A Study of the Characteristics of Atmospheric Water Vapor and Its Relationship with
Precipitation Using GPS Data
Su lijuan1 Dabuxilatu1 Lu shiqing1 Deng xiaodong2 Yan bing1
(1 Inner Mongolia Meteorological Institute, Hohhot 010051, China; 2 Inner Mongolia Center of Ecology and
Agriculture Meteorology, Hohhot 010051, China)
The technology of sensing water vapor using
2.
Data and quality analysis
ground GPS is a new method of the atmosphere
observation. It senses the content of water vapor in the
This data used in the paper began from January 1
atmosphere using high-precision ground GPS, through
to October 31 in 2008. It included the GPS/MET
measuring the GPS signals about the amount of delay
monitoring data, the meteorological sounding data, the
in the atmosphere. The sensing of water vapor of
ground
ground GPS has high resolution and millimeter level
ground-based
accuracy, which can fill the lack of data’s accuracy in
collected by the instrument of GPS/MET at the rate of
time and space to provide fast-changing water vapor
one time for 15 seconds; the high degree of the satellite
information. This information is very important on the
was 15. We received the real-time data from each
choice of weather modification operating conditions
observe station through the network , and the data file
and precipitation forecast. With using GPS equipment,
was formatted every 15 minutes in every station. And at
we finished the water vapor observation and tested the
the same time, we did some management of the data to
quality of the data. Then we analyzed of the
convert the raw data into the Rinex format needed in
relationship
between
the
the solver package of the vapor.
precipitation
through
the
monthly
changes
comparison
with
and
the
calculated sounding data of water vapor.
observation
data
precipitation
and
data.
The
conventional
data
was
Meanwhile, to text the validity of the data , this
study used the professional data quality analysis
software Translate Edit Quality Check(TEQC) to
1.
GPS / MET observation experiments of water
conducted a data quality test, the data was concluded
by the observation data of 10 consecutive days from
vapor
January 1 to 10 in 2008, and 960 data files from every
The tests chosed the observation points equipped with
station. In this text, we got the average data quality for
sounding, ground-based observation of meteorological
each station, and statistically analyzed the data quality
services business and the LAN of meteorological
of the three stations.
services business. The three test stations were laid in:
The effective acceptance ratio of the research
Inner Mongolia Meteorological Institute of Hohhot at N
institute station is 98.88%, mp1 is 0.22, mp2 is 0.24,
40°50’26.7 ", E111°39’16.5" and altitude 1050.551m;
and the effective acceptance ratio of Baita is 91.01%,
Hohhot Baita Airport at N 40°51’34.2 ", E 111°49’33.7 "
mp1 is 0.28, mp2 is 0.30, while the
and altitude 1076.451 m; Erenhot weather station at N
Erlianhaote is 99.93%、0.13、0.24, respectively.
43°38’53.8", E111° 58’5.5 " and elevation 941.5 m.
According to the principles of data quality inspection, if
There
ground
the effective acceptance ratio of the data exceeds over
Mongolia
85% and both mp1and mp2 are all less than 0.5, then
were
observation
the
sounding
station
station
around
and
Inner
station of
GPS
the data can be used effectively. Therefore, the
observation points were located in the sounding station
observation data of the three stations are all standard
and ground-based observations of the Bureau of
effective available.
Meteorological
Institute
of
Hohhot.
The
Meteorology Erenhot. Hohhot Baita Airport is equipped
with six elements ground automatic observation
3. Calculation method
stations.
