ARCHER MPERC eyewall replacement cycles were compared to NHC reports, with 41% of ERCs verified.

AJAS · 2022 Earth Science

Lorenzo Pulmano

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Overview

Eyewall replacement cycles (ERCs) are events that occur in intense tropical cyclones (TCs) and are difficult to predict. An ERC event involves a secondary outer eyewall that surrounds the inner eyewall. The outer eyewall slowly moves towards the eye and weakens the inner eyewall, eventually replacing the inner eyewall. During this process, wind speeds lower and the structure of a TC becomes disorganized, further weakening the storm. TCs often restrengthen after an ERC. Little is known about the process and as such, poses an obstacle to forecasters. The Automated Rotational Center Hurricane Eye Retrieval (ARCHER) Microwave-based Probability of Eyewall Replacement Cycle (MPERC) is an algorithm that uses 89-95 GHz passive microwave imagery and intensity estimates from the National Hurricane Center (NHC), Central Pacific Hurricane Center (CPHC), or the Joint Typhoon Warning Center (JTWC) to predict the possibility of an ERC. The effectiveness and ability of ARCHER MPERC was analyzed and compared to the NHC’s official reports on all Atlantic Basin tropical cyclones from 2017 to 2019. MPERC ultimately predicted seventeen ERCs in nine tropical cyclones. Of those, seven were valid ERCs. The algorithm works well, predicting approximately 41% of the total number of predictions correctly. However, MPERC did not predict five ERCs that were cited by the NHC. It was further found that it was true that MPERC produces incorrect results in sheared and dry environments.

My Research Story

In the 6th grade, I became highly interested in tropical cyclones.

Comparison of ARCHER MPERC to NHC Analysis

That interest became viable in September of 2020, when I was required to submit a science fair project during 9th grade. I decided to join the Science Research Honors class, and started a literature review of the eyewall replacement cycle (ERC) predictions from the Automated Rotational Center Hurricane Eye Retrieval (ARCHER) Microwave-based Probability of Eyewall Replacement Cycle (MPERC) to real cases of ERCs detailed in NHC Tropical Cyclone Reports.

In March of 2021, I was chosen to present at the Florida Junior Academy of Science (FJAS). I received the 2nd place award for Literary Science.

Later in the Spring of 2021, I was prompted by my mentor to get my research published. I submitted my paper to the Journal of Student Research (JSR), and on October 10, 2021, my paper was published.

Continuing Research

In September of 2021, I rejoined the Science Research Honors class and started on another project.

In January of 2022, I submitted the paper for FJAS Adjudication.

A Little Bit About Me

I'm Lorenzo Pulmano, a sophomore at American Heritage School Broward Campus in Plantation, Florida as of the 21-22 school year.

I like playing PC games (I enjoy strategy games), building with Lego bricks, and going on cruises.

From the student

Comparison of ARCHER MPERC to NHC Analysis

American Heritage School Broward Campus, Plantation, Florida

Author: Lorenzo Pulmano

Mentor: Leya M. Joykutty

Introduction

I started this project in September of 2020. I’ve been interested in tropical cyclones since I was in 6th grade, and I thought it would be appropriate to conduct a research project on hurricanes because of relevancy regarding location (I live in South Florida) and time (2020 North Atlantic Hurricane Season).

Objective

Compare the amount of predicted eyewall replacement cycles from ARCHER MPERC for Northern Atlantic basin storms from 2017-2019 to NHC Tropical Cyclone Reports

Eyewall Replacement Cycle (ERC)

The complete process of the replacement of the inner eyewall by an outer eyewall

Secondary eyewall forms when outer rainbands strengthen and organize into a ring of intense thunderstorms, gradually replaces the inner eyewall

Maximum wind (strength) decreases during an event because of structure and organization changes (Molinari et al., 2019)

Weakening phase often followed by reintensification

Occurs mostly in intense tropical cyclones (TCs)

ARCHER (Automated Rotational Center Hurricane Eye Retrieval)

Designed to “aid tropical cyclone forecasters in sifting through the increasing wealth of relevant satellite data to quickly and objectively arrive at key TC characteristics…to increase efficient use of analysis time.” (“Highlights,” n.d.)

Analyzes a multitude of satellite images to objectively determine the center of a storm

Main component of ARCHER that is relevant to MPERC is Ring Score: “the best fit of an inner eyewall (if it exists) to a circular shape” (“How ARCHER works,” n.d.)

MPERC (Microwave-based Probability of Eyewall Replacement Cycle)

Fixes TC position using 89 GHz imagery

Ring Score from ARCHER and Operational Vmax (latest intensity estimate from the NHC, CPHC, or JTWC) is used in Probability of ERC onset (model is known as Full Model)

Ring Score can detail eyewall structures in 2D graphs known as hovmullers

Trained using Atlantic basin storms from 1999-2011

Average start of weakening occurs roughly 9 hours after onset

Average start of reintensification occurs roughly 25 hours after onset

Can generate false positives of ERC events in heavily sheared and dry environments because of “noisier gradients” (“M-PERC introduction,” n.d.)

