Understanding and predicting tropical cyclone risks for the asia pacific region
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Understanding and Predicting Tropical Cyclone Risks for the Asia-Pacific Region. Johnny Chan. Guy Carpenter Asia-Pacific Climate Impact Centre City University of Hong Kong. Outline. Understanding Review of what you learned last year

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Understanding and predicting tropical cyclone risks for the asia pacific region l.jpg

Understanding and Predicting Tropical Cyclone Risks for the Asia-Pacific Region

Johnny Chan

Guy Carpenter Asia-Pacific Climate Impact Centre City University of Hong Kong


Outline l.jpg
Outline Asia-Pacific Region

Understanding

  • Review of what you learned last year

  • Some new results in understanding global warming and tropical cyclone activity

    Prediction

  • Traditional method

  • New Approaches

    Summary


Slide3 l.jpg
Adding a Custom Blue Color Value to Fonts Asia-Pacific RegionThe color is the same for both the white and grey templates

Should you need to apply the custom blue color to a font,please do the following…

Highlight the text you want to colorize and then go to the “Format” pull down menu to access the preferences for “Font”. Once the Font window appears, select the “Color” option and then choose “More Colors…” Under the “Custom” tab you will see value areas where you can type in the RGB values shown to the right. Once finished, click the “OK” button. This will apply the color to your highlighted type.

Understanding (1)What you learned last year

(R) Red = 0

(G) Green = 87

(B) Blue = 166




Slide6 l.jpg

Variations of Landfall in Each Area at Various Oscillation Periods

South China, Philippines and Vietnam

standardized anomalies

standardized anomalies

East China

standardized anomalies

standardized anomalies

Japan/Korea

standardized anomalies

standardized anomalies


Slide7 l.jpg

1977-88 Periods

Patterns of TC occurrence anomalies

TC occurrence anomalies

Pattern 1

1964-76

Pattern 2

Pattern 3

1989-97


Summary l.jpg
Summary Periods

  • Tropical cyclone activities (frequency, intensity and track) in the western North Pacific Ocean do not follow the trend of global warming.

  • Instead, such activities oscillate with periods of one or more decades

  • Such variations or oscillations are caused by similar variations in the atmosphere and/or the ocean


Slide9 l.jpg
Adding a Custom Blue Color Value to Fonts PeriodsThe color is the same for both the white and grey templates

Should you need to apply the custom blue color to a font,please do the following…

Highlight the text you want to colorize and then go to the “Format” pull down menu to access the preferences for “Font”. Once the Font window appears, select the “Color” option and then choose “More Colors…” Under the “Custom” tab you will see value areas where you can type in the RGB values shown to the right. Once finished, click the “OK” button. This will apply the color to your highlighted type.

Understanding (2)Some New Results

(R) Red = 0

(G) Green = 87

(B) Blue = 166


Background l.jpg
Background Periods

  • Tropical cyclone formation and development depends on two sets of factors:

    • thermodynamic (heat energy and the “conduciveness” of the atmosphere to the development of strong convection)

    • dynamic (wind flow and degree of rotation)


Background11 l.jpg
Background Periods

  • Thermodynamic conditions

    • ocean temperature

    • energy available for convection

    • atmospheric stability – “conduciveness” of atmosphere to the development of strong convection


Background12 l.jpg
Background Periods

  • Dynamic conditions

    • extent of “cyclonic” rotation of the wind flow

    • vertical wind shear (wind at 15 km minus that at 1.5 km) – strong shear will tear off the vertical integrity of the cyclone


Background13 l.jpg
Background Periods

  • Global warming leads to

    • an increase in the temperature near the earth’s surface (land and ocean)

    • an increase in the amount of water vapour in the atmosphere due to an increase in ocean temperature

  • No study has definitively demonstrated that the dynamic factors are modified by global warming (although some have suggested an increase in vertical wind shear).


Background14 l.jpg
Background Periods

  • Due to global warming, the thermodynamic factors have become more favourable for tropical cyclone formation and development.

  • To determine whether global warming has an impact on the frequency of occurrence of tropical cyclones or of intense cyclones, we need to examine whether the thermodynamic factors are related to the variations on such frequencies.

  • A good proxy of the thermodynamic factors is the Maximum Potential Intensity (MPI)


Background15 l.jpg
Background Periods

  • MPI = f(ocean temperature, outflow temperature, net amount of energy available for convection)

  • Because MPI gives the maximum possible intensity, a higher value of MPI summed over the ocean basin and over a season should imply a more thermodynamically energetic atmosphere, and more TCs could reach higher intensities

 a season with a higher value of MPI should have more intense TCs if the dominant control is thermodynamic




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21-year running correlations with NCat45 Periods

Correlations with MPI






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Summary Periods

  • Thermodynamic control on the frequency of intense TCs is important only in the Atlantic

  • Estimating the effect of global warming on the frequency of intense TCs therefore must also assess such an effect on the dynamic processes.


