Purpose. The work is purposed at studying spatio-temporal variability of the resulting long-wave radiation reflecting the ocean heat loss, on the surface of the northwestern Pacific Ocean and the Far Eastern seas based on the ERA5 reanalysis data for 1998–2021.

Methods and Results. The ERA5 reanalysis data on the resulting long-wave radiation in the region limited by 42°−60°N and 135°−180°E, and including the Far Eastern seas and the northwestern part of the Pacific Ocean constituted the material for the study. The array of monthly averages with a quarter degree spatial resolution was analyzed using the standard statistical methods. Average long-term distributions of long-wave radiation were constructed for each month and by seasons; the amplitudes and phases of the annual and semi-annual harmonics, and the linear trend coefficients were calculated in each spatial cell, also the empirical orthogonal functions decomposition was performed. The highest values of long-wave radiation were observed in winter, primarily in the Sea of Japan and in the area east of Honshu Island. The heat flux from the ocean to the atmosphere reached its significant values in the same areas in autumn, as well as in the coastal strip along the entire continental coast. The most probable reason for such features in the distribution of long-wave radiation is the atmospheric circulation, namely, the steady northwesterly wind (winter monsoon) characteristic of a cold season. In the open ocean, heat loss is less, especially in summer, which is facilitated by dense clouds. Similar results were obtained by the method of empirical orthogonal functions: the values of the first mode spatial distribution decrease from west to east (in absolute value).

Conclusions. It was revealed that heat losses in the studied area occur mainly in autumn and winter in its western part -- in the Sea of Japan, east of Honshu Island, and especially in a narrow strip along the entire mainland coast; but in winter in the areas north of 48°N (the Tatar Strait, the Sea of Okhotsk), they are damped by the ice cover. Unidirectional trends in the changes of long-wave radiation are pronounced relatively weakly, and differ in the same water areas in different seasons of a year.