Gamit software was used on GPS/data processing,
and IGS actual star calendar was adopted to calculate
was 0.1156 mm slightly higher. After compared water
the zenith per hour delay. Each hour, zenith the
vapor retrieved by GPS / MET with water vapor
troposphere delay is the sum of zenith statics delay Zh
sounding calculation, we found that overall water vapor
and wet Zw and a delay. It can be written as:
retrieved by GPS / MET is slightly higher than the value
∆D z =
∫ (n (s ) − 1)ds =
of sounding calculation. The difference of value
L
10 − 6 ∫ 77 .6
z
pd
e
e ⎞
⎛
dz + 10 − 6 ∫ ⎜ 27 + 3 .73 × 10 5 2 ⎟dz = Z h + Z w
z
T ⎠
T
⎝ T
changes with seasonal changes was not obvious, and it
was very stable as well as comparable. The water
Zenith statics delay Zh can be calculated by ground
vapor value from white tower was 1.96 mm higher than
pressure p0 (hpa):
sounding calculation and 2.0767 mm higher than
Z
= (2 . 279 ± 0 . 0024
h
)
p0
f (λ , H
research institutes. Average GPS/MET listed inversion
)
of vapor value was 2.0189 mm higher than sounding
f (λ , H ) = (1 − 0.00266 cos(2λ ) − 0.00028 H ) ,
calculation value. According to GPS/MET listed
λ is for
inversion of vapor map, showing that water vapor
the latitudes, H is for altitude (km).
content standing on Hohehot state on average monthly
Wet delay Zw is calculated by the following formula:
from high to low in turn for July, August, June,
Z
w
= 10
−6
⎛
∫ ⎜⎝ 77
z
.6
e
+ 3 . 73 × 10
T
5
T
e ⎞
dz = 10
2 ⎟
⎠
dz
September, April, May, October, March, January, on
e
∫ z T dz
average, summer water vapor content was the most as
e
−6
• PW R v k 2' + k 3
∫T
z
24.79 mm, followed by autumn as 14.1 mm, spring as
Pw is for atmospheric precipitation, Rv =
-1
9.55 mm, winter was the least as less than 5 mm.
-1
461.495J·kg ·K , as the gas constant of water vapor.
T
m
=
⎛
⎜
⎝
∫
∫
⎞
⎟
⎠
e
T
e
⎛
⎜
⎝
T
dz
⎞
⎟
⎠
2
dz
20
Tm = a + b • Ts
Bevis
gave the experience: a =70.2， b =0.72[1]。.
Therefore, the atmosphere rainfall can be calculated by
15
10
5
0
1m
the following formula:
PW = ∏ Z w ， ∏
= 10
gps-(mm)白塔
shuiqi-ave-探空
gps-(mm)科研所
25
Tm is average temperature, which can be determined
by experience coefficient:
mm 30
6
[Rv[
k3
+ k 2' ]]
Tm
sounding calculated value
4m
5m
6m
7m
8m
9m
10m 月
sounding in Huhhot
mm 40
探空水汽mm
gpswv(mm)
降水总量
35
30
4.1 Contrast on monthly change of water vapor and
3m
Fig.1 Air vapor month trend from GPS contrast to
−1
4. Analysis of water vapor
2m
25
20
15
10
It can calculate a water vapor value calculated by
5
GPS/MET listed inversion each observatory each hour,
0
and then it can conclude the water vapor average value
daily and monthly.
Vapor curve were almost the same with each other
1m
2m
3m
4m
5m
6m
7m
8m
9m
10m 月
Fig.2 Air vapor month trend from GPS contrast to sounding in
Erlianhot and precipitation
by the two sets of instrument measurement inversion of
Overall the value of water vapor calculated by
vapor curve in White tower and Research institutes,
GPS/MET listed inversion was higher than that by
showing that the stability of GPS/MET listed instrument
sounding calculation, the absolute difference value was
was very good, and the gap was that research station
obviously with season change over time, and for the
basic present out of water vapor obviously was the
represent the time with precipitation. From the fig.4, the
same change trend on month changing, namely: the
characteristics of the water vapor changes can be show
gap between them is bigger with the increase of vapor,
in the precipitation mechanism, namely, there is a
too. After the gradually increased in January-July, it
certain stage of moisture accumulation before the
decreased with water vapor reduction. But difference
precipitation, and then produce precipitation only when
value percentage of water vapor (sounding) and the
water vapor accumulated to peak, because the water in
changing trend of water vapor, was by contrast, the
clouds may has reached saturation. In addition,
more water vapor, the smaller percentage value.
precipitation generated in the stage of water vapor
Overall the gap with water vapor value calculated by
decline, probably due to consumption of a large
GPS/MET listed and sounding calculation was higher in
number of water vapor. After the start of precipitation,
Erlianhot stood than that in Hohehot, average
the atmospheric total water vapor reduces quickly.