Slide24 l.jpg
Adding a Custom Blue Color Value to Fonts PeriodsThe color is the same for both the white and grey templates

Should you need to apply the custom blue color to a font,please do the following…

Highlight the text you want to colorize and then go to the “Format” pull down menu to access the preferences for “Font”. Once the Font window appears, select the “Color” option and then choose “More Colors…” Under the “Custom” tab you will see value areas where you can type in the RGB values shown to the right. Once finished, click the “OK” button. This will apply the color to your highlighted type.

Prediction (1)Traditional Method

(R) Red = 0

(G) Green = 87

(B) Blue = 166


Statistical method l.jpg
Statistical method Periods

  • Identify a list of variables relating to the atmospheric and oceanographic conditions prior to the season that significantly correlate with seasonal tropical cyclone activity

  • Perform regressions to derive prediction equations


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Examples of Predictors used in the CityU Forecasts Periods

  • Index of the westward extent of the subtropical high over the western North Pacific

  • Index of the strength of the India-Burma trough (15-20oN, 80-120oE)

  • Primary mode of low-frequency variability over the North Pacific

  • Sea surface temperature (SST) anomalies in the NINO3.4 region (5oS-5oN,170-120oW)

  • Sea surface temperature (SST) anomalies in the NINO4 region (5oS-5oN, 160oE-150oW)

  • Equatorial Southern Oscillation Index (Equatorial SOI)

  • Equatorial Eastern Pacific SLP - Indonesia SLP (standardized anomalies)


Slide27 l.jpg

Typhoons Periods

All tropical cyclones

Tropical storms and typhoons

Forecasts of Annual Tropical Cyclone Activity over the western North Pacific (Deviations from Observations)


Slide28 l.jpg
Adding a Custom Blue Color Value to Fonts PeriodsThe color is the same for both the white and grey templates

Should you need to apply the custom blue color to a font,please do the following…

Highlight the text you want to colorize and then go to the “Format” pull down menu to access the preferences for “Font”. Once the Font window appears, select the “Color” option and then choose “More Colors…” Under the “Custom” tab you will see value areas where you can type in the RGB values shown to the right. Once finished, click the “OK” button. This will apply the color to your highlighted type.

Prediction (2)Statistical Dynamical Method

(R) Red = 0

(G) Green = 87

(B) Blue = 166


Statistical vs statistical dynamical methods l.jpg
Statistical vs. Statistical-dynamical Methods Periods

Problem with the statistical method

Relate the past events and future conditions by statistics

Inherent problem

assumes the future would behave the same as the past, which may not be correct

Statistical-dynamical method partly solves the inherent problem by

relating dynamical model predictions with future conditions

Dynamical atmospheric model

Predicted future conditions

Integrate over time

statistical prediction

Observations

statistical prediction

# TCs

Time

several months



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GC Periods

Tracks of FL/GC landfalling TCs 1980 – 2001,Aug – Sept

Subtropical High

Subtropical High

FL


Observed vs predicted east coast l.jpg
Observed vs. Predicted PeriodsEast Coast

Single model: CERFACS

Multimodel


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Observed vs. Predicted PeriodsGulf Coast

Single model: LODYC

Multimodel


Slide34 l.jpg

Observed vs. Predicted PeriodsFlorida

Single model: LODYC

Multimodel


Slide35 l.jpg
Adding a Custom Blue Color Value to Fonts PeriodsThe color is the same for both the white and grey templates

Should you need to apply the custom blue color to a font,please do the following…

Highlight the text you want to colorize and then go to the “Format” pull down menu to access the preferences for “Font”. Once the Font window appears, select the “Color” option and then choose “More Colors…” Under the “Custom” tab you will see value areas where you can type in the RGB values shown to the right. Once finished, click the “OK” button. This will apply the color to your highlighted type.

Prediction (3)Regional Climate Model

(R) Red = 0

(G) Green = 87

(B) Blue = 166


Dynamical method l.jpg
Dynamical method Periods

  • Run a global circulation model (GCM) with a relatively coarse resolution

  • Solutions from the GCM are used as boundary conditions for a regional model with a higher resolution that can “resolve” a tropical cyclone

  • Integrate the regional model to predict seasonal activity.



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Summary Periods

  • Statistical methods can provide some clues on tropical cyclone activity but suffers from an inherent problem of predicting future events based only on past conditions

  • Statistical-dynamical methods can provide predictive information and therefore should give better results, but still suffers from the statistical nature of the method.

  • Dynamical model forecasts should be the way forward to predict tropical cyclone risks although more research is still necessary on fine-tuning the regional model.



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