Evaluation of AMSU‐A and MHS Radiance Assimilation Strategies in MPAS–JEDI 4DEnVar for Mountain‐to‐Plain Convection Over Beijing, China

To improve numerical prediction of mountain‐to‐plain (MTP) convection over the Beijing region, this study uses the MPAS–JEDI four‐dimensional ensemble‐variational (4DEnVar) data assimilation system on a global 3–60 km variable‐resolution mesh to evaluate assimilation strategies for radiances from the Advanced Microwave Sounding Unit‐A (AMSU‐A) and Microwave Humidity Sounder (MHS). Ten representative MTP cases were examined. The baseline experiment assimilates only conventional observations (Ctrl), while six additional configurations assimilate the same conventional observations together with AMSU‐A, MHS, or both, under either clear‐sky or all‐sky settings. A composite ranking based on multi‐threshold ETS, POD, and 1–FAR scores for radar reflectivity and hourly precipitation shows that configurations assimilating AMSU‐A generally rank above Ctrl, whereas MHS‐only configurations perform worse. The all‐sky configuration underperforms its clear‐sky counterpart, and the clear‐sky AMSU‐A + MHS configuration (Exp_clrM_A) significantly outperforms the all‐sky MHS‐only configuration (Exp_allM), consistent with observation‐minus‐background (OMB) and observation‐minus‐analysis (OMA) diagnostics. Clear‐sky AMSU‐A tropospheric temperature channels provide a strong and stable constraint, while MHS humidity channels retain larger residual spread. Adding MHS to AMSU‐A can slightly increase OMA bias/spread in some low‐frequency all‐sky channels compared to AMSU‐A‐only, whereas adding AMSU‐A to MHS‐only reduces MHS bias but can modestly enlarge humidity‐channel spread. Thermodynamic–dynamical diagnostics further show that Exp_clrM_A produces a stronger cold pool, enhanced low‐level convergence and ascent, and a more continuous band of organized convection with attached stratiform echoes. In contrast, Exp_allM yields a warmer, drier lower troposphere, a weaker cold pool, and rapid convective decay.