GPS/MET listed inversion of water vapor was 4.996
水汽（mm）
50
45
40
35
30
25
20
15
10
5
0
1 21 41 61 81 101 121 141 161 181 201 221 241 261 281 301 321 341 361 381
时序
mm higher than sounding calculation.
According to GPS/MET listed inversion of vapor
map, showing that water vapor content standing on
Erlianhot state on average monthly from high to low in
turn for July, June, August, September, May, April,
October, March, February, January. On average,
summer water vapor content was the most as 25.15
mm, followed by autumn as 12.75 mm, spring as 9.77
mm, winter was the least as 3.82 mm.
Fig.4 Air vapor sequence change from GPS on May
4.2 The relation between water vapor changes and
4.3 A case study
precipitation
It can be seen from Figure 3 that monthly changes
There’s been a big rainfall process in hohehot area
in average content of water vapor are in consistently
in July 30-31, 2008. This process started from the
with precipitation and the corresponding monthly
continuous rain at 11:00 on the 30th and the
precipitation is also higher when monthly mean water
precipitation has been maintained to 14:00 on 31th.
vapor is high, so which can explain that the content of
The total rainfall is 97mm, reached rainstorm level.
0:00 on July 29 to 7:00 on July 30. Purple line in the
affect weather.
figure represents the precipitation period.
30
180
月降水（mm）
160
25
two-gps-ave
140
20
120
100
平均水汽（mm）
Fig.6 shows the changing curves of water vapor from
precipitation and the selection of conditions in artificially
月降水量（mm）
water vapor has a good indication for the forecast of
15
80
10
60
40
5
20
0
0
1m
2m
3m
4m
5m
6m
7m
8m
9m 10m
月
水汽（mm）
50
45
40
35
30
25
20
15
10
5
0
0
Fig.3 Air vapor month trend from GPS contrast to precipitation
in Huhhot
Fig.4 shows the hourly changes of water vapor in
August in Huhhot. Purple dots marked in circles
5
10
15
20
25
30
35
时次
Fig.5 Air vapor change from 0:00 on July 29 to 7:00 on July
31
From fig.5 we can see that, water vapor began to
accumulate gradually at 0:00 on July 29. After the two
3)
Water vapor retrieved by GPS / MET is higher than
phases of accumulation water vapor reached to peak at
the sounding calculated value, In Hohhot stood
5:00 on July 30, then maintained 6hours and state rain
about high 2mm, in 4.996 mm Erlianhot standing
at 11:00. After the start of precipitation the water vapor
tall.
declined rapidly to lowest value at 2:00 on July 31, then,
4)
Water vapor retrieved by GPS / MET is closely
there are compensation mechanisms allow the
related to rainfall in this site. Before precipitation
accumulation of water vapor again. Precipitation
occurred there is a certain stage of the
remained until at 14:00 on the 31th.
accumulation of water vapor, and then produce
precipitation only when water vapor accumulated
5
Conclusion
to peak, because the water in clouds may has
reached saturation. In addition, precipitation
1)
2)
The three observatories quasi-geoids data is
generated in the stage of water vapor decline,
effective and reliable.
probably due to consumption of a large number of
The maximum average water vapor content
presents in summer, reaching about 25mm,
autumn, and spring followed, and the winter was
the lowest with only 5mm or less.
water vapor. After the start of precipitation, the
atmospheric total water vapor reduces quickly