1.5.1. STATION CLIMATOLOGIES

Introduction

The climatology of surface meteorological observations at the four CMDL observatories is based on hourly average measurements of the resultant wind direction and speed, barometric pressure, ambient and dewpoint temperatures, and the precipitation amount. The 19-year station climatologies are an important record for the interpretation of measured values of aerosols, trace gases, atmospheric turbidity, and long-term changes in the records themselves. The records also serve to outline periods of local contamination. The sensors in use were selected for their high accuracy and their ability to withstand the extreme conditions of the polar region. Data is recorded as 1-minute average values so that the variability within the hourly averages can be determined. To the extent that is practical, World Meteorological Organization (WMO) siting standards [WMO, 1969] are followed. Thermometers are also positioned at the top of the sampling towers at BRW, MLO, and SPO to measure the temperature gradient to determine the stability of the surface boundary layer.

The Control and Monitoring System (CAMS) was replaced with a PC-based meteorological data acquisition system at BRW in April 1994, MLO in October 1993, SMO in June 1994, and SPO in January 1994. A detailed description of the new data acquisition system can be found in [Peterson and Rosson, 1994]. Table 1.7 describes the sensor disposition as of December 31, 1995.

TABLE 1.7. CMDL Meteorological Sensor Deployment December 31, 1995

	BRW			MLO			SMO			SPO
	Serial	Elevation,		Serial	Elevation,		Serial	Elevation,		Serial	Elevation,
Sensor	No.	m		No.	m		No.	m		No.	m
Primary anemometer†	14584	10.5		13864	10.0		15945	13.7		14583	10.0
Secondary anemometer†				13865	38.2
Pressure transducer‡	374199	9.5		374198	3398.4		374200	78.5		358960	2841.0
Mercurial barometer	641	9.5		278	3398.4		961	78.5		215	2841.0
Air temperature A§		2.2			2.0			14.0			2.0
Air temperature B§¶		16.3			37.4						22.0
Air temperature C**		2.0			2.0			12.8			2.0
Dewpoint temperature	G0001	2.0		G0004	2.0		G0008	12.8		G0007	2.0
Rain gauge		~4			0.8			~4

†Propeller Anemometer, model no. 05105, R. M. Young Company, Traverse City, Michigan.

‡Pressure Transducer, model no. 270, Setra Systems, Acton Massachusetts. Heights of all pressure sensors are given with respect to MSL.

§Platinum Resistance Probe, Logan 4150 Series, Logan Enterprises, Liberty, Ohio.

¶Thermometer, positioned at the top of the local sampling tower to facilitate an estimation of boundary layer stability.

**Hygrothermometer, Technical Services Laboratory model no. 1088-400, Fort Walton Beach, Florida.

Barrow

Descriptions of the BRW station and its climate are given in previous CMDL Summary Reports [e.g., DeLuisi, 1981]. Wind roses of hourly average resultant wind direction and speed are presented in 16 direction classes and 4 speed classes (Figure 1.2). Winds from the "clean air" sector, north-northeast to southeast occurred 58.8% of the time in 1994 and 62.8% in 1995 as compared to 62.1% for the 17-year climatology period of 1977 through 1993 (Figure 1.3). Wind speeds that were greater than 10 ms-1 for 1994 (9.1%) and 1995 (6.8%) were both lower than the 17-year climatology (12.1%). The average speed of 5.5 ms-1 in 1994 (Table 1.8) was the second lowest average while the 5.0 ms-1 in 1995 set the lowest average in the 19 years at the station. This could have been caused by lowering of the new anemometer to 9.5 m from 16.5 m on April 15, 1994, when the new system was installed.

Fig. 1.2. Wind rose of surface winds for BRW for 1994 (left) and 1995 (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes.

Fig. 1.3. Wind rose of surface winds for BRW for 1977-1993. The distribution of resultant wind direction and speed are given in units of percent occurrence for the 17-year period. Wind speed is displayed as a function of direction in three wind classes.

The average temperature of -13.1°C in 1994 was 0.5°C colder than the 17-year average (Table 1.8). In 1995, the average of -11.4°C was 1.2°C warmer than the 17-year average. June 1994 set a new record low temperature and December 1994 tied its lowest record. In 1995, April tied its record high and September set a new record high. A temperature of -44.4°C set the new record low temperature for March. The barometric pressure for 1994 was close to normal; however, 1995 was 2.0 hPa above the 17-year average. The summertime precipitation measured 85 mm in 1994 and 53 mm in 1995.

