Bering

15 January 2006 (Figs. 6, 7). Small mesoscale cyclone in the southwestern Bering Sea, which was formed in a cold dry air in the rear of another deep cyclone, was detected by Aqua MODIS, Envisat ASAR and QuikSCAT SeaWinds on 15 January 2005. As opposite to the deeper cyclone, it was not revealed in pressure field on the surface analysis map of the JMA (not shown). Cyclone is clearly visible as the spiral-like structure just off the coast.

Commander Islands are seen at the bottom of the images. A cloudless area in the center of the cyclone is its eye (Fig. 6a) where weak winds are observed (Fig. 6b). Open and closed mesoscale convective cells typical for cold air outbreaks are clearly seen to the east of bright convective band both on the daytime (Fig. 6a) and nighttime (Fig. 6c) MODIS images taken with the time difference of 13.5 h.

Mesoscale Banding
Fig. 6. Mesoscale cyclone over the southwestern Bering Sea on 15 January 2005: (a) and (c) Aqua MODIS image (a) visible at 00:55 UTC and (c) infrared at 14:25 UTC; (b) Envisat ASAR image at 10:21 UTC.

Circular and crescent imprints of the convective cells in the sea surface roughness as in the lower right of the ASAR image (Fig. 6b) are in close agreement with model calculations (Mitnik 1990, 1992). Several curvilinear features that spiral in towards the eye as well as the small-scale convective cells are distinguished to its southwest and south on all images (Fig. 6).

The cloudless center, convective spiral band, which extends far to the south, the mesoscale linear and cellular features to the east of the band are reliably detected on the AMSR-E 89-GHz image at horizontal polarization having a spatial resolution of 5 x 5 km (not shown). Variations of the brightness temperature 7^(89) in the cyclone's area exceed 60 K. From a comparison of MODIS infrared and AMSR-E 7BH(89) images acquired simultaneously it follows that the maximum 7Bh(89) values (>210 K) are observed in the convective bands near the cyclone's center. The lowest 7BH(89) values (<170 K) were measured over cloudless area to the south of the center.

—■■ I I ■ PW.I.I.I.I M l.w Mi, ■ WW.i.I.I.I ■

Cloud liquid water (kg/m2> »atir vapor (kg/m2) Clouds (kg/mil 15.02,06 87D vapor [kg/m2J 15.02.06 67D

Fig. 7. Fields of total cloud liquid water content (in kg/m2) (a) and (c) and total atmospheric water vapor content (in kg/m2) (b) and (d) derived from Aqua AMSR-E measurements taken on 15 January 2005 at 00:55 UTC (a) and (b) and at 14:55 UTC (c) and (d).

—■■ I I ■ PW.I.I.I.I M l.w Mi, ■ WW.i.I.I.I ■

Cloud liquid water (kg/m2> »atir vapor (kg/m2) Clouds (kg/mil 15.02,06 87D vapor [kg/m2J 15.02.06 67D

Fig. 7. Fields of total cloud liquid water content (in kg/m2) (a) and (c) and total atmospheric water vapor content (in kg/m2) (b) and (d) derived from Aqua AMSR-E measurements taken on 15 January 2005 at 00:55 UTC (a) and (b) and at 14:55 UTC (c) and (d).

The low is also detected as cyclonic structure in AMSR-E retrievals showing a distinct mesoscale signal in the fields of total cloud liquid water content Q and total water vapor content V (Fig. 7). Fields of Q and V were derived by application of algorithm (Mitnik and Mitnik 2003) to the measured brightness temperatures at 23.8 and 36.5 GHz at vertical polarization. Spiral structure is better expressed at 00:55 UTC (Fig. 7a, b) than at 14:25 UTC (Fig. 7c, d) that very likely reflects dissipation of the cyclone. Analysis of the brightness temperatures at all AMSR-E channels and the results of modeling allows to conclude that probability of precipitation is high in the spiral bands near the center where Q > 0.15 kg/m2. Mesoscale organized convection manifests itself in mesoscale variations of Q and V (Fig. 7c, d).

Fig. 8. Mesoscale cyclone over the Southwest Bering Sea on 21 February 2004: (a) Envisat ASAR image at 10:21 UTC; (b) Aqua MODIS visible image at 01:35 UTC and (c) QuikSCAT-derived wind field at 09:09 UTC.

21 February 2004 (Fig. 8). Cold air advection on the warmer sea surface in combination with influence of orography were responsible for intensive convective activity to the east of Kamchatka Peninsula on 21-22 February that was registered by Envisat ASAR and other satellite sensors. Envisat ASAR image acquired on 21 February at 10:34 UTC depicts the well-developed mesoscale cyclone in the Southwest Bering Sea (Fig. 8a). Kamchatka Peninsula, Karaginsky Island 1 and Commander Islands 2 are visible both on ASAR and on Aqua MODIS visible images. In spite of the time difference of 9 h, a good agreement is observed between cloud field and the radar signatures, which are determined mainly by the sea surface wind field. It may be concluded that synoptic situation changed slowly during this period. It follows also from the surface analysis maps of the Japan Meteorological Agency for 00:00 and 12 UTC on 21 February.

The most striking features of the ASAR image are associated with the polar low 3 and with the sharp frontal boundaries 4 and 5 of the second mesoscale cyclone. Its center 6 was located to the south from the first one (Fig. 8b) and to the west of ASAR swath. The second cyclone with the minimum central pressure 990 mb was shown on the weather maps of the JMA as opposite to the first one. The ASAR image illustrates, in detail, the spiral-form structure of the surface wind field around the eye of the low, wave-like features of the frontal boundaries, the zones with the increased wind speed and other features, which were revealed partially earlier (Chunchuzov et al. 2000; Mitnik et al. 1996). The surface wind convergence zones are characterized by sharp wind field gradients across the frontal boundary that converges toward the eye. QuikSCAT-derived wind field was obtained at 09:09 UTC (Fig. 8c). The centers of both cyclones and the sharp frontal boundaries are clearly distinguished in Figure 8c and correspond to the brightness field of ASAR image.

0 0

Post a comment