CESM-HYCOM GLBb0.08 vs. GLBt0.72

Experimental set-up: HYCOM+CICE+CAM(Atm)+CLM (Land)+RTM (river transports)

  1. GLBt0.72 (gh72): 0.72º (~75km) tripolar grid for Ocean and Ice and a 1.9ºx2.5º grid for the Atmosphere and Land

  2. GLBb0.08 (gh08): 0.08º (~8km) tripolar grid for Ocean and Ice and a 0.47ºx0.63º grid for the Atmosphere and Land

  3. Start from rest with the GDEM4 Climatology for the Ocean component and a constant cover/thickness in the Arctic and Antarctic for the  Ice component

  4. HYCOM: 32 hybrid sigma-2 layers, CAM: 26 levels, CICE: 5 categories

  5. No relaxation of sea surface temperature or salinity in HYCOM

  6. Simulation of 20 years in high resolution (6 months of computational time) to be compared with 25 years of low resolution (~70 hours).

  7. Evaluation is done against Observations and a 1/10º POP2+CICE+CAM+CLM (CCSM4-POP2) coupled simulation of 20 years described in McClean et al. 2011.

Surface Heat and Freshwater Flux

GLBt0.72

GLBb0.08

Heat Flux
Freshwater Flux

Total Kinetic Energy

  1.   Similar features in GLBt0.72 and GLBb0.08  with strong heat loss over western boundary currents and North Atlantic sub polar gyre, heat gain along the equator.

  2. GLBb0.08 colder in North and South Pacific gyres, south Indian Ocean.

  3. Similar feature in freshwater flux. Biggest difference in West Pacific.

McClean et al. 2011 (CCSM4 1/10º POP2)

GLBt0.72
GLBb0.08

Precipitation (mm/day)

  1.   Better representation of the precipitation over the Pacific warm pool in high resolution GLBb0.08 and compare well with CCSM4-POP2 simulation with 1/10º grid. (McClean et al. 2011)

  2. Lesser intensity of precipitation in HYCOM (GLBb0.08) compare with POP2, but closer to observations.

Evolution of total average Heat and Freshwater Flux

  1. Higher surface heat flux in low resolution.

  2. Slightly negative freshwater flux for both resolutions.

  3. Average Heat FLux:

  4. GLBt0.72: 4.8 ± 0.6 W/m2

  5. GLBb0.08: 1.9 ± 0.3 W/m2

  6. Average Freshwater Flux:

  7. GLBt0.72: -0.04 ± 0.01 mm/d

  8. GLBb0.08:-0.03 ± 0.01 mm/d

Wind Stress Magnitude

GLBt0.72

GLBb0.08

CORE2 Normal Year on GLBt0.72 grid

  1. Over estimation over the Southern Ocean for GLBt0.72 and GLBb0.08.

  2. Overestimation over the North Atlantic for GLBb0.08.

  3. Better representation of small features in GLBb0.08 compared with CORE2 in South Pacific.

Evolution of T,S,SST,SSS and SSH

  1. Global T increases more rapidly in GLBt0.72 due to the bigger heat flux imbalance.

             GLBt0.72: + 0.2ºC over 20 years

             GLBb0.08: + 0.09ºC over 20 years

  1. Slight increase of global S in both GLBt0.72 and GLBb0.08 due to the slight negative averaged freshwater flux.

            GLBt0.72: + 0.007 psu over 20 years

            GLBb0.08: + 0.005 psu over 20 years



SST and SSS Bias from Climatology

GLBt0.72

GLBb0.08

  1. Spatial biases different between GLBt0.72 and GLBb0.08.

  2. Less drift in SST overall everywhere in GLBb0.08 compared with GLBt0.72.

  3. Less SSS biases in GLBb0.08 overall, except for the Arctic region (ice differences).

GLBb0.08

  1. Similar biases between HYCOM and POP2 except North Atlantic and North Pacific where HYCOM present a positive bias while POP2 presents a negative one .

Barotropic Streamfunction

GLBt0.72

GLBb0.08

  1. Stronger circulation in the North Atlantic in GLBb0.08.

  2. Better representation of the circulation around in the Gulf of Mexico region in GLBb0.08.



GMOC and AMOC

GLBt0.72

GLBb0.08

GLBb0.08

  1. Stronger circulation in in GLBb0.08.


 

McClean et al. 2011

  1. Similar intensity of global circulation in GLBb0.08 compared with CCSM4-POP2 (McClean et al. 2011).

  2. Slightly stronger AMOC in GLBb0.08.

  1. Decrease of the AMOC in low resolution

  2. Increase of the AMOC in high resolution

Meridional Heat and Freshwater Transports

  1. Stronger heat transports in the mid-latitudes for high resolution GLBb0.08

  2. GLB0.08 Heat flux closer to Fasullo & Trenberth (2008).

  3. Slightly higher Global Heat transport in GLBb0.08 than in McClean et al. 2011.

  4. Similar transport in GLBb0.08 and GLBt0.72 in Indian and Pacific Ocean.

  5. Higher transport in GLBb0.08 in the Atlantic closer to Trenberth & Fasullo (2017,  max of 1.2PW)


Drift Global T and S

GLBt0.72

GLBb0.08

  1. Stronger biases in low resolution

  2. Cold/fresh drift at the surface in the Atlantic for GLBb0.08 instead of a warm/salty drift in GLBt0.72

Global
Atlantic
Global
Atlantic

Transports at several sections

  1. Stronger transport in GLBt0.72 at the Drake Passage, but transport decreasing.

  2. Similar transports at Bering

  3. Stronger transport in GLBb0.08 at Florida Straits since most of the transport by-passed the Gulf of Mexico in the low resolution.