TABLE 1.8. BRW 1994 and 1995 Monthly Climate Summary

	Jan.	Feb.	March	April	May	June	July	Aug.	Sept.	Oct.	Nov.	Dec.	Year
							1994
Prevailing wind	ENE	ESE	ENE	ENE	ENE	W	E	ESE	NE	ENE	ENE	NE	ENE
direction
Average wind	8.8	7.2	5.9	4.2	6.1	4.0	4.3	5.0	5.6	4.3	6.0	4.4	5.5
speed (m s-1)
Maximum wind	17	20	13	13	12	9	12	13	14	13	19	14	20
speed* (m s-1)
Direction of max.	67	95	73	72	64	270	90	231	264	71	66	210	95
wind* (deg.)
Average station	1028.5	1026.5	1016.1	1020.1	1014.6	1011.3	1010.0	1009.2	1012.3	1009.5	1006.9	1006.5	1014.3
pressure (hPa)
Maximum pressure*	1050	1050	1036	1036	1025	1023	1024	1030	1027	1022	1032	1025	1050
(hPa)
Minimum pressure*	1003	1003	995	1006	998	1001	995	995	998	991	980	987	980
(hPa)
Average air	-23.0	-23.2	-28.1	-17.8	-7.7	-0.3	3.6	5.5	-3.2	-13.0	-22.9	-27.2	-13.1
temperature (°C)
Maximum temperature*	-14	-2	-11	-2	2	9	17	20	7	-3	-6	-7	20
(°C)
Minimum temperature*	-35	-36	-40	-33	-18	-11	-3	-3	-12	-31	-36	-44	-44
(°C)
Average dewpoint	-26.0	-25.6	-30.9	-19.7	-9.1	-1.3	2.5	3.7	-5.0	-14.4	-25.1	-29.7	-15.1
temperature (°C)
Maximum dewpoint	-16	-4	-13	-4	0	8	11	15	7	-3	-7	-7	15
temperature (°C)
Minimum dewpoint	-38	-39	-43	-36	-19	-12	-3	-9	-13	-34	-40	-48	-48
temperature (°C)
Precipitation (mm)	0	0	0	0	2	1	15	48	3	0	0	16	85
							1995
Prevailing wind	ENE	E	ENE	ENE	ENE	NE	E	ENE	ENE	ENE	ENE	ENE	ENE
direction
Average wind	4.8	5.1	5.4	5.2	5.4	3.8	5.1	4.3	5.7	6.6	4.2	4.8	5.0
speed (m s-1)
Maximum wind	13	16	15	13	13	9	12	9	13	14	16	16	16
speed* (m s-1)
Direction of max.	104	50	112	226	58	258	74	246	72	64	292	72	50
wind* (deg.)
Average station	1010.4	1025.5	1023.6	1014.9	1017.5	1012.7	1012.4	1011.2	1011.2	1013.3	1020.7	1019.8	1016.0
pressure (hPa)
Maximum pressure*	1025	1042	1040	1024	1036	1028	1022	1025	1030	1025	1036	1034	1042
(hPa)
Minimum pressure*	986	1002	1002	997	1003	1000	1003	999	990	1001	1001	1002	986
(hPa)
Average air	-24.3	-26.8	-27.4	-13.7	-4.5	1.2	2.8	1.7	1.7	-7.2	-15.1	-24.5	-11.4
temperature (°C)
Maximum temperature*	-4	-7	-3	2	2	16	17	14	16	-1	-2	-12	17
(°C)
Minimum temperature*	-44	-46	-44	-35	-11	-6	-2	-3	-4	-27	-29	-35	-46
(°C)
Average dewpoint	-26.6	-29.4	-29.9	-15.2	-4.9	-0.9	0.9	1.4	0.4	-8.9	-16.1	-26.2	-12.8
temperature (°C)
Maximum dewpoint	-5	-8	-3	0	0	0	11	10	10	-2	-2	-12	11
temperature (°C)
Minimum dewpoint	-49	-50	-49	-37	-12	-7	-6	-5	-6	-28	-31	-37	-50
temperature (°C)
Precipitation (mm)	0	0	0	1	0	15	28	5	3	0	0	0	53

Instrument heights: wind, 10.5 m; pressure, 9.5 m (MSL); air temperature, 2.2 m; dewpoint temperature, 2.0 m. Wind and temperature instruments are on a tower 25 m northeast of the main building.

