1. Analysis of the Monterey Bay
Sea Breeze
Emily M Duvall
15 Sept 2003

2. Importance:
“Understanding the sea breeze is important because of who and what it affects: fire weather, air pollution, aviation, military operations, agriculture, recreation, urban development, shipping, and transportation (Banta, 1995). “
-See above;
The sea breeze also influences coastal currents, which affect coastal erosion and beach development, coastal marine ecosystems, and activities such as fishing and shellfishing.
It is one of the most studied atmospheric phenomena due to the heavy concentration of the world’s population along the coastline of oceans (Banta et al, 1993).
I choose to study the sea breeze because it is a part of my thesis work, which I begin next quarter with Dr. Nuss.
The purpose of this project was to collect, compare, and analyze data from the summer cruise.

3. Background
development of coastal thermal gradient
an onshore directed pressure gradient arises to which the air must respond by accelerating toward the coastline
typically form and begin their flow inland during the mid- to late- morning hours
circulation intensifies as solar heating reaches its maximum.
afternoon is the most active time of day
The basic forcing mechanism driving sea breeze circulations is the development of a coastal thermal gradient to which the wind responds.
A horizontal temperature gradient develops due to the differential radiative properties of the water and land surfaces.
This temperature gradient will produce a pressure gradient.
The warm air over land tends to lower the surface pressure relative to the unchanged or cooler boundary layer air over the water.
Thus, an onshore directed pressure gradient arises to which the air must respond by accelerating toward the coastline
Sea breezes typically form and begin their flow inland during the mid- to late-morning hours, when daytime temperature gradient between land and ocean is fairly strong.
The sea breeze circulation intensifies as solar heating reaches its maximum.
Afternoon is the most active time of day for this circulation, as sea breeze penetration reaches a maximum and winds are strongest.

4. Method of Investigation
Compare data between the meteorological measurements and Monterey Bay area surface stations.
Those measurements included:
1) rawinsonde profiles
2) ship’s sail data
3) surface stations

5. SURFACE STATIONS
MRY
ORD
SNS
(courtesy of Dick Lind)

6. Data and Method of Collection:
The present study will focus on three days: July 25, 26, and 27. The ship’s position and rawinsonde launches provide the best information to compare with other instrumentation.
Ft. Ord profiler information obtained from Dick Lind, NPS Dept. of Meteorology.
Surface station data obtained from Prof. Wendell Nuss, NPS Dept. of Meteorology.

7. Area of Collection (courtesy of J. Horne)
Surface-station measurements include: the NPS 915 MHz Profiler located at Fort Ord, station MRY (Monterey) located at 36.59o
o, and station SNS (Salinas) located at 36.66o –121.61o.
Rawinsonde launches were taken at the above locations.
It would have been nice to access data from a more inland and southern surface station, however it could not be acquired from Dr. Nuss.
(courtesy of J. Horne)

8. R/V POINT SUR Collection Platforms (SAIL) Wind Direction Time (UTC)
Wind Speed Air Temperature
Position Relative Humidity
Sea Surface Temperature

9. Collection Platforms
Rawinsonde:
Height
Temperature
Dew Point
Wind Speed
Wind Direction

10. Collection Platforms
Surface Stations
Wind Direction Time (UTC)
Wind speed Air Temperature
Position Dew point

11. Rawinsonde (MATLAB program provided by Guest):
Data Analysis
Rawinsonde (MATLAB program provided by Guest):
temperature and dew point vs height
wind speed and direction vs height
Surface station:
temperature and dew point vs time
wind speed and direction vs time
Ship:
temperature, dew point, sst vs time
Because the rawinsonde was launched from the ship but also returned to the surface, up and down components were plotted.
Each rawinsonde went to different heights, but since the sea breeze occurs at a lower level, the parameters were plotted up to 2000 m.
Dr. Nuss provided me with all the surface station data from July that he uses in his Monterey Bay analysis to generate plots of surface winds (located on the NPS Meteorology website), I had to manually extract SNS and MRY from all the files. Each file contained the numerous stations with its hourly observation. The hourly obs were extracted for both SNS and MRY to create a plot for each day.

