31
0844	BUNIA	1.34	30.15
0917	MOSCOW	55.47	37.31
0923	SIMFEROPOL	44.57	34.06
0946	NAIROBI	-1.17	36.49
1013	ARCHANGELSK	64.34	40.32
1021	ROSTOV-ON-DON	47.14	39.42
1080	SYOWA STATION	-69.00	39.35
1119	GORKY	56.20	44.00
1124	TBILISI	42.09	44.71
1139	DJIBOUTI	11.36	43.09
1254	TANANARIVE	-18.55	47.31
1305	TIKHAJA BAY	80.33	52.80
1327	TEHRAN	35.40	51.26
1405	KRENKEL POLAR STATION	80.50	58.00
1456	LA REUNION	-21.06	55.36
1510	AMDERMA	69.45	61.39
1517	SVERDLOVSK	56.51	61.07
1522	NOVO KAZAKINSK	45.50	62.10
1526	ASHKHABAD	37.95	58.12
1679	MAWSON	-67.36	62.52
1712	SALEKHARD	66.33	66.35
1724	TASHKENT	41.20	69.18
1820	KARAGANDA	49.50	73.10
1834	AHMEDABAD	23.02	72.35
1836	BOMBAY	19.11	72.50
1870	KERGUELEN ISLAND	-49.15	69.10
1923	ALMA ATA	43.15	76.57
1931	DELHI	28.37	77.12
1940	KODAIKANAL	10.23	77.46
1941	THUMBA/TRIVANDRUM	8.53	76.87
1979	DAVIS	-68.35	77.58
2008	DIKSON ISLAND/DIXON ISLAND	73.54	80.56
2036	HYDERABAD	17.41	78.56
2038	MADRAS	13.04	80.16
2040	TIRUCHIRAPELLI	10.48	78.41
2117	TOMSK	56.47	84.93
2118	NOVOSIBIRSK	55.02	82.55
2210	NORILSK	69.20	88.06
2214	PODKAMENNAYA TUNGUSKA	61.45	90.13
2378	MIRNEY	-66.33	93.00
2451	COCOS ISLANDS	-12.10	96.55
2538	BANGKOK	13.45	100.31
2619	IRKUTSK	52.17	104.45
2644	SINGAPORE	1.17	103.50
2730	CHUNGKING	29.39	106.34
2784	VOSTOK	-78.45	106.87
2807	PREOBRAZHENIYA	74.66	112.93
2819	CHITA	52.03	113.30
2832	CANTON	23.09	113.34
2834	MACAU	22.14	113.35
2835	HAIKOU	20.06	110.21
2856	LEARMONTH	-22.25	114.08
2878	CASEY/WILKES	-66.17	110.32
2920	MANCHOULI	49.35	117.22
2925	BEIJING	39.55	116.25
2960	WATHEROO	-30.32	115.88
2961	MUNDARING	-31.54	116.10
3032	TAIPEI/CHUNG-LI	24.95	121.22
3038	MANILA	14.35	120.59
3209	TIXIE BAY	71.58	128.48
3214	YAKUTSK	62.02	129.72
3226	SEOUL	37.33	126.58
3232	OKINAWA	26.31	127.59
3329	YAMAGAWA	31.12	130.39
3351	DARWIN	-12.28	130.50
3355	TENNANT CREEK	-19.40	134.10
3357	ALICE SPRINGS	-23.42	133.53
3421	KHABAROVSK	48.50	135.10
3446	BIAK	-1.18	136.12
3460	WOOMERA	-31.31	137.10
3522	WAKKANAI	45.25	141.40
3525	AKITA	39.43	140.07
3527	TOKYO	35.42	139.46
3546	VANIMO	-2.40	141.20
3562	SALISBURY	-34.46	138.38
3578	ADELIE LAND	-66.66	140.02
3622	YUZHNO-SAKHALINSK	46.95	142.72
3638	GUAM	13.58	144.87
3650	CAPE YORK	-14.00	142.30
3715	MAGADAN	59.34	150.48
3750	PORT MORESBY	-9.30	147.10
3755	TOWNSVILLE	-19.16	146.48
3763	CANBERRA	-35.17	149.08
3766	HOBART	-42.53	147.19
3859	BRISBANE	-27.28	153.02
3862	CAMDEN	-34.03	150.42
4018	PETROPAVLOVSK	52.90	158.64
4072	MACQUARIE ISLAND	-54.30	158.56
4182	TERRA NOVA BAY	-74.45	164.30
4260	NORFOLK ISLAND	-29.02	167.57
4271	CAMPBELL ISLAND	-52.30	169.00
4284	SCOTT BASE	-77.85	166.78
4367	CHRISTCHURCH	-43.42	172.38
4381	CAPE HALLETT	-72.19	170.18
4464	AUCKLAND	-36.53	174.45
4511	CAPE SCHMIDT	68.80	179.50
4619	ADAK	51.52	183.61
4660	RAOUL ISLAND/KERMADEC ISLANDS	-29.50	181.85
4712	WELLEN	66.13	190.17
4713	PROVIDENIE BAY	64.23	186.82
4755	NIUE	-19.03	190.08
4942	PALMYRA	5.52	197.94