*Maximum and minimum values are hourly averages.

Mauna Loa

The climatology of MLO is best understood when it is considered in two distinctive wind direction regimes, the night (downslope) period (1800-0559 Hawaiian Standard Time (HST)) and the day (upslope) period (0600-1759 HST). The 17-year night and day wind roses illustrate the two distinct wind patterns (Figure 1.4).

Night Regime. The 17-year wind rose (Figure 1.4) shows that 91.2% of all winds observed had a southerly component. The percentage of occurrence of southerly winds in 1994 was 94.2% (Figure 1.5) and 90.9% in 1995 (Figure 1.6). Pressure gradient controlled winds (WS>10 ms-1) from predominately westerly and south-easterly directions occurred 5.0% of the time in 1994 and 8.4% in 1995 while the 17-year record shows a 6.1% occurrence. The annual average wind speed for both 1994 and 1995 was not significantly different from the long-term mean (Tables 1.9 and 1.10). The upslope or northerly component winds (north-northwest through east-northeast) that occurred 2.0% of the time in 1994 and 1.9% in 1995, are the result of daytime, upslope flow extending into the early evening hours.

Day Regime. The 1994 and 1995 wind roses (Figures 1.5 and 1.6) indicate that winds from the west-northwest through east-northeast occurred 58.4% and 55.4% of the time respectively, compared with the expected occurrence of 58.5% indicated by the 17-year climatology. Pressure gradient controlled winds (WS>10 ms-1) occurred 4.1% of the time in 1994 and 8.7% in 1995 while the 17-year average shows an expected occurrence of 5.7%. In 1994, the pressure gradient winds, which are usually associated with storms, followed the expected pattern of fewer occurrences during the day regime. In 1995, these winds had approximately the same number of occurrences in the day and night regimes. The day wind rose is more uniformly distributed in the light wind classes than the night wind rose. This is due to the occurrence of variable wind directions during the transition periods at dawn and dusk, most of which are included in this regime.

The average ambient temperature for 1994 and 1995 (Tables 1.9 and 1.10), combining both the day and night records, was 7.8°C and 8.4°C respectively, both considerably higher than the long-term average of 7.0°C. September 1995 set a new record high temperature for the month. The January 1994 and November 1995 average wind speeds set new minimums for the month. The barometric pressure for 1994 and 1995 (679.7 hPa and 680.0 hPa respectively) were both lower than the long-term average pressure of 680.5 hPa. July 1994 and March 1995 each tied its record minimum pressure for those months and April 1995 set a new record minimum for the month. The precipitation amounts for 1994 and 1995 (438 mm and 188 mm respectively) were both significantly lower than the long-term average amount of 500 mm. The 1995 amount is the lowest amount ever received at the station.

Fig. 1.5. Wind roses of the surface winds for MLO for 1994 night (left) and day (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes.

Fig. 1.6. Wind roses of the surface winds for MLO for 1995 night (left) and day (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes.