12. Comparison of Data
25 JULY 2003

13. For each day, the rawinsonde profiles of temperature and dewpoint, wind speed and direction, ship’s temperature, dew point, and sst, and finally ship’s wind speed and direction were compared.
The launch on July 25 took place at 2345Z. This corresponds to approximately on the graphs.
2345 – converted to local time by subtracting 7 hrs /2400 to get a decimal. This decimal was added to .29 (the beginning of the time).
The rawinsonde shows westerly, northwesterly flow until approximately 1000 m, with the highest wind speeds (9 m/s) at 500 m.
The ship’s sensor indicates an air temperature of about 14.2 C, which is verified with the temperature reading obtained from the rawinsonde.
The ship’s sensor also indicates a westerly, northwesterly wind of about 3.5 m/s.
Keep in mind that the ship’s sensor was about 13 m above sea surface. (roughly)

14. The MRY station is indicating a wind speed of about 6 m/s with decreasing winds as time progresses. It also shows that the flow is from the west – northwest at the time of the launch.
MRY is showing a temperature of about 18 C, with decreasing temperatures as time progresses.
Salinas is indicating a wind speed of about 7.5 m/s with northwesterly winds
Salinas is showing a temperature of 18.5 C with decreasing temperatures in the next few hours.

15. Rawinsonde
2345Z
Because the launch was at 2345Z, the profiler data from July 24 and 25 is shown to illustrate the atmospheric environment surrounding the time of the rawinsonde launch.
The Ft. Ord profiler displays time increasing from right to left. The 25 July plot runs from 00Z to 2330Z. Since the launch took place at 2345Z, both the 24 and 26 July plots were looked at to verify conditions.
At the time of the rawinsonde launch, the profiler shows flow from the west up to about 900 meters with speeds of about 5 meters per second.
It also indicates a surface temperature of about 15 C.
A study by Banta observed two different sea breeze layers occurred on the same day. A shallow sea breeze began between 0900 and 1000 (LT) but remained less than 300 m deep. After 1200, the flow between 300 m and 1000 m reversed and began to flow onshore. The lower-level shear that had existed atop the shallower sea breeze at 300 m disappeared as the deeper sea breeze absorbed the shallower sea breeze.
This can be seen in the present study.

16. rawinsonde data shows onshore flow
Results for 25 July
rawinsonde data shows onshore flow
SAIL indicates westerly flow at the time of launch
data from the SAIL shows a change from southerly to westerly winds
wind shift is accompanied by a decrease in wind speed
SAIL indicates a decrease in air temperature
MRY displays a reversal of winds
Sea breeze cannot be deduced from SNS
The rawinsonde data shows onshore flow at the lower levels with a southerly flow aloft. The max wind speed occurred at 500 meters on the up route.
The ship’s sensor also shows onshore flow with a wind speeds fluctuating between 2 and 4 meters per second after the rawinsonde launch.
The ship’s sensor shows a change in direction of winds going to more westerly from southerly around The westerly winds last for a few hours.
The measured air temperature from the ship shows a decrease around the same time that there was a shift in winds. This shift in direction is accompanied by a decrease in winds. The wind speed increase lags the wind shift.
The onshore flow is verified with the Ft. Ord profiler.
MRY shows a reversal of winds at about the same time as the ship’s data, with a lag in the increase of wind speed, consistent with the ship. Once the winds are out of the west, the air temperature begins to decrease.
The sea breeze cannot be deduce from SNS because the winds are westerly to northerly throughout the day.

17. Comparison of Data
26 JULY 2003

18. First launch at 1758Z which converts to 1058 LT, or 207.73
Second launch at 2341Z which converts to 1641 LT, or
The rawinsonde shows a very shallow layer of westerly flow up to about 300 meters. There is a max wind speed of almost 6 meters per second at about 100 meters.
The second rawinsonde indicates westerly to northwesterly flow occurring up to approximately 800 meters, with a wind max of about 7 meters per second at 250 meters.

19. The ship’s sensor shows an increase in wind speeds around 1000 LT
The ship’s sensor shows an increase in wind speeds around 1000 LT. This increase in wind speeds lags the change in wind direction which occurs just a little earlier. The westerly winds last throughout the rest of the day.
The wind shift is accompanied by a rise in air temperature according to the SAIL data.

20. MRY shows an increase in wind speeds about the same time the ship does
MRY shows an increase in wind speeds about the same time the ship does. The increase lasts for several hours.
There is some indication of onshore flow early in the morning (0500-), but better indication of the afternoon sea breeze 1500.
The wind shift is associated with a decrease in temperature.
Salinas indicates a wind shift to westerly early in the morning, and remaining westerly throughout the day. The wind speed increase lags the change in direction.
It is hard to deduce a true sea breeze with this data, as illustrated in the previous day.

