The Marine Boundary Layer Height over the Western North Pacific Based on GPS Radio Occultation, Island Soundings, and Numerical Models

Abstract

This paper estimates marine boundary layer height (MBLH) over the western North Pacific (WNP) based on Global Positioning System Radio Occultation (GPS-RO) profiles from the Formosa Satellite Mission 3 (FORMOSAT-3)/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites, island soundings, and numerical models. The seasonally-averaged MBLHs computed from nine years (2007⁻2015) of GPS-RO data are inter-compared with those obtained from sounding observations at 15 island stations and from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA-Interim) and National Centers for Environmental Prediction Global Forecast System (NCEP GFS) data over the WNP from 2012 to 2015. It is found that the MBLH using nine years of GPS-RO data is smoother and more consistent with that obtained from sounding observations than is the MBLH using four years of GPS-RO data in a previous study. In winter, higher MBLHs are found around the subtropical latitudes and over oceans east of Japan, which are approximately located within the paths of the North Equatorial Current and the Kuroshio Current. The MBLH is also significantly higher in winter than in summer over the WNP. The above MBLH pattern is generally similar to those obtained from the analysis data of the ERA-Interim and NCEP GFS, but the heights are about 200 m higher. The verification with soundings suggests that the ERA-Interim has a better MBLH estimation than the NCEP GFS. Thus, the MBLH distributions obtained from both the nine-year GPS-RO and the ERA-Interim data can represent well the climatological MBLH over the WNP, but the heights should be adjusted about 30 m lower for the former and ~200 m higher for the latter. A positive correlation between the MBLH and the instability of the lower atmosphere exists over large near-shore areas of the WNP, where cold air can move over warm oceans from the land in winter, resulting in an increase in lower-atmospheric instability and providing favorable conditions for convection to yield a higher MBLH. During summer, the lower-atmospheric instability becomes smaller and the MBLH is thus lower over near-shore oceans.

Keywords: FORMOSAT-3/COSMIC; GPS radio occultation; marine boundary layer height.

Figure 1

Locations of the 15 island sounding stations (blue dots) over the western North Pacific Ocean. Tiny red crosses show 0–5 km traces of the nearby GPS-RO profiles that are used for evaluation, with a black cross indicating the location at 5 km. The winter sea surface temperature (SST) averaged in December, January, and February, from 2012–2015, is plotted in green lines (2 °C interval) and purple lines (1 °C interval), using the National Oceanic and Atmospheric Administration (NOAA) Extended Reconstructed Sea Surface Temperature (ERSST) data. The Kuroshio Current and the North Equatorial Current are also denoted.

Figure 2

An example of an island sounding observation taken at Minamitorishima (24.3° N, 154° E) at 00:00 UTC 17 March 2012. (a) Potential temperature (K, scale on the bottom) and water vapor mixing ratio (g·kg⁻¹, scale on the top) are plotted in solid and dashed lines, respectively. (b) Temperature (°C) and dew point temperature are plotted in solid and dashed lines, respectively. The estimated MBLH is indicated by a red line. Height is from 0 to 10 km.

Figure 3

(a) The seasonally-averaged MBLH for winter using GPS-RO data in 2012–2015 (shading), with numerals showing the MBLH computed from island soundings. Cross points denote the locations of soundings. (b) Numerals are MBLH from island soundings, same as in (a). Contour lines are plotted with a 100 m interval using the C1 surface interpolation method.

Figure 4

(a) The seasonally-averaged MBLH for summer using GPS-RO data in 2012–2015 (shading), with numerals showing the MBLH computed from island soundings. Cross points denote the locations of soundings. (b) Numerals are MBLH from island soundings, same as in (a). Contour lines are plotted with a 100 m interval using the C1 surface interpolation method.

Figure 5

The seasonally-averaged MBLH for (a) winter, (b) spring, (c) summer, and (d) autumn, using the GPS-RO profiles from 2007 to 2015. The numerals denote the MBLH computed from island soundings.

Figure 6

Scattered diagrams of the seasonally-averaged MBLH estimated from island radiosonde stations (the abscissa) and from GPS-RO profiles (the ordinate) using the GPS-RO data in (a) 2012–2015 and (b) 2007–2015. The sample size is 60 (15 island stations and 4 seasons).

Figure 7

(a) Seasonal correlation coefficient (CC) between the seasonally-averaged MBLH and the lower-atmospheric instability from 2007 to 2015. (b) Spatial correlation coefficient between the seasonally-averaged MBLH and SST for the four seasons (started by winter) from 2007 to 2015.

Figure 8

The seasonally-averaged MBLH (shown in both color and contour) for (a) winter and (b) summer using the ERA-Interim data (EC) from 2012 to 2015 based on the MXP-BA method. The scale is denoted at the bottom and the contour interval is 100 m. Grid points over land are masked.

Figure 9

The seasonally-averaged MBLH (shown in both color and contour) for (a) winter and (b) summer using the NCEP GFS data (NC) from 2012 to 2015 based on the MXP-BA method. The scale is denoted at the bottom and the contour interval is 100 m. Grid points over land are masked.