1.The meridional atmospheric and oceanic heat sources dataset for the Indian Ocean-Third Pole region (2000-2019)

The atmospheric and oceanic thermal conditions over the Indian Ocean-Third Pole (Qinghai-Tibet Plateau) are important for affecting the Asian monsoon activity and pan-Third Pole climate. At seasonal and interannual timescales, the meridional atmospheric and oceanic heat sources are closely related to Indian monsoon, Bay of Bengal monsoon, and the sea surface temperature (SST) mode in the tropical Indian Ocean. Therefore, we calculate and establish the meridional atmospheric and oceanic heat sources dataset for the Indian Ocean-Third pole section. In order to obtain the horizontal distribution of atmospheric heating rate on each pressure level, we use the inverse algorithm from Yanai et al. (1973): Q_1=c_p [∂T/∂t+V ⃑∙∇T+(p/p_0 )^κ ω ∂θ/∂p] Q_1 is the atmospheric apparent heat source, which can be affected by temperature local variation, temperature advection and potential temperature vertical variation. T, θ, V ⃑, and ω respectively represent the temperature, potential temperature, horizontal wind vector, and vertical velocity. p_0=1013.25hPa. κ=R/c_p, R and c_p are the gas constant and specific heat of dry air at constant pressure respectively, κ≈0.286。 Based on the ERA5 Atmospheric Reanalysis data from 2000 to 2019, we calculate the monthly meridional (along 60°E, 70°E, 80°E, 90°E) atmospheric heating rate (unit: K/s) for the Indian Ocean-Third pole section (30°S-60°N) with horizontal resolution of 1°×1° and vertical range of 1000-100hPa at 27 levels. With reference to Hall and Bryden (1982), the vertical Ocean Heat Transport (OHT) at given longitudes can be calculated by the following formula: OHT=∮_(Θ=Θ_i)▒∫_(z_b)^(z_0)▒〖ρ_0 c_p (θ-θ_r ) 〗∙udz Where ρ_0, c_p, θ, θ_r, and u represent the density, specific heat, capacity potential temperature, reference temperature (0℃), and zonal velocity of sea water respectively. z_0 and z_b are the depths of sea surface and sea floor. Based on the CMEMS (Copernicus Marine Service) Oceanic Reanalysis data from 2000 to 2019, we calculate the monthly meridional (along 60°E, 70°E, 80°E, 90°E) OHT (eastward positive, unit: PW(1015W)) over the Indian Ocean-Third pole region (30°S-30°N) with horizontal resolution of 1°×1° and vertical range from sea surface to sea floor at a depth of about 5900m on 75 levels. This dataset can reflect the close relationship between meridional atmospheric and oceanic thermal conditions of Indo-Tibetan Plateau region and Indian monsoon, Bay of Bengal monsoon, and SST mode over tropical Indian Ocean. For example, from the monthly evolution of meridional atmospheric heating rate along 70°E for the Indian Ocean-Third pole section (Figure 1), the atmospheric heat source area above the tropical southern Indian Ocean gradually advances northward from Marth to May. In particular, from May to June, this tropical atmospheric heat source area moves to the tropical northern Indian Ocean with its intensity strengthened and scope expanded, at the same time, the Indian summer monsoon onsets. For instance, from the monthly evolution of meridional atmospheric heating rate along 90°E for the Indian Ocean-Third pole region (Figure 2), we can see that the atmospheric heat source area above the tropical Indian Ocean expands to the south of Qinghai-Tibet Plateau and increases significantly from April to June, coinciding with the onset and northward advance of the Bay of Bengal monsoon. Another example, from the monthly evolution of meridional OHT along 60°E and 90°E for the Indian Ocean-Third pole section (Figures 3 and 4), it can be found the ocean heat at the equatorial Indian Ocean subsurface transports from west to east, and its position is very close to the Equatorial undercurrent. And this subsurface OHT intensity in the west is obviously higher than that in the east, which is related to the wind-thermocline-SST feedback mechanism. It is also worth noting that this subsurface OHT is strong in spring (March-May), weakens in summer, and significantly strengthens in late autumn and early winter (October-December), interacting with the development and formation of Indian Ocean Dipole.

LI Delin , XIAO Ziniu, ZHAO Liang

   TPDC

doi: 10.11888/Atmos.tpdc.272722 509 82 Open Access 2022-07-20