21. For the same reasons stated before, the 26 and 27 July plots are needed.
The profiler data shows a very shallow layer of westerly flow up to about 300 meters beginning at 1100 LT and lasting only a few hours.
The shallow layer seems to be absorbed by a much deeper sea breeze around 1400 LT. This layer reaches about 850 meters.
This characteristic of the sea breeze is fairly consistent with the previous day

22. SAIL data indicates westerly flow beginning earlier and persisting
Results for 26 July
rawinsonde data shows the very shallow layer of onshore flow early in the day with a deeper sea breeze in the afternoon
SAIL data indicates westerly flow beginning earlier and persisting
SAIL data displays an increase in air temperature after the wind shift
MRY shows some indication of westerly flow early that may correspond to that of the profiler
SNS shows westerly flow most of the day
The rawinsonde data is comparable to the profiler data in that it displays both the shallow and deep layers of onshore flow.
The ship’s sensors indicate that the onshore flow begins early in the morning and persisting throughout most of the day.
An increase in wind speed lags the change to onshore flow
There is an increase in air temperature after the wind shift according to the ship’s sensors.
MRY shows some indication of the shallow onshore flow observed in the profiler, and clearly depicts the afternoon sea breeze
SNS, however, shows the wind shift occurring only once – and is early in the morning.

23. Comparison of Data
27 JULY 2003

24. Rawinsonde launches took place at 1802Z (1102 LT) and 2348Z (1648 LT)
Rawinsonde launches took place at 1802Z (1102 LT) and 2348Z (1648 LT). This corresponds to and , respectively.
There is indication of shallow westerly flow, up to about 550 meters on the first launch. The wind speed are light and variable.
On the second launch, a much deeper layer of westerly flow exists up to about 1000 meters. The wind speeds have increased since the first launch.

25. The ship’s data indicates that there is a wind shift occurring around 1000 LT. These westerly winds last throughout the rest of the day.
The wind shift corresponds to an increase in wind speed
The sensor indicates a rise in air temperature after the wind shift.

26. MRY gives clear indication of an afternoon sea breeze
MRY gives clear indication of an afternoon sea breeze. The wind direction fluctuates so much in the morning that it is hard to deduce the morning shallow layer of onshore flow.
The temperature rises when the shift takes place, but then decreases.
Salinas indicates a sea breeze, beginning around the time of the first rawinsonde launch.
The temperature begins to decrease around this time as well.

27. The profiler data doesn’t display the shallow layer of onshore flow as well as it did in the previous days. It depicts onshore flow occurring around 1200 LT and persisting for several hours.
The level of onshore flow is up to 800 meters.

28. Rawinsonde data has evidence of the two different sea breeze layers
Results for 27 July
Rawinsonde data has evidence of the two different sea breeze layers
SAIL data indicates a one-time change of wind direction with an increase of speed
SNS has onshore flow beginning earlier than MRY
MRY shows an afternoon sea breeze
SNS onshore flow is persistent
Rawinsonde data supports Banta’s findings of the two different sea breeze layers occurring on the same day.
The ship’s sensors do not contain evidence of this, but display a early change of wind direction and increase in speed that lasts throughout most of the day.
The surface station data shows Salinas reporting onshore winds earlier than Monterey.
The onshore flow at Salinas lasts much longer than that of Monterey.

29. Rawinsondes give only single location data (Intrieri et al, 1990)
Remarks
Rawinsondes give only single location data
(Intrieri et al, 1990)
Surface stations do not measure in the vertical
Profiler and rawinsonde show depth
Coastal topography is complex (Banta, 1995)
Evidence of two layers
Because rawinsondes give only single location data, important details on the evolution and growth of the sea breeze remains unknown (Intrieri et al, 1990).
Surface stations do not measure in the vertical so the depth of the sea breeze could not be determined at these locations.
Only the profiler and rawinsonde show the depth of the onshore flow.
Because the topography of the California coast is highly complex, it is not surprising that the sea breeze here in Monterey Bay is also complex (Banta, 1995)
There is evidence of the two different sea breeze layers, as shown in previous research.
It is hard to deduce the spatial scale of the Monterey Bay sea breeze with the data presented here.

30. more rawinsonde launches compare more surface stations
Recommendations:
more rawinsonde launches
compare more surface stations
incorporate aircraft data
Surface lidars
Recommendations for future sea breeze studies include more rawinsonde launches. This may help show more of a diurnal cycle.
More surface station data would aid in the spatial scale of the sea breeze
Incorporating aircraft data would be a useful remote sensing tool to verify the ground observations.
Observational gaps could be filled in with the use of surface lidar. It would aid in the vertical and horizontal structure of the sea breeze.

31. References
Banta, R.M. et al : Evolution of the Monterey Bay Sea-Breeze Layer as Observed by Pulsed Doppler Lidar. J. of Atmospheric Sciences, 50, 24, 3959, 3982.
Banta, R.M. 1995: Sea Breezes Shallow and Deep on the California Coast. Monthly Weather Review, 123, 12,
Intrieri, J. M. et al : The Land/Sea Breeze Experiment (LASBEX). Bulletin of the American Meteorological Society, 71, 5,
Matlab programs provided by P. Guest
(picture)
** Special thanks to Dick Lind, Prof. Nuss, Prof. Guest, and Mary Jordan