5056	RAROTONGA	-21.14	200.54
5109	POINT BARROW	71.30	203.22
5135	KIHEI/MAUI	20.45	203.85
5144	CHRISTMAS ISLAND	1.52	202.80
5308	EIELSON AFB	64.50	213.00
5313	COLLEGE/FAIRBANKS	64.82	212.13
5314	ANCHORAGE	61.17	209.98
5354	TARAVAO/TAHITI	-17.56	210.39
5718	PRINCE RUPERT	54.18	229.83
5926	SAN FRANCISCO	37.77	237.57
6027	POINT ARGUELLO	34.35	239.62
6028	VANDENBURG AFB	34.43	239.67
6085	BYRD	-79.98	240.00
6329	WHITE SANDS	32.22	253.77
6425	BOULDER	40.13	254.77
6528	DYESS AFB	32.25	260.49
6535	MEXICO CITY/EL CERILLO	19.24	260.91
6608	RESOLUTE BAY	74.69	265.11
6613	BAKER LAKE	64.15	263.97
6616	CHURCHILL	58.47	265.88
6620	WINNIPEG/KENORA	49.47	265.71
6730	BATON ROUGE	30.53	268.85
6829	EGLIN AFB	30.29	273.70
7032	GRAND BAHAMA ISLAND	26.40	281.80
7040	PANAMA CANAL ZONE	9.20	280.70
7047	TALARA	-4.63	278.75
7122	OTTAWA	45.25	284.58
7125	FORT BELVOIR/WASHINGTON	38.85	282.97
7126	WALLOPS ISLAND	37.52	284.73
7143	BOGOTA	4.18	285.52
7151	HUANCAYO	-12.05	284.67
7223	MAYNARD	42.30	288.67
7224	BOSTON	42.37	288.97
7225	FORT MONMOUTH	40.19	285.98
7263	CONCEPCION	-36.50	286.97
7307	THULE	77.48	290.83
7310	CLYDE RIVER	70.25	291.70
7316	FORT CHIMO	58.10	291.70
7336	SAN JUAN/PUERTO RICO	18.12	293.85
7353	LA PAZ	-16.30	291.91
7372	USHUAIA	-54.47	291.80
7458	TUCUMAN	-26.49	294.87
7477	ARGENTINE ISLANDS/PORT LOCKROY	-65.25	295.73
7518	GOOSE BAY	53.19	299.76
7540	TRINIDAD	10.30	298.85
7562	BUENOS AIRES	-34.36	301.73
7576	DECEPCION	-62.57	299.62
7642	PARAMARIBO	5.81	304.78
7671	PORT STANLEY	-51.42	302.49
7710	GODHAVN	69.15	306.67
7721	ST JOHNS	47.60	307.32
7857	SAO PAULO	-23.32	313.63
7914	NARSSARSSUAQ	60.54	314.80
8084	ELLSWORTH	-77.40	318.90
8172	SOUTH GEORGIA	-54.15	323.55
8383	HALLEY BAY	-75.52	333.40
8513	REYKJAVIK	64.09	338.49
8638	DAKAR	14.40	342.74
8726	LISBON	38.43	350.92
8816	SOUTH UIST	57.15	352.76
8828	RABAT	34.02	353.49
8829	CASABLANCA	33.39	352.65
8916	INVERNESS/FRASERBURGH/BURGHEAD	57.27	356.51
8921	LANNION	48.44	356.72
8939	OUAGADOUGOU	12.22	358.69
8980	SANAE	-70.31	357.59

Stations sorted alphabetically:

IPS STATION NUMBER	STATION NAME	LATITUDE	LONGITUDE
4619	ADAK	51.52	183.61
3578	ADELIE LAND	-66.66	140.02
1834	AHMEDABAD	23.02	72.35
3525	AKITA	39.43	140.07
3357	ALICE SPRINGS	-23.42	133.53
1923	ALMA ATA	43.15	76.57
1510	AMDERMA	69.45	61.39
5314	ANCHORAGE	61.17	209.98
1013	ARCHANGELSK	64.34	40.32
7477	ARGENTINE ISLAND	-65.25	295.73
1526	ASHKHABAD	37.95	58.12
0626	ATHENS	37.58	23.43
4464	AUCKLAND	-36.53	174.45
0121	BAGNEUX	48.48	5.88
6613	BAKER LAKE	64.15	263.97
2538	BANGKOK	13.45	100.31
0543	BANGUI	4.22	18.35
6730	BATON ROUGE	30.53	268.85
2925	BEIJING	39.55	116.25
0524	BEKESCSABA	46.41	21.06
0523	BEOGRAD	44.50	20.30
3446	BIAK	-1.18	136.12
7143	BOGOTA	4.18	285.52
1836	BOMBAY	19.11	72.50
7224	BOSTON	42.37	288.97
6425	BOULDER	40.13	254.77
3859	BRISBANE	-27.28	153.02
0521	BUDAPEST	47.30	19.05
7562	BUENOS AIRES	-34.36	301.73
0844	BUNIA	1.34	30.15
8916	BURGHEAD	57.27	356.51