  4. Stronger Indonesian Throughflow in GLBb0.08 but similar interannual variability


  1. GLBb0.08 closer to the observations than GLBt0.72 and CCSM4-POP2


Ice Cover

  1. GLBb0.08 ice cover closer to the observations than GLBt0.72 especially in the Arctic.

  2. Labrador Sea covered with ice in GLBt0.72 during winter

GLBt0.72

GLBb0.08

SSMI/NSIDC

Winter

SSMI/NSIDC

Summer

GLBt0.72

GLBb0.08

Ice Thickness

Winter

IceSat/NSIDC

GLBt0.72

GLBb0.08

  1. Better distribution of Sea Ice thickness in GLBb0.08 than in GLBt0.72.

  2. Not enough volume in GLBb0.08 and too much in GLBt0.72.

Summer

IceSat/NSIDC

GLBt0.72

GLBb0.08

Evolution of ice extent and volume

  1. Higher maximum extent in high resolution in Arctic than in the Observations.

  2. Linear increase of the sea-ice extent in lower resolution in Arctic.

  3. Extent above observations in GLBb0.08 and CCSM4-POP2 in the Arctic but closer to the observations for GLBb0.08.

  4. Extent below observations in GLBb0.08 and CCSM4-POP2 in the Antarctic but closer to the observations for GLBb0.08.

  5. Decrease of the sea-ice volume in GLBb0.08 between year 10 and 20.

GLBt0.72

GLBb0.08

Averaged Meridional Atlantic Section

GLBt0.72

GLBb0.08

Averaged Meridional Global Section

  1. Stronger biases in low resolution


  1. Stronger cold/fresh biases in Nordic Seas in low resolution than in high resolution.

  2. Biases in the Atlantic explain most of the Global biases.


Averaged T and S profile drift per latitudes (Year 0020 - Year 0001)


  1. CCSM4 ocean potential temperature (C) (left) and salinity (right) change from model year 19 – model year 1. Red line depicts high latitude regions (50–90), green lines are mid-latitudes (20–50), blue line is the tropics (20S–20N), and black lines are global. Thick and thin lines represent the Northern Hemisphere and Southern Hemispheres, respectively. (McClean et al. 2011)


  1. Lower global drifts in T and S in HYCOM compared with  POP

  2. Higher drifts at the surface in HYCOM in mid-latitudes, while POP has a maximum around 500m.

  3. Larger drifts in the tropics in HYCOM

GLBb0.08

GLBt0.72

  1. Overall lower drift in GLBb0.08 compared to GLBt0.72

  2. Strong positive temperature and negative salinity drift at ~100m and surface respectively in the low resolution in the tropical regions (20ºS-20ºN)

  3. Strong Salinity drift in Northern Hemisphere mid-latitude in low resolution

Comparison low resolution experiments -100 years-

Experimental set-up: HYCOM+CICE+CAM(Atm)+CLM (Land)+RTM (river transports)

  1. HYCOM GLBt0.72 (gh72): 0.72º (~75km) tripolar grid for Ocean and Ice and a 1.9ºx2.5º grid for the Atmosphere and Land

  2. POP gx1v6 (g16): 1º (~100km) bipolar grid for Ocean and Ice and a 1.9ºx2.5º grid for the Atmosphere and Land

  3. Start from rest with the Levitus-PHC2 Climatology for the Ocean components and a constant cover/thickness in the Arctic and Antarctic for the  Ice component

  4. HYCOM: 32 hybrid sigma-2 layers; POP: 60 z-coord levels, CAM: 26 levels, CICE: 5 categories

  5. No relaxation of sea surface temperature or salinity in HYCOM/POP

  6. Simulation of 100 years in starting from rest.

Outgoing longwave radiation (top of the atmosphere):

CESM-HYCOM f19

CESM-POP f19

Observations

High and low cloud fraction:

Precipitation:

CESM-HYCOM f19

CESM-POP f19

Observations

CESM-HYCOM f19

CESM-POP f19

Observations

Surface heat/freshwater flux and wind stress:

CESM-HYCOM f19

CESM-POP f19

CESM-HYCOM f19

CESM-POP f19

Surface atmospheric variables:

Surface biases:

CESM-HYCOM f19

CESM-POP f19

SST
SSS
CESM-HYCOM f19
CESM-POP f19

Salinity

Temperature

Temperature and Salinity evolution:

Evolution of water masses in the Atlantic:

Evolution of water masses total:

Transports at different straits:

Ice cover and thickness:

CESM-HYCOM f19

CESM-POP f19

Observations

WINTER ICE COVER

CESM-HYCOM f19

CESM-POP f19

Observations

SUMMER ICE COVER

CESM-HYCOM f19

CESM-POP f19

Observations

WINTER ICE THICKNESS

CESM-HYCOM f19

CESM-POP f19

Observations

SUMMER ICE THICKNESS

Barotropic Streamfunction and SSH:

CESM-HYCOM f19

CESM-POP f19

Vertical Streamfunction:

CESM-HYCOM f19

CESM-POP f19

Northward heat and freshwater transports:

Niño 3.4 index:

  1. Two ITCZ present in HYCOM and POP

  1. Overestimation of Specific Humidity and Temperature

  1. Longwave down and shortwave down close to observations

  1. HYCOM warmer and saltier than POP at the surface

  2. Global surface salinity bias higher than POP mostly because of the polar regions.

  3. Lower global salinity bias when using Sref for salt flux conversion. (Strong freshening of the polar region and Labrador Sea region)

  1. HYCOM global T and S drifts are higher than POP’s even when using Sref for the salt flux.

  2. POP almost stable after 100 years. HYCOM is still showing a strong positive trend.

  1. HYCOM presents a stronger positive drift in temperature at each depth than in POP.


  1. Except in the northern mid-latitude, HYCOM salinity drifts less than POP’s.


  1. Strong surface salinity drift over the northern polar region due to the Sref in salt flux in HYCOM.


(N.B: Drift is average of Years 0081-0100 - Year 0.)



  1. Most of the volume change appears between 27.6 and 27.9 in HYCOM.

  2. HYCOM seems to transform denser water into lighter water (27.8-27.9 into 27.7-27.8) 


  1. Most of the volume change appears between 27.7 and 28.0 in POP.

  2. POP seems to transform lighter water into denser water (27.7-27.9 into 27.9-28.0)

  1. As in the Atlantic : Most of the volume change appears between 27.6 and 27.9 in HYCOM.

  2. HYCOM seems to transform denser water into lighter water (27.8-27.9 into 27.7-27.8) 


  1. As in the Atlantic: Most of the volume change appears between 27.6 and 28.0 in POP.

  2. POP seems to transform lighter water into denser water (27.6-27.9 into 27.9-28.0)

Obs.: 136.7 +/- 7.8 Sv

Obs.: 0.8 +/- 0.16 Sv

Obs.: -15 Sv

Obs.: -2. +/- 2.7 Sv

  1. HYCOM Drake transport is lower than POP, closer to observations

  2. HYCOM Fram strait is drifting into a positive net northward transport as is usually the behavior of the model at that resolution.

  3. POP Fram strait stays negative and close to the observations.


  1. Transports at Bering and through the Indonesian Throughflow for HYCOM and POP are similar. (lower for Sref)

  2. Probably due to the resolution, HYCOM and POP shows a low transport at the Indonesian Throughflow. (Lower for Sref)

  1. Overestimation of ice cover over the Labrador Sea in HYCOM

  2. POP close to observations


  1. Less ice in the Southern Ocean for HYCOM than in POP.


  1. Overestimation of ice cover in the Arctic in the summer in HYCOM.

  2. POP underestimates the ice cover in the summer.


  1. Less ice in the Southern Ocean for HYCOM than in POP.


  1. Ice thickness higher in HYCOM than POP.



  1. Overestimation of ice thickness in POP and underestimation in HYCOM.


  1. Underestimation of ice thickness in both HYCOM and POP.



  1. Quasi-disappearance of ice in the summer in the Southern Ocean in HYCOM.

  2. Overestimation of ice thickness in the Southern Ocean in POP.



  1. HYCOM’s Ice cover and ice thickness is slowly decreasing over the 100 years of simulation but is stable after year 60.

  2. POP’s ice cover and thickness is stable over the 100 years of simulation.



  1. HYCOM ice cover and thickness is stable over the 100 years.

  2. Less seasonal cycle in HYCOM than in POP.

  3. Ice thickness stabilizes after years 50-60.



  1. North Atlantic gyres stronger in POP than in HYCOM


  1. Vertical Streamfunctions (Global and Atlantic) are stronger in POP than in HYCOM

  2. AMOC too strong in POP (over 20Sv)

  3. AMOC too weak in HYCOM (under 15 SV)

  4. AMOC very weak in HYCOM with Sref because of the freshening of the Labrador Sea region.


  1. As with the streamfunctions, POP presents higher northward heat transports in every basins.

  2. POP is closer to Observations.



  1. Higher variability in HYCOM than in POP (more events in HYCOM than in POP).

  2. Stronger and longer events in POP than in HYCOM.

SSH and SSH anomalies

GLBt0.72

GLBb0.08

Station-Based NAO index:

CESM-HYCOM f19 (Sref)

CESM-HYCOM Sref  f19

CESM-HYCOM Sref f19

CESM-HYCOM Sref  f19

CESM-HYCOM f19

CESM-POP f19

CESM-HYCOM Sref  f19