Cooperative Institute for Research in Environmental Sciences

Prashant Sardeshmukh

Prashant Sardeshmukh

Diagnosis, modeling, and predictability of large-scale weather and climate variations on time scales of days to millennia.

Current Research

How has global warming affected the tropical Pacific Walker Circulation?

The tropical Pacific Walker Circulation (PWC) is a planetary scale east-west overturning of the equatorial atmosphere with ascent over the western Pacific and descent over the eastern Pacific ocean. There’s great interest in how the PWC has been affected by 20th century global warming. As yet, however, there’s no clear observational consensus on whether it has weakened, strengthened, or stayed unchanged. On the other hand, a general slowdown of overturning atmospheric circulations has been argued to be physically necessary to explain the relatively weak response of global precipitation to global warming obtained in many climate models, but it’s not clear to what extent such an argument applies to regional overturning circulations such as the PWC. Still, many climate models do also simulate a 20th century weakening of the PWC. Is this correct?

We have recently published a detailed study (Sandeep et al., 2014) of 20th century PWC changes and their physical mechanisms using a combination of observational data sets and atmosphere-ocean coupled climate model simulations included in the latest Intergovernmental Panel on Climate Change report. The PWC weakens over the century in the coupled model simulations, but strengthens in the observational 20th Century Reanalysis data set and also in separate uncoupled atmospheric general circulation model (AGCM) simulations with prescribed observed changes in radiative forcings and sea surface temperatures (SSTs). We argue that the weakening in the coupled simulations is not a consequence of a reduced global convective mass flux expected from the simple argument outlined above, but is rather due to a weakening of the zonal equatorial Pacific SST gradient.

We provide further clarification through additional uncoupled AGCM simulations in which portions of the observed SST changes that are related or unrelated to the El Niño Southern Oscillation (ENSO) are prescribed separately as lower boundary conditions. Both sets of SST fields have a global warming trend, and both sets of simulations produce a weakening of the global convective mass flux (see figure). However, consistent with the strong role of the zonal SST gradient, the PWC strengthens in the simulations with the ENSO-unrelated SST forcing, which has a strengthening zonal SST gradient, despite the weakening of the global convective mass flux. Overall, our results suggest that the PWC strengthened during 20th century global warming, but also that this strengthening was partly masked by a weakening trend associated with ENSO-related PWC variability.

Sandeep, S, F Stordal, PD Sardeshmukh, and GP Compo. 2014. Pacific Walker Circulation variability in coupled and uncoupled models. Climate Dynam. 43(1-2):103- 117.


Variations of a PWC index and atmospheric convective mass flux (Mc) in NCAR/CAM4 model simulations in which only the ENSO-related and ENSO-unrelated portions of observed SST changes are prescribed.

