Biases in the Tropical Indian Ocean subsurface temperature ...MOES/rac-2019/Rashmi-Kakatkar.pdf ·...
1
Biases in the Tropical Indian Ocean subsurface temperature variability in a coupled model Rashmi Kakatkar*, C. Gnanaseelan, J. S. Chowdary, J. S. Deepa, Anant Parekh Climate Variability and Data Assimilation Research, Indian Institute of Tropical Meteorology, Pune Rashmi Kakatkar*, C. Gnanaseelan, J. S. Chowdary, J. S. Deepa, Anant Parekh Climate Variability and Data Assimilation Research, Indian Institute of Tropical Meteorology, Pune Introduction : v Unrealistic rapid decay of TIO basin-wide SST warming is seen in CFSv2 during the developed to decaying phases of El Niño v CFSv2 failed to capture the subsurface – surface interaction in south-western TIO during DJF and MAM as compared to ORAS4 or observations v Thus, detailed study of subsurface mode and its impact on surface and air-sea interaction in coupled models is very important, especially for prediction purposes v This has motivated us to understand the TIO subsurface variability, the forcing mechanisms, the characteristics etc., in CFSv2 Data and Methodology: • ORAS4 and ARGO ocean temperature • ERA40-Interim • CFSv2 Free run [Roxy (2014)] • EOF analysis • Correlation analysis • Regression analysis Results and Discussions Reference: • Rashmi Kakatkar, C. Gnanaseelan, J. S. Chowdary, J. S. Deepa, Anant Parekh, 2018, Biases in the Tropical Indian Ocean subsurface temperature variability in a coupled model, Climate Dynamics, online, https://doi.org/10.1007/s00382-018-4455-1. Acknowledgements : Authors acknowledge the support and facilities provided by ESSO-IITM, Pune and MoES Chowdary et al., 2016, CD Correlation between 100m temp anomalies and SST anomalies CFSv2 fails to capture the intensification of the mode in DJF(0): Southern warming weakens with no extension to the west and the northern cooling almost disappears Peak warm anomalies are at around 100 m in the reanalysis where as they are at about 150 m in the model. This discrepancy in the model could be due to the deeper than observed thermocline • Upward propagation of warm anomalies in the central to western region: strengthen the subsurface surface interaction and in turn amplify the air–sea interaction • Such upward propagation of warm anomalies is underestimated in the model contributing to the suppression of thermocline SST coupling Summary : CFSv2 displays early decay of the subsurface mode in DJF season. The misrepresentation of equatorial surface wind anomalies, associated Ekman transport as well as the Ekman pumping and misrepresentation of surface anticyclonic circulations resulted in the early weakening of the TIO subsurface mode in CFSv2. The anomalously prolonged decay phase of El Niño in CFSv2 is found only during the El Niño, IOD co-occurrence years. It is also found that the misrepresentation of subsurface variability in CFSv2 during DJF is closely associated with the rapid decay of El Niño forced TIO warming. The subsurface-surface interaction is not well captured by CFSv2 mainly during DJF. Proper temporal and spatial evolution of TIO subsurface temperature modes in models feedback to surface thereby improving the air–sea interactions. wind stress curl anomalies (shaded,×10 −7 N/m 3 ) and wind stress anomalies (vectors,×10 −2 N/m 2 ) at 1000 hPa Ekman pumping velocity (shaded,×10 −6 m/s) and Ekman meridional transport (contours, m 2 /s) at 1000 hPa • Surface wind anomalies and associated Ekman transport and Ekman pumping are not represented well in CFSv2 L Weaker downwelling Rossby waves •Equatorial easterlies are not represented well in CFSv2 L Weak upwelling Kelvin wave propagation Stream function (shaded, s −1 ) and rotational component of wind anomalies (vectors, m/s) at 1000 hPa • The southern anticyclone is not correctly positioned in the model, while northern anticyclone is much weaker. • This resulted in the misrepresentation of surface equatorial winds and in turn the north– south mode in the model Composite of normalized SST anomalies averaged over TIO (40 o E to 100 o E, 20 o S to 20 o N) Correlation coefficient and Regression coefficient Without IOD Without IOD Without ENSO Without ENSO Regression coefficient Anomalously prolonged decay phase of El Niño in CFSv2 is found only during the El Niño, IOD co-occurrence years The misreprese ntation of subsurface variability in CFSv2 during DJF is closely associated with the rapid decay of El Niño forced TIO warming CFSv2 is able to represent inter- annual variability patterns during SON season Evolution of subsurface temperature mode in TIO in CFSv2 Mechanisms behind early decay of subsurface dipole in TIO in CFSv2 Impact of subsurface temperature mode in TIO on SST in CFSv2
Transcript of Biases in the Tropical Indian Ocean subsurface temperature ...MOES/rac-2019/Rashmi-Kakatkar.pdf ·...
