MERRA-2 Notes, Questions, and Discussion

Black Carbon Angstrom parameter [470-870 nm] Black Carbon Column Mass Density Black Carbon column u-wind mass flux Black Carbon column v-wind mass flux Black Carbon Extinction AOT [550 nm] Black Carbon Scattering AOT [550 nm] Black Carbon Surface Mass Concentration DMS Column Mass Density __ENSEMBLE__ DMS Surface Mass Concentration __ENSEMBLE__ Dust Angstrom parameter [470-870 nm] Dust Column Mass Density Dust Column Mass Density - PM 2.5 Dust column u-wind mass flux Dust column v-wind mass flux Dust Extinction AOT [550 nm] Dust Extinction AOT [550 nm] - PM 2.5 Dust Scattering AOT [550 nm] Dust Scattering AOT [550 nm] - PM 2.5 Dust Surface Mass Concentration Dust Surface Mass Concentration - PM 2.5 Organic Carbon Angstrom parameter [470-870 nm] __ENSEMBLE__ Organic Carbon Column Mass Density __ENSEMBLE__ Organic Carbon column u-wind mass flux __ENSEMBLE__ Organic Carbon column v-wind mass flux __ENSEMBLE__ Organic Carbon Extinction AOT [550 nm] __ENSEMBLE__ Organic Carbon Scattering AOT [550 nm] __ENSEMBLE__ Organic Carbon Surface Mass Concentration __ENSEMBLE__ Sea Salt Angstrom parameter [470-870 nm] Sea Salt Column Mass Density Sea Salt Column Mass Density - PM 2.5 Sea Salt column u-wind mass flux Sea Salt column v-wind mass flux Sea Salt Extinction AOT [550 nm] Sea Salt Extinction AOT [550 nm] - PM 2.5 Sea Salt Scattering AOT [550 nm] Sea Salt Scattering AOT [550 nm] - PM 2.5 Sea Salt Surface Mass Concentration Sea Salt Surface Mass Concentration - PM 2.5 SO2 Column Mass Density __ENSEMBLE__ SO2 Surface Mass Concentration __ENSEMBLE__ SO4 Angstrom parameter [470-870 nm] __ENSEMBLE__ SO4 Column Mass Density __ENSEMBLE__ SO4 column u-wind mass flux __ENSEMBLE__ SO4 column v-wind mass flux __ENSEMBLE__ SO4 Extinction AOT [550 nm] __ENSEMBLE__ SO4 Scattering AOT [550 nm] __ENSEMBLE__ SO4 Surface Mass Concentration __ENSEMBLE__ Total Aerosol Angstrom parameter [470-870 nm] Total Aerosol Extinction AOT [550 nm] Total Aerosol Scattering AOT [550 nm] 

MEERA2 data have above parameters    I want AOD for my analysis and so How I can calculate AOD??

Please explain with details.
 

I want to download the Monthly Aerosol Mixing Ratio for monthly analysis PM1 and PM10, but all I can see is the hourly version "Instantaneous Three-Dimensional Collections inst3_3d_aer_Nv (M2I3NVAER): Aerosol Mixing Ratio"

Is there a link that I can locate the monthly version of the same data set?

Hi!

I'm utilizing the dataset, M2T1NXAER of MERRA-2. I have a query: What is the meaning of single-level in this dataset (M2T1NXAER)?  

Thanks for helping, and best regards, Omar Ramos 

Hi

Can I extract the MERRA-2 point data of AOD to validate with ground station point data at one of the AERONET stations? Is it acceptable in the research community for publication?  

Hi, 

I am currently trying to estimate Radiative Forcing due to different aerosol types, for which the basic parameters such as AOD, SSA, and Asymmetry parameters are the essential components. However, MERRA-2 straight away gives AOD and SSA parameters for 5 aerosol types including Sea Salt, Black Carbon, Organic Carbon, Dust, and Sulfate.