View Publications

  • Sardeshmukh, PD and C Penland (2015), Understanding the distinctively skewed and heavy tailed character of atmospheric and oceanic probability distributions. Chaos Version: 1 25 (3) , Art. No. 36410, issn: 1054-1500, ids: CF1OB, doi: 10.1063/1.4914169, PubMed ID: 25833448
  • Capotondi, A and PD Sardeshmukh (2015), Optimal precursors of different types of ENSO events. Geophys. Res. Lett. Version: 1 42 (22) 9952-9960, issn: 0094-8276, ids: DB2MO, doi: 10.1002/2015GL066171
  • Muller, WA, D Matei, M Bersch, JH Jungclaus, H Haak, K Lohmann, GP Compo, PD Sardeshmukh and J Marotzke (2015), A twentieth-century reanalysis forced ocean model to reconstruct the North Atlantic climate variation during the 1920s. Clim. Dyn. Version: 1 44 (8-Jul) 1935-1955, issn: 0930-7575, ids: CD9YS, doi: 10.1007/s00382-014-2267-5
  • Stucki, P, S Bronnimann, O Martius, C Welker, R Rickli, S Dierer, DN Bresch, GP Compo and PD Sardeshmukh (2015), Dynamical Downscaling and Loss Modeling for the Reconstruction of Historical Weather Extremes and Their Impacts: A Severe Foehn Storm in 1925. Bull. Amer. Meteorol. Soc. Version: 1 96 (8) , issn: 0003-0007, ids: CR5FG, doi: 10.1175/BAMS-D-14-00041.1
  • Bronnimann, S, AM Fischer, E Rozanov, P Poli, GP Compo and PD Sardeshmukh (2015), Southward shift of the northern tropical belt from 1945 to 1980. Nat. Geosci. Version: 1 8 (12) 969-U110, issn: 1752-0894, ids: CZ6GW, doi: 10.1038/NGEO2568
  • Sardeshmukh, PD, GP Compo and C Penland (2015), Need for Caution in Interpreting Extreme Weather Statistics. J. Clim. Version: 1 28 (23) 9166-9187, issn: 0894-8755, ids: CX7DC, doi: 10.1175/JCLI-D-15-0020.1
  • Sandeep, S, F Stordal, PD Sardeshmukh and GP Compo (2014), Pacific Walker Circulation variability in coupled and uncoupled climate models. Clim. Dyn. Version: 1 43 (2-Jan) 103-117, issn: 0930-7575, ids: AK3PS, doi: 10.1007/s00382-014-2135-3
  • Compo, GP, PD Sardeshmukh, JS Whitaker, P Brohan, PD Jones and C McColl (2013), Independent confirmation of global land warming without the use of station temperatures. Geophys. Res. Lett. Version: 1 40 (12) 3170-3174, issn: 0094-8276, ids: 185FJ, doi: 10.1002/grl.50425
  • Wang, XLL, Y Feng, GP Compo, VR Swail, FW Zwiers, RJ Allan and PD Sardeshmukh (2013), Trends and low frequency variability of extra-tropical cyclone activity in the ensemble of twentieth century reanalysis. Clim. Dyn. Version: 1 40 (12-Nov) 2775-2800, issn: 0930-7575, ids: 149ZU, doi: 10.1007/s00382-012-1450-9
  • Bronnimann, S, O Martius, H von Waldow, C Welker, J Luterbacher, GP Compo, PD Sardeshmukh and T Usbeck (2012), Extreme winds at northern mid-latitudes since 1871. Meteorol. Z. Version: 1 21 (1) 13-27, issn: 0941-2948, ids: 906XQ, doi: 10.1127/0941-2948/2012/0337
  • Newman, M, GN Kiladis, KM Weickmann, FM Ralph and PD Sardeshmukh (2012), Relative Contributions of Synoptic and Low-Frequency Eddies to Time-Mean Atmospheric Moisture Transport, Including the Role of Atmospheric Rivers. J. Clim. Version: 1 25 (21) 7341-7361, issn: 0894-8755, ids: 036BZ, doi: 10.1175/JCLI-D-11-00665.1
  • Penland, C and PD Sardeshmukh (2012), Alternative interpretations of power-law distributions found in nature. Chaos Version: 1 22 (2) , Art. No. 23119, issn: 1054-1500, ids: 966JM, doi: 10.1063/1.4706504, PubMed ID: 22757526
  • Shin, SI, PD Sardeshmukh and SW Yeh (2011), Sensitivity of the northeast Asian summer monsoon to tropical sea surface temperatures. Geophys. Res. Lett. Version: 1 38 , Art. No. L22702, issn: 0094-8276, ids: 851HH, doi: 10.1029/2011GL049391
  • Shin, SI and PD Sardeshmukh (2011), Critical influence of the pattern of Tropical Ocean warming on remote climate trends. Clim. Dyn. Version: 1 36 (8-Jul) 1577-1591, issn: 0930-7575, ids: 744PA, doi: 10.1007/s00382-009-0732-3