TABLE 1.9. MLO 1994 Monthly Climate Summary

	Jan.	Feb.	March	April	May	June	July	Aug.	Sept.	Oct.	Nov.	Dec.	Year
							Night
Prevailing wind	SW	SW	SW	SSE	SSE	SSE	SSE	SSE	SSE	SSE	SSE	SSE	SSE
direction
Average wind	3.7	4.3	4.8	4.1	4.4	3.4	5.9	4.1	3.9	3.3	5.4	6.5	4.5
speed (m s-1)
Maximum wind	12	12	13	12	13	10	16	14	13	9	13	17	17
speed* (m s-1)
Direction of max.	248	241	129	150	148	157	153	154	155	166	158	143	143
wind* (deg.)
Average station	678.1	677.9	679.1	679.6	680.2	680.4	680.6	680.9	680.0	679.6	679.8	680.3	679.7
pressure (hPa)
Maximum pressure*	682	682	684	683	683	684	683	684	683	683	682	684	684
(hPa)
Minimum pressure*	675	673	672	676	678	678	677	678	677	676	677	677	672
(hPa)
Average air	4.0	3.7	4.7	5.5	6.5	7.1	7.7	7.1	6.7	6.5	4.8	6.0	5.9
temperature (°C)
Maximum temperature*	10	9	12	11	12	15	13	13	11	10	10	11	15
(°C)
Minimum temperature*	0	0	0	1	1	2	4	3	3	3	1	2	0
(°C)
Average dewpoint	-16.7	-8.6	-14.3	-17.6	-13.5	-11.1	-6.1	-3.7	-3.9	-12.1	-9.0	-22.8	-11.7
temperature (°C)
Maximum dewpoint	4	5	4	4	7	9	8	9	8	6	4	-3	9
temperature (°C)
Minimum dewpoint	-32	-24	-30	-29	-30	-29	-24	-16	-18	-29	-29	-32	-32
temperature (°C)
Precipitation (mm)	38	23	22	0	0	1	13	4	7	0	31	0	140
							Day
Prevailing wind	NW	NNW	NW	NNW	NNW	NNW	ESE	NNW	NNW	NNW	SE	SE	NNW
direction
Average wind	3.9	4.3	4.4	3.5	3.7	2.8	5.0	3.7	3.1	2.7	4.5	5.8	4.0
speed (m s-1)
Maximum wind	12	12	15	13	13	8	15	13	11	10	13	16	16
speed* (m s-1)
Direction of max.	259	214	104	141	153	106	142	147	152	160	142	124	124
wind* (deg.)
Average station	678.1	677.9	679.1	679.7	680.3	680.6	680.8	681.0	679.9	679.6	679.7	680.3	679.8
pressure (hPa)
Maximum pressure*	682	683	684	683	682	684	683	683	683	683	683	684	684
(hPa)
Minimum pressure*	675	673	672	677	678	678	677	678	677	676	677	677	672
(hPa)
Average air	7.3	6.5	8.3	9.8	10.6	11.2	11.4	11.2	10.3	10.4	7.9	10.2	9.7
temperature (°C)
Maximum temperature*	12	13	16	15	15	17	16	15	15	15	14	16	17
(°C)
Minimum temperature*	0	0	0	2	3	4	5	4	4	3	1	2	0
(°C)
Average dewpoint	-11.7	-5.7	-8.9	-9.6	-6.1	-4.4	-1.6	-0.3	0.6	-5.9	-4.6	-18.4	-6.5
temperature (°C)
Maximum dewpoint	6	6	6	8	8	9	9	9	10	8	7	2	10
temperature (°C)
Minimum dewpoint	-32	-24	-30	-28	-28	-27	-22	-18	-21	-26	-27	-31	-32
temperature (°C)
Precipitation (mm)	29	42	38	0	0	10	19	56	58	12	34	0	298

Instrument heights: wind, 10.0 m; pressure, 3398.4 m (MSL); air temperature, 2.0 m; dewpoint temperature, 2.0 m. Wind and temperature instruments are on a tower 15 m southwest of the main building.

*Maximum and minimum values are hourly averages.

