Variability of the subtropical winter circulation in North America and its influence in Mexico Rosa Beatriz Luna Niño and Tereza Cavazos Baja California, Mexico
Introduction 2
Research questions ⊚ Has the wintertime subtropical circulation in North America changed in the last 30 years? ⊚ How will the subtropical winter circulation of North America change as a result of global warming? ⊚ Will the frequency and intensity of the cold fronts and Norte winds in Mexico be different in the second half of the 21st century? 3
Specific objectives for the historical period 1. To evaluate the skill of RegCM4.7 and its forcing GCMs in the simulation of the boreal winter climate over the CORDEX-CAM domain. 2. To analyse the historical winter circulation at synoptic and re- gional scale (apply different detection methods for the subtropi- cal jet stream, winter cyclones, cold fronts, and Norte winds). 3. To determine the possible role of large-scale teleconnections indices (AO, PDO, PNA, ENSO) on the inter-annual and decadal variability of the winter circulation. 4
Study region (m) 5
Data for the historical evaluation (1980-2010) ⊚ CRU Climatic Research Unit (Harris et al., 2014). Monthly, 50 km; temperature and precipitation ⊚ GPCP Global Precipitation Climatology Project (Adler et al., 2003). Daily, 1° ; precipitation ⊚ CHIRPS Climate Hazard Group InfraRed Precipitation with Station data (Funk et al., 2015). Daily, 5.5 km; precipitation ⊚ Livneh US-Climate Computing Project (Livneh et al., 2013). Daily, 6 km; temperature, precipitation and near-surface winds ⊚ ERA-Interim (Dee et al., 2011). Reanalysis, 6 hrs, 0.75° ; temperature, precipitation, and winds ⊚ MERRA2 The Modern-Era Retrospective analysis for Research and Applications, Version 2 (Gelaro et al., 2017). Reanalysis, 6 hrs, 0.5°x 0.65° ; temperature, precipitation, and winds 6
CMIP5 GCMs ⊚ HadGEM2-ES Hadley Center Global Environment Model version 2. (Collins et al., 2008) 1.875°x 1.25° ⊚ MPI-ES Max Planck Institute Earth System Model. 1.875°x 1.875° ⊚ GFDL Geophysical Fluid Dynamics Laboratory Model. (Dunne et al., 2008) 2.5°x 2.0° ⇓ RegCM4.7 Regional Climate Model (Giorgi et al., 2012) 25 km x 25 km The numerical experiments are carried out by the climate modelling group of the ICTP 7
Evaluation of surface variables during Nov-Apr (1980-2010)
Mean winter tas bias (° C) with respect to MERRA2 (Nov-Apr, 1980-2010) 9 RegCM4.7 biases?
Mean winter pr bias (mm) with respect to GPCP (Nov-Apr, 1980-2010) 10 RegCM4.7 biases?
Intercomparison of the PDFs of daily winter precipitation over Eastern Mexico (Nov-Apr, 1980-2010) Eastern Mexico 10 0 1 10 10 2 10 3 Probability 10 4 10 5 10 6 10 7 10 8 0 100 200 300 400 500 600 Precipitation (mm day 1 ) Livneh CHIRPS MERRA2 ERA75 HADGEM MPI GFDL 11
Spatial Taylor diagrams for Eastern Mexico (Nov-Apr, 1980 - 2010) Temperature Precipitation 0 . 0 0 . 0 0.2 0.2 7 0 45 . 0.4 4 5.6 0 5 Correlation Correlation 40 0.6 0.6 4.8 0.7 0.7 35 CRU 4.0 Livneh CRU 0.8 30 0.8 40 CHIRPS Livneh 5 GPCP MERRA2 3.2 25 MERRA2 ERA75 0 0 . . 9 9 20 HADGEM ERA75 2.4 HADGEM MPI 0 0 . . 15 9 9 5 MPI 5 GFDL 1.6 GFDL 10 0 0.99 . 0.8 9 10 5 9 0 2 1 30 3 0 1 0.0 1 . 5 15 45 . 0.0 0.8 1.6 2.4 3.2 4.0 4.8 5.6 0 10 20 25 30 35 40 0 0 Standard deviation ( ◦ C) Standard deviation (mm month − 1 ) 12
Detection of the position and intensity of the Subtropical Jet Stream during DJF 1980-2010 13
Bias of wind speed at 250 hPa during DJF (1980-2010) MERRA2 - database RegCM4.7 biases? 14
Detection methods of the STJ at 250 hPa using winds from ERA75 Jet core ⊚ Strong and Davis (2007) Relative maximum based on ∂ 2 V ∂ y 2 < 0 and V ≥ 25.7 ms − 1 (50 kt) Jet axis ⊚ Based on gradient of wind speed ∂ y � 0 and V ≥ 25.7 ms − 1 (50 kt) ∂ V 15
Trends of the jet core frequency ( days decade − 1 ) at 250 hPa during winter (DJF, 1980-2010) 50°N R3 R1 40°N R4 30°N R2 20°N 160°W 140°W 120°W 100°W 80°W 60°W 40°W 5 4 3 2 1 0 1 2 3 4 5 Coefficient of determination ( R 2 ) (days decade − 1 ) Climatological position of the STJ xxx Significant trend at 95%
Pacific STJ axis as a function of the PNA and ENSO (DJF, 1980-2010) Pacific ↑ ↓ Coastal Pacific 17
