A Composite Analysis of Cross-Equatorial Heat Transport by Tropical Cyclones Benjamin A. Schenkel Daniel Keyser, and Lance F. Bosart University at Albany, State University of New York Motivation  Upper-tropospheric outflow of tropical cyclones (TCs) is confined to outflow jets that can extend thousands of km from the TC (Frank 1982)  Low-latitude TCs generally characterized by equatorward directed outflow jets (Frank 1982) that may transport heat from Northern Hemisphere (NH) TC into Southern Hemisphere (SH)  Cross-equatorial heat transport by TC outflow jet may alter SH subtropical jet through thermal wind considerations by altering tropical and subtropical SH meridional temperature gradient Objective Examine whether western North Pacific (WPAC) TCs yield significant upper-tropospheric cross-equatorial heat transport from NH to SH Motivation  Upper-tropospheric outflow of tropical cyclones (TCs) is confined to outflow jets that can extend thousands of km from the TC (Frank 1982)  Low-latitude TCs generally characterized by equatorward directed outflow jets (Frank 1982) that may transport heat from Northern Hemisphere (NH) TC into Southern Hemisphere (SH)  Cross-equatorial heat transport by TC outflow jet may alter SH subtropical jet through thermal wind considerations by altering tropical and subtropical SH meridional temperature gradient Objective Examine whether western North Pacific (WPAC) TCs yield significant upper-tropospheric cross-equatorial heat transport from NH to SH This research is sponsored by an NSF Atmospheric and Geospace Sciences Postdoctoral Research Fellowship. The authors thank Robert Hart (FSU), Ming Cai (FSU), Aiguo Dai (UAlbany), and Aaron Donohoe (UW) for fruitful discussions. 1. Introduction Fig. 1: Composite 150-hPa temperature anomalies (K; shaded), wind speed anomalies (kt; black contours), and vector wind anomalies (kt; black arrows) for (a) three days prior to TC passage, (b) during TC passage, (c) two days after TC passage, (d) four days after TC passage, and (e) seven days after TC passage at domain center. Anomalies are only shown if they are statistically significant at 95% confidence level. TC position is denoted by black TC symbol. 4. Results: Trajectory Analysis of Parcel Source Region for Warm Temperature Anomalies 2. Methodology 7. Acknowledgments 6. Summary Data WPAC TCs with maximum 10-m wind speeds greater than or equal to 64 kt at or equatorward of 20°N during 1979– 2010 (N = 422) in Joint Typhoon Warning Center Best-Track (Chu et al. 2002) are examined 6-h 0.5° NCEP Climate Forecast System Reanalysis (CFSR; Saha et al. 2010) are used to represent TC and its environment Methods Composite analyses centered at TC longitude during TC passage constructed from CFSR 1,000-sample bootstrap resampling test used to determine statistical significance of anomalies at 95% confidence level Version 4.0 of NOAA Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model (Draxler 1999) used to study life cycle of temperature anomalies induced by TC Data WPAC TCs with maximum 10-m wind speeds greater than or equal to 64 kt at or equatorward of 20°N during 1979– 2010 (N = 422) in Joint Typhoon Warning Center Best-Track (Chu et al. 2002) are examined 6-h 0.5° NCEP Climate Forecast System Reanalysis (CFSR; Saha et al. 2010) are used to represent TC and its environment Methods Composite analyses centered at TC longitude during TC passage constructed from CFSR 1,000-sample bootstrap resampling test used to determine statistical significance of anomalies at 95% confidence level Version 4.0 of NOAA Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model (Draxler 1999) used to study life cycle of temperature anomalies induced by TC 3. Results: Structure of Composite Anomalies Overview Analysis of structure of composite upper-tropospheric temperature and wind anomalies for TC and its environment during TC passage Synopsis  Upper-tropospheric warm temperature anomalies and TC outflow jet extend from TC into SH during and immediately after TC passage (Figs. 1b,c)  Upper-tropospheric warm temperature anomalies maximized immediately after TC passage (Fig. 1c)  Upper-tropospheric warm temperature anomalies dissipate several days after TC passage (Fig. 1d,e)  Timing and location of upper-tropospheric warm temperature anomalies suggests anomalies