Eight years (1980-87) of twice-daily high-resolution radiosonde data from
a tropical mid-Pacific island station are analyzed to generate time series of the
planetary boundary layer (PBL) top pressure, an ageostrophic parameter (related to
the divergence), and a parameter of mean PBL specific humidity. Sample spectra
of these time series are calculated along with a spectra for nighttime outgoing
longwave radiation (OLR) data (centered at a gridpoint near the island station)
and compared in order to investigate the relationship between the ageostrophy
and dynamical phenomena of the tropical Pacific.
Methods of boundary layer top diagnosis are compared. Data derived methods
include temperature inversion detection, humidity jump detection, and wind shear
detection. The model based diagnosis method uses a Richardson number scheme.
Comparisons between data derived methods and model based methods show good
agreement. Correlation coefficients for comparisons are all above 0.91.
In each sample spectra, the dominant peak corresponds to the frequency of
the annual cycle. With an estimated annual cycle removed from each of the
time series the nighttime (12 GMT) sample spectra for PBL top pressure shows
a peak at a frequency that corresponds to the 30-60 day Intraseasonal Oscillation
(ISO). Removal of an estimated annual cycle was unsuccessful for the daytime (0
GMT) sample spectra for PBL top pressure, PBL mean specific humidity, and the
ageostrophic parameter. Sample spectra of the ageostrophic parameter show peaks
in the ISO frequency range for both 12 GMT and 0 GMT even before removal
of the annual cycle was attempted. The ISO range peaks remained in the 12
GMT ageostrophic parameter spectrum when the annual cycle was successfully
removed.
The nighttime OLR spectrum is dominated by the annual cycle peak and its
harmonics. The OLR spectrum also shows a significant peak in the ISO range
of periods. Removal of an estimated annual cycle intensifies the peak in the ISO
range.
The ageostrophic parameter time series is compared to the results of an EOF
analysis performed on the same 8 years of radiosonde humidity measurements.
The first three EOF modes of specific humidity give sample spectra which are
dominated by the annual cycle. With the annual cycle removed the sample spectra
of the first and third EOF modes of specific humidity both show significant peaks
in the ISO frequency range, while the second EOF mode sample spectrum is
dominated by two peaks at frequencies corresponding to periods of approximately
4 and 5 months.
The presence of common frequencies in the ISO range of the power spectra
of the ageostrophic parameter (a measure of divergence), the nighttime OLR (a
measure of deep convection), the nighttime planetary boundary layer top, and the
first EOF mode of specific humidity, lends support to theories that relate the ISO
to the interaction of dynamics and moist processes. / Graduation date: 1995
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28801 |
| Date | 28 April 1994 |
| Creators | McCandlish, Cole B. |
| Contributors | Levy, Gad |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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