But I have not come across any information about how to estimate the Asymmetry Parameter for these 5 aerosol types globally. In this case, can anyone suggest how I can get the Asymmetry Parameter datasets across the globe? Or else, if the information about the Asymmetry Parameters datasets (globally) has already been provided somewhere that I have not come across, can you please share the same?

Thanks in advance

Hi,

I'm a student learning to work with MERRA2 datasets. However, I have a trouble with understanding some of values in a file.

Can you help me understand about the variable in MERRA2_tavgM_3d_odt_Np dataset? The set contains variables such as ozone tendency, and I can't fully understand them. I tried to find a document and guess through units, but that was not crystal clear for me.

Does ozone tendency mean ozone trend? and does odd oxygen due to moist processes mean the value only considers  odd oxygen related to a moist? Same with turbulences and chemistry.

How can I work with the dataset to make a comparison between ozone dataset which has a ppmv unit?

Thanks in advance,

June

Hi,

I'm a student learning to work with MERRA2 datasets. However, I have a trouble with understanding some of values in a file.

Can you help me understand about the variable in MERRA2_tavgM_3d_odt_Np dataset? The set contains variables such as ozone tendency, and I can't fully understand them. I tried to find a document and guess through units, but that was not crystal clear for me.

Does ozone tendency mean ozone trend? and does odd oxygen due to moist processes mean the value only considers  odd oxygen related to a moist? Same with turbulences and chemistry.

How can I work with the dataset to make a comparison between ozone dataset which has a ppmv unit?

Thanks in advance,

June

I downloaded tavg1_2d_aer_Nx: Aerosol Diagnostics data which is the product of MERRA2 GMI in order to get PM2.5 data. My country of interest is Thailand. I found that many pixels contain extremely high value of PM2.5 in the range of 1e-06 - 2e-06 kg m-3, which is equivalent to 1000-2000 microgram m-3. Do I misunderstand anything? Or, any other conversion factors needed in this case?

For more information, I tried to check each component of PM2.5 following the equation PM2.5 = 1.375*SO4 + 1.8*OC + BC + DS +SS, and found that OC was also extremely high.

Best regards

Sir

In MERRA, there are hourly data (24 layers in monthly layer) in monthly files, what does it means? And how to get monthly total evaporation in millimeters?

Thanks

Umar

Hi,

I am thinking of using MERRA-2 data to estimate the surface PM1 and PM10 concentration. But I found two different equations. 

First one,

PM1 = (1.375*SO4 + BCphobic + BCphilic + OCphobic + OCphilic + 0.7 * DU001 + SS01 + SS002) * AIRDENS

PM10 = (1.375*SO4 + BCphobic + BCphilic + OCphobic + OCphilic + DU001 + DU002 + DU003 + 0.74 * DU004 + SS01 + SS002 + SS003 + SS004) * AIRDENS,

which is from the website of Goddard Space Flight Center (https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/FAQ/)

Second one, 

PM10 = (1.375*SO4 + BCphobic + BCphilic + 1.8*OCphobic + 1.8*OCphilic + DU001 + DU002 + DU003 + 0.74 * DU004 + SS01 + SS002 + SS003 + SS004) * delp/g, which is from a discussion of this website.

We can notice that the second equation multiply the OC aerosols by 1.8 and the first one does not. So I would like to know which one is correct?

On the other hand, I also cannot find a paper including these equations. So can you provide a reference that we can cite these equations?

Thanks.

Shuai Yin

Hi,

I am thinking of using MERRA-2 data to estimate the surface PM1 and PM10 concentration. But I found two different equations. 

First one,

PM1 = (1.375*SO4 + BCphobic + BCphilic + OCphobic + OCphilic + 0.7 * DU001 + SS01 + SS002) * AIRDENS

PM10 = (1.375*SO4 + BCphobic + BCphilic + OCphobic + OCphilic + DU001 + DU002 + DU003 + 0.74 * DU004 + SS01 + SS002 + SS003 + SS004) * AIRDENS,

which is from the website of Goddard Space Flight Center (https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/FAQ/)

Second one, 

PM10 = (1.375*SO4 + BCphobic + BCphilic + 1.8*OCphobic + 1.8*OCphilic + DU001 + DU002 + DU003 + 0.74 * DU004 + SS01 + SS002 + SS003 + SS004) * delp/g, which is from a discussion of this website.