forced by TC Fig. 2: 48-h backward trajectories (shaded by pressure) starting at 150 hPa in region of warm temperature anomalies two days after TC passage calculated from composites of (a) TC passage and (b) climatology. Trajectories are overlaid upon 175–150-hPa layer-averaged wind speed (kt, shaded) and wind vectors (kt; black arrows) at end of trajectory (i.e., 48 h prior to trajectory start). Black TC symbol denotes TC location. Overview Determine parcel source region and processes responsible for forcing upper-tropospheric warm temperature anomalies during TC passage using backward trajectories Synopsis  During TC passage, parcels originating from TC and immediate upper-tropospheric environment are advected southwestward by upper-tropospheric TC outflow jet and tropical easterly jet (Figs. 2a, 3a)  Climatological parcels advected slowly west- southwestward intro tropical easterly jet (Figs. 2b, 3b)  Mean trajectory equivalent potential temperature is consistently higher during TC passage compared to climatology (Fig. 4b) due to high equivalent potential temperature parcel source region of TC and immediate environment  Results suggest upper-tropospheric warm temperature anomalies result from southwestward advection of relatively high equivalent potential temperature parcels from TC and its immediate environment by TC and tropical easterly jet Fig. 4: Time series of mean trajectory (a) pressure (hPa) and (b) equivalent potential temperature (K) for backward trajectories in Fig. 3 calculated from composites during TC passage and climatology. Shading denotes standard deviation of pressure and equivalent potential temperature. 2. Methodology Fig. 8: Schematic depicting the salient processes and features associated with cross-equatorial heat transport by WPAC TCs. The numbers in schematic correspond to numbers in discussion to left. Discussion  Life cycle of upper-tropospheric warm temperature anomalies in SH during TC passage summarized by following points corresponding to schematic on right (Fig. 8): 1. High equivalent potential temperature parcels from TC and immediate environment advected southwestward by upper-tropospheric TC outflow jet as TC moves west- northwestward 2. Southwestward advection by TC yields upper-tropospheric warm temperature anomalies extending from TC into SH 3. Upper-tropospheric warm temperature anomalies dissipate upon moving farther southward, likely due to suppressed radiative heating as parcels turn eastward into equatorward flank of SH subtropical jet  Present study suggests TCs can have significant cross-equatorial thermodynamic impacts due to advection by upper-tropospheric TC outflow jet 5. Results: Trajectory Analysis of Dissipation of Warm Temperature Anomalies Overview Examine dissipation of upper-tropospheric warm temperature anomalies after TC passage using forward trajectories Synopsis  During TC passage, parcels move southwestward more rapidly compared to climatology due to TC outflow jet (Fig. 5)  Stronger initial southwestward motion during TC passage relative to climatology causes parcels to turn eastward more rapidly into SH subtropical jet (Figs. 5, 6)  During TC passage, equivalent potential temperature of parcels increases less rapidly than climatology, causing equivalent potential temperature of parcels to return back to climatology (Fig. 7b)  Return of upper-tropospheric warm temperature anomalies during TC passage to climatology possibly due to suppressed radiative heating AGU Poster: A33L-3383 Fig. 5: 48-h forward trajectories (shaded by pressure) starting at 150 hPa in region of warm temperature anomalies two days after TC passage calculated from composites of (a) TC passage and (b) climatology. Trajectories are overlaid upon 150–125-hPa layer-averaged wind speed (kt, shaded) and wind vectors (kt; black arrows) at start of trajectory. Fig. 7: As in Fig. 4, but for 120-h forward trajectories in Fig. 6. Fig. 3: As in Fig. 2, but for 120-h backward trajectories overlaid upon 300–150-hPa layer-averaged wind speed (kt, shaded) and wind vectors (kt; black arrows) at end of trajectory (i.e., 120 h prior to trajectory start). Fig. 6: As in Fig. 5, but for 120-h forward trajectories overlaid upon 150–125-hPa layer-averaged wind speed (kt, shaded) and wind vectors (kt; black arrows) at 48 h after trajectory start.