TABLE 1.10. MLO 1995 Monthly Climate Summary

	Jan.	Feb.	March	April	May	June	July	Aug.	Sept.	Oct.	Nov.	Dec.	Year
							Night
Prevailing wind	SE	WSW	WSW	SW	SE	SE	SSE	SE	SSE	SE	SSE	SSE	SE
direction
Average wind	5.4	7.0	6.5	6.1	4.5	4.4	3.8	3.9	3.5	4.3	3.8	4.4	4.8
speed (m s-1)
Maximum wind	17	15	16	16	13	12	11	11	11	15	13	14	17
speed* (m s-1)
Direction of max.	249	241	224	224	241	164	169	164	141	140	152	160	249
wind* (deg.)
Average station	680.0	677.4	678.7	678.4	680.2	681.1	680.6	680.3	680.9	680.1	680.4	680.8	679.9
pressure (hPa)
Maximum pressure*	683	681	684	682	684	684	683	683	684	684	684	684	684
(hPa)
Minimum pressure*	677	673	669	672	677	678	678	678	678	677	677	676	669
(hPa)
Average air	5.8	4.2	5.7	5.7	6.5	8.8	8.1	7.3	8.5	6.9	5.6	5.5	6.6
temperature (°C)
Maximum temperature*	11	11	13	11	11	14	14	13	14	13	10	11	14
(°C)
Minimum temperature*	1	-1	-1	0	2	5	2	2	3	1	2	1	-1
(°C)
Average dewpoint	-12.8	-15.0	-15.0	-12.5	-12.7	-15.9	-11.2	-13.1	-15.2	-14.7	-5.5	-12.3	-13.0
temperature (°C)
Maximum dewpoint	5	3	1	5	8	7	8	7	7	6	6	6	8
temperature (°C)
Minimum dewpoint	-30	-38	-30	-32	-28	-25	-24	-27	-28	-29	-24	-31	-38
temperature (°C)
Precipitation (mm)	5	18	5	1	1	0	3	0	0	0	12	3	49
							Day
Prevailing wind	WSW	WNW	W	NNW	NNW	NE	NE	NE	NE	NNW	NNW	NNW	NNW
direction
Average wind	5.1	7.1	6.5	6.5	4.7	3.8	3.6	3.5	3.1	3.8	3.0	3.4	4.5
speed (m s-1)
Maximum wind	17	14	17	16	13	10	14	12	13	13	13	12	17
speed* (m s-1)
Direction of max.	248	297	233	233	251	144	148	155	125	147	155	234	248
wind* (deg.)
Average station	680.0	677.5	678.8	678.4	680.3	681.2	680.8	680.5	681.0	680.2	680.3	680.7	680.0
pressure (hPa)
Maximum pressure*	683	682	684	682	684	683	684	683	684	683	684	685	685
(hPa)
Minimum pressure*	677	673	670	673	677	678	678	678	678	677	678	676	670
(hPa)
Average air	9.4	7.6	9.7	9.7	10.6	13.0	11.7	11.2	12.2	10.5	8.9	9.0	10.3
temperature (°C)
Maximum temperature*	16	15	17	15	16	17	16	17	19	17	14	15	19
(°C)
Minimum temperature*	1	-1	1	2	3	7	5	4	5	2	2	2	-1
(°C)
Average dewpoint	-10.4	-10.9	-10.6	-7.9	-4.7	-7.7	-2.8	-3.8	-5.8	-7.1	-2.2	-7.7	-6.8
temperature (°C)
Maximum dewpoint	5	4	6	6	9	8	9	10	9	7	8	6	10
temperature (°C)
Minimum dewpoint	-30	-38	-30	-30	-26	-24	-22	-27	-26	-29	-23	-31	-38
temperature (°C)
Precipitation (mm)	7	16	7	10	11	0	8	16	9	10	25	19	140

Instrument heights: wind, 10.0 m; pressure, 3398.4 m (MSL); air temperature, 2.0 m; dewpoint temperature, 2.0 m. Wind and temperature instruments are on a tower 15 m southwest of the main building.

*Maximum and minimum values are hourly averages.

Samoa

A comparison of SMO's 1994 and 1995 wind roses (Figure 1.7) to that of the 17-year period (Figure 1.8) shows a lower percentage (57.7%) of "clean air" sector winds (north-northwest through southeast) in 1994 while 1995 shows a higher percentage (61.2%) than the long-term average of 59.8%. The occurrence of winds in the 10 ms-1 or greater class was 6.7% in 1994 and 3.9% in 1995 while the expected occurrence based on the 17-year record is 4.9%. The average wind speed for both 1994 and 1995, 4.8 ms^-1 (Table 1.11) is close to normal. The monthly average for May 1995 set a new minimum record for the month.

The average ambient temperature for 1994 and 1995 was 27.3°C and 27.0°C respectively, which are both very close to the 17-year average of 27.1°C. Five new record highs were set in 1994 that occurred during the months of February through June with a new record low occurring during the month of June. In 1994, temperatures during the first 7 months were above their monthly means and the other 5 months were below their respective monthly means. The average barometric pressure for 1994 and 1995 (Table 1.11) was 1.2 hPa and 1.9 hPa above the 17-year average of 999.3 hPa at Cape Matatula respectively. The months of January and June in 1995 both tied the record maximum pressure for the month. The amount of precipitation in 1994 measured near normal amounts during the first 6 months of the year while the last 6 months were wetter than normal. In 1995, the precipitation amount was again near normal for the first 6 months; however, the last 6 months were drier than normal.

Fig. 1.7. Wind rose of surface winds for SMO for 1994 (left) and 1995 (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes.