Best practice to assign ERC onset when it crosses 50% and is substantiated (“M-PERC introduction,” n.d.), see image in presentation

Methodology: Data Collection

Acquiring Storm Directories

Navigate to http://tropic.ssec.wisc.edu/real-time/archerOnline/cyclones/

Obtain storm directory

Navigate to the link labelled “web/” and it will lead to the files necessary.

Navigate to the link labelled “erc/” and it will lead to the images of the hovmullers that include ARCHER Ring Score, Probability of ERC onset, and Operational Vmax.

All directory links are entered into an Excel spreadsheet for easy access during analysis with each link attributed to the respective storm.

Acquiring NHC Tropical Cyclone Reports

Navigate to https://www.nhc.noaa.gov/data/

Under the heading “Tropical Cyclone Reports,” there exists a dropdown menu for subheading “Atlantic, Caribbean, and the Gulf of Mexico.” Select the year.

The webpage should update with the list of storms in the selected year and the respective Tropical Cyclone Reports.

The .pdf files are linked in the same Excel spreadsheet that holds the directory links.

Repeat for all storms 2017-2019.

Methodology: Analysis

Analysis

Looking at the hovmullers

In accordance with “M-PERC introduction” (n.d.), a sustained probability of MPERC Full Model (*) over 50% is considered a prediction

Should a storm have such a prediction, a screenshot is taken of the hovmuller that includes time of onset, probability of ERC onset, and Ring Score. Screenshot should also include the time period after time of onset.

The total number of ERC predictions is recorded in a table on the Excel spreadsheet.

Repeat for all storms 2017-2019.

Confirming or Rejecting

Read the Tropical Cyclone Report on the storm in question

Sections “Synoptic History” (explains meteorological history) and “Track Table” (displays timestamp, position, wind speed) confirm or reject prediction

Make note or screenshot where a prediction is confirmed or rejected

For further proof, the hovmullers can be used for analysis.

Ring Score details eyewall structures (May be misleading because of faulty results produced from noisy gradients of sheared environments

Operational Vmax provides intensity

The total number of ERCs detailed in the report is recorded in the same table on the Excel spreadsheet

Repeat for all storms 2017-2019.

Results

17 predictions, 7 verified (approximately 41% of predictions were correct)

The algorithm did not indicate 5 events (2 in Irma, 2 in Lee, 1 in Lorenzo)

Most ERCs (predicted and confirmed) occurred in Category 5 (C5) storms, no ERCs in less intense storms (tropical depressions (TDs), tropical storms (TSs), Category 1 (C1))

Most ERCs (predicted and confirmed) in Hurricane Irma

Implications

ARCHER MPERC appears to perform well, and can be used to forecast intensity changes

Important to provide ample warning because of wind field expansion (Wimmers, 2018)

Wind field expansion increases amount of ocean water affected and can increase storm surge

Wind field expansion reduces the already small window of time for preparation and evacuation (Sitkowski et al., 2011)

Reintensification may erupt as rapid intensification (RI), resulting in a more intense hurricane (Sitkowski et al., 2011)

More diagnostic and predictive resources should be available in order to protect life and property during tropical cyclone emergencies

Citations

Index of /real-time/archerOnline/cyclones. (n.d.). Retrieved from http://tropic.ssec.wisc.edu/real-time/archerOnline/cyclones/

How ARCHER works. (n.d.). Retrieved November 22, 2020, from https://groups.ssec.wisc.edu/groups/archer/how-archer-works

M-PERC introduction. (n.d.). Retrieved November 22, 2020, from https://groups.ssec.wisc.edu/groups/archer/archer-erc-introduction

ARCHER (Automated Rotational Center Hurricane Eye Retrieval). (n.d.). Retrieved from http://tropic.ssec.wisc.edu/real-time/archerOnline/web/index.shtml

Highlights. (n.d.). Retrieved from https://groups.ssec.wisc.edu/groups/archer/highlights

Sitkowski, M., Kossin, J., & Rozoff, C. (2011, December 1). Intensity and Structure Changes during Hurricane Eyewall Replacement Cycles. Retrieved from https://journals.ametsoc.org/view/journals/mwre/139/12/mwr-d-11-00034.1.xml?rskey=NmJ0xP

Wimmers, A. (2018, November 29). Wimmers_197_progress_reportFINAL_113018.pdf [PDF]. NHC.

Molinari, J., Zhang, J., Rogers, R., & Vollaro, D. (2019, June 1). Repeated Eyewall Replacement Cycles in Hurricane Frances (2004). Retrieved from https://journals.ametsoc.org/view/journals/mwre/147/6/mwr-d-18-0345.1.xml?rskey=NmJ0xP, https://doi.org/10.1175/MWR-D-18-0345.1

Acknowledgements

I would like to my research mentor, Leya M. Joykutty, for assisting and guiding me.