We can notice that the second equation multiply the OC aerosols by a factor of 1.8 and the first one does not. So I would like to know which one is correct?

On the other hand, I also cannot find a paper including these equations. So can you provide a reference that we can cite these equations?

Thanks.

Shuai Yin

Hi,

I have a query regarding the way 1)  PM10 is calculated using MERRA-2 aerosol species i.e,  BC, OC, SS, SU, and DU.

equation given - PM10 = (1.375*SO4 + BCphobic + BCphilic + 1.8*OCphobic + 1.8*OCphilic + DU001 + DU002 + DU003 + 0.74 * DU004 + SS01 + SS002 + SS003 + SS004) * delp/g

I want to know where the values of the factors you are multiplying different components with

(like SO4 with 1.375, OC with 1.8, DU with 0.74) come from?

2) Is there a way with which we can ad nitrate particulate concentration if we know ammonia gas concentration

in the atmosphere?

3) How can we calculate PM concentration with the provided the species concentration? Just in the same manner as PM10 is calculated, but including all the bins?

I have a query regarding bin size of aerosol species.

I am using the mass-mixing ratio of 3-d, 3-hourly, instantaneous aerosol and ozone for my research.

species. I wanted to use the bin which has species' diameter less than 2.5 micrometers as I'll be extracting data for PM2.5.

Please clarify which bin should I use for this purpose for dust, sea salt, black carbon, organic carbon and sulfate?

could you please let me know the bin size for different aerosol species?

like dust have 5 bins size such as 0.1--1, 1--1.8, 1.8--3, 3--6, 6--10 so, how about

black carbon (2bin size), organic carbon (2 bin size), sulfate (4 bin size), sea salt (5 bin size).

could you please provide some information on that.  

Hi,

I wonder if you could give me information about the averaging of radiation data. For example, SWGDN at 01:00 is the average of the SWGDN between 00:00 and 01:00? Or is it centered at 01:00? I am having problems using SWGDN data on PVLIB package to estimate PV output power. 

Thanks!

Hi,

I want to download MERRA-2 radiation data: 

Surface net shortwave radiation

Surface net longwave radiation

Both sensible and latent fluxes.

For the two first one I've gone through the specification doc but it is in my sense not clear enough. Thus for shortwave radiation all these 03 parameters seem to be what I want:

-surface net downward shortwave flux SWGNT (I think this should be the one I need but I am not confident because of the "downward"),

-surface incoming shortwave flux SWGDN(what's the difference between the "downward" and the "incoming") and 

-surface net downward shortwave flux SWNETSRF in the vertically integrated collection (clearly what makes the difference between SWGNT and SWNETSRF?).

I would like then to know which one is the real surface NET SW radiation  (not only downward) so that I may be able to derive the "upward" one as well. 

For longwave radiation, similar confusions exist between LWGNT and  LWGNET (this time there is no GDN). The question here is then which one is the "net" one as well.

Regarding turbulent fluxes, I have opted for EFLUX (latent) and HFLUX (sensible). I hope I have done right.

Your inputs are very appreciated.

Regards

GUIGMA 

Hi,

Can you please help me understand about the variable "relative humidity after moist"? What is that mean actually. Normally we find RH in percentage %, whereas here the unit is 1, whereas the data range varies from -1e+15 to 1e+15. How can I compare it with other RH values which follow the normal % unit?

Though I have gone through the documents, still this variable is not much clear to me.

Thanks in advance,

Ipsita

I am a PhD student at the University of Nairobi, Kenya and I am using Black Carbon Mass Concentration data to check for its spatial-temporal characteristics over Eastern Africa region (28E,-12S,42E,6N). I would like to know MERRA-2.0/MERRA-2.1 Reanalysis Data is from which Satellite, can I get the satellite photograph, platform/instrument, methods it uses to generate data, whether the data is synthetic or observational one, possible sources of error and accuracy percentage.