Biases in the Tropical Indian Ocean subsurface temperature variability in a coupled model
Rashmi Kakatkar*, C. Gnanaseelan, J. S. Chowdary, J. S. Deepa, Anant ParekhClimate Variability and Data Assimilation Research, Indian Institute of Tropical Meteorology, Pune
Rashmi Kakatkar*, C. Gnanaseelan, J. S. Chowdary, J. S. Deepa, Anant ParekhClimate Variability and Data Assimilation Research, Indian Institute of Tropical Meteorology, Pune
Introduction:vUnrealistic rapid decay of TIO basin-wide SST warming is seen inCFSv2 during the developed to decaying phases of El Niño
vCFSv2 failed to capture the subsurface – surface interaction insouth-western TIO during DJF and MAM as compared to ORAS4 orobservations
vThus, detailed study of subsurface mode and its impact on surfaceand air-sea interaction in coupled models is very important,especially for prediction purposes
vThis has motivated us to understand the TIO subsurface variability,the forcing mechanisms, the characteristics etc., in CFSv2
Data and Methodology:
• ORAS4 and ARGO ocean temperature
• ERA40-Interim• CFSv2 Free run
[Roxy (2014)]• EOF analysis• Correlation analysis• Regression analysis
Results and Discussions
Reference:• Rashmi Kakatkar, C. Gnanaseelan, J. S. Chowdary, J. S. Deepa, Anant Parekh, 2018, Biases in the Tropical Indian Ocean subsurface temperature variability in a coupled model, Climate Dynamics, online, https://doi.org/10.1007/s00382-018-4455-1. Acknowledgements: Authors acknowledge the support and facilities provided by ESSO-IITM, Pune and MoES
Chowdary et al., 2016, CD Correlation between 100m temp anomalies and SST anomalies
CFSv2 fails to capture the intensification of themode in DJF(0): Southern warming weakenswith no extension to the west and the northerncooling almost disappears
Peak warmanomalies are ataround 100 m inthe reanalysiswhere as theyare at about 150m in the model.This discrepancyin the modelcould be due tothe deeper thanobservedthermocline
• Upward propagation of warm anomalies in thecentral to western region: strengthen thesubsurface surface interaction and in turnamplify the air–sea interaction• Such upward propagation of warm anomaliesis underestimated in the model contributing tothe suppression of thermocline SST coupling
Summary: CFSv2 displays early decay of the subsurface mode in DJF season. Ø The misrepresentation of equatorial surface wind anomalies, associated Ekman transport as well as the Ekman pumping and
misrepresentation of surface anticyclonic circulations resulted in the early weakening of the TIO subsurface mode in CFSv2.Ø The anomalously prolonged decay phase of El Niño in CFSv2 is found only during the El Niño, IOD co-occurrence years. It is also found that
the misrepresentation of subsurface variability in CFSv2 during DJF is closely associated with the rapid decay of El Niño forced TIO warming.The subsurface-surface interaction is not well captured by CFSv2 mainly during DJF.
Ø Proper temporal and spatial evolution of TIO subsurface temperature modes in models feedback to surface thereby improving the air–seainteractions.
wind stress curl anomalies (shaded,×10−7 N/m3) and wind stress anomalies (vectors,×10−2 N/m2) at 1000 hPa
Ekman pumping velocity (shaded,×10−6 m/s) and Ekman meridional transport (contours, m2/s) at 1000 hPa
• Surface windanomalies andassociatedEkmantransport andEkmanpumping arenot representedwell in CFSv2è WeakerdownwellingRossby waves
•Equatorialeasterlies arenot representedwell in CFSv2è WeakupwellingKelvin wavepropagation
Stream function (shaded, s−1) and rotational component of wind anomalies (vectors, m/s) at 1000 hPa
• The southern anticyclone is not correctlypositioned in the model, while northernanticyclone is much weaker.• This resulted in the misrepresentation ofsurface equatorial winds and in turn the north–south mode in the model
Composite of normalized SST anomalies averaged over TIO (40oE to 100oE, 20oS to 20oN)
Correlation coefficient and Regression coefficient
Without IODWithout IOD
Without ENSOWithout ENSO
Regression coefficient
Anomalously prolonged decay phase of El Niñoin CFSv2 is found only during the El Niño, IODco-occurrence years
Themisrepresentation ofsubsurfacevariability inCFSv2during DJFis closelyassociatedwith therapid decayof El Niñoforced TIOwarming
CFSv2 is able torepresent inter-annual variabilitypatterns duringSON season
Evolution of subsurface temperature mode in TIO in CFSv2
Mechanisms behind early decay of subsurface dipole in TIO in CFSv2
Impact of subsurface temperature mode in TIO on SST in CFSv2