Fig. 1.8. Wind rose of surface winds for SMO for 1977-1993. The distribution of resultant wind direction and speed are given in units of percent occurrence for the 17-year period. Wind speed is displayed as a function of direction in three speed classes.

TABLE 1.11. SMO 1994 and 1995 Monthly Climate Summary

	Jan.	Feb.	March	April	May	June	July	Aug.	Sept.	Oct.	Nov.	Dec.	Year
							1994
Prevailing wind	SE	NW	SSE	NW	SE	SSE	SE	SE	SSE	SE	SE	SSE	SE
direction
Average wind	3.8	3.1	3.5	3.7	4.6	6.5	5.5	7.3	4.8	3.7	6.5	4.0	4.8
speed (m s-1)
Maximum wind	9	8	14	14	12	13	13	15	11	12	14	11	15
speed* (m s-1)
Direction of max.	310	140	334	315	144	138	146	145	112	113	138	151	145
wind* (deg.)
Average station	998.7	999.3	999.5	999.1	1001.0	1001.8	1001.2	1002.8	1002.7	1001.8	1000.3	997.8	1000.5
pressure (hPa)
Maximum pressure*	1003	1003	1004	1003	1005	1006	1004	1007	1007	1005	1004	1003	1007
(hPa)
Minimum pressure*	991	996	992	994	996	998	998	997	999	998	994	992	991
(hPa)
Average air	28.7	29.5	29.1	28.2	27.7	26.9	26.3	25.5	25.9	26.4	26.8	27.3	27.3
temperature (°C)
Maximum temperature*	35	37	36	36	34	34	29	27	28	29	29	30	37
(°C)
Minimum temperature*	23	23	24	23	21	23	23	23	23	23	23	24	21
(°C)
Average dewpoint	23.2	23.5	23.8	23.6	22.4	22.8	23.0	21.7	22.8	24.0	23.8	25.0	23.3
temperature (°C)
Maximum dewpoint	26	25	26	26	25	25	26	25	25	26	26	27	27
temperature (°C)
Minimum dewpoint	21	22	22	20	20	19	18	15	17	21	20	23	15
temperature (°C)
Precipitation (mm)	215	121	181	288	283	84	233	200	65	299	201	332	2503
							1995
Prevailing wind	SSE	SE	ESE	SSE	SSE	SE	SE	SE	SE	SSE	SSE	E	SSE
direction
Average wind	5.9	3.1	3.2	3.1	3.4	6.6	6.1	6.1	6.9	5.7	4.1	2.1	4.8
speed (m s-1)
Maximum wind	14	10	8	10	12	11	15	13	13	13	12	6	15
speed* (m s-1)
Direction of max.	322	138	323	118	156	153	124	164	130	130	87	64	124
wind* (deg.)
Average station	998.7	1000.1	1000.6	1000.0	1001.0	1002.9	1002.5	1002.9	1003.7	1001.8	1000.2	999.0	1001.2
pressure (hPa)
Maximum pressure*	1005	1004	1005	1003	1004	1007	1006	1007	1007	1006	1005	1005	1007
(hPa)
Minimum pressure*	992	995	996	997	997	999	999	999	1000	998	995	995	992
(hPa)
Average air	27.2	27.7	27.8	27.3	27.1	27.2	26.8	26.4	26.4	26.3	26.8	27.6	27.0
temperature (°C)
Maximum temperature*	29	30	29	30	30	29	28	30	29	28	29	30	30
(°C)
Minimum temperature*	24	24	24	23	23	24	24	23	23	24	23	25	23
(°C)
Average dewpoint	23.9	24.4	24.6	23.9	24.0	23.4	23.5	23.3	22.7	22.9	23.9	23.8	23.7
temperature (°C)
Maximum dewpoint	26	27	26	26	26	26	25	25	25	25	26	27	27
temperature (°C)
Minimum dewpoint	21	21	22	20	22	20	21	20	17	20	22	21	17
temperature (°C)
Precipitation (mm)	288	128	192	258	183	85	143	273	119	103	149	39	1960

Instrument heights: wind, 13.7 m; pressure, 78.5 m (MSL); air temperature, 14.0 m; dewpoint temperature, 12.8 m. Wind and temperature instruments are on Lauagae Ridge, 110 m northeast of the main building.

*Maximum and minimum values are hourly averages.