  • Pegion, K and PD Sardeshmukh (2011), Prospects for Improving Subseasonal Predictions. Mon. Weather Rev. Version: 1 139 (11) 3648-3666, issn: 0027-0644, ids: 840XP, doi: 10.1175/MWR-D-11-00004.1
  • Compo, GP, JS Whitaker, PD Sardeshmukh, N Matsui, RJ Allan, X Yin, BE Gleason, RS Vose, G Rutledge, P Bessemoulin, S Bronnimann, M Brunet, RI Crouthamel, AN Grant, PY Groisman, PD Jones, MC Kruk, AC Kruger, GJ Marshall, M Maugeri, HY Mok, O Nordli, TF Ross, RM Trigo, XL Wang, SD Woodruff and SJ Worley (2011), The Twentieth Century Reanalysis Project. Q. J. R. Meteorol. Soc. Version: 1 137 (654) 1-28, issn: 0035-9009, ids: 724QX, doi: 10.1002/qj.776
  • Shin, SI, PD Sardeshmukh and RS Webb (2010), Optimal Tropical Sea Surface Temperature Forcing of North American Drought. J. Clim. Version: 1 23 (14) 3907-3917, issn: 0894-8755, ids: 643FK, doi: 10.1175/2010JCLI3360.1
  • Giese, BS, GP Compo, NC Slowey, PD Sardeshmukh, JA Carton, S Ray and JS Whitaker (2010), THE 1918/19 EL NINO. Bull. Amer. Meteorol. Soc. Version: 1 91 (2) 177-183, issn: 0003-0007, ids: 572XH, doi: 10.1175/2009BAMS2903.1
  • Compo, GP and PD Sardeshmukh (2010), Removing ENSO-Related Variations from the Climate Record. J. Clim. Version: 1 23 (8) 1957-1978, issn: 0894-8755, ids: 594LE, doi: 10.1175/2009JCLI2735.1
  • Shin, SI, PD Sardeshmukh and K Pegion (2010), Realism of local and remote feedbacks on tropical sea surface temperatures in climate models. J. Geophys. Res.-Atmos. Version: 1 115 , Art. No. D21110, issn: 2169-897X, ids: 676UT, doi: 10.1029/2010JD013927
  • Compo, GP and PD Sardeshmukh (2009), Oceanic influences on recent continental warming. Clim. Dyn. Version: 1 32 (3-Feb) 333-342, issn: 0930-7575, ids: 389IO, doi: 10.1007/s00382-008-0448-9
  • Sardeshmukh, PD and P Sura (2009), Reconciling Non-Gaussian Climate Statistics with Linear Dynamics. J. Clim. Version: 1 22 (5) 1193-1207, issn: 0894-8755, ids: 426AZ, doi: 10.1175/2008JCLI2358.1
  • Newman, M, PD Sardeshmukh and C Penland (2009), How Important Is Air-Sea Coupling in ENSO and MJO Evolution?. J. Clim. Version: 1 22 (11) 2958-2977, issn: 0894-8755, ids: 467SR, doi: 10.1175/2008JCLI2659.1
  • Sura, P and PD Sardeshmukh (2009), A global view of air-sea thermal coupling and related non-Gaussian SST variability. Atmos. Res. Version: 1 Special Session on Ocean-Atmosphere Coupling held at the 24th IUGG 94 (1) 140-149, Perugia, ITALY, JUL 02-12, 2007, issn: 0169-8095, ids: 496HR, doi: 10.1016/j.atmosres.2008.08.008
  • Sura, P and PD Sardeshmukh (2008), A Global view of non-Gaussian SST variability. J. Phys. Oceanogr. Version: 1 38 (3) 639-647, issn: 0022-3670, ids: 276EQ, doi: 10.1175/2007JPO3761.1
  • Newman, M and PD Sardeshmukh (2008), Tropical and stratospheric influences on extratropical short-term climate variability. J. Clim. Version: 1 21 (17) 4326-4347, issn: 0894-8755, ids: 345JC, doi: 10.1175/2008JCLI2118.1
  • Sardeshmukh, PD and P Sura (2007), Multiscale impacts of variable heating in climate. J. Clim. Version: 1 20 (23) 5677-5695, issn: 0894-8755, ids: 239RG, doi: 10.1175/2007JCLI1411.1
  • Compo, GP, JS Whitaker and PD Sardeshmukh (2006), Feasibility of a 100-year reanalysis using only surface pressure data. Bull. Amer. Meteorol. Soc. Version: 1 87 (2) 175-+, issn: 0003-0007, ids: 021CW, doi: 10.1175/BAMS-87-2-175
  • Barsugli, JJ, SI Shin and PD Sardeshmukh (2006), Sensitivity of global warming to the pattern of tropical ocean warming. Clim. Dyn. Version: 1 27 (5) 483-492, issn: 0930-7575, ids: 076KM, doi: 10.1007/s00382-006-0143-7
  • Shin, SI, PD Sardeshmukh, RS Webb, RJ Oglesby and JJ Barsugli (2006), Understanding the mid-Holocene climate. J. Clim. Version: 1 19 (12) 2801-2817, issn: 0894-8755, ids: 057ZT, doi: 10.1175/JCLI3733.1
  • Sura, P, M Newman, C Penland and P Sardeshmukh (2005), Multiplicative noise and non-gaussianity: A paradigm for atmospheric regimes?. J. Atmos. Sci. Version: 1 62 (5) 1391-1409, issn: 0022-4928, ids: 929IB, doi: 10.1175/JAS3408.1
