Figure 1: Time series of late summer tropical Atlantic sea surface temperature (blue) and the Power Dissipation Index (green), a measure of hurricane activity which depends on the frequency, duration, and intensity of hurricanes over a season. The annual data have been smoothed with a low-pass filter to emphasize fluctuations on time scales of several years and longer. From Emanuel (2007)
Figure 2: The top diagram shows how Atlantic hurricane power dissipation is well correlated to a time series of local Atlantic sea surface temperature. The bottom diagram shows that the power dissipation is even more closely correlated with an alternative sea surface temperature measure--local Atlantic sea surface temperature relative to tropical mean sea surface temperature. From Swanson (2008)
Figure 3: Time series of Atlantic tropical cyclone counts including
adjustment for missing storms based on ship track densities (black). Red line is
the 5-yr running mean adjusted storm count. The solid blue line is the
adjustment applied to the data (the estimated number of missing storms each
year), while the dashed blue line is a sensitivity case requiring one ship/storm
encounter for detection instead of two, as in the base case. The green and
orange solid lines are linear trend fits to the data for 1878-2006 and 1900-2006, respectively. Black shading indicates the two-sided, 95% method
uncertainty, estimated from the probability density function of the estimated
adjustments. From
Vecchi and Knutson (2008)
Figure 4: Time series of Atlantic hurricane counts (black), major hurricane
counts (red) and U.S. landfalling hurricane counts (blue) from 1851-2006. A
five-year running mean smoothing has been applied. Statistically significant
(p=0.05) and insignificant linear trends are denoted by *'s and o's,
respectively, at the starting year for the trend test, with all trends extending
to 2006. U.S. landfalling hurricane trends were not tested. From
CCSP 3.3 (2008), Figure 2.17, page 60
Figure 5: Model versus observed Atlantic hurricane counts (August-October).
The regional model uses observed SSTs and large-scale nudging of the interior
solution towards reanalyses. Correlation: 0.84; linear trends :+0.21 storms/yr (model) and +0.15 storms/yr (observed). From
Knutson et
al. (2008)
Figure 6: Left: Distributions of wind speeds for Atlantic tropical storms and
hurricanes (August-October). Black curve shows observed distribution, blue curve
the simulated distribution for present day climate, and red curve the simulated
distribution for the late 21st century (IPCC A1B forcing scenario). The
strongest observed hurricane intensities are not reproduced by the model, and
there is a strong reduction in the number of storms in the warm climate
experiments, compared to the control (present day). There is an increase in the
number of the very strongest simulated storms in the warm climate, relative to
the control. Right: The normalized histogram (right) was obtained by dividing
the values from each curve on the left by the total number of storms observed or
simulated during the 27 yr period. This controls for differences in storm
frequency between the control and warming experiments or between the control and
observations. The storms that do occur in the warmer climate simulation are more
intense on average than those in the control (present day) simulation. From
Knutson et
al. (2008)
Figure
1 (old): Comparison of simulated hurricane intensities for present-day
(thin line) and future (thick line) climate conditions assuming an 80-year
build-up of atmospheric CO2 at 1%/yr compounded. The results are aggregated from
sets of experiments using nine different global climate model projections and
four different versions of a high-resolution hurricane prediction model.
Figure
2 (old): Top: a tropical storm as simulated in a global climate model.
Shown are surface temperature (shading), pressure and winds. Bottom: the same
storm case, but as simulated with the hurricane prediction model. Shown are
surface winds and precipitation on the inner grid of the hurricane model. The
vector spacing illustrates the resolution of the two models (250 km for the
global model vs. 18 km for the hurricane model.)
Figure
3 (old): Sea surface temperatures (SSTs, light contours and color
shading, in degrees Celsius) and sea level pressure (dark contours, in millibars)
from an idealized coupled hurricane model/ocean model experiment. The "cool
wake" in SSTs produced by the hurricane is indicated by the lower SSTs to the
east-southeast of the storm. The storm motion is toward the west-northwest.