South Pole

The distribution of the surface wind direction in 1994 and 1995 (Figure 1.9) shows a higher percentage of "clean air" sector (grid north-northwest through east-southeast) winds (95.0%) in 1994 while 1995 showed a lower percentage (92.4%) from the than the 17-year average (93.9%) (Figure 1.10). A lower percentage of winds in the 10 ms^-1 class (3.5% in 1994 and 3.1% in 1995) were observed as compared to the 17-year average (4.0%). The average wind speeds for 1994 and 1995 were very close to the long-term average of 5.4 ms^-1. May 1995 tied its maximum wind speed record. The monthly average wind speed for January 1995 set a new minimum for the month.

The average temperature for 1994 (-49.5°C) and 1995 (-49.7°C) were both colder than the 17-year average of -49.0°C. September 1994 set a new record maximum and July 1995 tied its record maximum temperature for the month. January 1995 tied its record minimum temperature for the month. The minimum temperature of -74°C for 1994 occurred in May and September while the minimum of -77°C in 1995 occurred in September. The annual average station pressures for 1994 (679.7 hPa) and 1995 (679.6 hPa) (Table 1.12) were both above the 17-year average of 679.1 hPa. June 1994 tied its record high pressure for the month and July 1995 set a new record high pressure.

Fig. 1.9. Wind rose of surface winds for SPO for 1994 (left) and 1995 (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes.

Fig. 1.10. Wind rose of surface winds for SPO for 1977-1993. The distribution of resultant wind direction and speed are given in units of percent occurrence for the 17-year period. Wind speed is displayed as a function of direction in three speed classes.

TABLE 1.12. SPO 1994 and 1995 Monthly Climate Summary

	Jan.	Feb.	March	April	May	June	July	Aug.	Sept.	Oct.	Nov.	Dec.	Year
							1994
Prevailing wind	N	ENE	N	E	N	NE	ENE	NE	E	NNE	NNE	ENE	NNE
direction
Average wind	5.3	4.7	6.2	4.7	5.8	6.2	6.0	5.8	6.6	5.7	4.3	3.4	5.4
speed (m s-1)
Maximum wind	11	10	12	10	13	14	12	12	13	10	9	7	14
speed* (m s-1)
Direction of max.	359	5	13	40	7	214	20	359	30	17	25	116	214
wind* (deg.)
Average station	688.3	680.0	674.7	681.9	674.8	691.2	675.4	670.9	676.8	677.3	685.1	680.9	679.7
pressure (hPa)
Maximum pressure*	697	687	684	696	693	705	691	687	697	693	693	690	705
(hPa)
Minimum pressure*	679	669	664	666	661	677	660	653	651	663	675	672	651
(hPa)
Average air	-28.3	-44.0	-53.7	-57.3	-58.3	-54.9	-62.5	-58.5	-56.9	-51.3	-37.4	-28.7	-49.5
temperature (°C)
Maximum temperature*	-23	-35	-37	-38	-35	-37	-45	-37	-31	-34	-27	-22	-22
(°C)
Minimum temperature*	-37	-55	-64	-70	-74	-68	-72	-73	-74	-63	-47	-34	-74
(°C)
Average dewpoint	-31.3	-51.1	-59.5	-62.2	-59.3	-59.7	-65.9	-61.0	-56.7	-57.3	-44.5	-34.1	-52.6
temperature (°C)
Maximum dewpoint	-24	-42	-42	-42	-39	-41	-50	-41	-34	-38	-33	-26	-24
temperature (°C)
Minimum dewpoint	-52	-63	-71	-71	-71	-71	-71	-71	-71	-70	-56	-41	-71
temperature (°C)
Precipitation (mm)	0	0	0	0	0	0	0	0	0	0	0	0	0
							1995
Prevailing wind	E	N	NNE	N	ESE	E	NE	E	ESE	ENE	N	N	N
direction
Average wind	3.0	5.1	5.7	6.2	5.8	5.1	6.2	5.4	4.8	6.6	5.3	3.6	5.2
speed (m s-1)
Maximum wind	7	10	11	13	14	10	15	12	11	13	10	8	15
speed* (m s-1)
Direction of max.	351	22	23	340	9	4	28	36	6	11	3	6	28
wind* (deg.)
Average station	681.9	682.1	682.0	676.6	671.9	680.5	686.2	676.3	671.4	679.3	683.7	683.6	679.6
pressure (hPa)
Maximum pressure*	691	692	690	691	688	697	705	695	685	692	693	692	705
(hPa)
Minimum pressure*	675	673	670	655	662	666	673	660	662	669	673	678	655
(hPa)
Average air	-31.3	-40.3	-52.6	-58.3	-59.0	-58.6	-55.6	-61.8	-64.6	-48.9	-37.9	-27.3	-49.7
temperature (°C)
Maximum temperature*	-24	-28	-40	-44	-37	-39	-34	-49	-50	-31	-27	-20	-20
(°C)
Minimum temperature*	-38	-51	-66	-74	-76	-72	-68	-74	-77	-66	-49	-33	-77
(°C)
Average dewpoint	-38.2	-46.0	-58.1	-63.8	-65.6	-63.7	-61.7	-70.1	-71.8	-54.3	-42.3	-31.1	-54.7
temperature (°C)
Maximum dewpoint	-27	-32	-44	-49	-42	-43	-37	-54	-55	-35	-30	-23	-23
temperature (°C)
Minimum dewpoint	-47	-60	-73	-81	-85	-79	-75	-81	-86	-73	-55	-37	-86
temperature (°C)
Precipitation (mm)	0	0	0	0	0	0	0	0	0	0	0	0	0