  • Barsugli, J, SI Shin and PD Sardeshmukh (2005), Tropical climate regimes and global climate sensitivity in a simple setting. J. Atmos. Sci. Version: 1 62 (4) 1226-1240, issn: 0022-4928, ids: 918EL, doi: 10.1175/JAS3404.1
  • Compo, GP and PD Sardeshmukh (2004), Storm track predictability on seasonal and decadal scales. J. Clim. Version: 1 17 (19) 3701-3720, issn: 0894-8755, ids: 860RZ, doi: 10.1175/1520-0442(2004)017<3701:STPOSA>2.0.CO;2
  • Newman, M, PD Sardeshmukh, CR Winkler and JS Whitaker (2003), A study of subseasonal predictability. Mon. Weather Rev. Version: 1 131 (8) 1715-1732, issn: 0027-0644, ids: 704NY, doi: 10.1175//2558.1
  • Sardeshmukh, PD, C Penland and M Newman (2003), Drifts induced by multiplicative red noise with application to climate. Europhys. Lett. Version: 1 63 (4) 498-504, issn: 0295-5075, ids: 709GU, doi: 10.1209/epl/i2003-00550-y
  • Barsugli, JJ and PD Sardeshmukh (2002), Global atmospheric sensitivity to tropical SST anomalies throughout the Indo-Pacific basin. J. Clim. Version: 1 15 (23) 3427-3442, issn: 0894-8755, ids: 615WH, doi: 10.1175/1520-0442(2002)015<3427:GASTTS>2.0.CO;2
  • Ricciardulli, L and PD Sardeshmukh (2002), Local time- and space scales of organized tropical deep convection. J. Clim. Version: 1 15 (19) 2775-2790, issn: 0894-8755, ids: 593RQ, doi: 10.1175/1520-0442(2002)015<2775:LTASSO>2.0.CO;2
  • Compo, GP, PD Sardeshmukh and C Penland (2001), Changes of subseasonal variability associated with El Nino. J. Clim. Version: 1 14 (16) 3356-3374, issn: 0894-8755, ids: 464WF, doi: 10.1175/1520-0442(2001)014<3356:COSVAW>2.0.CO;2
  • Winkler, CR, M Newman and PD Sardeshmukh (2001), A linear model of wintertime low-frequency variability. Part I: Formulation and forecast skill. J. Clim. Version: 1 14 (24) 4474-4494, issn: 0894-8755, ids: 504XE, doi: 10.1175/1520-0442(2001)014<4474:ALMOWL>2.0.CO;2
  • Sardeshmukh, PD, GP Compo and C Penland (2000), Changes of probability associated with El Nino. J. Clim. Version: 1 13 (24) 4268-4286, issn: 0894-8755, ids: 385EF, doi: 10.1175/1520-0442(2000)013<4268:COPAWE>2.0.CO;2
  • Newman, M, PD Sardeshmukh and JW Bergman (2000), An assessment of the NCEP, NASA, and ECMWF reanalyses over the tropical west Pacific warm pool. Bull. Amer. Meteorol. Soc. Version: 1 81 (1) 41-48, issn: 0003-0007, ids: 270GT, doi: 10.1175/1520-0477(2000)081<0041:AAOTNN>2.3.CO;2
  • Smith, CA and PD Sardeshmukh (2000), The effect of ENSO on the intraseasonal variance of surface temperatures in winter. Int. J. Climatol. Version: 1 20 (13) 1543-1557, issn: 0899-8418, ids: 376EP, doi: 10.1002/1097-0088(20001115)20:13<1543::AID-JOC579>3.0.CO;2-A
  • Huang, HP and PD Sardeshmukh (2000), Another look at the annual and semiannual cycles of atmospheric angular momentum. J. Clim. Version: 1 13 (18) 3221-3238, issn: 0894-8755, ids: 364MN, doi: 10.1175/1520-0442(2000)013<3221:ALATAA>2.0.CO;2
  • Whitaker, JS and PD Sardeshmukh (1998), A linear theory of extratropical synoptic eddy statistics. J. Atmos. Sci. Version: 1 55 (2) 237-258, issn: 0022-4928, ids: YT205, doi: 10.1175/1520-0469(1998)055<0237:ALTOES>2.0.CO;2
  • Newman, M and PD Sardeshmukh (1998), The impact of the annual cycle on the North Pacific North American response to remote low-frequency forcing. J. Atmos. Sci. Version: 1 55 (8) 1336-1353, issn: 0022-4928, ids: ZJ701, doi: 10.1175/1520-0469(1998)055<1336:TIOTAC>2.0.CO;2
  • Hall, NMJ and PD Sardeshmukh (1998), Is the time-mean northern hemisphere flow baroclinically unstable?. J. Atmos. Sci. Version: 1 55 (1) 41-56, issn: 0022-4928, ids: YQ943, doi: 10.1175/1520-0469(1998)055<0041:ITTMNH>2.0.CO;2
  • KLINKER, E and PD SARDESHMUKH (1992), THE DIAGNOSIS OF MECHANICAL DISSIPATION IN THE ATMOSPHERE FROM LARGE-SCALE BALANCE REQUIREMENTS. J. Atmos. Sci. Version: 1 49 (7) 608-627, issn: 0022-4928, ids: HQ272, doi: 10.1175/1520-0469(1992)049<0608:TDOMDI>2.0.CO;2