6085	BYRD	-79.98	240.00
3862	CAMDEN	-34.03	150.42
4271	CAMPBELL ISLAND	-52.30	169.00
3763	CANBERRA	-35.17	149.08
2832	CANTON	23.09	113.34
4381	CAPE HALLETT	-72.19	170.18
4511	CAPE SCHMIDT	68.80	179.50
0562	CAPE TOWN	-33.55	18.22
3650	CAPE YORK	-14.00	142.30
8829	CASABLANCA	33.39	352.65
2878	CASEY	-66.17	110.32
2819	CHITA	52.03	113.30
4367	CHRISTCHURCH	-43.42	172.38
5144	CHRISTMAS ISLAND	1.52	202.80
2730	CHUNGKING	29.39	106.34
3032	CHUNG-LI	24.95	121.22
6616	CHURCHILL	58.47	265.88
7310	CLYDE RIVER	70.25	291.70
2451	COCOS ISLANDS	-12.10	96.55
5313	COLLEGE	64.82	212.13
7263	CONCEPCION	-36.50	286.97
8638	DAKAR	14.40	342.74
0040	DAPANGO	10.52	0.12
3351	DARWIN	-12.28	130.50
1979	DAVIS	-68.35	77.58
0119	DE BILT	52.06	5.10
7576	DECEPCION	-62.57	299.62
1931	DELHI	28.37	77.12
2008	DIKSON ISLAND	73.54	80.56
2008	DIXON ISLAND	73.54	80.56
1139	DJIBOUTI	11.36	43.09
0120	DOURBES	50.24	3.47
6528	DYESS AFB	32.25	260.49
6829	EGLIN AFB	30.29	273.70
5308	EIELSON AFB	64.50	213.00
6535	EL CERILLO	19.24	260.91
0751	ELIZABETHVILLE	-11.40	27.28
8084	ELLSWORTH	-77.40	318.90
5313	FAIRBANKS	64.82	212.13
7125	FORT BELVOIR	38.85	282.97
7316	FORT CHIMO	58.10	291.70
7225	FORT MONMOUTH	40.19	285.98
8916	FRASERBURGH	57.27	356.51
0221	FREIBURG	47.59	7.51
0122	GARCHY	47.30	3.10
0326	GIBILMANNA	37.59	14.01
7710	GODHAVN	69.15	306.67
7518	GOOSE BAY	53.19	299.76
1119	GORKY	56.20	44.00
0662	GRAHAMSTOWN	-33.28	26.48
7032	GRAND BAHAMA ISLAND	26.40	281.80
0421	GRAZ	47.05	15.27
0019	GREAT BADDOW	51.43	0.29
3638	GUAM	13.58	144.87
2835	HAIKOU	20.06	110.21
8383	HALLEY BAY	-75.52	333.40
0319	HARZ	52.58	11.10
0562	HERMANUS	-33.55	18.22
3766	HOBART	-42.53	147.19
7151	HUANCAYO	-12.05	284.67
2036	HYDERABAD	17.41	78.56
0141	IBADAN	7.43	3.90
8916	INVERNESS	57.27	356.51
2619	IRKUTSK	52.17	104.45
0758	JOHANNESBURG	-26.15	28.10
0318	JULIUSRUH	54.60	13.40
0518	KALININGRAD	54.43	20.30
1820	KARAGANDA	49.50	73.10
6620	KENORA	49.47	265.71
1870	KERGUELEN ISLAND	-49.15	69.10
4660	KERMADEC ISLANDS	-29.50	181.85
3421	KHABAROVSK	48.50	135.10
0820	KIEV	50.72	30.31
5135	KIHEI	20.45	203.85
0447	KINSHASA-BINZA	-4.18	15.18
0511	KIRUNA	67.83	20.42
0315	KJELLER	60.00	11.10
0221	KOCHEL	47.59	7.51
1940	KODAIKANAL	10.23	77.46
1405	KRENKEL POLAR STATION	80.50	58.00
8921	LANNION	48.44	356.72
7353	LA PAZ	-16.30	291.91
1456	LA REUNION	-21.06	55.36
2856	LEARMONTH	-22.25	114.08
0815	LENINGRAD	59.55	30.15
0447	LEOPOLDVILLE	-4.18	15.18
0319	LINDAU	52.58	11.10
8726	LISBON	38.43	350.92
0406	LONGYEARBYEN	78.12	15.40
0612	LULEA	65.34	22.10
0746	LWIRO	-2.30	28.80
0513	LYCKSELE	64.36	18.40
2834	MACAU	22.14	113.35
4072	MACQUARIE ISLAND	-54.30	158.56
2038	MADRAS	13.04	80.16
3715	MAGADAN	59.34	150.48
2920	MANCHOULI	49.35	117.22
3038	MANILA	14.35	120.59
5135	MAUI	20.45	203.85
1679	MAWSON	-67.36	62.52
7223	MAYNARD	42.30	288.67
6535	MEXICO CITY	19.24	260.91
0519	MIEDZESZYN	52.15	20.40
2378	MIRNEY	-66.33	93.00
0223	MONTE CAPELLINO	44.55	8.96