Instrument heights: wind, 10.0 m; pressure, 2841 m (MSL); air temperature, 2.0 m; dewpoint temperature, 2.0 m. Wind and temperature instruments were on a tower 100 m grid east-southeast of the CAF until November 9, 1995, when the tower was moved to a location 183 m grid northeast of the CAF.

*Maximum and minimum values are hourly averages.

1.5.2. METEOROLOGY OPERATIONS

New Dewpoint Sensors and Electronics Upgrade

Three new hygrothermometers and transmit logic boards from Technical Services Laboratory (TSL) were purchased for the BRW, SMO, and SPO observatories. The model 1088-400 replaced the model 1063-104 at BRW in August 1995, at SMO in December 1995, and at SPO in November 1995. The new model hygrothermometer was installed at MLO when the new data acquisition was initially installed in October 1993. The upgrade improvements include tighter tolerances in the electronic components for greater data accuracy, better radiation shielding of the temperature sensors, and a higher volume of ambient air flow past the temperature sensors to minimize the effects of heat buildup in the sensor housing.

SPO Meteorological Sampling Tower Relocation and Sensor Recalibrations

Prior to moving the meteorological sampling tower, all of the SPO meteorological sensors listed in Table 1.7, except for the Setra pressure transducer, were removed and located on the grid north (upwind) railing of the clean air facility (CAF). The alignment of the wind direction sensor was approximate. From November 9 through November 22, 1995, the tower was disassembled, moved from a location at approximately 100 m along a grid 110 from the current CAF to a location approximately 183 m grid northeast of the CAF, and reassembled. The new location will put the tower approximately 91 m at grid 340 from the new CAF. Nearly two full 2-m sections were buried under snow at the old location. The increase in snow height at the old location was 267 mm per year on average since 1983. The move resulted in a gain of 3 to 3.4 m of tower height and an ability to use all 24 m of the tower. During this time, the new TSL 1088-400 hygrothermometer was put into operation and calibrated. The platinum resistance probes (RTDs) were calibrated by using an ice bath at 0°C. From November 22 through December 2, 1995, a new cable for the RS-485 data communications line was prepared, and hardware for the AC power and the meteorological sensors was installed on the tower at the new location. The azimuth orientation of the anemometer was set by using a solar azimuth alignment tool and tables of solar position. Table 1.13 describes the sensor heights before and after the move of the sampling tower.

TABLE 1.13. SPO Sensor Instrument Heights Before and After Tower Move

Instrument	Height Before Move (m)	Height After Move (m)
Primary anemometer	10.0	10.0
Pressure transducer	2841.0	2841.0
Air temperature A	1.1	2.0
Air temperature B	20.0	22.0
Air temperature C	1.6	2.0
Dewpoint temperature	1.6	2.0
Non-aspirated temperature	1.4	2.0

Heights are in meters above snow surface, except for barometric pressure, which is with respect to MSL.

Refer to Table 1.7 for sensor information.

[back] [contents] [next]