Sabrina Abesamis, Lily Dove, Ryan Truchelut, and Robert E. Hart
Young Scholars Program, Florida State University Background Due to
modern enhancements to satellite technology, the detection of
present-day tropical cyclones (TCs) has greatly improved in
accuracy. The lack of such scientific means preceding the 1960s has
generated concern regarding the oversight of prior undetected TCs,
which may have created a possible bias in the historical record
before and including the early 20 th century. As seen in Figure 1,
this under sampling is particularly significant in the Pacific
basins in the pre- satellite era. This study is capable of
improving the historical record, furthering research involving
long- term TC trends and the possible increase in storms per year
due to global climate change. Methodology Our reanalysis has been
concentrated on the Southern and Western Pacific Basins during the
1920s-1940s due to the considerable undercount present in the
current archives (see Figure 1). By utilizing a thickness algorithm
developed by Truchelut and Hart 2011, the technique of identifying
candidate events is completely automated, which has greatly
expedited the process compared to former manual methods.
Classification was based on National Hurricane Center (NHC)
criteria (Landsea et al., 2008) in order to ensure consistent and
reliable results. The center panel displays more information about
the three classifications. Candidate Event Classification Criteria
Conclusion The data collected from this research indicate that an
average of about 9.7 events per year from the Southern Pacific and
18 from the Western Pacific were generated by the automatic
reanalysis technique. Of these candidate events, an average of 0.41
and 6.18 missing TCs per year were found in the Southern and
Western Pacific basins, respectively. From this data, we can
conclude that the Western Pacific Basins candidate events provided
more observations and opportunities for higher classification as a
Type 3 than those events found in the Southern Pacific Basin. The
thickness algorithm has already identified thousands more events
that await observational verification. With further use of this
reanalysis process, the accuracy and completeness of the historical
record of tropical cyclones can continue to grow and expand.
Landsea, C. W., et al 2008: A Reanalysis of the 1911-20 Atlantic
Hurricane Database. J.Climate. Truchelut, R. E., and R. E. Hart
(2011), Quantifying the possible existence of undocumented Atlantic
warmcore cyclones in NOAA/CIRES 20th Century Reanalysis data,
Geophys. Res. Lett.,38 Truchelut, Ryan and Robert Hart. "Global
Identification of Previously Undetected Tropical Cyclone Candidates
in NOAA/CIRES 20th Century Reanalysis Data." 30th Conference on
Hurricanes and Tropical Meteorology, Ponte Vedra Beach, FL. 16
April 2012. Conference presentation. Truchelut, R., R. Hart, and B.
Luthman, 2013: Global identification of previously undetected
pre-satellite era tropical cyclone candidates in NOAA/CIRES 20th
Century Reanalysis data. J. Appl. Meteor. Climatol.
doi:10.1175/JAMC-D-12-0276.1, in press. Observational Verification
of Previously Unidentified Tropical Cyclones in the Western &
Southern Pacific Basins Discussion In the present day, the average
tropical cyclone seasons in the Western and Southern Pacific Basins
experience 20 to 25 storms per year. Although the reanalysis method
used in this study is useful in detecting and presenting potential
pre- satellite storms (designated as Type 3s), the lack of
observations in multiple candidate events caused many promising
events to be classified as ambiguous, or Type 2, particularly in
the Southern Pacific. This significant weakness of the method used
can be seen in our results displayed in Figure 7 a and b. Type 3
Type 3 status is designated towards events which are considered
possible missing tropical cyclones. In order to receive this
classification, events must have a closed circulation around a
well-defined center as well as two or more observations of either
winds greater than 33 knots or sea level pressures less than 1002
millibars within any six hour observational time period. Such
observations do not have to be present during the entire life of an
event. These events are clearly non-frontal and must have thickness
anomalies which are fairly symmetrical about the estimated center
of circulation. Type 1 A Type 1 Event is one for which sufficient
data provides evidence that no TC was present at the time. For this
conclusion to be drawn, no closed surface circulation which
involves winds from all cardinal directions within the same
observation time is present. Winds greater than 33 knots or sea
level pressures below 1002 millibars are typically not observed. If
an event is definitively non-tropical/frontal or there is clearly
no closed surface circulation, it is automatically classified as
Type 1, regardless of whether strong winds or low pressures are
present. Type 2 Type 2 events are those which cannot be fully
placed into either the Type 1 or Type 3 category. Events which
receive this classification often have few or limited observations,
which may occur within a candidate. Other events classified as Type
2 are those for which a closed circulation is present without low
pressures or strong winds or vice versa. Figure 4 This Type 2
example lacks sufficient observations. Figure 7 (a & b) Results
of each event type received for both the Southern Pacific and the
Western Pacific Basins. Results for the Reanalysis of TCs in
Southern & Western Pacific Basins Both graphs display the total
number of candidate events for each type in each of the respective
basins. Western Pacific (1920-1929, 1937-1944) Figure 1 This plot
(Truchelut and Hart, 2013) reveals the notable undercount of TCs
present in the Pacific basins before the mid-20 th century. The
years reanalyzed by this study are enclosed in the boxes. 6 6
Figure 3Figure 5 Southern Pacific (1920-1937) This Type 1 event
shows a frontal nature due to its asymmetrical shape. It also
demonstrates weak winds and average pressures. This Type 3 example
exhibits excellent symmetry around a well-defined circulation
center. It has multiple observations of 37 knot winds and pressures
below 1000 millibars. This sample observation describes the sets of
four numbers located on the candidate event study maps. Figure
2