0917	MOSCOW	55.47	37.31
2961	MUNDARING	-31.54	116.10
0810	MURMANSK	68.63	33.25
0946	NAIROBI	-1.17	36.49
7914	NARSSARSSUAQ	60.54	314.80
4755	NIUE	-19.03	190.08
4260	NORFOLK ISLAND	-29.02	167.57
2210	NORILSK	69.20	88.06
1522	NOVO KAZAKINSK	45.50	62.10
2118	NOVOSIBIRSK	55.02	82.55
0615	NURMIJARVI	60.28	24.48
3232	OKINAWA	26.31	127.59
7122	OTTAWA	45.25	284.58
8939	OUAGADOUGOU	12.22	358.69
4942	PALMYRA	5.52	197.94
7040	PANAMA CANAL ZONE	9.20	280.70
7642	PARAMARIBO	5.81	304.78
0121	PARIS	48.48	5.88
4018	PETROPAVLOVSK	52.90	158.64
2214	PODKAMENNAYA TUNGUSKA	61.45	90.13
6027	POINT ARGUELLO	34.35	239.62
5109	POINT BARROW	71.30	203.22
0022	POITIERS	46.35	0.20
0090	POLE STATION	-89.99	346.68
7477	PORT LOCKROY	-65.25	295.73
3750	PORT MORESBY	-9.30	147.10
7671	PORT STANLEY	-51.42	302.49
2807	PREOBRAZHENIYA	74.66	112.93
5718	PRINCE RUPERT	54.18	229.83
4713	PROVIDENIE BAY	64.23	186.82
0420	PRUHONICE	49.99	14.55
7336	PUERTO RICO	18.12	293.85
8828	RABAT	34.02	353.49
4660	RAOUL ISLAND	-29.50	181.85
5056	RAROTONGA	-21.14	200.54
6608	RESOLUTE BAY	74.69	265.11
8513	REYKJAVIK	64.09	338.49
0324	ROME	41.54	12.29
1021	ROSTOV-ON-DON	47.14	39.42
0318	RUGEN	54.60	13.40
7721	ST JOHNS	47.60	307.32
0218	ST PETER-ORDING	54.18	8.37
0815	ST PETERSBURG	59.55	30.15
1712	SALEKHARD	66.33	66.35
3562	SALISBURY	-34.46	138.38
8980	SANAE	-70.31	357.59
5926	SAN FRANCISCO	37.77	237.57
7336	SAN JUAN	18.12	293.85
7857	SAO PAULO	-23.32	313.63
0222	SCHWARZENBERG	46.49	7.21
4284	SCOTT BASE	-77.85	166.78
3226	SEOUL	37.33	126.58
0923	SIMFEROPOL	44.57	34.06
2644	SINGAPORE	1.17	103.50
0711	SODANKYLA	67.29	26.32
0624	SOFIA	42.41	23.19
0222	SOTTENS	46.49	7.21
8172	SOUTH GEORGIA	-54.15	323.55
8816	SOUTH UIST	57.15	352.76
1517	SVERDLOVSK	56.51	61.07
1080	SYOWA STATION	-69.00	39.35
5354	TAHITI	-17.56	210.39
3032	TAIPEI	24.95	121.22
7047	TALARA	-4.63	278.75
0134	TAMANRASSET	22.79	5.53
1254	TANANARIVE	-18.55	47.31
5354	TARAVAO	-17.56	210.39
1724	TASHKENT	41.20	69.18
1124	TBILISI	42.09	44.71
1327	TEHRAN	35.40	51.26
3355	TENNANT CREEK	-19.40	134.10
4182	TERRA NOVA BAY	-74.45	164.30
7307	THULE	77.48	290.83
1941	THUMBA	8.53	76.87
1305	TIKHAJA BAY	80.33	52.80
2040	TIRUCHIRAPELLI	10.48	78.41
3209	TIXIE BAY	71.58	128.48
3527	TOKYO	35.42	139.46
2117	TOMSK	56.47	84.93
0025	TORTOSA	40.48	0.31
3755	TOWNSVILLE	-19.16	146.48
7540	TRINIDAD	10.30	298.85
1941	TRIVANDRUM	8.53	76.87
0510	TROMSO	69.66	18.94
0455	TSUMEB	-19.13	17.42
7458	TUCUMAN	-26.49	294.87
0415	UPPSALA	50.90	17.35
7372	USHUAIA	-54.47	291.80
6028	VANDENBURG AFB	34.43	239.67
3546	VANIMO	-2.40	141.20
2784	VOSTOK	-78.45	106.87
3522	WAKKANAI	45.25	141.40
7126	WALLOPS ISLAND	37.52	284.73
7125	WASHINGTON	38.85	282.97
2960	WATHEROO	-30.32	115.88
4712	WELLEN	66.13	190.17
6329	WHITE SANDS	32.22	253.77
2878	WILKES	-66.17	110.32
6620	WINNIPEG	49.47	265.71
3460	WOOMERA	-31.31	137.10
3214	YAKUTSK	62.02	129.72
3329	YAMAGAWA	31.12	130.39
3622	YUZHNO-SAKHALINSK	46.95	142.72

