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Research Note

Undergraduate Research @ Peking University & Caltech/UCR

Zhenyu He · Jobs Stroustrup 4 min read

Related pages: This page only indexes research projects (umbrella pointer page). For class monitor / student union / teaching support / love society / softball team leadership & service, see PKU Leadership & Service @ Peking University (2018-2022); for all awards and honors, see Academic Honors @ PKU (2018-2022).

Basic Info

  • Period: Sep 2018 — Jun 2022 (4 years undergraduate)
  • Role: Undergraduate Independent Researcher (4 independent projects across 3 labs / 3 institutions)
  • Organizations: Peking University (Prof. Jing Li, Prof. Yongyun Hu, Prof. Ji Nie) + Caltech / UC Riverside (Prof. Yuk Yung / Prof. King-Fai Li)
  • Location: Beijing / Remote
  • Support: PKU President Fellowship + undergraduate research training program

4 Projects Overview (Chronological — see dedicated pages via pointers)

1. Walker/Hadley Circulation Response Under Global Warming (Oct 2019 — May 2020, Ji Nie) → Dedicated page: Walker/Hadley Circulation Response Under Global Warming @ PKU → TL;DR: Sophomore-autumn first project under Ji Nie. Quantified Walker/Hadley intensity changes under different CO₂ levels and decomposed contributions to total tropical mass flux. 2019-11-04 first long report (43 slides) already demonstrated 3-method comparison on Walker strength (velocity potential / integral / precip+850hPa wind) — earliest evidence of Zhenyu’s multi-method comparison discipline (6 years before PhD SWTG “failed cancellation”). Includes Ji Nie lab onboarding + 4-advisor candidate evaluation + 2 reading clubs (~30+ papers across monsoon/BL/Walker/Hadley/ENSO in 2 months) + 2020-09 lab-wide meeting establishing Walker metric (ω@500mb WEP-EEP diff) identical to Walker paper v6 §3.1 — 1 year 7 months ahead.

2. Walker Circulation Width Dependence (Nov 2020 — Oct 2021, Ji Nie + ) → Dedicated page: Walker Circulation Dynamics @ PKU → TL;DR: Junior-autumn through senior-autumn (12 months). CAM3 aqua-planet 10 cases × 30-yr runs (D60-D180 step 20° + Wonly/Conly/Aqua). 2021-07-13 breakthrough: Zhenyu proposed the Linear Superposition framework, endorsed on-the-spot by Ji Nie (4-field correlations 0.83-0.93). Paper draft v6 (3663 words, 11 refs, 2021-10-22) not submitted due to Ji Nie’s private context (held until 2026-06-10). 27,882 MATLAB+NCL lines + 20 NCAR CAM3 .F90 source mods (including somoce MLDANN 50→30m key dep) + Tianhe-II (undergraduate Tianhe-II account) 48-PE parallel + 5-stage HPC pipeline.

3. MCMC Retrieval Methods (Mar 2021 — Mar 2022, Yuk L. Yung + King-Fai Li, Caltech / UCR remote) → Dedicated page: DSCOVR Inverse Problem + Regularization Methods @ Caltech / UCR → TL;DR: Junior-spring through senior-spring. Attempted to retrieve Earth’s land-ocean distribution from DSCOVR single-point light curve. 4 original contributions: (a) Hansen σ² vs σ⁴ 80× bug catch (numerical-implementation bug in Hansen’s textbook); (b) Pre-whitening L-curve (systematic comparison of L-Curve / L-Curve Curvature / GCV / Morozov discrepancy); (c) Hardened Balancing Principle 90-paragraph writeup (recognized by Siteng Fan, Sep 2021); (d) Direction of Noise Vector discovery (Zhenyu’s own discovery of ill-posed structure, Sep 2021). 5 programming languages (IDL / MATLAB / Python / Mathematica / R) + 29 group_meeting pptx. Self-studied Hansen Discrete Inverse Problems + Bishop PRML + Golub 1979 original GCV paper, reproducing each numerical experiment. Repo: .

4. MODIS+CALIPSO Joint Aerosol Retrieval (Senior Thesis) (Dec 2021 — Jun 2022, Jing Li) → Dedicated page: Aerosol Joint Retrieval Senior Thesis @ PKU → TL;DR: Senior-spring senior thesis. First iteratively-coupled MODIS+CALIPSO joint retrieval (replaced MODIS lookup tables with CALIPSO-retrieved aerosol extinction profiles + added MODIS AOD as boundary condition for CALIPSO, iterating until convergence). CALIPSO L2 -10⁴ non-physical bug catch + 4 Beijing case studies (absolute ↓ 0.011-0.032, relative ↓ 3-20%) + 9-version thesis auto-diff (316→1350 words in 27 days) + 4-person lab scaffolding (Jing Li + Chang Liang + Li Chong + Dong Yueming + Caltech bridge).

Early Exploration Prequel Phase (Apr 2019 — Oct 2019, pre-Ji Nie onboarding)

Undergraduate research did not start when the Ji Nie first project launched in Oct 2019; an 18-month prequel came before:

  • Phase 0.A: 2019-03-17 Physics Dept. undergraduate research sharing event (7 senior talks covering HEP / Quantum / Biology / ML / Galaxy / Planetary Climate) + 4-advisor candidate evaluation across quantitative-biology / optics / quantum-materials / climate; ultimately selected Ji Nie ([Moment 1 of Independent Judgment narrative — held until 2026-06-10])

  • Phase 0.B: Spring 2019 — drafted a private critical reflection note on undergraduate research, which informed subsequent advisor selection (Li Jing + Ji Nie chosen partly because they belong to the minority who proactively deemphasize their own credit).

  • Phase 0.C-G: 2 group reading clubs (BL 8 papers + monsoon 6 papers) + first CAM5 aqua-planet experiment (Apr-May 2020, data_summary_big_picture.pptx 22 slides) + 2020-09 lab-wide meeting establishing Walker/Hadley metric (Walker paper v6 metric source-of-truth 1 year 7 months ahead) + 2020-09-27 Zhenyu’s first appearance in Hu group (28 slides)

Skills Used