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Zhenyu He · Jobs Stroustrup
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Research Note

Walker/Hadley Circulation Response Under Global Warming @ PKU

Zhenyu He · Jobs Stroustrup 5 min read

Basic Info

  • Period: Oct 2019 — May 2020 (~7 months, sophomore fall to end of sophomore year)
  • Role: Undergraduate research (first project in Ji Nie’s group — undergraduate research onboarding)
  • Organization: School of Physics, Department of Atmospheric and Oceanic Sciences, Peking University
  • Advisor: Ji Nie (primary PI)
  • Location: Beijing / Tianhe-II NSCC-GZ (early (undergraduate Tianhe-II account) account)
  • Support: PKU undergraduate research training program (Zhenyu selected the climate dynamics direction from 4 advisor candidates)

Core Problem

Walker Cell and Hadley Cell strength changes under global warming (different CO₂ levels: Picontrol vs Abrupt2xCO₂ vs Abrupt4xCO₂) + decomposition of each cell’s contribution to total tropical mass-flux change.

Signature Contribution: Earliest Multi-Method Comparison (3 parallel Walker-strength metrics)

2019-11-04 first long report (the impact on the strength of tropical circulations 2.pptx, 43 slides) — Zhenyu’s first long PPT report at the Ji Nie sophomore-year group meeting; see .

Walker strength quantification — 3-method comparison:

  1. Velocity potential @ 200 hPa peak (Tanaka et al. 2004 method)
  2. Integral (combined vertical velocity + zonal wind, longitude-height domain 120E-60W × 925-150 hPa, 3 latitudinal zones) — later inherited as the Walker-paper-v6 §3.1 Walker-strength metric source
  3. Precipitation + 850 hPa wind velocity vector

5-paper comparison table (Walker strengthening vs weakening trend contradiction):

  • Tanaka et al. 2004 (velocity potential decomposition method)
  • Strengthening of Walker Circulation under Global Warming in an Aqua-Planet (MRI Japan, 3 cumulus parameterizations YS/AS/KF in parallel)
  • CMIP5 projected weakening papers
  • NCEP/NCAR observational records
  • Holton 2004 An Introduction to Dynamic Meteorology textbook reference

Each paper is given an advantage + defect review (“the measuring method adopted by the author contradicts to some other scholars’ results, the author doesn’t explain Table 2 in detail”) — multi-method critical comparison alongside paper-review capability was already crystallized in the sophomore-November first long report. This is Multi-Method Comparison Spine (2019-2025) root evidence (6 years before PhD Phase 4.5 SWTG failed cancellation, 1.5 years before Walker-paper-v6 ω-vs-u, 2 years before Caltech DSCOVR’s 7-method regularization comparison).

2020-09 Lab-wide Group Meeting Walker-Metric Source-of-Truth Evidence

聂绩202009刚开学不久的全员大组会_我的报告 Abrupt4xCo2 vs Picontrol.pptx (16 slides, junior fall, lab-wide group meeting):

  • All data averaged on 140th-150th year
  • Hadley strength = max mass-streamfunction: Picontrol 7.9097e+10 (600 hPa, 13.66°N) / 2xCO₂ 8.807e+10 (12.7°N) / 4xCO₂ 8.4451e+10 (10.84°N, peak shifts equatorward)
  • Walker strength = ω@500mb WEP-EEP diff (WEP 10N-10S × 100E-150E, EEP 10N-10S × 180-100W): Picontrol 0.0913 / 2xCO₂ 0.0587 / 4xCO₂ 0.0909 (monotonic non-trend)

→ This metric definition is completely identical to Walker-paper-v6 §3.1, articulated 1 year and 7 months earlier than the paper v6 (2021-10-22). The Walker-paper metric was not decided at the paper-drafting stage; it was already settled during Phase 0 reading + ENSO-literature review — early lock-in of research taste in junior fall.

Key Achievements

  1. 3-method Walker-strength parallel comparison (velocity potential / integral / precip+850hPa wind) in the 2019-11-04 43-slide report — earliest evidence of multi-method discipline

  2. Contribution decomposition to total tropical mass-flux change — Walker vs Hadley separately quantified

  3. Cross-reading breadth: across monsoon (6 papers, co-leading peers) + Boundary Layer (8 papers: Lindzen-Nigam / Matsuno 1966 / Gill 1980 / Betts 1989 / Chiang 2001 / West Indian / Back 2009 MLM / Entrainment-Rayleigh-Friction) + Walker/Hadley/ENSO literature = ~30+ papers across 2 months

  4. Tianhe-II HPC onboarding: a junior labmate’s .bashrc inheritance → Zhenyu’s .bashrc → (undergraduate Tianhe-II account) (early Ji Nie lab account) — same-lab HPC inheritance trail; familiar with all 5 manuals: Fortran 95 textbook + Tianhe-II V1.1 / V1.4.1 / CESM1_on_Tianhe2

  5. First CAM5 aqua-planet experiment (2020-04 → 2020-05, data_summary_big_picture.pptx 22 slides + data_summary_contrast.pptx 11 slides): first model experiment in sophomore spring + first self-observation comparison; slide 22 observation:

    “热带辐合带那里，相比之前，是由 0-8°S 变成 0-5°S，只是变窄一些，但是仍然是偏南方”

    (English gloss: At the ITCZ, compared with before, the band changed from 0-8°S to 0-5°S — only narrower, but still on the southern side.)

  6. 2020-09-27 Zhenyu’s first appearance in Hu’s group (hzy_Hu's group meeting 20200927.pptx 28 slides) — title “Correlation between Hadley Circulation and Walker Circulation: 1. Under ENSO conditions (literature review) + 2. Under warming conditions (in research)”; this was 7 months before the Walker Circulation Dynamics @ PKU project’s 2021-04-01 mid-term

Continuity with the Walker/width Project (2020-11 transition)

This project is the direct prequel to Walker Circulation Dynamics @ PKU (2020.11 — 2021.10):

  • Walker-paper-v6 §3.1 metric = the metric in this project’s 2020-09 lab-wide group meeting (completely identical)
  • Walker-paper-v6 §2 cites Merlis 2013 + Ceppi/Hwang 2013 = PDFs in this project’s 2020-11 cam3 reference-paper folder
  • Walker-paper-v6 ω-vs-u stream-function methodology + multi-method comparison = capability spine of this project’s 2019-11-04 43-slide first-long-report 3-method comparison
  • 2020-11 transition from cam6 ((undergraduate Tianhe-II account) account, 14-slide cam6水球运行.pptx) → cam3 ((undergraduate Tianhe-II account) Walker account); even the Tianhe account was inherited
  • Moment 1 of Independent Judgment narrative (held until 2026-06-10) spine — 4-advisor evaluation ([four PKU faculty across quantitative-biology / optics / quantum-materials / climate]); Zhenyu in sophomore spring selected Ji Nie’s climate direction (consistent with the age-18 critical reflection on the academic-credit system; see Evidence Preservation Discipline (private companion) conceptual parallel)

Skills Used

Sources

  • research_wiki/projects/early_exploration/overview.md (285 lines, complete capture of the 18-month prequel phase)
  • research_wiki/resume_angles/independent_judgment.md §Extended: First Long Report 2 Months After Choice