SD 13: The Indian Ocean s Influence on Regional Hydroclimate

Transcription

1 SD 13: The Indian Ocean s Influence on Regional Hydroclimate Caroline C. Ummenhofer, WHOI, USA NASA (2015) Halosteric component of ITF transport Felton et al. (2014) Hu & Sprintall (2017)

2 Variability in hydrological cycle spans across timescales: (sub)seasonal interannual decadal and beyond NASA (2015) Halosteric component of ITF transport Felton et al. (2014) Hu & Sprintall (2017)

3 Variability in hydrological cycle spans across timescales: (sub)seasonal interannual decadal and beyond Close connection to upper-ocean thermal structure NASA (2015) Feng et al. (2015) Hu & Sprintall (2017)

4 Indian monsoon and ENSO- Asian monsoon-teleconnection (e.g., Ashok et al. 2001, 2004, Ihara et al. 2007, Ummenhofer et al. 2011a) Enhanced rainfall & flooding in East Africa (e.g., Behera et al. 1999, 2005, Birkett et al. 1999, Webster et al. 1999, Black et al. 2003, Ummenhofer et al. 2009a) Droughts and wildfires in Indonesia (e.g., Abram et al. 2003, Field et al. 2009, D Arrigo et al. 2011) Rainfall, droughts and bushfires in Southeast Australia (e.g., Ashok et al. 2003, Cai et al. 2009a,b, Ummenhofer et al. 2009b, 2011b) Schematic highlighting influence of Indian Ocean SSTA on regional rainfall, using AGCM simulations. Specific regions with SSTA characteristic of (sub)tropical dipoles are employed in simulations, with poles indicated by dashed boxes. Anomalous rainfall associated with these regions of SSTA shown by circles in Indian Ocean rim countries.

5 E African rainfall anomalies associated with SST poles in AGCM simulations SSTA for entire Indian Ocean SSTA for eastern & western poles SSTA for western pole Enhanced East African short rains mainly due to warm SST anomalies in western pole Ummenhofer et al. (2009a)

6 SE Australian rainfall anomalies associated with SST poles in AGCM simulations SE Australian cool season rainfall mainly due to meridional SST gradient Ummenhofer et al. (2009b)

7 Interannual to longer-term variability SE Australia 5-year running mean of anomalies prolonged dry and wet periods (= intervals) superimposed Ummenhofer et al. (2011)

8 Interannual to longer-term variability SE Australia 10 driest/wettest years prolonged drought/pluvial Ummenhofer et al. (2011)

9 Interannual to longer-term variability SE Australia 10 driest/wettest years prolonged drought/pluvial Interannual timescales Decadal timescales ENSO IOD Ummenhofer et al. (2011)

10 Low-frequency IO subsurface thermal characteristics linked to IO SST variations cf. Annamalai et al. (2005) Ummenhofer et al. (2017)

11 Essential Ocean Variables - EOVs 1. Surface variables at air-sea interface (e.g., SST, SSS, surface winds, fluxes) needed at daily timescale across the entire Indo-Pacific region with large-scale coverage (e.g., satellite observations). 2. Direct observations of quantities related to hydrological cycle (e.g., precipitation, riverine input/runoff, and evaporation) warranted at daily resolution, especially for Maritime Continent region, NW shelf off Australia, BoB with its large riverine input. 3. Concurrent measurements of surface meteorology, air-sea fluxes of heat, freshwater, and momentum, as well as near-surface ocean temperature, salinity, and velocity at sub-daily timescale from in situ observations needed in key locations (e.g., SCTR, Arabian Sea, BoB, eastern & western equatorial Indian Ocean, and NW shelf off Australia). 4. Upper-ocean properties, primarily temperature and salinity, for top 300m at weekly resolution that relate to thermocline variations with focus on SCTR, Arabian Sea, BoB, eastern equatorial upwelling region off Sumatra and Java, western equatorial Indian Ocean, NW shelf off Australia.

12 Actionable Recommendations a. Maintain existing satellite observations for relevant variables at the air-sea interface with basin-scale coverage over the Indo-Pacific region. b. Maintain and replace SSS-sensing satellites with improved capabilities over marginal seas and coastal regions (cf. SMAP, Aquarius, SMOS). c. Maintain and improve river gauge network to observe runoff and riverine input from Indian Ocean rim countries along coasts. d. Maintain current RAMA array along the equator and meridional sections, especially for 90 E into BoB, 55 E and 67 E for the SCTR, and in eastern Indian Ocean ( E). e. Complete equatorial RAMA sites near 55 E in western Indian Ocean. f. Establish RAMA surface mooring and flux reference site on northwest shelf off Australia.

13 Reviewer Comments a. Chapter covers broad topic spanning many phenomena & timescales; better to merge this with discussions around key climate modes? b. Importance of SSS remote sensing particularly important for IO, where salinity in many regions sets upper ocean stratification as option to monitor freshwater input if river gauge network not viable? c. Emphasize crucial role that surface drifters & long mooring records play for cal./val. of satellite SST & reanalyses d. RAMA ends near ~15ºS; is that sufficient to cover areas of interest? Role of surface drifters/argo?