Longwave Cloud Forcing Due to Tropical Cyclone Presence: August 1995 Cristy King

What I want to know If tropical cyclone (tropical depression, tropical storm, and hurricane) cloud cover affects the outgoing longwave radiation If tropical cyclone (tropical depression, tropical storm, and hurricane) cloud cover affects the outgoing longwave radiation

Data NOAA Interpolated Outgoing Longwave Radiation at TOA from the NOAA14 satellite NOAA Interpolated Outgoing Longwave Radiation at TOA from the NOAA14 satellite Spatial Coverage: 2.5 X 2.5 degree grid Spatial Coverage: 2.5 X 2.5 degree grid

Data Continued Spatial: Spatial: Tropical Atlantic Tropical Atlantic 75W to 20W 75W to 20W 10N to 30N 10N to 30N Temporal: Temporal: Daily OLR Daily OLR August 22, 1995 to August 31,1995 August 22, 1995 to August 31, cyclones present 4 cyclones present

Storm Tracks 8 Humberto 9 Iris 11 Karen 12 Luis

August 27,1995 Anomalous OLR Anomalous OLR

Threshold Hartmann et al used a threshold of 30 W/m^2 Hartmann et al used a threshold of 30 W/m^2 Test statistic revealed at 95% confidence level a range of - 28 < mean < +28 Test statistic revealed at 95% confidence level a range of - 28 < mean < +28 Threshold=30 W/m^2 Threshold=30 W/m^2 96.4% of longterm mean OLR lie between 220 – 280 with a mean value of 260 W/M^2

In any direction about the core of the cyclone, TOA OLR increases By offsetting the above OLR values by 30 (the threshold) we obtain the LWCRF due to the presence of the cyclone

Distribution of OLR about the core

Of total LWCRF: Of total LWCRF: 37% comes from within a radius of 1 grid box (242km) 37% comes from within a radius of 1 grid box (242km) 65% comes from within a radius of 2 grid boxes(484km) 65% comes from within a radius of 2 grid boxes(484km) 82% comes from within a radius of 3 grid boxes(726km) 82% comes from within a radius of 3 grid boxes(726km)

Correlation TOA OLR w/ Storm Category = -.15 TOA OLR w/ Storm Category = -.15 TD=1 TD/TS= 1.5 TS=2 TS/H=2.5 H=3 TD=1 TD/TS= 1.5 TS=2 TS/H=2.5 H=3 TOA OLR w/ SST =.23 TOA OLR w/ SST =.23 This is expected because if correlation w/ SST was strong, we would conclude that there is no net LWCRF induced by the cyclone

Conclusions/Comments Tropical cyclone cloud cover does significantly affect the outgoing longwave radiation Tropical cyclone cloud cover does significantly affect the outgoing longwave radiation Similar results were found for all 4 storms Similar results were found for all 4 storms SWCRF may balance the LWCRF leading to a NET CRF close to 0 but SW values are needed on a daily timescale as opposed to monthly SWCRF may balance the LWCRF leading to a NET CRF close to 0 but SW values are needed on a daily timescale as opposed to monthly Contours of monthly OLR washed out much of the signal Contours of monthly OLR washed out much of the signal