| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
|
| Initial Amendment Date: | May 7, 2019 |
| Latest Amendment Date: | May 7, 2019 |
| Award Number: | 1911671 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Yu Gu
ygu@nsf.gov (703)292-8796 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | June 1, 2019 |
| End Date: | May 31, 2024 (Estimated) |
| Total Intended Award Amount: | $408,577.00 |
| Total Awarded Amount to Date: | $408,577.00 |
| Funds Obligated to Date: |
|
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
3203 N DOWNER AVE # 273 MILWAUKEE WI US 53211-3153 (414)229-4853 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
3200 N Cramer St Milwaukee WI US 53211-3029 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): |
PREEVENTS - Prediction of and, Physical & Dynamic Meteorology |
| Primary Program Source: |
|
| Program Reference Code(s): |
|
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The energy that fuels a tropical storm's or a hurricane's winds is typically drawn from warm ocean waters. However, for some tropical cyclones, the maximum surface winds have been observed to be maintained or even increase over land. A particularly noteworthy case is given by Tropical Storm Erin over Oklahoma, which dramatically and unexpectedly intensified into a strong tropical storm as it approached Oklahoma City from the west, resulting in millions of dollars of wind-related damage. The few prior investigations into this phenomenon generally agree that the required energy is drawn from the underlying land surface. However, they disagree on the extent to which the energy is associated with land warmth versus wetness, as well as on the physical processes that allow for a sufficient amount of energy to be concentrated near the surface so that it can be transferred to the tropical cyclones. Furthermore, the ideas advanced by these previous studies have generally been developed using highly simplified numerical weather prediction model simulations, with few instances in which these ideas have been tested for actual tropical cyclones. Consequently, this project seeks to significantly advance basic understanding of the energetics supporting tropical cyclone maintenance and strengthening over land while rigorously testing this understanding for a large sample of observed events. A partnership with the Ronald E. McNair Post-Baccalaureate Achievement Program at University of Wisconsin-Milwaukee will support the professional development and academic persistence of an undergraduate scholar from a traditionally underrepresented background, helping to increase representation of minority individuals within the workforce pipeline in the atmospheric and related sciences.
This research tests three guiding hypotheses: remote surface energy exchange is the primary but not exclusive control on tropical cyclone intensity change over land; non-desert soils cannot be sufficiently warmed to result in sufficient upward enthalpy flux for tropical cyclone maintenance or intensification over land; and intensity change over land is equally sensitive to surface energy exchange and initial finite-amplitude atmospheric variability. Factor separation applied to idealized numerical simulations is used to test the first two hypotheses, whereas ensemble-initialized real-data simulations are used to test the applicability of the idealized simulation results to the real atmosphere. An expanded climatology of atmospheric and substrate properties associated with overland tropical cyclone maintenance and intensification is to support the numerical model simulations and advance knowledge of the environments in which these events occur. Through these activities, this research will reconcile competing theories regarding the thermodynamic processes necessary to support non- or weakly baroclinic tropical cyclone maintenance and intensification over land through quantifying the respective contributions of local and non-local land-surface energy exchange to overland tropical cyclone intensity change. Given the ongoing scientific debate regarding the surface latent heat flux magnitudes needed to permit tropical cyclone intensification over water, findings from the research will also advance knowledge of the energetics of the traditional overwater tropical cyclone intensification process.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
This project sought to identify the physical processes most responsible for the intensification and maintenance of tropical cyclones -- which derive their energy from the evaporation of very warm ocean waters -- over land. We used three approaches to study this problem:
- Simplified numerical weather prediction model simulations to assess the influence of soil parameters such as soil type, temperature, and moisture content on overland tropical cyclone intensity.
- A collection of 50 numerical weather prediction model simulations, known as an ensemble, of a real-world overland tropical cyclone intensification event (Tropical Storm Erin in 2007 over Oklahoma) to assess the influence of atmospheric conditions and uncertainty on overland tropical cyclone intensity.
- A climatology, or historical accounting, of the atmospheric and land surface conditions during and immediately before overland tropical cyclone intensification and maintenance events.
The first approach identified that marginally stable, yet warm and moist, atmospheric boundary layer conditions, facilitated either by cold soil temperature (cooling the atmosphere by conduction) or by high soil water content (cooling the atmosphere by evaporation), are needed for overland tropical cyclone intensification or maintenance. Such conditions mitigate rainbands outside of the cyclone's center that otherwise result in evaporative cooling into the atmospheric boundary layer that is far more stable (i.e., less energy available for the cyclone) than in the cases with ambient antecedant atmospheric boundary layer stability.
The second approach highlighted the limited predictive ability for Tropical Storm Erin's intensification over Oklahoma, with only a few forecasts faithfully depicting the observed intensity change. This indicates that favorable land surface conditions, which were present in all ensemble member forecasts, are not sufficient to allow for overland tropical cyclone intensification. Whether specific atmospheric conditions are also necessary remains unclear, however; the relative contributions of atmospheric conditions and random thunderstorm organizational processes are not able to be delineated through this approach.
The third approach led to the creation of an updated global record of overland tropical cyclone intensification and maintenance events. This climatology includes 64 distinct intensifying or intensity-maintaining cyclones over land between 1981 and 2021, predominantly over Australia and North America. These cyclones were and remained relatively weak while over land and generally occurred 300-700 km inland from the nearest ocean. Atmospheric and land-surface properties associated with these events generally indicate elevated soil water content and moisture exchange from the underlying soil to the atmosphere ahead of an intensification or intensity maintenance event.
This project supported the academic, professional, and personal development of three students: one at the M.S. and Ph.D. levels (completed M.S., accepted private-sector employment after completing his Ph.D. prospectus), one at the M.S. level (now in local government emergency management in Maine), and one at the B.S. level (now in the National Weather Service). It also resulted in two M.S. theses, one B.S. thesis, thirteen presentations, and two in-progress publications for peer-reviewed atmospheric science journals.
Last Modified: 02/27/2025
Modified by: Allen Clark Evans
Please report errors in award information by writing to: awardsearch@nsf.gov.
