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Friday, September 10, 2010
This emphasis on full-scale measurements and understanding the structure of severe winds led to the development of our existing Hurricanes at Landfall Project. In the late 90's, Dr. John Schroeder (then conducting his doctoral dissertation research) went searching for high-resolution data from the eyewall of landfalling hurricanes and was unsuccessful. This is due to typical failure of conventional weather stations used by the National Weather Service (NWS) to fail in sustained wind speeds of only 50 mph. Most believe that the stations are simply destroyed. Well in most cases this is not the truth at all. Unfortunately our conventional network of observing stations is powered by our standard electrical grid with no backup power supply. Also stations do not have an internal data logger and must rely on data transmission back to the NWS. So when the power goes out in an area, so do the observations. Question why 50 mph? these are typical sustained winds that begin to produce damage, such as downed trees which often fall on power lines. A recent study from the Florida Coastal Monitoring Program found an 80% failure rate of conventional automated surface observing stations (ASOS) in sustained winds of 50 mph.
So the question was asked, if there is no data why can't we just go and collect it ourselves? That is exactly what scientists here at TTU set out to do. In 1998 Texas Tech developed its first ruggedized instrumented tower which could be deployed in the path of a landfalling hurricane. The experiment was called the Wind Engineering Mobile Instrument Tower Experiment or WEMITE for short. Dr. Schroeder designed WEMITE #1 (image to the left) to be self-sustaining with its own power supply and be rugged enough to survive the severe winds found in hurricane eyewalls. WEMITE #1 was a telescoping lattice 10 m tower mounted on a trailer platform. The tower was anchored by 6 guy wires using modified mobile home anchors as well as outriggers attached to the trailer which were also attached to the ground through the same type of anchor. The system was powered by a bank of several marine batteries within a debris-proof enclosure. A small wind generator was also added to allow for continuous charging of the battery bank. An internal laptop computer handled the acquisition and storage of data. Multiple wind sensors (anemometers) were place on the tower as well as temperature/relative humidity and barometric pressure sensors. WEMITE #1 was completed in time for the 1998 Atlantic Hurricane season and Texas Tech became the first institution to deploy an instrumented meterological tower in the path of a landfalling hurricane when Hurricane Bonnie made landfall in North Carolina. WEMITE #1 would become the work horse of the fleet making 20 deployments between 1998 and 2005.
In 1999 WEMITE #2 was added. This platform was also a trailer mounted ruggedized tower. Three more single mast non-ruggedized towers were added to the fleet in 2002 bringing TTUHRT's capacity to 5 platforms. During this time the Florida Coastal Monitoring Program (FCMP) was developed by Dr. Tim Reinhold. This was a collaboration between the University of Florida, Clemson, and Florida International to develop and deploy ruggedized towers in the path of landfalling tropical cyclones. FCMP has been one of our closest collaborators over the years and we look forward to continued scientific study between our groups. TTUHRT also joined the SMART-Radar coallition with Oklahoma University, Texas A&M, and the National Severe Storms Laboratory. The two SMART-Radars are C-band mobile Doppler radar systems and provide higher resolution data than conventional NWS Doppler radars (WSR-88D). TTUHRT deployed both radars for Hurricanes Lili (2002), Hurricane Isabel (2003), and Hurricane Frances (2004). Data from the SMART-radars coupled with tower measurements have shed some light on the turbulent structure of hurricane winds and coherent features of alternating strong and weak wind speeds known as streaks.