I got confused about these two terms. The mid_layer_heights apparently follow the topography. The geopotential heights, defined as the adjustment relative to the mean sea level, supposedly to be ~5 km over the Tibetan plateau at 1000-hPa. But from the MERRA2 "inst6_3d_ana_Np" data, when you look at the 1000 hPa level, the geopotential heights over the Tibetan plateau is about 100-200m. Why is that? 

Hi, I need to know what variables (T, UV winds, surface pressure, etc.) MERRA2 assimilates from land met stations and moored buoy arrays such as TAO, TRITON and RAMA.

Also, does MERRA assimilates any variables measured by moored buoys offshore the Spanish Atlantic coast, operated by the Spanish Agency Puertos del Estado?

Any help would be much appreciated, thanks!

Hi,

I was just looking into the wind speed profiles provided by MERRA-2. I merged the 3d field with the 10m and 50m wind speed and plottet the resulting profiles. Surprisingly, I found the 50m wind speed being exactly the same value as the lowest level 3d wind speed. The lowest level 3d wind speed is given at an height of about 65m. This is the lowest entry of the mid_level_heights variable.

Is this known? Do I have done something wrong?

Christopher

We were comparing MERRA 2 wind and temperature data to measured data in Mexico. The bias from MERRA2 was very large compared to METAR stations data. Any thoughts  ?

Thanks,

Alemu

I am thinking of using MERRA2 for WRF but conducting research about this topic on the web has gotten me more confused.

Some webpages are indicating that you need to combine MERRA and another source of land data e.g. GLDAS

http://lundquistgroup.blogspot.com/2014/04/using-input-datasets-in-real-wrf-runs.html

On the other hand, there are numerous changes which directly use MERRA2 with out mentioning this requirement.

Can someone please explain the right way to configure MERRA2 data for use as WRF reanalyses dataset?

Thanks,

VK

Dear Mike, 

I'm trying to extrapolate the roughness lengths from tavg1_2d_flx_Nx (M2T1NXFLX). I'm struggling to understand the datas, from the description the surface roughness should be in [m] but I can't figure how the value are so low. Could you give me some details or text me some references to better understand the values? Many thanks for that.

Just to let you know I'm assuming that a roughness length of 0.002 m is interpretable as a flat surface and a length of 0.8 as an high density metropolitan area.

Thanks a lot.

Emanuele  

I have just shifted from using MERRA reanalysis dataset to MERRA-2. My observation regards to the U50m, V50m winds from collection tavg1_2d_slv_Nx. The analysis area is Greece. I have noticed a large systematic change in the wind speed calculated for almost adjacent nodes of MERRA2 and MERRA. The "new" winds are about 25% lower than before. The correlation of the wind speeds are ~94% between the data sets but how is this large change explained.

Best regards

Hi 

I was trying to estimate trends in tropical middle atmosphere. The trends are very small compared to the earlier reports. I look back in the time series then I came to know that there was sudden shift in the winds around 2000. Does it something due to the input data?

I got doubt whether the MERRA is suitable for trend analysis or not.

kishore

To access MERRA data (for example const_2d_asm_Nx, inst6_3d_ana_Np, tavg1_2d_rad_Nx, tavg1_2d_slv_Nx), I developed an Excel Tool in VBA, which allows the download and the conversation to Excel format for selected subsets of this data.
Now I want to enhance this tool to MERRA-2. But this data are password protected and I don't know, how and to which address the login information has to be transmitted from the Excel-VBA procedure to the MERRA-2 Database. Exists a help Information for VBA programmers or generally for Software developers, how to solve the login procedure to access the MERRA-2 database from Software tools, developed for such purposes?
It's no Problem for me, to download the needed data in numerous single steps with the web browser, but this way of conversation by hand into the calculation tools in Excel is much too time consuming and hardly practicable.

Thanks for help an best regards, Matthias Popp