# Presentation: 099870

## Extending HIRS High Cloud Trends with MODIS 

**Donald P. Wylie**
**Richard Frey**
**Hong Zhang**
**W. Paul Menzel**
**12 year trends**
**Effects of orbit drift and ancillary Tsfc**
**Comparison with MODIS**
**July 2002**

## Slide 2

**Notes:**
The average plot, COMBINED.GIF, shows mostly constant cloud cover with time except for a drop in the northern hemisphere, 30-60 N, starting with the winter of 98 which had about 5% less cloud cover than the previous winters. Note the annual cycle is largest in the northern hemisphere.

## Slide 3

**Notes:**
Cloud cover over oceans, OCEANAVE.GIF, remained nearly constant with time. There is a slight drop in 2000-01, probably because of NOAA 16. NOAA 15 has not been used because we believe its statistics are low. We haven't found the cause of this problem.NOAA 11 is included in both COMBINED.GIF and OCEANAVE.GIF.

## Cloud Properties from CO2 Slicing

- RTE for cloudy conditions indicates dependence of cloud forcing (observed minus clear sky radiance) on cloud amount () and cloud top pressure (pc)
- 	                              pc
- 	(I - Iclr)  =          dB .
- 	                             ps
- Higher colder cloud or greater cloud amount produces greater cloud forcing; dense low cloud can be confused for high thin cloud.  Two unknowns require two equations.
- pc can be inferred from radiance measurements in two spectral bands where cloud emissivity is the same.   is derived from the infrared window, once pc is known.

## Different ratios 

**Different ratios **
**reveal cloud properties **
**at different levels**
**hi - 14.2/13.9**
**mid - 13.9/13.6**
**low - 13.6/13.3**
**Meas          Calc**
**	****            ****p****c****	**
**(I********1****-I********1****clr****)    ************1**** ******** ************1**** dB********1**
**	****            ****p****s**
**----------- = ----------------**
**	****            ****p****c****	**
**(I********2****-I********2****clr****)    ************2**** ******** ************2**** dB********2**
**	****            ****p****s**

## Generating HIRS Clear Sky Radiances in Cloudy FOVs

*Use IR Window Moisture Corrected Brightness Temperature Test against a priori surface temperature to identify nearby clear sky FOVs*
- BT11 + aPW * (BT11 - BT12) - Sfc Temp < 2 C
- 	*aPW of 0.8 has been used*
*	**Sfc Temp estimated from GDAS*
*Estimate I****clr**  by interpolating nearby clear FOVs *
*	**	**cld  =**	**x**	**x**	**x**	**o**	**o  =  clr*
*	**	**	**x**	**x**	**x**	**o**	**o*
*	**	**	**o**	**x**	**x**	**o**	**o*
*	**	**	**o**	**x**	****x****	**x**	**o*
*	**	**	**o**	**x**	**x**	**o**	**o*
*	**	**	**x**	**x**	**x**	**o**	**o*
*	**	**	*
*Attempt to derive CO2 cloud properties in x (note that CO2 cloud algorithm attempt on x can change FOV to o)*

## Determining Cloud Presence and Properties with HIRS 

*Use bands where (I**** - I****clr**)*  > *1 mW/m2/ster/cm-1 in CO2 slicing estimation of p**c*
*Estimate ****IRW** using IRW radiances*
*If more than one p**c  **is estimated, use RTE for all bands to select best one*
*If no bands qualify, try IR window estimate for opaque cld*
*If too low in atmosphere, declare FOV clear*

## Ratio of measured cloud signal 

**Ratio of measured cloud signal **
**for spectrally close bands yields Pc**

## Slide 9

**Notes:**
The tropics show the same changes as 30-60 north over land - TROLND.GIF.

## Slide 10

## GOES Sounder detecting diurnal change of cloud cover

**GOES Sounder detecting diurnal change of cloud cover**

## Wielicki et al (2002) CERES deviation of reflected shortwave flux wrt 1985-89 mean for 20N-20S 

**Wielicki et al (2002) CERES deviation of reflected shortwave flux wrt 1985-89 mean for 20N-20S**** **

## NH (36% land)

- Tropics (11% land)

- SH (very little land)

## Determining Cloud Presence and Properties with MODIS 

*Use MODIS Cloud Mask to determine cloud presence*
*Calculate I****clr** from GDAS*
*Attempt CO2 slicing estimation of p**c** on 5x5 FOV average when (I**** - I****clr**)*  > *1 mW/m2/ster/cm-1*
*Estimate ****IRW** using IRW radiances*
*If no bands qualify, try IR window estimate for opaque cld*

## Differences in MODIS and HIRS Cloud Property Processing

_**MODIS**_**	****	****	****	**_**HIRS**_
- 5 km 					20 km
- multi-detector				single detector
- contiguous				every 3rd element every 3rd line
- uses MODIS cloud mask		uses split window comparison
- 						with Tsfc
- forward calc of I(clear) 		interpolate neighboring I(clear)
- no radiance bias correction		radiance bias correction

## MODIS and HIRS global mean CO2 band brightness temperatures

## Slide 17

**Notes:**
cloud products in 20 km resolution on 2-3 June 2001 

## Slide 18

**Notes:**
cloud products in 20 km resolution on 2-3 June 2001 

## Slide 19

## Slide 20

## Conclusions

**Conclusions**
- Trends are beginning to emerge in HIRS data; orbit drift issues; pathfinder reprocessing enabling new look
- HIRS & MODIS total cloud cover is roughly the same
- 	over water
- (c) MODIS has more high and middle clouds than HIRS over both land and water surface;
- (d) HIRS found more high thin clouds than MODIS in tropics over both land and water for day and night, but MODIS has more high thick clouds than HIRS in both tropics & 20-60N.
- (e) More work remains