9:30 AM - 9:45 AM
[AAS03-03] Two Types of the Convectively-Coupled Westward Inertia-Gravity Wave
Keywords:Tropical meteorology, convectively-coupled equatorial waves
In equatorial regions, atmospheric waves accompanied by moist convection are referred to as convectively coupled equatorial waves (CCEWs). Convectively-coupled westward inertia-gravity waves (WIGs) are one of the dominant CCEWs in the tropics, and are characterized by a wavelength of 2000-4000 km, a period of about 2 days, and a phase velocity of 10-30 m/s. The WIG is one of the main building-blocks in an intra-seasonal oscillation, such as Madden-Julian Oscillation, and bridges the large-scale circulation of the tropics and mesoscale convective systems. However, many aspects of the CCEW, including the propagation mechanisms, are not fully understood (Kiladis et al., 2009).
Yasunaga and Mapes (2014) demonstrated that even within the same type of the CCEW, the associated precipitation shows different characteristics depending on equivalent depths; faster and deeper WIGs have more convective rainfall than slower and shallower WIGs. In addition, Sumi and Masunaga (2019) explored the propagation speed of the WIG with reference to the equivalent depth and temperature variations. Although these previous studies have revealed several important aspects of the coupling mechanisms between the WIG and convection, the slowness of the propagation mechanism of WIG is not fully explained.
Motivated by the incomplete understanding of the propagation mechanisms, the present paper conducted a spectral and composite analysis of the convectively-coupled WIGs, focusing on the equivalent depth. The data used include the Global Satellite Mapping of Precipitation (GSMaP) for precipitation and the ERA-Interim reanalysis data provided by the European Center for Medium-Range Weather Forecasts (ECMWF) for dynamic and physical variables. The analysis region covers the Warm Pool (15°S–15°N, 40°E–220°E) during the period from April 1, 2000, 01Z to August 24, 2019, 00Z.
Two types of the convectively-coupled WIG are identified, regarding to the equivalent depth; deeper and shallower modes with equivalent depths of 12-30 m and 25-50 m, respectively. Deeper (shallower) WIG is characterized by the prominent zonal (meridional) wind variations. Precipitation areas associated with deeper (shallower) WIG are extended to the meridional direction, consistent with the Rossby deformation radius. Furthermore, compared to deeper WIG, shallower WIG is associated with larger amplitudes of water vapor variations, indicating shallower WIG may has “moisture mode” characteristic, where water vapor plays a significant role in wave propagation, while deeper WIG is mainly controlled by temperature variations.
Yasunaga and Mapes (2014) demonstrated that even within the same type of the CCEW, the associated precipitation shows different characteristics depending on equivalent depths; faster and deeper WIGs have more convective rainfall than slower and shallower WIGs. In addition, Sumi and Masunaga (2019) explored the propagation speed of the WIG with reference to the equivalent depth and temperature variations. Although these previous studies have revealed several important aspects of the coupling mechanisms between the WIG and convection, the slowness of the propagation mechanism of WIG is not fully explained.
Motivated by the incomplete understanding of the propagation mechanisms, the present paper conducted a spectral and composite analysis of the convectively-coupled WIGs, focusing on the equivalent depth. The data used include the Global Satellite Mapping of Precipitation (GSMaP) for precipitation and the ERA-Interim reanalysis data provided by the European Center for Medium-Range Weather Forecasts (ECMWF) for dynamic and physical variables. The analysis region covers the Warm Pool (15°S–15°N, 40°E–220°E) during the period from April 1, 2000, 01Z to August 24, 2019, 00Z.
Two types of the convectively-coupled WIG are identified, regarding to the equivalent depth; deeper and shallower modes with equivalent depths of 12-30 m and 25-50 m, respectively. Deeper (shallower) WIG is characterized by the prominent zonal (meridional) wind variations. Precipitation areas associated with deeper (shallower) WIG are extended to the meridional direction, consistent with the Rossby deformation radius. Furthermore, compared to deeper WIG, shallower WIG is associated with larger amplitudes of water vapor variations, indicating shallower WIG may has “moisture mode” characteristic, where water vapor plays a significant role in wave propagation, while deeper WIG is mainly controlled by temperature variations.