Atlantic STJ axis as a function of the PNA (DJF, 1980-2010) Subtropical Jet Stream: pending activities ⊚ Can the RegCM4.7 forced with ERA75 reproduce the trends and variability of the STJ? 18
Preliminary conclusions ⊚ The Pacific STJ is modulated mainly by the PNA and ENSO . • PNA + The jet axis is more intense over the Pacific. • ENSO + The jet axis is further south over the coastal Pacific. The Pacific STJ has become less frequent in the southern part of the climatological jet suggesting a poleward shift. ⊚ The Atlantic STJ is modulated mainly by the PNA and AO . • PNA + The jet axis is farther south over the eastern United States and the Gulf of Mexico. The Atlantic STJ has become more frequent in the southeastern quadrant of the climatological jet suggesting an equatorward shift . 19
Next steps ⊚ To add the regional model RegCM4.7 in the evaluation of surface variables and upper winds. To quantify the added value of RegCM4.7. ⊚ To apply detection methods for winter processes: cyclones, cold fronts and Norte winds. ⊚ To investigate the future changes of the winter circulation at synoptic and regional scale. Grazie, Gracias, Thank you rluna@cicese.edu.mx 20
References ⊚ Allen, R. J., and Sherwood, S. C. 2008. Warming maximum in the tropical upper troposphere deduced from thermal winds. Nature Geoscience, 1(6), 399. Barnes, E. A., and Screen, J. A. 2015. The impact of Arctic warming on the mid-latitude jet- stream: Can it? ⊚ Has it? Will it? Wiley Interdisciplinary Reviews: Climate Change, 6(3), 277–286. Cohen, J., Screen, J. A., Furtado, J. C., Barlow, M., Whittleston, D., Coumou, D., ... and Jones, J. 2014. ⊚ Recent Arctic amplification and extreme mid-latitude weather. Nature geoscience, 7(9), 627. Collins, W. J., Bellouin, N., Doutriaux-Boucher, M., Gedney, N., Hinton, T., Jones, C. D., ... Senior, C. 2008. ⊚ Evaluation of the HadGEM2 model. Hadley Cent. Tech. Note, 74. Di Luca, A., de Elía, R., and Laprise, R. 2015. Challenges in the quest for added value of regional climate ⊚ dynamical downscaling. Current Climate Change Reports, 1(1), 10-21. Dosio, A., Panitz, H. J., Schubert-Frisius, M., and Lüthi, D. (2015). Dynamical downscaling of CMIP5 global ⊚ circulation models over CORDEX-Africa with COSMO-CLM: evaluation over the present climate and analysis of the added value. Climate Dynamics, 44(9-10), 2637-2661. Dunne, J. P ., John, J. G., Adcroft, A. J., Griffies, S. M., Hallberg, R. W., Shevliakova, E., ... Krasting, J. P . ⊚ 2012. GFDL ’s ESM2 global coupled climate–carbon earth system models. Part I: Physical formulation and baseline simulation characteristics. Journal of Climate, 25(19), 6646-6665. Francis, J. A., and Vavrus, S. J. 2012. Evidence linking Arctic amplification to extreme weather in ⊚ midlatitudes. Geophysical Research Letters, 39(6). Giorgi F, Coppola E, Solmon F, Mariotti L ...and C, Brankovic.2012. RegCM4: model description and ⊚ preliminary tests over multiple CORDEX domains. Clim Res 52:7-29. Strong, C., and Davis, R. E. 2007. Winter jet stream trends over the Northern Hemisphere. Quarterly ⊚ Journal of the Royal Meteorological Society: A journal of the atmospheric sciences, applied meteorology and physical oceanography, 133(629), 2109-2115. 21
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Study region Mean annual cycle of tas (° C) and pr (mm) in the study region during 1980-2010 28 300 Livneh Livneh CRU CHIRPS 26 250 MERRA2 CRU Precipitation (mm month − 1 ) ERA75 GPCP HadGEM MERRA2 Temperature ( ◦ C) 24 200 MPI ERA75 GFDL HadGEM MPI 22 150 GFDL 20 100 18 50 16 J F M A M J J A S O N D J F M A M J J A S O N D 23
67.5 Day 800 50°N 62.5 Jet axis 57.5 40°N 52.5 (ms − 1 ) 30°N 47.5 42.5 20°N 37.5 10°N - - Based on relative vorticity 32.5 0° ( ξ � 0 and V ≥ 25.7 ms − 1 ) 27.5 10°S 160°W 140°W 120°W 100°W 80°W 60°W 40°W - - Based on wind speed gradient ( ∂ V ∂ y � 0 and V ≥ 25.7 ms − 1 ) 50 Year 16 50°N 45 40°N (ms − 1 ) 40 30°N 20°N 35 10°N 0° 30 24 10°S 160°W 140°W 120°W 100°W 80°W 60°W 40°W
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