Qualifying Letters
A: Less than. Used only when fbEs is deduced from foEs because total blanketing of higher layers is present.
D: Greater than
E: Less than
I: Missing values has been replace by an interpolated value.
J: Ordinary component characteristic deduced from the extraordinary component.
M: Interpretation of measurement questionable because ordinary and extraordinary components are not distinguishable. Used with descriptive letter which shows why components are not distinguishable.
O: Extraordinary component characteristic deduced from the ordinary component.
T: Value determined by a sequence of observations, the actual observation being inconsistent or doubtful.
U: Uncertain or doubtful numerical value.
Z: Measurement deduced from the third magneto-electronic component.

Descriptive Letters
A: Measurement influenced by, or impossible because of, the presence of a lower then layer, for example, ES.
B: Measurement influenced by, or impossible because of, absorption in the vicinity of fmin.
C: Measurement influenced by, or impossible because of, any non-ionospheric reason.
D: Measurement influenced by, or impossible because of, the upper limit of the normal frequency range.
E: Measurement influenced by, or impossible because of, the lower limit of the normal frequency range.
F: Measurement influenced by, or impossible because of, the presence of spread echoes.
G: Measurement influenced by, or impossible because the ionisation density of the reflecting layer is too small to enable it to be made accurately.
H: Measurement influenced by, or impossible because of, the presence of stratification.
K: Presence of a particle E layer.
L: Measurement influenced by, or impossible because the trace has no sufficiently definite cusp between the layers.
M: Interpretation of measurement questionable because ordinary and extraordinary components are not distinguishable. Used when interpretation is doubtful and a qualifying letter needed for other reasons (e.g., U, D, E).
N: Conditions are such that the measurement cannot be interpreted.
O: Measurement refers to the ordinary component.
P: Measurement influenced by, or impossible because of, the presence of polar spurs.
Q: Measurement influenced by, or impossible because of, the presence of range spread.
R: Measurement influenced by, or impossible because of, attenuation in the vicinity of the critical frequency.
S: Measurement influenced by, or impossible because of, interference or atmospherics.
T: Value determined by a sequence of observations, the actual value or observation being inconsistent or doubtful.
V: Forked trace, which may influence the measurement.
W: Measurement influenced by, or impossible because the echo lies outside the height range recorded.
X: Measurement refers to the extraordinary component.
Y: Lacuna phenomena, severe layer tilt.
Z: Third magneto-electronic component present.