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We present new spectroscopic observations of Lyman-$\alpha$ (Ly$\alpha$) Blob2 ($z \sim$ 3.1). We observed extended Ly$\alpha$ emission in three distinctregions, where the highest Ly$\alpha$ surface brightness (SB) center is faraway from the known continuum sources. We searched through the MOSFIRE slitsthat cover the high Ly$\alpha$ SB regions, but were unable to detect anysignificant nebular emission near the highest SB center. We further mapped theflux ratio of the blue peak to the red peak and found it is anti-correlatedwith Ly$\alpha$ SB with a power-law index of $\sim$ -0.4. We used radiativetransfer models with both multiphase, clumpy and shell geometries andsuccessfully reproduced the diverse Ly$\alpha$ morphologies. We found that mostspectra suggest outflow-dominated kinematics, while 4/15 spectra imply inflows.A significant correlation exists between parameter pairs, and the multiphase,clumpy model may alleviate previously reported discrepancies. We also modeledLy$\alpha$ spectra at different positions simultaneously and found that thevariation of the inferred clump outflow velocities can be approximatelyexplained by line-of-sight projection effects. Our results support the `centralpowering + scattering' scenario, i.e. the Ly$\alpha$ photons are generated by acentral powering source and then scatter with outflowing, multiphase HI gaswhile propagating outwards. The infalling of cool gas near the blob outskirtsshapes the observed blue-dominated Ly$\alpha$ profiles, but its energycontribution to the total Ly$\alpha$ luminosity is less than 10%, i.e. minorcompared to the photo-ionization by star-forming galaxies and/or AGNs.

Where Outflows Meet Inflows: Gas Kinematics in SSA22 Lyman-$\alpha$ Blob 2 Decoded by Advanced Radiative Transfer Modelling