CGMS-40, JMA-WP-09 Prepared by JMA
Agenda Item: II/8
Discussed in WG II
CLOUD AND VOLCANIC ASH PRODUCT
This paper reports on JMA’s cloud and volcanic ash product.In 2012, JMA started providing convective clouds information as a nowcasting product to support aviation safety in addition to three rapid scan imagery products provided since 2011.
JMA started developing advanced cloud product.
JMA also started developing volcanic ash product.
CGMS-40, JMA-WP-09 Prepared by JMA
Agenda Item: II/8
Discussed in WG II
1RAPID SCAN OPERATION AND CONVECTIVE CLOUDS INFORMATION PRODUCT
1.1SUMMARY OF RAPID SCAN OPERATION
JMA began rapid scan operation using MTSAT-1R in 2011 to capture short-lived but severe weather phenomena so that aviation users can be informed of them in advance. As shown in Table 1, observations are made in a small area around Japan from 00 UTC to 09 UTC at five-minute intervals in the summer season during operation.
JMA observed a number of heat thunderstorms in 2011 and verified the accuracy of the derived product. Following this validation, the Agency began providing a new nowcast product derived from rapid scan data on 1 June, 2012.
Table 1 Specifications of rapid-scan operation
Observation interval / 5 minutesTime / Daytime only (00:00 to 09:00 UTC)
Period / Summer only (1 June to 30 September)
Objective / To provide information for aviation safety
Observation area / Bounding box around Japan
1.2RAPID SCAN IMAGERY PRODUCTS FOR AVIATION USERS
JMA now provides four imagery products as shown in Figure 1 for aviation users. Three of these ((a) visible images, (b) visible and infrared color composite images, and (c) cloud top height images) have been provided since 2011. In addition, the provision of (d) convective clouds information began in 2012. This new product is described in the next section.
(a) Visible images /
(b) Visible and infrared color composite images
(c) Cloud top height images /
(d) Convective clouds information
(a) Black-and-white images of visible albedo data
(b) Color composite images generated by overlaying yellow visible albedo data and blue 10.8-μm IR brightness temperature data
(c) Cloud top height calculated from 10.8-μm infrared brightness temperature data with reference to NWP forecast fields
(d) Three detected convective cloud areas are shown in the visible albedo data images.
Figure 1 Rapid scan imagery products for aviation users
1.3CONVECTIVE CLOUDS INFORMATION FOR AVIATION USERS
As detailed above, JMA began providing convective clouds information on 1 June, 2012. The product shows (a) rapidly developing cumulus areas (RDCAs), (b) cumulonimbus areas, and (c) mid/low unknown cloud areas. RDCAs indicate the potential for heavy rainfall, and the others show mature convective cloud. A key technique in RDCA identification involves detecting temporal increases in the asperity and altitude of the cloud top surface. VIS data are especially fundamental for checking for temporal increases in asperity at the cloud top surface. Figure 2 shows a schematic diagram of these elements.
The results of RDCA evaluation performed in summer 2011 in relation to lightning observation are shown in Figure 3. The hit rate (derived from dividing the number of hits by the sum of the number of hits and false alarms) was almost 70% while heat-lightning was very active, and was close to 40% when frontal zone cloud brought lightning. Figure 4 shows a good example of the former case. Lightning was observed 20 to 40 minutes after the detection of areas of A, B and C, marked by a yellow oval in the upper-left image. This indicates that RDCAs can highlight potential thunderstorm areas at least 20 minutes before cumulus clouds develop into cumulonimbus.
2CLOUD PRODUCT
JMA has produced an objective cloud product analyzing cloud type, cloud amount and cloud top height from GMS-5 and MTSAT satellite images since 1999. The product is used for the aid of weather watch and automatic weather analysis.
JMA’s next generation satellites Himawari-8/9 will carry the advanced imager called AHI, which has capability to observe with 16 channels and 2.5-minute intervals. Using Himawari-8/9’s images, the generation of advanced cloud product is expected.
To develop the advanced product, JMA is studying the similar product for Meteosat Second Generation (MSG) developed by EUMETSAT/NWC SAF and GOES-R by NOAA/NESDIS. The new cloud product is expected to be used not only for weather analysis but also as a fundamental product to compute atmospheric motion vectors for height assignment and sea surface temperature (SST), clear sky radiance (CSR) and aerosol contents for cloud masking.
3VOLCANIC ASH
Volcanic ash directly affects airplane flight plans, and is monitored by JMA’s Tokyo Volcanic Ash Advisory Center (VAAC). Currently, differences between MTSAT 10.8 m and 12.0 m images are used for monitoring the spread of ash. However, quantitative information is also required.
From Himawari-8/9 observations, quantitative data such as ash density and height are expected. JMA plans to develop the product based on a EUMETSAT METEOSAT algorithm and a NOAA/NESDIS GOES-R algorithm. The Agency has already started a review of both methods, and will continue related research.
In the GOES-R algorithm, single scattering calculation results are examined to be used in order to distinct types of aerosol. JMA tries to compute single scattering parameters for various types of aerosol. The calculation is performed monochromatically for the central wavelength of HIMAWAI-8/9 infrared channels as 8.5 m, 11.2 m and 12.3 m. The shape of aerosol particle is spherical, and log-normal distribution of radius is assumed. Using complex refractive index data by Hale et.al. 1973, Pollack et.al. 1973, Roush et.al. 1991, Warren et.al. 2008 and WMO 1983 (Figure 5), extinction cross-section ext, single scatter albedo and asymmetry parameter g are calculated for effective radius from 1m to 12 m with 1 m intervals. Figure 6 shows the 2-dimentonal diagram of beta-ratio between 12.3 m and 11.2 m of scaled extinction cross section (1 g)ext versus that between 8.5 m and 11.2 m. The left figure shows the JMA calculation and the right figure shows GOES-R ATBD (NOAA/NESDIS, 2010). These figures indicate the use of 8.5 m in addition to 11.2 m and 12.3 m data enhances discrimination of aerosol types. The apparent difference between the two charts is recognized for “Dust (kaolinite)”.
Figure 5 Complex refractive index
The left chart shows real part and the right chart shows imaginary part. The horizontal axis shows wavelength (m)
Figure 6 2-dimentional diagram of beta-ratios
The left chart shows JMA calculation result, and the right chart is from GOES-R ATBD.
References
NOAA NESDIS, (2010): GOES-R Advanced Baseline Imager (ABI) Algorithm Theoretical Basis Document for volcanic Ash (Detection and Height), 84pp, Version 2.0, September 15, 2010.
Hale, G.M., M.R.Querry, (1973), Appl. Opt., 12:555-563.
Pollack, J.B., O.B. Toon, B.N. Khare, (1973), Icarus, 19:372-389.
Roush, T., J. Pollack, J. Orenberg, (1991), Icarus, 94:191-208.
Warren, S.G., R.E. Brandt, (2008), J. Geophys. Res., 113: 14220,doi:10.1029/2007JD009744.
WMO, (1983), Report of the Experts Meeting on Aerosols and Their Climatic Effects 107pp WCP-55.
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