The prolific Atlantic hurricane season's of 2004 and 2005 kept TTUHRT busy with seven deployments over the 2 seasons. In 2005, TTUHRT collected the only complete wind data record from Hurricane Katrina's Mississippi landfall. These seasons also highlighted the need for even more measurements in order to understand the variability in a hurricane's wind field at landfall. In 2005, the Atmospheric Science Group and the Wind Science and Engineering Research Center set out to develop a multi-use rapidly deployable surface observing station. A design competition was held within a graduate course in field measurements. What resulted was affectionately dubbed "StickNet" which is a 2.25 m rapidly deployable weather station which can be used to measure a variety of phenomena. StickNet platforms are far less rugged than the original WEMITE towers but are estimated to withstand a 3-second gust wind speed of 140 mph. The costs to produce a single StickNet probe are far less than a single WEMITE tower. TTUHRT currently maintains 24 StickNet probes. Although the probes are not the standard measuring height of 10 m, the group was willing to sacrifice this in order to gain a significantly larger number of observations from the landfall area. Additionally, the small footprint of StickNet probes allows them the versatility to be deployed in locations where the much larger WEMITE towers could not go. This allows for vital data collection closer to the immediate shoreline. The hurricane configuration of a StickNet allows for a deployment time of only 5-10 minutes while a WEMITE tower would take four people at least 1 hour. A good example of this came during Hurricane Dolly (2008), where a probe was deployed on a dune structure on South Padre Island. Hurricane Ike (2008) also provided a unique deployment opportunity at Fort Travis on the western tip of the Bolivar Peninsula. These types of deployments highlighted the benefits of the StickNet platforms. StickNet probes were first deployed into the hurricane environment for Hurricane Dolly (2008). Two other deployments were made in 2008 for Hurricane Gustav and Hurricane Ike. With the implementation of the StickNet project, the original WEMITE towers have been retired from service but remain in working order housed in the Wind Science and Engineering Research Center's Reese facility.
Excerpt from the National Hurricane Center's official cyclone report for Hurricane Ike...
"A 1-minute sustained wind of 71 kt was recorded by a Texas Tech University Hurricane Research Team (TTUHRT) anemometer near Winnie, Texas, between Houston and Beaumont. A 3-second gust of 95 kt was reported by a separate TTUHRT sensor near Hankamer, Texas. The pressure of 950 mb at landfall is based on a minimum pressure of 950.7 mb reported by a TTUHRT sensor at Port Bolivar near the entrance to Galveston Bay and a pressure of 951.7 mb reported at the Galveston Pleasure Pier"
In 2006 the Atmospheric Science Group and the Wind Science and Engineering were awarded a grant from the TTU Office of the Vice President for Research to develop two mobile Doppler radar systems for use in making measurements of boundary layer wind flows in a variety of conditions. TTUKA-1 was completed in time for the 2009 Atlantic hurricane season and made its first tropical deployment for Tropical Storm Ida. TTUKA-2 recently was completed and participated in the VORTEX 2 tornado field research project. The two radars make measurements at a finer scale than the SMART-radars allowing for a more detailed view of the structure of hurricane winds.
Following the 2008 hurricane season, scientists at institutions around the country who study hurricanes at landfall met to discuss future collaborations. What came out of this meeting was the Digital Hurricane Consortium (DHC). The consortium is under the oversight of the Applied Technology Council who works closely with the Federal Government. The goal of the consortium is to provide comprehensive data and analyses from landfalling hurricanes in order to mitigate the effects of these systems on life and property. The DHC includes: Texas Tech University, the Florida Coastal Monitoring Program, The Center for Severe Weather Research, University of Alabama at Huntsville, Oklahoma University, Louisiana State University, South Alabama University, University of Colorado, University of North Florida, and Notre Dame. Government partners include the USGS and NOAA's Hurricane Research Division.
Since the project's inception in 1998, data collected from TTUHRT platforms has directly appeared in 12 peer-reviewed journal publications, NHC and FEMA post-storm reports, 9 technical reports, and over 40 conference presentations and proceedings.
Well this was our story and how we came to be... in some later blogs we hope to talk about each of our instrument platforms in more detail as well as deployment strategies. We also hope to provide information regarding active cyclones in which landfall operations are being considered and provide updates from the field during deployments. The principal investigator and director of the project is Dr. John Schroeder. He is also the Director of the Wind Science and Engineering Research Center.